dc Josephson Effect in s-Wave Superconductor/Ferromagnet Insulator/p-Wave Superconductor Junctions

The Josephson currents in s-wave superconductor/ferromagnet insulator/p-wave superconductor（s/FI/p） junctions are calculated as a function of temperature and the phase taking into account the roughness scattering effect at interface. The phase dependence of the Josephson current I （φ） between s-wave and px-wave superconductor is predicted to be sin（2φ）. The ferromagnet scattering effect, the barrier strength, and the roughness strength at interface suppress the dc currents in s/FI/p junction.

Effect of the mixing of s-wave and chiral p-wave pairings on electrical shot noise properties of normal metal/superconductor tunnel junctions

We study theoretically the electrical shot noise properties of tunnel junctions between a normal metal and a superconductor with the mixture of singlet s-wave and chiral triplet p-wave pairing due to broken inversion symmetry. We investigate how the shot noise properties vary as the relative amplitude between the two parity components in the pairing potential is changed. It is demonstrated that some characteristics of the electrical shot noise properties of such tunnel junctions may depend sensitively on the relative amplitude between the two parity components in the pairing potential, and some significant changes may occur in the electrical shot noise properties when the relative amplitude between the two parity components is varied from the singlet s-wave pairing dominated regime to the chiral triplet p-wave pairing dominated regime. In the chiral triplet p-wave pairing dominated regime, the ratio of noise power to electric current is close to 2e both in the in-gap and in the out-gap region. In the singlet s-wave pairing dominated regime, the value of this ratio is close to 4e in the inner gap region but may reduce to about 2e in the outer gap region as the relative amplitude of the chiral triplet pairing component is increased. The variations of the differential shot noise with the bias voltage also exhibit some significantly different features in different regimes. Such different features can serve as useful diagnostic tools for the determination of the relative magnitude of the two parity components in the pairing potential.

Evolution of Superconducting-Transition Temperature with Superfluid Density and Conductivity in Pressurized Cuprate Superconductors

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.

Strong Anisotropic Order Parameters at All-Nitride Ferromagnet/Superconductor Interfaces

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.

Controversy Clouds Real Progress in Superconductor Research

In the 8 March 2023 issue of the journal Nature,a paper attracted global attention with the report of a new superconductor material exhibiting ground-breaking properties[1,2].A group led by Ranga P.Dias,assistant professor of mechanical engineering at the University of Rochester(Rochester,NY,USA),described a hydride material that superconducted at around room temperature,albeit at pressures 10000 times greater than atmospheric pressure[3].

Design of high-temperature superconductors at moderate pressures by alloying AlH3 or GaH3

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.

Prediction of novel layered indium halide superconductors

We design two new layered indium halide compounds LaOInF_(2)and LaOInCl_(2)by means of first-principles calculations and evolutionary crystal structure prediction.We find both compounds crystallize in a tetragonal structure with P4/nmm space group and have indirect band gaps of 2.58 eV and 3.21 eV,respectively.By substituting O with F,both of them become metallic and superconducting at low temperature.The F-doping leads to strong electron-phonon coupling in the low-energy acoustic phonon modes which is mainly responsible for the induced superconductivity.The total electron-phonon coupling strength are 1.86 and 1.48,while the superconducting transition temperature(T_(c))are about 7.2 K and 6.5 K with 10%and 5%F doping for LaOInF_(2)and LaOInCl_(2),respectively.

Two-fold symmetry of the in-plane resistance in kagome superconductor Cs(V_(1-x)Ta_(x))_(3)Sb_(5) with enhanced superconductivity

The kagome superconductor CsV_(3)Sb_(5) has attracted widespread attention due to its rich correlated electron states including superconductivity, charge density wave(CDW), nematicity, and pair density wave. Notably, the modulation of the intertwined electronic orders by the chemical doping is significant to illuminate the cooperation/competition between multiple phases in kagome superconductors. In this study, we have synthesized a series of tantalum-substituted Cs(V_(1-x)Ta_(x))_(3)Sb_(5) by a modified self-flux method. Electrical transport measurements reveal that CDW is suppressed gradually and becomes undetectable as the doping content of x is over 0.07. Concurrently, the superconductivity is enhanced monotonically from T_(c) ~ 2.8 K at x = 0 to 5.2 K at x = 0.12. Intriguingly, in the absence of CDW, Cs(V_(1-x)Ta_(x))_(3)Sb_(5)(x = 0.12) crystals exhibit a pronounced two-fold symmetry of the in-plane angular-dependent magnetoresistance(AMR) in the superconducting state, indicating the anisotropic superconducting properties in the Cs(V_(1-x)Ta_(x))_(3)Sb_(5). Our findings demonstrate that Cs(V_(1-x)Ta_(x))_(3)Sb_(5) with the non-trivial band topology is an excellent platform to explore the superconductivity mechanism and intertwined electronic orders in quantum materials.

Topological superconductors with spin-triplet pairings and Majorana Fermi arcs

We construct a three-dimensional topological superconductor Bogoliubov–de Gennes(BdG)Hamiltonian with the normal state being a three-dimensional topological insulator.By introducing inter-orbital spin-triplet pairings term△3,there are topological Majorana nodes in the bulk and they are connected by Majorana Fermi arcs on the surface,similar to the case of Weyl semimetal.Furthermore,by adding an inversion-breaking term to the normal state,momentum-independent pairing terms with different parities can coexist in the Bd G Hamiltonian,which creates more Majorana modes similar to Andreev bound states and a richer phase diagram.

High Harmonic Spectroscopy Retrieves Electronic Structure of High-pressure Superconductors

High pressure has revealed surprising physics and creates novel states in condensed matter.Exciting examples include near-roomtemperature superconductivity(T_(c)>200 K)in highlypressured hydrides such as H_(3)S and LaH_(10).

Electronic Structure Investigation of 12442 Iron-Based Superconductors Based on Block-Layer Model

Superconducting transition temperature(Tc),as a crucial parameter,exploring its relationship with various macroscopic and microscopic factors helps to understand the mechanism of high-temperature superconductivity from multiple perspectives,aiding in a multidimensional comprehension of high-temperature superconductivity mechanisms.Drawing inspiration from the block-layer structure models of cuprate superconductors,we computationally investigated the interlayer interaction energies in the 12442-type iron-based superconducting materials AkCa_(2)Fe_(4)As_(4)F_(2)(Ak=K,Rb,Cs)systems based on the block-layer model and explored their relationship with Tc.We observed that an increase in interlayer combinative energy leads to a decrease in Tc,while conversely,a decrease in interlayer combination energy results in an increase in Tc.Further,we found that the contribution of the Fe 3d band structure,especially the 3dz2 orbital,to charge transfer is significant.

Impurity- and magnetic-field-induced quasiparticle states in chiral p-wave superconductors

Both impurity- and magnetic-field-induced quasiparticle states in chiral p-wave superconductors are investigated theoretically by solving the Bogoliubov-de Gennes equations self-consistently. At the strong scattering limit, we find that a universal state bound to the impurity can be induced for both a single nonmagnetic impurity and a single magnetic impurity. Furthermore, we find that different chiral order parameters and the corresponding supercurrents have uniform distributions around linear impurities. Calculations of the local density of states in the presence of an external magnetic field show that the intensity peak of the zero-energy Majorana mode in the vortex core can be enhanced dramatically by tuning the strength of the external magnetic field or pairing interaction.

Kondo screening cloud in a superconductor with mixed s-wave and p-wave pairing states

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.

Spin-polarized quasiparticle transport in ferromagnet/insulator/p-wave superconductor junction

We have studied the tunneling conductance in ferromagnet/insulator/p-wave superconductor junctions,taking into account the rough interface scattering effect. We find that there exist zero-bias conductance peaks and single-minimum structure in tunneling spectroscopy. As the exchange energy increases,the Andreev reflection is always suppressed and the differential conductance decreases. The differential conductance depends on the barrier strength and the roughness at the interface.

Stimulated Holographic P-wave Superconductors

Using classical time-average approximation, critical temperature and condensed solution in holographic pwave superconductors with a time-dependent source is investigated in probe limit. By choosing suitable gauge field ansatz, the equation of motion for a vector field is presented. With the help of the Sturm-Liouville equation, concrete values of phase transition temperature and criticaJ frequency are obtained. It is shown that the phase transition temperature enhances as the frequency of the time-dependent source raises in high frequency regime, which means that the operators on the boundary field theory will be easier to condense.

Holographic p-Wave Superconductors in Quintessence AdS Black Hole Spacetime

We construct a holographic p-wave superconductor model in the background of quintessence AdS black hole with an SU（2） Yang-Mills gauge field and then probe the effects of quintessence on the holographic p-wave superconduc- tor. We investigate the relation between the critical temperature and the state parameter of quintessence, and present the numerical results for electric conductivity. It is shown that the condensation of the vector field becomes harder as the absolute value of the state parameter increases. Unlike the scalar condensate in the s-wave model, the condensation of the vector field in p-wave model can occur in the total value range of the state parameter wq of quintessence. These results could help us know more about holographic superconductor and dark energy.

Customizing topological phases in the twisted bilayer superconductors with even-parity pairings

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.

Gate-Tunable Negative Differential Conductance in Hybrid Semiconductor–Superconductor Devices

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.

Abnormal magnetoresistance effect in the Nb/Si superconductor–semiconductor heterojunction

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.

Anisotropy of Electronic Spin Texture in the High-Temperature Cuprate Superconductor Bi_(2)Sr_(2)CaCu_(2)O_(8+δ)

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.