The present study tries to evaluate the validity of the Wiedemann-Franz law in a granular s-wave superconductor in the presence of concentrated impurities. By using Green's function method and the Kubo formula techni...The present study tries to evaluate the validity of the Wiedemann-Franz law in a granular s-wave superconductor in the presence of concentrated impurities. By using Green's function method and the Kubo formula technique, three distinct contributions of the Aslamazov-Larkin, the Maid-Thompson and, the density of states are calculated for both the electrical conductivity and the thermal conductivity in a granular s-wave superconductor. It is demonstrated that these different con- tributions to the fluctuation conductivity depend differently on the tunneling because of their different natures. This study examines the transport in a granular superconductor system in three dimensions in the limit of large tunneling conductance, which makes it possible to ignore all localization effects and the Coulomb interaction. We find that the tunneling is efficient near the critical temperature and that there is a crossover to the characteristic behavior of a homogeneous system. When it is far from the critical temperature, the tunneling is not effective and the system behaves as an ensemble of real zero-dimensional grains. The results show that the Wiedemann-Franz law is violated in both temperature regions.展开更多
We have studied the characteristics of current-induced nonequilibrium spin polarization in semiconductor-nanowire/swave superconductor junctions with strong spin–orbit coupling. It was found that within some paramete...We have studied the characteristics of current-induced nonequilibrium spin polarization in semiconductor-nanowire/swave superconductor junctions with strong spin–orbit coupling. It was found that within some parameter regions the magnitude of the current-induced nonequilibrium spin polarization density in such structures will increase(or decrease) with the decrease(or increase) of the charge current density, in contrast to that found in normal spin–orbit coupled semiconductor structures. It was also found that the unusual characteristics of the current-induced nonequilibrium spin polarization in such structures can be well explained by the effect of the Andreev reflection.展开更多
We investigate a Josephson junction between a one-band and a multi-band s-wave superconductor.When the multi-band lead is an s±-wave superconductor,we find that the critical Josephson current may change its sign ...We investigate a Josephson junction between a one-band and a multi-band s-wave superconductor.When the multi-band lead is an s±-wave superconductor,we find that the critical Josephson current may change its sign when the temperature changes.Our result confirms that this is a widespread effect of the s±-wave superconductor,independent of the type of the junction,the ratios of the gaps and superconducting transition temperatures,as long as the tunneling matrix elements have suitable values.This novel effect comes directly from the opposite gap signs.We propose that the observation of this phenomena can be used to detect the s±-wave pairing symmetry in iron-based superconductors.展开更多
Proximity effects between superconductors and ferromagnets(SC/FM)hold paramount importance in comprehending the spin competition transpiring at their interfaces.This competition arises from the interplay between Coope...Proximity effects between superconductors and ferromagnets(SC/FM)hold paramount importance in comprehending the spin competition transpiring at their interfaces.This competition arises from the interplay between Cooper pairs and ferromagnetic exchange interactions.The proximity effects between transition metal nitrides(TMNs)are scarcely investigated due to the formidable challenges of fabricating high-quality SC/FM interfaces.We fabricated heterostructures comprising SC titanium nitride(TiN)and FM iron nitride(Fe_(3)N)with precise chemical compositions and atomically well-defined interfaces.The magnetoresistance of Fe_(3)N/TiN heterostructures shows a distinct magnetic anisotropy and strongly depends on the external perturbations.Moreover,the superconducting transition temperatureT_(C) and critical field of TiN experience notable suppression when proximity to Fe_(3)N.We observe the intriguing competition of interfacial spin orientations near𝑇T_(C)(∼1.25 K).These findings not only add a new materials system for investigating the interplay between superconductor and ferromagnets,but also potentially provide a building block for future research endeavors and applications in the realms of superconducting spintronic devices.展开更多
What factors fundamentally determine the value of superconducting transition temperature Tc in high temperature superconductors has been the subject of intense debate.Following the establishment of an empirical law kn...What factors fundamentally determine the value of superconducting transition temperature Tc in high temperature superconductors has been the subject of intense debate.Following the establishment of an empirical law known as Homes'law,there is a growing consensus in the community that the Tc value of the cuprate superconductors is closely linked to the superfluid density(ρ_(s))of its ground state and the conductivity(σ)of its normal state.However,all the data supporting this empirical law(ρ_(s)=AσT_(c))have been obtained from the ambientpressure superconductors.In this study,we present the first high-pressure results about the connection of the quantities of ρ_(s) and σ with T_(c),through the studies on the Bi_(1.74)Pb_(0.38)Sr_(1.88)CuO_(6+δ)and Bi_(2)Sr_(2)CaCu_(2)O_(8+δ),in which the value of their high-pressure resistivity(ρ=1/σ)is achieved by adopting our newly established method,while the quantity ofρs is extracted using Homes'law.We highlight that the Tc values are strongly linked to the joint response factors of magnetic field and electric field,i.e.,ρ_(s) and σ,respectively,implying that the physics determining T_(c) is governed by the intrinsic electromagnetic fields of the system.展开更多
Since the discovery of hydride superconductors,a significant challenge has been to reduce the pressure required for their stabilization.In this context,we propose that alloying could be an effective strategy to achiev...Since the discovery of hydride superconductors,a significant challenge has been to reduce the pressure required for their stabilization.In this context,we propose that alloying could be an effective strategy to achieve this.We focus on a series of alloyed hydrides with the AMH_(6)composition,which can be made via alloying A15 AH_(3)(A=Al or Ga)with M(M=a group IIIB or IVB metal),and study their behavior under pressure.Seven of them are predicted to maintain the A15-type structure,similar to AH_(3)under pressure,providing a platform for studying the effects of alloying on the stability and superconductivity of AH_(3).Among these,the A15-type phases of AlZrH_(6)and AlHfH_(6)are found to be thermodynamically stable in the pressure ranges of 40–150 and 30–181 GPa,respectively.Furthermore,they remain dynamically stable at even lower pressures,as low as 13 GPa for AlZrH_(6)and 6 GPa for AlHfH_(6).These pressures are significantly lower than that required for stabilizing A15 AlH3.Additionally,the introduction of Zr or Hf increases the electronic density of states at the Fermi level compared with AlH3.This enhancement leads to higher critical temperatures(Tc)of 75 and 76 K for AlZrH_(6)and AlHfH_(6)at 20 and 10 GPa,respectively.In the case of GaMH_(6)alloys,where M represents Sc,Ti,Zr,or Hf,these metals reinforce the stability of the A15-type structure and reduce the lowest thermodynamically stable pressure for GaH_(3) from 160 GPa to 116,95,80,and 85 GPa,respectively.Particularly noteworthy are the A15-type GaMH_(6)alloys,which remain dynamically stable at low pressures of 97,28,5,and 6 GPa,simultaneously exhibiting high Tc of 88,39,70,and 49 K at 100,35,10,and 10 GPa,respectively.Overall,these findings enrich the family of A15-type superconductors and provide insights for the future exploration of high-temperature hydride superconductors that can be stabilized at lower pressures.展开更多
We study the Kondo screening of a spin-1/2 magnetic impurity coupled to a superconductor,which is fabricated by combination of an s-wave superconductor,a ferromagnet and a semiconductor with Rashba spin-orbit coupling...We study the Kondo screening of a spin-1/2 magnetic impurity coupled to a superconductor,which is fabricated by combination of an s-wave superconductor,a ferromagnet and a semiconductor with Rashba spin-orbit coupling(RSOC).The proximity induced superconducting states include the s-wave and p-wave pairing components with the aids of RSOC,and the ferromagnet induces a Zeeman field which removes the spin degeneracy of the quasiparticles in the triplet states.Thus,the Kondo screening of magnetic impurity involves the orbital degrees of freedom,and is also affected by the Zeeman field.Using the variational method,we calculate the binding energy and the spin-spin correlation between the magnetic impurity and the electrons in the coexisting s-wave and p-wave pairing states.We find that Kondo singlet forms more easily with stronger RSOC,but Zeeman field in general decreases the binding energy.The spin-spin correlation decays fast in the vicinity of the magnetic impurity.Due to the RSOC,the spatial spin-spin correlation becomes highly anisotropic,and the Zeeman field can induce extra asymmetry to the off-diagonal components of the spin-spin correlation.Our study can offer some insights into the studies of extrinsic topological superconductors fabricated from the hybrid structures containing chains of magnetic impurities.展开更多
We investigate the topological properties of twisted bilayer superconductors with different even-parity pairings in each layer.In the presence of spin-orbit coupling,the Hamiltonian is mapped into an effective odd-par...We investigate the topological properties of twisted bilayer superconductors with different even-parity pairings in each layer.In the presence of spin-orbit coupling,the Hamiltonian is mapped into an effective odd-parity superconductor.Based on this,we deduce the topological properties by examining the relative configuration between Fermi surface and Dirac pairing node.We show that mixed Rashba and Dresselhaus spin-orbit coupling and anisotropic hopping terms,which break the C_(4)symmetry of the Fermi surface,can induce first-order topological superconductors with non-zero bulk Chern number.This provides a versatile way to control the topological phases of bilayer superconductors by adjusting the twisted angle and chemical potential.We demonstrate our results using a typical twisted angle of 53.13°,at which the translation symmetry is restored and the Chern number and edge state are calculated using the Moir′e momentum.展开更多
Negative differential conductance(NDC)serves as a crucial characteristic that reveals various underlying physics and transport process in hybrid superconducting devices.We report the observation of gate-tunable NDC ou...Negative differential conductance(NDC)serves as a crucial characteristic that reveals various underlying physics and transport process in hybrid superconducting devices.We report the observation of gate-tunable NDC outside the superconducting energy gap on two types of hybrid semiconductor–superconductor devices,i.e.,normal metal–superconducting nanowire–normal metal and normal metal–superconducting nanowire–superconductor devices.Specifically,we study the dependence of the NDCs on back-gate voltage and magnetic field.When the back-gate voltage decreases,these NDCs weaken and evolve into positive differential conductance dips;and meanwhile they move away from the superconducting gap towards high bias voltage,and disappear eventually.In addition,with the increase of magnetic field,the NDCs/dips follow the evolution of the superconducting gap,and disappear when the gap closes.We interpret these observations and reach a good agreement by combining the Blonder–Tinkham–Klapwijk(BTK)model and the critical supercurrent effect in the nanowire,which we call the BTK-supercurrent model.Our results provide an in-depth understanding of the tunneling transport in hybrid semiconductor–superconductor devices.展开更多
Ultrathin superconducting Nb films of about 8 nm thick have been deposited on heavily doped Si substrates through DC magnetron sputtering and then the high-quality Nb/Si superconductor–semiconductor heterojunctions h...Ultrathin superconducting Nb films of about 8 nm thick have been deposited on heavily doped Si substrates through DC magnetron sputtering and then the high-quality Nb/Si superconductor–semiconductor heterojunctions have been fabricated by electron beam lithography and reactive ion etching.An abnormal magnetoresistance effect,which manifests itself as a zero field resistance peak under a magnetic field applied perpendicular to the interface,has been distinctly observed when the Nb film is in the superconductiing state.By considering the heterojunction interface being equivalent to the structure of superconductor–barrier layer–superconductor configuration,we could generally understand this unusual effect based on the Andreev reflection mechanism.Our results can be of help for the future development on compatibility and scalability of the silicon-based nanoscale superconducting devices for integrated circuits and superconducting quantum electronics.展开更多
Seeking new order parameters and the related broken symmetry and studying their relationship with phase transition have been important topics in condensed matter physics.Here,by using spin-and angle-resolved photoemis...Seeking new order parameters and the related broken symmetry and studying their relationship with phase transition have been important topics in condensed matter physics.Here,by using spin-and angle-resolved photoemission spectroscopy,we confirm the helical spin texture caused by spin-layer locking in the nodal region in the cuprate superconductor Bi_(2)Sr_(2)CaCu_(2)O_(8+δ)and discover the anisotropy of spin polarizations at nodes alongΓ–X andΓ–Y directions.The breaking of C_(4)rotational symmetry in electronic spin texture may give deeper insights into understanding the ground state of cuprate superconductors.展开更多
Recently,superconductors with higher-order topology have stimulated extensive attention and research interest.Higher-order topological superconductors exhibit unconventional bulk-boundary correspondence,thus allow exo...Recently,superconductors with higher-order topology have stimulated extensive attention and research interest.Higher-order topological superconductors exhibit unconventional bulk-boundary correspondence,thus allow exotic lower-dimensional boundary modes,such as Majorana corner and hinge modes.However,higher-order topological superconductivity has yet to be found in naturally occurring materials.We investigate higher-order topology in a two-dimensional Josephson junction comprised of two s-wave superconductors separated by a topological insulator thin film.We find that zero-energy Majorana corner modes,a boundary fingerprint of higherorder topological superconductivity,can be achieved by applying magnetic field.When an in-plane Zeeman field is applied to the system,two corner modes appear in the superconducting junction.Furthermore,we also discover a two-dimensional nodal superconducting phase which supports flat-band Majorana edge modes connecting the bulk nodes.Importantly,we demonstrate that zero-energy Majorana corner modes are stable when increasing the thickness of topological insulator thin film.展开更多
We successfully grow a new superconductor GaBa2Ca3Cu4O11+δ(Ga-1234) with a transition temperature of 113 K, using the Walker-type high-pressure synthesis apparatus. X-ray diffraction measurements on the powderized sa...We successfully grow a new superconductor GaBa2Ca3Cu4O11+δ(Ga-1234) with a transition temperature of 113 K, using the Walker-type high-pressure synthesis apparatus. X-ray diffraction measurements on the powderized samples show a mixture of the Ga-1234 phase and the Ca0.85CuO2phase, and the former is dominant. Under the scanning electron microscope, plate-like crystals of the Ga-based 1234 phase with shiny surfaces can be seen.The obtained local chemical compositions revealed by energy dispersion x-ray spectroscopy are very close to the stoichiometric values. On some sub-millimeter crystal-like samples of the 1234 phase, we obtain a full Meissner shielding volume. From the temperature-dependent magnetizations, we determine the irreversibility fields and find that the system exhibits a highly anisotropic behavior.展开更多
The competition between different magnetic structures in hole-doped Fe-pnicitides is explored based on an extended five-orbital Hubbard model including long-range Coulomb interactions.Our results show that the stabili...The competition between different magnetic structures in hole-doped Fe-pnicitides is explored based on an extended five-orbital Hubbard model including long-range Coulomb interactions.Our results show that the stabilized magnetic structure evolves with increasing hole doping level.Namely,the stripe antiferromagnetic phase dominates at zero doping,while magnetic structures with more antiferromagnetic linking numbers such as the staggered tetramer,staggered trimer,and staggered dimer phases become energetically favorable as the hole density increases.At a certain doping level,energy degeneracy of different magnetic structures appears,indicating strong magnetic frustration and magnetic fluctuations in the system.We suggest that the magnetic competition induced by the hole doping may explain the fast decrease of the Neel temperature TNand the moderately suppressed magnetic moment in the hole doped Fe-pnicitides.Moreover,our results show a sign reversal of the kinetic energy anisotropy as the magnetic ground state evolves,which may be the mechanism behind the puzzling sign reversal of the in-plane resistivity anisotropy in hole-doped Fe-pnicitides.展开更多
On September 16,2021,a MS6.0 earthquake struck Luxian County,one of the shale gas blocks in the Southeastern Sichuan Basin,China.To understand the seismogenic environment and its mechanism,we inverted a fine three-dim...On September 16,2021,a MS6.0 earthquake struck Luxian County,one of the shale gas blocks in the Southeastern Sichuan Basin,China.To understand the seismogenic environment and its mechanism,we inverted a fine three-dimensional S-wave velocity model from ambient noise tomography using data from a newly deployed dense seismic array around the epicenter,by extracting and jointly inverting the Rayleigh phase and group velocities in the period of 1.6–7.2 s.The results showed that the velocity model varied significantly beneath different geological units.The Yujiasi syncline is characterized by low velocity at depths of~3.0–4.0 km,corresponding to the stable sedimentary layer in the Sichuan Basin.The eastern and western branches of the Huayingshan fault belt generally exhibit high velocities in the NE-SW direction,with a few local low-velocity zones.The Luxian MS6.0 earthquake epicenter is located at the boundary between the high-and low-velocity zones,and the earthquake sequences expand eastward from the epicenter at depths of 3.0–5.0 km.Integrated with the velocity variations around the epicenter,distribution of aftershock sequences,and focal mechanism solution,it is speculated that the seismogenic mechanism of the main shock might be interpreted as the reactivation of pre-existing faults by hydraulic fracturing.展开更多
The noncentrosymmetric superconductor CaPtAs with time-reversal symmetry breaking in its superconducting state was previously proposed to host nodal superconductivity.Here,by employing ultralow-temperature thermal con...The noncentrosymmetric superconductor CaPtAs with time-reversal symmetry breaking in its superconducting state was previously proposed to host nodal superconductivity.Here,by employing ultralow-temperature thermal conductivity measurement on CaPtAs single crystal,we study its superconducting gap structure.A negligible residual linear term of thermal conductivity(κ_(0)/T)in zero magnetic field and the field dependence ofκ_(0)/T indicate that CaPtAs has multiple superconducting gaps with a dominant s-wave component.This is consistent with recent nuclear quadrupole resonance measurements on CaPtAs.Our work puts a strong constraint on the theories to describe the superconducting pairing symmetry of CaPtAs.展开更多
The Ising spin–orbit coupling could give rise to the spin-triplet Cooper pairs and equal-spin Andreev reflection(AR)in Ising superconductors.Here we theoretically study the valley-dependent equal-spin AR in a ferroma...The Ising spin–orbit coupling could give rise to the spin-triplet Cooper pairs and equal-spin Andreev reflection(AR)in Ising superconductors.Here we theoretically study the valley-dependent equal-spin AR in a ferromagnet/Ising superconductor junction with a circularly polarized light applied to the ferromagnet.Because of the spin-triplet Cooper pairs and the optical irradiation,eight kinds of AR processes appear in the junction,including equal-spin AR and normal AR,the strengths and properties of which strongly depend on the valley degree of freedom.The AR probabilities for the incident electron from the two valleys exhibit certain symmetry with respect to the magnetization angle and the effective energy of light.The equal-spin AR and normal AR present different features and resonant behaviors near the superconducting gap edges.Due to equal-spin-triplet Cooper pairs,not only charge supercurrent but also spin supercurrent can transport in the Ising superconductors.The differential spin conductance for electron injecting from the two valleys can be controlled by the circularly polarized light.展开更多
The Ningdu basin,located in southern Jiangxi province of southwest China,is one of the Mesozoic basin groups which has exploration prospects for geothermal energy.A study on the detailed velocity structure of the Ning...The Ningdu basin,located in southern Jiangxi province of southwest China,is one of the Mesozoic basin groups which has exploration prospects for geothermal energy.A study on the detailed velocity structure of the Ningdu basin can provide important information for geothermal resource exploration.In this study,we deployed a dense seismic array in the Ningdu basin to investigate the 3D velocity structure and discuss implications for geothermal exploration and geological evolution.Based on the dense seismic array including 35 short-period(5 s-100 Hz)seismometers with an average interstation distance of~5 km,Rayleigh surface wave dispersion curves were extracted from the continuous ambient noise data for surface wave tomographic inversion.Group velocity tomography was conducted and the 3D S-wave velocity structure was inverted by the neighborhood algorithm.The results revealed obvious low-velocity anomalies in the center of the basin,consistent with the low-velocity Cretaceous sedimentary rocks.The basement and basin-controlling fault can also be depicted by the S-wave velocity anomalies.The obvious seismic interface is about 2 km depth in the basin center and decreases to 700 m depth near the basin boundary,suggesting spatial thickness variations of the Cretaceous sediment.The fault features of the S-wave velocity profile coincide with the geological cognition of the western boundary basincontrolling fault,which may provide possible upwelling channels for geothermal fluid.This study suggests that seismic tomography with a dense array is an effective method and can play an important role in the detailed investigations of sedimentary basins.展开更多
To study the influence of thickness on the magnetic properties of ReBCO(Re = Y, Gd, Sm, Nd, etc.) bulk superconductors, a single domain gadolinium barium copper oxide(GdBCO) bulk superconductor fabricated by the Re + ...To study the influence of thickness on the magnetic properties of ReBCO(Re = Y, Gd, Sm, Nd, etc.) bulk superconductors, a single domain gadolinium barium copper oxide(GdBCO) bulk superconductor fabricated by the Re + 011 top seeded infiltration growth(Re + 011 TSIG) method was continuously sliced along the bottom to obtain samples of different thickness. The levitation force and attractive force of these samples were tested at 77 K in the zero-field-cooled(ZFC)state. It is found that as the sample thickness decreases, the levitation force decreases gradually whereas the attractive force increases. This is related to the varied ability to resist the penetration of magnetic field occasioned by varying sample thickness, which are deeply revealed by combining with the characteristics of the non-ideal type-II superconductor. Further,the levitation force exhibits a trend of slow initial change followed by rapid change, which may be attributed to the growth of the sample. Measurement of the trapped field shows that a similar distribution of trapped field at the top and bottom surfaces can be achieved by removing some materials from the bottom of the bulk. These results provide a reference for meeting the actual requirements of ReBCO bulks of different thicknesses and greatly contribute to practical designs and applications.展开更多
基金Project supported by Shahid Chamran University of Ahvaz
文摘The present study tries to evaluate the validity of the Wiedemann-Franz law in a granular s-wave superconductor in the presence of concentrated impurities. By using Green's function method and the Kubo formula technique, three distinct contributions of the Aslamazov-Larkin, the Maid-Thompson and, the density of states are calculated for both the electrical conductivity and the thermal conductivity in a granular s-wave superconductor. It is demonstrated that these different con- tributions to the fluctuation conductivity depend differently on the tunneling because of their different natures. This study examines the transport in a granular superconductor system in three dimensions in the limit of large tunneling conductance, which makes it possible to ignore all localization effects and the Coulomb interaction. We find that the tunneling is efficient near the critical temperature and that there is a crossover to the characteristic behavior of a homogeneous system. When it is far from the critical temperature, the tunneling is not effective and the system behaves as an ensemble of real zero-dimensional grains. The results show that the Wiedemann-Franz law is violated in both temperature regions.
基金Project supported by the National Natural Science Foundation of China(Grant No.11474106)
文摘We have studied the characteristics of current-induced nonequilibrium spin polarization in semiconductor-nanowire/swave superconductor junctions with strong spin–orbit coupling. It was found that within some parameter regions the magnitude of the current-induced nonequilibrium spin polarization density in such structures will increase(or decrease) with the decrease(or increase) of the charge current density, in contrast to that found in normal spin–orbit coupled semiconductor structures. It was also found that the unusual characteristics of the current-induced nonequilibrium spin polarization in such structures can be well explained by the effect of the Andreev reflection.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11104099,10974086 and 11023002the Ministry of Science and Technology of China under Grant Nos 2011CBA00108 and 2011CB922101+1 种基金the Open Foundation from National Laboratory of Solid State Microstructures under Grant No M22010the Natural Science Foundation of the Educational Department of Anhui Province under Grant No KJ2010B184.
文摘We investigate a Josephson junction between a one-band and a multi-band s-wave superconductor.When the multi-band lead is an s±-wave superconductor,we find that the critical Josephson current may change its sign when the temperature changes.Our result confirms that this is a widespread effect of the s±-wave superconductor,independent of the type of the junction,the ratios of the gaps and superconducting transition temperatures,as long as the tunneling matrix elements have suitable values.This novel effect comes directly from the opposite gap signs.We propose that the observation of this phenomena can be used to detect the s±-wave pairing symmetry in iron-based superconductors.
基金supported by the National Key Research and Development Program of China(Grant Nos.2020YFA0309100 and 2019YFA0308500)the National Natural Science Foundation of China(Grant Nos.U22A20263,52250308,and 11974390)+3 种基金the CAS Project for Young Scientists in Basic Research(Grant No.YSBR-084)(E.J.G.)Special Research Assistant(Q.J.),the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB33030200)(K.J.)the China Postdoctoral Science Foundation(Grant No.2022M723353)the Guangdong-Hong Kong-Macao Joint Laboratory for Neutron Scattering Science and Technology(Grant No.HTCSNS-DG-CD-0080/2021).
文摘Proximity effects between superconductors and ferromagnets(SC/FM)hold paramount importance in comprehending the spin competition transpiring at their interfaces.This competition arises from the interplay between Cooper pairs and ferromagnetic exchange interactions.The proximity effects between transition metal nitrides(TMNs)are scarcely investigated due to the formidable challenges of fabricating high-quality SC/FM interfaces.We fabricated heterostructures comprising SC titanium nitride(TiN)and FM iron nitride(Fe_(3)N)with precise chemical compositions and atomically well-defined interfaces.The magnetoresistance of Fe_(3)N/TiN heterostructures shows a distinct magnetic anisotropy and strongly depends on the external perturbations.Moreover,the superconducting transition temperatureT_(C) and critical field of TiN experience notable suppression when proximity to Fe_(3)N.We observe the intriguing competition of interfacial spin orientations near𝑇T_(C)(∼1.25 K).These findings not only add a new materials system for investigating the interplay between superconductor and ferromagnets,but also potentially provide a building block for future research endeavors and applications in the realms of superconducting spintronic devices.
基金supported by the National Key Research and Development Program of China(Grant Nos.2021YFA1401800 and 2022YFA1403900)the National Natural Science Foundation of China(Grant Nos.U2032214,12122414,12104487,and 12004419)+1 种基金the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB25000000)supported by the US Department of Energy,Office of Basic Energy Sciences(Grant No.DOE-sc0012704)。
文摘What factors fundamentally determine the value of superconducting transition temperature Tc in high temperature superconductors has been the subject of intense debate.Following the establishment of an empirical law known as Homes'law,there is a growing consensus in the community that the Tc value of the cuprate superconductors is closely linked to the superfluid density(ρ_(s))of its ground state and the conductivity(σ)of its normal state.However,all the data supporting this empirical law(ρ_(s)=AσT_(c))have been obtained from the ambientpressure superconductors.In this study,we present the first high-pressure results about the connection of the quantities of ρ_(s) and σ with T_(c),through the studies on the Bi_(1.74)Pb_(0.38)Sr_(1.88)CuO_(6+δ)and Bi_(2)Sr_(2)CaCu_(2)O_(8+δ),in which the value of their high-pressure resistivity(ρ=1/σ)is achieved by adopting our newly established method,while the quantity ofρs is extracted using Homes'law.We highlight that the Tc values are strongly linked to the joint response factors of magnetic field and electric field,i.e.,ρ_(s) and σ,respectively,implying that the physics determining T_(c) is governed by the intrinsic electromagnetic fields of the system.
基金supported by the Natural Science Foundation of China(Grant Nos.52022089,52372261,52288102,and 11964026)the National Key R&D Program of China(Grant No.2022YFA1402300)+5 种基金the Natural Science Foundation of Hebei Province(Grant No.E2022203109)the Doctoral Fund of Henan University of Technology(Grant No.31401579)P.L.thanks the Science and Technology Leading Talents and Innovation Team Building Projects of the Inner Mongolia Autonomous Region(Grant No.GXKY22060)financial support from the Spanish Ministry of Science and Innovation(Grant No.FIS2019-105488GB-I00)the Department of Education,Universities and Research of the Basque Government and the University of the Basque Country(Grant No.IT1707-22)the National Science Foundation(Grant No.DMR-2136038)for financial support.
文摘Since the discovery of hydride superconductors,a significant challenge has been to reduce the pressure required for their stabilization.In this context,we propose that alloying could be an effective strategy to achieve this.We focus on a series of alloyed hydrides with the AMH_(6)composition,which can be made via alloying A15 AH_(3)(A=Al or Ga)with M(M=a group IIIB or IVB metal),and study their behavior under pressure.Seven of them are predicted to maintain the A15-type structure,similar to AH_(3)under pressure,providing a platform for studying the effects of alloying on the stability and superconductivity of AH_(3).Among these,the A15-type phases of AlZrH_(6)and AlHfH_(6)are found to be thermodynamically stable in the pressure ranges of 40–150 and 30–181 GPa,respectively.Furthermore,they remain dynamically stable at even lower pressures,as low as 13 GPa for AlZrH_(6)and 6 GPa for AlHfH_(6).These pressures are significantly lower than that required for stabilizing A15 AlH3.Additionally,the introduction of Zr or Hf increases the electronic density of states at the Fermi level compared with AlH3.This enhancement leads to higher critical temperatures(Tc)of 75 and 76 K for AlZrH_(6)and AlHfH_(6)at 20 and 10 GPa,respectively.In the case of GaMH_(6)alloys,where M represents Sc,Ti,Zr,or Hf,these metals reinforce the stability of the A15-type structure and reduce the lowest thermodynamically stable pressure for GaH_(3) from 160 GPa to 116,95,80,and 85 GPa,respectively.Particularly noteworthy are the A15-type GaMH_(6)alloys,which remain dynamically stable at low pressures of 97,28,5,and 6 GPa,simultaneously exhibiting high Tc of 88,39,70,and 49 K at 100,35,10,and 10 GPa,respectively.Overall,these findings enrich the family of A15-type superconductors and provide insights for the future exploration of high-temperature hydride superconductors that can be stabilized at lower pressures.
基金Project supported by the Zhejiang Provincial Natural Science Foundation of China(Grant No.LY19A040003)。
文摘We study the Kondo screening of a spin-1/2 magnetic impurity coupled to a superconductor,which is fabricated by combination of an s-wave superconductor,a ferromagnet and a semiconductor with Rashba spin-orbit coupling(RSOC).The proximity induced superconducting states include the s-wave and p-wave pairing components with the aids of RSOC,and the ferromagnet induces a Zeeman field which removes the spin degeneracy of the quasiparticles in the triplet states.Thus,the Kondo screening of magnetic impurity involves the orbital degrees of freedom,and is also affected by the Zeeman field.Using the variational method,we calculate the binding energy and the spin-spin correlation between the magnetic impurity and the electrons in the coexisting s-wave and p-wave pairing states.We find that Kondo singlet forms more easily with stronger RSOC,but Zeeman field in general decreases the binding energy.The spin-spin correlation decays fast in the vicinity of the magnetic impurity.Due to the RSOC,the spatial spin-spin correlation becomes highly anisotropic,and the Zeeman field can induce extra asymmetry to the off-diagonal components of the spin-spin correlation.Our study can offer some insights into the studies of extrinsic topological superconductors fabricated from the hybrid structures containing chains of magnetic impurities.
基金Project supported by the National Natural Science Foundation of China(Grant No.11974293)。
文摘We investigate the topological properties of twisted bilayer superconductors with different even-parity pairings in each layer.In the presence of spin-orbit coupling,the Hamiltonian is mapped into an effective odd-parity superconductor.Based on this,we deduce the topological properties by examining the relative configuration between Fermi surface and Dirac pairing node.We show that mixed Rashba and Dresselhaus spin-orbit coupling and anisotropic hopping terms,which break the C_(4)symmetry of the Fermi surface,can induce first-order topological superconductors with non-zero bulk Chern number.This provides a versatile way to control the topological phases of bilayer superconductors by adjusting the twisted angle and chemical potential.We demonstrate our results using a typical twisted angle of 53.13°,at which the translation symmetry is restored and the Chern number and edge state are calculated using the Moir′e momentum.
基金the National Key Research and Development Program of China(Grant Nos.2022YFA1403400 and 2017YFA0304700)the National Natural Science Foundation of China(Grant Nos.12074417,92065203,92065106,61974138,11774405,11527806,and 12104489)+3 种基金the Strategic Priority Research Program B of Chinese Academy of Sciences(Grant Nos.XDB28000000 and XDB33000000)the Synergetic Extreme Condition User Facility sponsored by the National Development and Reform Commissionthe Innovation Program for Quantum Science and Technology(2021ZD0302600)the support from Youth Innovation Promotion Association,Chinese Academy of Sciences(Grant Nos.2017156 and Y2021043).
文摘Negative differential conductance(NDC)serves as a crucial characteristic that reveals various underlying physics and transport process in hybrid superconducting devices.We report the observation of gate-tunable NDC outside the superconducting energy gap on two types of hybrid semiconductor–superconductor devices,i.e.,normal metal–superconducting nanowire–normal metal and normal metal–superconducting nanowire–superconductor devices.Specifically,we study the dependence of the NDCs on back-gate voltage and magnetic field.When the back-gate voltage decreases,these NDCs weaken and evolve into positive differential conductance dips;and meanwhile they move away from the superconducting gap towards high bias voltage,and disappear eventually.In addition,with the increase of magnetic field,the NDCs/dips follow the evolution of the superconducting gap,and disappear when the gap closes.We interpret these observations and reach a good agreement by combining the Blonder–Tinkham–Klapwijk(BTK)model and the critical supercurrent effect in the nanowire,which we call the BTK-supercurrent model.Our results provide an in-depth understanding of the tunneling transport in hybrid semiconductor–superconductor devices.
基金the National Natural Science Foundation of China and the Ministry of Science and Technology of China.
文摘Ultrathin superconducting Nb films of about 8 nm thick have been deposited on heavily doped Si substrates through DC magnetron sputtering and then the high-quality Nb/Si superconductor–semiconductor heterojunctions have been fabricated by electron beam lithography and reactive ion etching.An abnormal magnetoresistance effect,which manifests itself as a zero field resistance peak under a magnetic field applied perpendicular to the interface,has been distinctly observed when the Nb film is in the superconductiing state.By considering the heterojunction interface being equivalent to the structure of superconductor–barrier layer–superconductor configuration,we could generally understand this unusual effect based on the Andreev reflection mechanism.Our results can be of help for the future development on compatibility and scalability of the silicon-based nanoscale superconducting devices for integrated circuits and superconducting quantum electronics.
基金the National Natural Science Foundation of China(Grant Nos.U1632266,11927807,and U2032207)the National Key R&D Program of China(Grant No.2017YFA 0305400)supported by the US Department of Energy,Office of Basic Energy Sciences(Grant Nos.DOE-sc0012704)。
文摘Seeking new order parameters and the related broken symmetry and studying their relationship with phase transition have been important topics in condensed matter physics.Here,by using spin-and angle-resolved photoemission spectroscopy,we confirm the helical spin texture caused by spin-layer locking in the nodal region in the cuprate superconductor Bi_(2)Sr_(2)CaCu_(2)O_(8+δ)and discover the anisotropy of spin polarizations at nodes alongΓ–X andΓ–Y directions.The breaking of C_(4)rotational symmetry in electronic spin texture may give deeper insights into understanding the ground state of cuprate superconductors.
基金supported by the National Natural Science Foundation of China(Grant Nos.12074108,11974256,and 12147102)the Priority Academic Program Development(PAPD)of Jiangsu Higher Education Institutionthe Natural Science Foundation of Chongqing(Grant No.CSTB2022NSCQMSX0568)。
文摘Recently,superconductors with higher-order topology have stimulated extensive attention and research interest.Higher-order topological superconductors exhibit unconventional bulk-boundary correspondence,thus allow exotic lower-dimensional boundary modes,such as Majorana corner and hinge modes.However,higher-order topological superconductivity has yet to be found in naturally occurring materials.We investigate higher-order topology in a two-dimensional Josephson junction comprised of two s-wave superconductors separated by a topological insulator thin film.We find that zero-energy Majorana corner modes,a boundary fingerprint of higherorder topological superconductivity,can be achieved by applying magnetic field.When an in-plane Zeeman field is applied to the system,two corner modes appear in the superconducting junction.Furthermore,we also discover a two-dimensional nodal superconducting phase which supports flat-band Majorana edge modes connecting the bulk nodes.Importantly,we demonstrate that zero-energy Majorana corner modes are stable when increasing the thickness of topological insulator thin film.
基金supported by the National Natural Science Foundation of China(Grant Nos.11927809,13001241,and E0209/52072170)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB25000000)。
文摘We successfully grow a new superconductor GaBa2Ca3Cu4O11+δ(Ga-1234) with a transition temperature of 113 K, using the Walker-type high-pressure synthesis apparatus. X-ray diffraction measurements on the powderized samples show a mixture of the Ga-1234 phase and the Ca0.85CuO2phase, and the former is dominant. Under the scanning electron microscope, plate-like crystals of the Ga-based 1234 phase with shiny surfaces can be seen.The obtained local chemical compositions revealed by energy dispersion x-ray spectroscopy are very close to the stoichiometric values. On some sub-millimeter crystal-like samples of the 1234 phase, we obtain a full Meissner shielding volume. From the temperature-dependent magnetizations, we determine the irreversibility fields and find that the system exhibits a highly anisotropic behavior.
基金the Guangxi Natural Science Foundation,China(Grant Nos.2022GXNSFAA035560and GuikeAD20159009)the Scientific Research Foundation of Guilin University of Technology(Grant No.GLUTQD2017009)。
文摘The competition between different magnetic structures in hole-doped Fe-pnicitides is explored based on an extended five-orbital Hubbard model including long-range Coulomb interactions.Our results show that the stabilized magnetic structure evolves with increasing hole doping level.Namely,the stripe antiferromagnetic phase dominates at zero doping,while magnetic structures with more antiferromagnetic linking numbers such as the staggered tetramer,staggered trimer,and staggered dimer phases become energetically favorable as the hole density increases.At a certain doping level,energy degeneracy of different magnetic structures appears,indicating strong magnetic frustration and magnetic fluctuations in the system.We suggest that the magnetic competition induced by the hole doping may explain the fast decrease of the Neel temperature TNand the moderately suppressed magnetic moment in the hole doped Fe-pnicitides.Moreover,our results show a sign reversal of the kinetic energy anisotropy as the magnetic ground state evolves,which may be the mechanism behind the puzzling sign reversal of the in-plane resistivity anisotropy in hole-doped Fe-pnicitides.
基金This work was supported by the Special Fund of the Institute of Geophysics,China Earthquake Administration(Nos.DQJB22B19,DQJB22R29 and DQJB22B26)the National Natural Science Foundation of China(Nos.41974066,U1839209 and 42074053)。
文摘On September 16,2021,a MS6.0 earthquake struck Luxian County,one of the shale gas blocks in the Southeastern Sichuan Basin,China.To understand the seismogenic environment and its mechanism,we inverted a fine three-dimensional S-wave velocity model from ambient noise tomography using data from a newly deployed dense seismic array around the epicenter,by extracting and jointly inverting the Rayleigh phase and group velocities in the period of 1.6–7.2 s.The results showed that the velocity model varied significantly beneath different geological units.The Yujiasi syncline is characterized by low velocity at depths of~3.0–4.0 km,corresponding to the stable sedimentary layer in the Sichuan Basin.The eastern and western branches of the Huayingshan fault belt generally exhibit high velocities in the NE-SW direction,with a few local low-velocity zones.The Luxian MS6.0 earthquake epicenter is located at the boundary between the high-and low-velocity zones,and the earthquake sequences expand eastward from the epicenter at depths of 3.0–5.0 km.Integrated with the velocity variations around the epicenter,distribution of aftershock sequences,and focal mechanism solution,it is speculated that the seismogenic mechanism of the main shock might be interpreted as the reactivation of pre-existing faults by hydraulic fracturing.
基金Project supported by the National Natural Science Foundation of China (Grant No.12174064)the National Key R&D Program of China (Grant No.2022YFA1402200)the Shanghai Municipal Science and Technology Major Project (Grant No.2019SHZDZX01)。
文摘The noncentrosymmetric superconductor CaPtAs with time-reversal symmetry breaking in its superconducting state was previously proposed to host nodal superconductivity.Here,by employing ultralow-temperature thermal conductivity measurement on CaPtAs single crystal,we study its superconducting gap structure.A negligible residual linear term of thermal conductivity(κ_(0)/T)in zero magnetic field and the field dependence ofκ_(0)/T indicate that CaPtAs has multiple superconducting gaps with a dominant s-wave component.This is consistent with recent nuclear quadrupole resonance measurements on CaPtAs.Our work puts a strong constraint on the theories to describe the superconducting pairing symmetry of CaPtAs.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11974153,12374034 and 11921005)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302403)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB28000000)。
文摘The Ising spin–orbit coupling could give rise to the spin-triplet Cooper pairs and equal-spin Andreev reflection(AR)in Ising superconductors.Here we theoretically study the valley-dependent equal-spin AR in a ferromagnet/Ising superconductor junction with a circularly polarized light applied to the ferromagnet.Because of the spin-triplet Cooper pairs and the optical irradiation,eight kinds of AR processes appear in the junction,including equal-spin AR and normal AR,the strengths and properties of which strongly depend on the valley degree of freedom.The AR probabilities for the incident electron from the two valleys exhibit certain symmetry with respect to the magnetization angle and the effective energy of light.The equal-spin AR and normal AR present different features and resonant behaviors near the superconducting gap edges.Due to equal-spin-triplet Cooper pairs,not only charge supercurrent but also spin supercurrent can transport in the Ising superconductors.The differential spin conductance for electron injecting from the two valleys can be controlled by the circularly polarized light.
基金supported by China Geological Survey (DD20190083, DD20221662)National Natural Science Foundation of China (41904044, 41974064, 42174076, 41874069)Youth Innovation Promotion Association CAS (2019330).
文摘The Ningdu basin,located in southern Jiangxi province of southwest China,is one of the Mesozoic basin groups which has exploration prospects for geothermal energy.A study on the detailed velocity structure of the Ningdu basin can provide important information for geothermal resource exploration.In this study,we deployed a dense seismic array in the Ningdu basin to investigate the 3D velocity structure and discuss implications for geothermal exploration and geological evolution.Based on the dense seismic array including 35 short-period(5 s-100 Hz)seismometers with an average interstation distance of~5 km,Rayleigh surface wave dispersion curves were extracted from the continuous ambient noise data for surface wave tomographic inversion.Group velocity tomography was conducted and the 3D S-wave velocity structure was inverted by the neighborhood algorithm.The results revealed obvious low-velocity anomalies in the center of the basin,consistent with the low-velocity Cretaceous sedimentary rocks.The basement and basin-controlling fault can also be depicted by the S-wave velocity anomalies.The obvious seismic interface is about 2 km depth in the basin center and decreases to 700 m depth near the basin boundary,suggesting spatial thickness variations of the Cretaceous sediment.The fault features of the S-wave velocity profile coincide with the geological cognition of the western boundary basincontrolling fault,which may provide possible upwelling channels for geothermal fluid.This study suggests that seismic tomography with a dense array is an effective method and can play an important role in the detailed investigations of sedimentary basins.
基金supported by the National Natural Science Foundation of China (Grant No. 52072229)the Key-grant Project of the Ministry of Education of China (Grant No. 311033)+1 种基金the Fundamental Research Funds for the Central Universities (Grant No. GK201706001)the Teaching Reform and Innovation Project of Higher Education in Shanxi Province, China (Grant No. J2021719)。
文摘To study the influence of thickness on the magnetic properties of ReBCO(Re = Y, Gd, Sm, Nd, etc.) bulk superconductors, a single domain gadolinium barium copper oxide(GdBCO) bulk superconductor fabricated by the Re + 011 top seeded infiltration growth(Re + 011 TSIG) method was continuously sliced along the bottom to obtain samples of different thickness. The levitation force and attractive force of these samples were tested at 77 K in the zero-field-cooled(ZFC)state. It is found that as the sample thickness decreases, the levitation force decreases gradually whereas the attractive force increases. This is related to the varied ability to resist the penetration of magnetic field occasioned by varying sample thickness, which are deeply revealed by combining with the characteristics of the non-ideal type-II superconductor. Further,the levitation force exhibits a trend of slow initial change followed by rapid change, which may be attributed to the growth of the sample. Measurement of the trapped field shows that a similar distribution of trapped field at the top and bottom surfaces can be achieved by removing some materials from the bottom of the bulk. These results provide a reference for meeting the actual requirements of ReBCO bulks of different thicknesses and greatly contribute to practical designs and applications.