We theoretically investigate the reflected spatial Imbert–Fedorov(IF)shift of transverse-electric(TE)-polarized beam illuminating on a bulk Weyl semimetal(WSM).The spatial IF shift is enhanced significantly at two di...We theoretically investigate the reflected spatial Imbert–Fedorov(IF)shift of transverse-electric(TE)-polarized beam illuminating on a bulk Weyl semimetal(WSM).The spatial IF shift is enhanced significantly at two different frequencies close to the epsilon-near-zero(ENZ)frequency,where large values of reflection coefficients|r_(pp)|/|r_(ss)|are obtained due to the ENZ response induced different rapid increasing trends of|r_(pp)|and|r_(ss)|.Particularly,the tunable ENZ effect with tilt degree of Weyl cones and Fermi energy enables the enhanced spatial IF shift at different frequencies.The enhanced spatial IF shift also shows the adjustability of WSM thickness,incident angle and Weyl node separation.Our findings provide easy and available methods to enlarge and adjust the reflected IF shift of TE-polarized light with a WSM.展开更多
One could tune a topological double-Weyl semimetal or a topological triple-Weyl semimetal to become a topologically trivial insulator by opening a band gap.This kind of quantum phase transition is characterized by the...One could tune a topological double-Weyl semimetal or a topological triple-Weyl semimetal to become a topologically trivial insulator by opening a band gap.This kind of quantum phase transition is characterized by the change of certain topological invariant.A new gapless semimetallic state emerges at each topological quantum critical point.Here we perform a renormalization group analysis to investigate the stability of such critical points against perturbations induced by random scalar potential and random vector potential.We find that the quantum critical point between double-Weyl semimetal and band insulator is unstable and can be easily turned into a compressible diffusive metal by any type of weak disorder.The quantum critical point between triple-Weyl semimetal and band insulator flows to a stable strong-coupling fixed point if the system contains a random vector potential merely along the z-axis,but becomes a compressible diffusive metal when other types of disorders exist.展开更多
Ta As,the first experimentally discovered Weyl semimetal material,has attracted a lot of attention due to its high carrier mobility,high anisotropy,nonmagnetic properties and strong interaction with light.These make i...Ta As,the first experimentally discovered Weyl semimetal material,has attracted a lot of attention due to its high carrier mobility,high anisotropy,nonmagnetic properties and strong interaction with light.These make it an ideal candidate for the study of Weyl fermions and applications in quantum computation,thermoelectric devices,and photodetection.For further basic physics studies and potential applications,large-size and high-quality Ta As films are urgently needed.However,it is difficult to grow As-stoichiometry Ta As films due to the volatilization of As during the growth.To solve this problem,we attempted to grow Ta As films on different substrates using targets with different As stoichiometric ratios via pulsed laser deposition(PLD).In this work,we found that partial As ions of the Ga As substrate are likely to diffuse into the Ta As films during growth,which was preliminarily confirmed by structural characterization,surface topography and composition analysis.As a result,the As content in the Ta As film was improved and the Ta As phase was achieved.Our work presents an effective method for the fabrication of Ta As films using PLD,enabling possible use of the Weyl semimetal film for functional devices.展开更多
Non-stoiehiometry effect on the extreme magnetoresistanee is systematically investigated for the Weyl semimetal WTe2. Magnetoresistance and Hall resistivity are measured for the as-grown samples with a slight differen...Non-stoiehiometry effect on the extreme magnetoresistanee is systematically investigated for the Weyl semimetal WTe2. Magnetoresistance and Hall resistivity are measured for the as-grown samples with a slight difference in Te vacancies and the annealed samples with increased Te vacancies. The fits to a two-band model show that the magnetoresistanee is strongly dependent on the residual resistivity ratio (i.e., the degree of non-stoichiometry), which is eventually understood in terms of electron doping that not only breaks the balance between electron-type and hole-type carrier densities, but also reduces the average carrier mobility. Thus the compensation effect and ultrahigh mobility are probably the main driving force of the extreme magnetoresistance in WTe2.展开更多
Recently, the Dirac and Weyl semimetals have attracted extensive attention in condensed matter physics due to both the fundamental interest and the potential application of a new generation of electronic devices. Here...Recently, the Dirac and Weyl semimetals have attracted extensive attention in condensed matter physics due to both the fundamental interest and the potential application of a new generation of electronic devices. Here we review the exotic electrical transport phenomena in Dirac andWeyl semimetals. Section 1 is a brief introduction to the topological semimetals(TSMs). In Section 2 and Section 3, the intriguing transport phenomena in Dirac semimetals(DSMs) andWeyl semimetals(WSMs) are reviewed, respectively. The most widely studied Cd_3A_(s2) and the TaAs family are selected as representatives to show the typical properties of DSMs and WSMs, respectively. Beyond these systems, the advances in other TSM materials,such as ZrTe_5 and the MoTe_2 family, are also introduced. In Section 4, we provide perspectives on the study of TSMs especially on the magnetotransport investigations.展开更多
Due to non-saturating magnetoresistance(MR)and the special compensation mechanism,the Weyl semimetal Ta As single crystal has attracted considerable attention in condensed matter physics.Herein,we use maximum entropy ...Due to non-saturating magnetoresistance(MR)and the special compensation mechanism,the Weyl semimetal Ta As single crystal has attracted considerable attention in condensed matter physics.Herein,we use maximum entropy mobility spectrum analysis(MEMSA)to extract charge carrier information by fitting the experimentally measured longitudinal and transverse electric transport curves of Ta As.The carrier types and the number of bands are obtained without any hypothesis.Study of the temperature dependence shows details of carrier property evolution.Our quantitative results explain the nonsaturated magnetoresistance and Hall sign change phenomena of TaAs.展开更多
Motivated by the fact that Weyl fermions can emerge in a three-dimensional topological insulator on breaking either time-reversal or inversion symmetries,we propose that a topological quantum phase transition to a Wey...Motivated by the fact that Weyl fermions can emerge in a three-dimensional topological insulator on breaking either time-reversal or inversion symmetries,we propose that a topological quantum phase transition to a Weyl semimetal phase occurs under the off-resonant circularly polarized light,in a three-dimensional topological insulator,when the intensity of the incident light exceeds a critical value.The circularly polarized light effectively generates a Zeeman exchange field and a renormalized Dirac mass,which are highly controllable.The phase transition can be exactly characterized by the first Chern number.A tunable anomalous Hall conductivity emerges,which is fully determined by the location of the Weyl nodes in momentum space,even in the doping regime.Our predictions are experimentally realizable through pump-probe angle-resolved photoemission spectroscopy and raise a new way for realizing Weyl semimetals and quantum anomalous Hall effects.展开更多
We study the behaviors of three-dimensional double and triple Weyl fermions in the presence of weak random potential.By performing the Wilsonian renormalization group(RG)analysis,we reveal that the quasiparticle expe...We study the behaviors of three-dimensional double and triple Weyl fermions in the presence of weak random potential.By performing the Wilsonian renormalization group(RG)analysis,we reveal that the quasiparticle experiences strong renormalization which leads to the modification of the density of states and quasiparticle residue.We further utilize the RG analysis to calculate the classical conductivity and show that the diffusive transport is substantially corrected due to the novel behavior of the quasiparticle and can be directly measured by experiments.展开更多
We perform a series of high-pressure synchrotron x-ray diffraction (XRD) and resistance measurements on the Weyl semimetal NbAs. The crystal structure remains stable up to 26 GPa according to the powder XRD data. Th...We perform a series of high-pressure synchrotron x-ray diffraction (XRD) and resistance measurements on the Weyl semimetal NbAs. The crystal structure remains stable up to 26 GPa according to the powder XRD data. The resistance of NbAs single crystal increases monotonically with pressure at low temperature. Up to 20 GPa, no superconducting transition is observed down to 0.3 K. These results show that the Weyl semimetal phase is robust in NbAs, and applying pressure may not be a good way to obtain a topological superconductor from Weyl semimetal NbAs.展开更多
We grew single crystals of vanadium-substituted,ferromagnetic Weyl semimetal candidate Zr1-xVxCo1.6Sn from molten tin flux.These solid solutions all crystallize in a full Heusler structure(L21)while their Curie temper...We grew single crystals of vanadium-substituted,ferromagnetic Weyl semimetal candidate Zr1-xVxCo1.6Sn from molten tin flux.These solid solutions all crystallize in a full Heusler structure(L21)while their Curie temperatures and magnetic moments are enhanced by V-substitution.Their resistivity gradually changes from bad-metal-like to semiconductor-like with increasing x while the anomalous Hall effect(AHE),which can be well fitted by Tian-Ye-Jin(TYJ)scaling,[1]is also enhanced.Moreover,we find an apparent electron-electron interaction(EEI)induced quantum correction in resistivity at low temperature.The anomalous Hall conductivity(AHC)dominated by the intrinsic term is not corrected.展开更多
The tantalum arsenide (TaAs) is a topological Weyl semimetal which is a class of materials of gapless with three- dimensional topological structure. In order to develop a comprehensive description of the topological...The tantalum arsenide (TaAs) is a topological Weyl semimetal which is a class of materials of gapless with three- dimensional topological structure. In order to develop a comprehensive description of the topological properties of the Weyl semimetal, we use the density functional theory to study several defects of TaAs after H irradiation and report the electronic dispersion curves and the density of states of these defects. We find that various defects have different influences on the topological properties. Interstitial H atom can shift the Fermi level. Both Ta vacancy with a concentration of 1/64 and As vacancy with a concentration of 1/64 destruct a part of the Weyl points. The substitutional H atom on a Ta site could repair only a part of the Weyl points, while H atom on an As site could repair all the Wevl points.展开更多
The influence of the off-resonant circularly polarized light on the Josephson current in the time-reversal broken superconducting Weyl semimetal junctions is investigated by using the Bogoliubov–de Gennes equation an...The influence of the off-resonant circularly polarized light on the Josephson current in the time-reversal broken superconducting Weyl semimetal junctions is investigated by using the Bogoliubov–de Gennes equation and the transfer matrix approach.Both the zero momentum BCS pairing states and the finite momentum Fulde–Ferrell–Larkin–Ovchinnikov(FFLO)pairing states are considered for the Weyl superconductors.When a circularly polarized light is applied,it is shown that the current phase relation remains unchanged for the BCS pairing with the increasing of incident radiation intensity A_(0).For FFLO pairing,the Josephson current exhibits the 0–πtransition and periodic oscillation as a function of A_(0).The dependence of free energy and critical current on A_(0) are also investigated.展开更多
The quantum Hall effect(QHE),which is usually observed in two-dimensional systems,was predicted theoretically and observed experimentally in three-dimensional(3 D)topological semimetal.However,there are some inconsist...The quantum Hall effect(QHE),which is usually observed in two-dimensional systems,was predicted theoretically and observed experimentally in three-dimensional(3 D)topological semimetal.However,there are some inconsistencies between the theory and the experiments showing the theory is imperfect.Here,we generalize the theory of the 3 D QHE of Fermi arcs in Weyl semimetal.Through calculating the sheet Hall conductivity of a Weyl semimetal slab,we show that the 3 D QHE of Fermi arcs can occur in a large energy range and the thickness dependences of the QHE in different Fermi energies are distinct.When the Fermi energy is near the Weyl nodes,the Fermi arcs give rise to the QHE which is independent of the thickness of the slab.When the Fermi energy is not near the Weyl nodes,the two Fermi arcs form a complete Fermi loop with the assistance of bulk states giving rise to the QHE which is dependent on the sample thickness.We also demonstrate how the band anisotropic terms influence the QHE of Fermi arcs.Our theory complements the imperfections of the present theory of 3 D QHE of Fermi arcs.展开更多
We investigate high-order harmonic generations(HHGs)under comparison of Weyl cones in two types.Due to the hyperboloidal electron pocket structure,strong noncentrosymmetrical generations in high orders are observed ar...We investigate high-order harmonic generations(HHGs)under comparison of Weyl cones in two types.Due to the hyperboloidal electron pocket structure,strong noncentrosymmetrical generations in high orders are observed around a single type-ⅡWeyl point,especially at zero frequency.Such a remarkable DC signal is proved to have attributions from the intraband transition after spectral decomposition.Under weak pulse electric field,the linear optical response of a nontilted Weyl cone is consistent with the Kubo theory.With extensive numerical simulations,we conclude that the non-zero chemical potential can enhance the even-order generations,from the slightly tilted system to the over-tilted systems.In consideration of dynamical symmetries,type-Ⅰand type-ⅡWeyl cones also show different selective responses under the circularly polarized light.Finally,using a more realistic model containing two pairs of Weyl points,we demonstrate that paired Weyl points with opposite chirality can suppress the overall even-order generations.展开更多
The Onsager-Casimir reciprocal relations are a fundamental symmetry of nonequilibrium statistical systems.Here we study an unusual chirality-dependent Hall effect in a tilted Weyl semimetal Co_(3)Sn_(2)S_(2) with brok...The Onsager-Casimir reciprocal relations are a fundamental symmetry of nonequilibrium statistical systems.Here we study an unusual chirality-dependent Hall effect in a tilted Weyl semimetal Co_(3)Sn_(2)S_(2) with broken time-reversal symmetry.It is confirmed that the reciprocal relations are satisfied.Since two Berry curvature effects,an anomalous velocity and a chiral chemical potential,contribute to the observed Hall effect,the reciprocal relations suggest their intriguing connection.展开更多
We demonstrate the existence of the chirai magnetic effect in a simple lattice model of Weyl semimetal, which is a hallmark of chiral anomaly in the Weyl semimetal, by calculating the anomalous charge current directly...We demonstrate the existence of the chirai magnetic effect in a simple lattice model of Weyl semimetal, which is a hallmark of chiral anomaly in the Weyl semimetal, by calculating the anomalous charge current directly. We identify that the uniform external magnetic field can induce a non-dissipative charge current along its direction in Weyl semimetal, even in the absence of an external electric field if the right and left handed Weyl points are separated in energy, and that the anomalous current is proportional to the strength of the magnetic field and the energy separation with a universal coetticient e2/h2, which coincide with the ones predicted on the basis of the field theory treatment. Our results give the possibility to detect these nontrivial electrodynamic phenomena in real materials of Weyl semimetal.展开更多
Topological Dirac semimetals are a parent state from which other exotic topological phases of matter, such as Weyl semimetals and topological insulators, can emerge. In this study, we investigate a Dirac semimetal pos...Topological Dirac semimetals are a parent state from which other exotic topological phases of matter, such as Weyl semimetals and topological insulators, can emerge. In this study, we investigate a Dirac semimetal possessing sixfold rotational symmetry and hosting higher-order topological hinge Fermi arc states, which is irradiated by circularly polarized light. Our findings reveal that circularly polarized light splits each Dirac node into a pair of Weyl nodes due to the breaking of time-reversal symmetry, resulting in the realization of the Weyl semimetal phase. This Weyl semimetal phase exhibits rich boundary states, including two-dimensional surface Fermi arc states and hinge Fermi arc states confined to six hinges.Furthermore, by adjusting the incident direction of the circularly polarized light, we can control the degree of tilt of the resulting Weyl cones, enabling the realization of different types of Weyl semimetals.展开更多
The advancement of 6G technology relies on the development of high-performance terahertz detectors that can operate at room temperature.These detectors are crucial for Internet of Things(Io T)applications,which requir...The advancement of 6G technology relies on the development of high-performance terahertz detectors that can operate at room temperature.These detectors are crucial for Internet of Things(Io T)applications,which require sensitive environmental sensing and efficient reception of 6G signals.One significant research focus is on detection technology with high responsiveness and low equivalent noise power for 6G signals,which experience high losses in the air.To meet the demand for ultra-sensitive detectors in 6G technology,we have employed several techniques.Firstly,we prepared a large area of Weyl-semimetal layer through magnetron sputtering.Secondly,we obtained a high-quality Weyl-semimetal active layer by carefully controlling the annealing conditions.Next,a thin nano-Au layer was introduced as a micro-cavity reflection layer to enhance the device's detection rate.Additionally,we incorporated an electromagnetic induction well to improve carrier confinement and enhance the detection sensitivity.This proposed high-performance terahertz detector,with its potential for industrial production,offers a valuable technical solution for the advancement of 6G technology.展开更多
It has now become recognized that the electron-phonon coupling(EPC)may play an important role in governing the phonon transport,especially for metallic and semiconducting systems at high carrier concentration.Here we ...It has now become recognized that the electron-phonon coupling(EPC)may play an important role in governing the phonon transport,especially for metallic and semiconducting systems at high carrier concentration.Here we focus on the Weyl semimetals TaAs and NbAs and give a comparative study on their phonon transport properties by explicitly including the EPC in first-principles calculations.It is found that the lattice thermal conductivities of both systems are significantly reduced by the EPC,which is more pronounced for the TaAs compared with the NbAs at the same carrier concentration.Detailed analysis indicates that the TaAs exhibits smaller EPC phonon relaxation time,as characterized by stronger EPC strength which is associated with larger deformation potential constant and Born effective charge.Moreover,we see that the TaAs exhibits obviously larger overlap between the EPC relaxation time and that from intrinsic phonon-phonon scattering,which could further reduce the lattice thermal conduc-tivity.Our work not only highlights the vital importance of EPC in accurately predicting the phonon transport behaviors,but also offers a simple alternative to evaluate the EPC strength of various material systems.展开更多
Topological magnetic Weyl semimetals have been proposed to host controllable chiral domain walls which bear a great prospect in device applications. To exploit them in applications, it is important to have a proper wa...Topological magnetic Weyl semimetals have been proposed to host controllable chiral domain walls which bear a great prospect in device applications. To exploit them in applications, it is important to have a proper way to tune and manipulate these domain walls. One possible means is through magnetoelastic coupling. The involvement of rare earth in the lately proposed RAl X(R =rare earth, X = Si and Ge) family magnetic Weyl semimetals may provide such a platform. Here we present the transport and thermodynamic properties of Ce Al Ge under hydrostatic pressure. We find that pressure enhances the antiferromagnetic exchange in Ce Al Ge but essentially retains its magnetic structure. A large topological Hall effect with a pronounced loop shape is observed within the magnetically ordered state, and it splits into two regions under pressure. Such an unusual electromagnetic response is inferred to be a consequence of chiral magnetic domain walls. The unprecedented concomitance of its evolution under pressure and the reentrance of antiferromagnetic order strongly suggest the capability of switching on/off this electromagnetic response in noncentrosymmetric magnetic Weyl semimetals via magnetoelastic coupling.展开更多
基金the National Natural Science Foundation of China(Grant Nos.61875133 and 11874269).
文摘We theoretically investigate the reflected spatial Imbert–Fedorov(IF)shift of transverse-electric(TE)-polarized beam illuminating on a bulk Weyl semimetal(WSM).The spatial IF shift is enhanced significantly at two different frequencies close to the epsilon-near-zero(ENZ)frequency,where large values of reflection coefficients|r_(pp)|/|r_(ss)|are obtained due to the ENZ response induced different rapid increasing trends of|r_(pp)|and|r_(ss)|.Particularly,the tunable ENZ effect with tilt degree of Weyl cones and Fermi energy enables the enhanced spatial IF shift at different frequencies.The enhanced spatial IF shift also shows the adjustability of WSM thickness,incident angle and Weyl node separation.Our findings provide easy and available methods to enlarge and adjust the reflected IF shift of TE-polarized light with a WSM.
基金the Natural Science Foundation of Anhui Province,China(Grant No.2208085MA11)the National Natural Science Foundation of China(Grants Nos.11974356,12274414,and U1832209)。
文摘One could tune a topological double-Weyl semimetal or a topological triple-Weyl semimetal to become a topologically trivial insulator by opening a band gap.This kind of quantum phase transition is characterized by the change of certain topological invariant.A new gapless semimetallic state emerges at each topological quantum critical point.Here we perform a renormalization group analysis to investigate the stability of such critical points against perturbations induced by random scalar potential and random vector potential.We find that the quantum critical point between double-Weyl semimetal and band insulator is unstable and can be easily turned into a compressible diffusive metal by any type of weak disorder.The quantum critical point between triple-Weyl semimetal and band insulator flows to a stable strong-coupling fixed point if the system contains a random vector potential merely along the z-axis,but becomes a compressible diffusive metal when other types of disorders exist.
基金Project supported by the National Key Research and Development Program of China(Grant No.2021YFA0718700)the National Natural Science Foundation of China(Grant No.12174347)+1 种基金the Synergetic Extreme Condition User Facility(SECUF)the Center for Materials Genome。
文摘Ta As,the first experimentally discovered Weyl semimetal material,has attracted a lot of attention due to its high carrier mobility,high anisotropy,nonmagnetic properties and strong interaction with light.These make it an ideal candidate for the study of Weyl fermions and applications in quantum computation,thermoelectric devices,and photodetection.For further basic physics studies and potential applications,large-size and high-quality Ta As films are urgently needed.However,it is difficult to grow As-stoichiometry Ta As films due to the volatilization of As during the growth.To solve this problem,we attempted to grow Ta As films on different substrates using targets with different As stoichiometric ratios via pulsed laser deposition(PLD).In this work,we found that partial As ions of the Ga As substrate are likely to diffuse into the Ta As films during growth,which was preliminarily confirmed by structural characterization,surface topography and composition analysis.As a result,the As content in the Ta As film was improved and the Ta As phase was achieved.Our work presents an effective method for the fabrication of Ta As films using PLD,enabling possible use of the Weyl semimetal film for functional devices.
基金Supported by the National Key R&D Program of China under Grant Nos 2016YFA0300404 and 2017YFA0403600the National Natural Science Foundation of China under Grant Nos 51603207,U1532267,11574288 and 11674327the Natural Science Foundation of Anhui Province under Grant No 1708085MA08
文摘Non-stoiehiometry effect on the extreme magnetoresistanee is systematically investigated for the Weyl semimetal WTe2. Magnetoresistance and Hall resistivity are measured for the as-grown samples with a slight difference in Te vacancies and the annealed samples with increased Te vacancies. The fits to a two-band model show that the magnetoresistanee is strongly dependent on the residual resistivity ratio (i.e., the degree of non-stoichiometry), which is eventually understood in terms of electron doping that not only breaks the balance between electron-type and hole-type carrier densities, but also reduces the average carrier mobility. Thus the compensation effect and ultrahigh mobility are probably the main driving force of the extreme magnetoresistance in WTe2.
基金Project supported by the National Basic Research Program of China(Grant Nos.2018YFA0305604,2017YFA0303300,and 2013CB934600)the Research Fund for the Doctoral Program of Higher Education(RFDP)of China(Grant No.20130001110003)+2 种基金the Open Project Program of the Pulsed High Magnetic Field Facility(Grant No.PHMFF2015002) at the Huazhong University of Science and Technologythe Open Research Fund Program of the State Key Laboratory of Low-Dimensional Quantum Physics,Tsinghua University(Grant No.KF201703)the Key Research Program of the Chinese Academy of Sciences(Grant No.XDPB08-2)
文摘Recently, the Dirac and Weyl semimetals have attracted extensive attention in condensed matter physics due to both the fundamental interest and the potential application of a new generation of electronic devices. Here we review the exotic electrical transport phenomena in Dirac andWeyl semimetals. Section 1 is a brief introduction to the topological semimetals(TSMs). In Section 2 and Section 3, the intriguing transport phenomena in Dirac semimetals(DSMs) andWeyl semimetals(WSMs) are reviewed, respectively. The most widely studied Cd_3A_(s2) and the TaAs family are selected as representatives to show the typical properties of DSMs and WSMs, respectively. Beyond these systems, the advances in other TSM materials,such as ZrTe_5 and the MoTe_2 family, are also introduced. In Section 4, we provide perspectives on the study of TSMs especially on the magnetotransport investigations.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11674054,U1932217,and 11704067)。
文摘Due to non-saturating magnetoresistance(MR)and the special compensation mechanism,the Weyl semimetal Ta As single crystal has attracted considerable attention in condensed matter physics.Herein,we use maximum entropy mobility spectrum analysis(MEMSA)to extract charge carrier information by fitting the experimentally measured longitudinal and transverse electric transport curves of Ta As.The carrier types and the number of bands are obtained without any hypothesis.Study of the temperature dependence shows details of carrier property evolution.Our quantitative results explain the nonsaturated magnetoresistance and Hall sign change phenomena of TaAs.
基金Project supported by the National Natural Science Foundation of China(Grant No.11804070)Zhejiang Provincial Natural Science Foundation of China(Grant No.LQ19A040007).
文摘Motivated by the fact that Weyl fermions can emerge in a three-dimensional topological insulator on breaking either time-reversal or inversion symmetries,we propose that a topological quantum phase transition to a Weyl semimetal phase occurs under the off-resonant circularly polarized light,in a three-dimensional topological insulator,when the intensity of the incident light exceeds a critical value.The circularly polarized light effectively generates a Zeeman exchange field and a renormalized Dirac mass,which are highly controllable.The phase transition can be exactly characterized by the first Chern number.A tunable anomalous Hall conductivity emerges,which is fully determined by the location of the Weyl nodes in momentum space,even in the doping regime.Our predictions are experimentally realizable through pump-probe angle-resolved photoemission spectroscopy and raise a new way for realizing Weyl semimetals and quantum anomalous Hall effects.
基金Project supported by the National Natural Science Foundation of China(Grant No.11874337).
文摘We study the behaviors of three-dimensional double and triple Weyl fermions in the presence of weak random potential.By performing the Wilsonian renormalization group(RG)analysis,we reveal that the quasiparticle experiences strong renormalization which leads to the modification of the density of states and quasiparticle residue.We further utilize the RG analysis to calculate the classical conductivity and show that the diffusive transport is substantially corrected due to the novel behavior of the quasiparticle and can be directly measured by experiments.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11422429 and 11421404the National Basic Research Program of China under Grant Nos 2012CB821402 and 2015CB921401+5 种基金the China Postdoctoral Science Foundation under Grant No 2014M560288the Program for Professor of Special Appointment(Eastern Scholar) at Shanghai Institutions of Higher Learningthe Science and Technology Commission of Shanghai Municipality of China under Grant No 15XD1500200HPCAT operations are supported by DOE-NNSA under Award No DE-NA0001974DOE-BES under Award No DE-FG02-99ER45775partial instrumentation funding by NSF
文摘We perform a series of high-pressure synchrotron x-ray diffraction (XRD) and resistance measurements on the Weyl semimetal NbAs. The crystal structure remains stable up to 26 GPa according to the powder XRD data. The resistance of NbAs single crystal increases monotonically with pressure at low temperature. Up to 20 GPa, no superconducting transition is observed down to 0.3 K. These results show that the Weyl semimetal phase is robust in NbAs, and applying pressure may not be a good way to obtain a topological superconductor from Weyl semimetal NbAs.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11774007 and U1832214)the National Key R&D Program of China(Grant No.2018YFA0305601)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB28000000).
文摘We grew single crystals of vanadium-substituted,ferromagnetic Weyl semimetal candidate Zr1-xVxCo1.6Sn from molten tin flux.These solid solutions all crystallize in a full Heusler structure(L21)while their Curie temperatures and magnetic moments are enhanced by V-substitution.Their resistivity gradually changes from bad-metal-like to semiconductor-like with increasing x while the anomalous Hall effect(AHE),which can be well fitted by Tian-Ye-Jin(TYJ)scaling,[1]is also enhanced.Moreover,we find an apparent electron-electron interaction(EEI)induced quantum correction in resistivity at low temperature.The anomalous Hall conductivity(AHC)dominated by the intrinsic term is not corrected.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11635003,11025524,and 11161130520)the National Basic Research Program of China(Grant No.2010CB832903)the European Commissions of 7th Framework Programme(FP7-PEOPLE-2010-IRSES)(Grant No.269131)
文摘The tantalum arsenide (TaAs) is a topological Weyl semimetal which is a class of materials of gapless with three- dimensional topological structure. In order to develop a comprehensive description of the topological properties of the Weyl semimetal, we use the density functional theory to study several defects of TaAs after H irradiation and report the electronic dispersion curves and the density of states of these defects. We find that various defects have different influences on the topological properties. Interstitial H atom can shift the Fermi level. Both Ta vacancy with a concentration of 1/64 and As vacancy with a concentration of 1/64 destruct a part of the Weyl points. The substitutional H atom on a Ta site could repair only a part of the Weyl points, while H atom on an As site could repair all the Wevl points.
基金the National Key Research and Development Program of China(Grant No.2017YFA0303203)the National Natural Science Foundation of China(Grant No.11474149)。
文摘The influence of the off-resonant circularly polarized light on the Josephson current in the time-reversal broken superconducting Weyl semimetal junctions is investigated by using the Bogoliubov–de Gennes equation and the transfer matrix approach.Both the zero momentum BCS pairing states and the finite momentum Fulde–Ferrell–Larkin–Ovchinnikov(FFLO)pairing states are considered for the Weyl superconductors.When a circularly polarized light is applied,it is shown that the current phase relation remains unchanged for the BCS pairing with the increasing of incident radiation intensity A_(0).For FFLO pairing,the Josephson current exhibits the 0–πtransition and periodic oscillation as a function of A_(0).The dependence of free energy and critical current on A_(0) are also investigated.
基金supported by the National Natural Science Foundation of China(Grant No.11974168)(L.S.)。
文摘The quantum Hall effect(QHE),which is usually observed in two-dimensional systems,was predicted theoretically and observed experimentally in three-dimensional(3 D)topological semimetal.However,there are some inconsistencies between the theory and the experiments showing the theory is imperfect.Here,we generalize the theory of the 3 D QHE of Fermi arcs in Weyl semimetal.Through calculating the sheet Hall conductivity of a Weyl semimetal slab,we show that the 3 D QHE of Fermi arcs can occur in a large energy range and the thickness dependences of the QHE in different Fermi energies are distinct.When the Fermi energy is near the Weyl nodes,the Fermi arcs give rise to the QHE which is independent of the thickness of the slab.When the Fermi energy is not near the Weyl nodes,the two Fermi arcs form a complete Fermi loop with the assistance of bulk states giving rise to the QHE which is dependent on the sample thickness.We also demonstrate how the band anisotropic terms influence the QHE of Fermi arcs.Our theory complements the imperfections of the present theory of 3 D QHE of Fermi arcs.
基金performed at the Chinese Academy of Science Terahertz Science Centersupported by the National Natural Science Foundation of China(Grant No.61988102)
文摘We investigate high-order harmonic generations(HHGs)under comparison of Weyl cones in two types.Due to the hyperboloidal electron pocket structure,strong noncentrosymmetrical generations in high orders are observed around a single type-ⅡWeyl point,especially at zero frequency.Such a remarkable DC signal is proved to have attributions from the intraband transition after spectral decomposition.Under weak pulse electric field,the linear optical response of a nontilted Weyl cone is consistent with the Kubo theory.With extensive numerical simulations,we conclude that the non-zero chemical potential can enhance the even-order generations,from the slightly tilted system to the over-tilted systems.In consideration of dynamical symmetries,type-Ⅰand type-ⅡWeyl cones also show different selective responses under the circularly polarized light.Finally,using a more realistic model containing two pairs of Weyl points,we demonstrate that paired Weyl points with opposite chirality can suppress the overall even-order generations.
基金Project supported by the National Key Basic Research Program of China (Grant No. 2020YFA0308800)the National Natural Science Foundation of China (Grant Nos. 11774009 and 12074009)+1 种基金the Natural Science Foundation of Beijing (Grant No. Z200008)the Youth Innovation Promotion Association of the Chinese Academy of Sciences (Grant No. 2021008)
文摘The Onsager-Casimir reciprocal relations are a fundamental symmetry of nonequilibrium statistical systems.Here we study an unusual chirality-dependent Hall effect in a tilted Weyl semimetal Co_(3)Sn_(2)S_(2) with broken time-reversal symmetry.It is confirmed that the reciprocal relations are satisfied.Since two Berry curvature effects,an anomalous velocity and a chiral chemical potential,contribute to the observed Hall effect,the reciprocal relations suggest their intriguing connection.
基金Supported by the National Natural Science Foundation of China under Grant No 11275180the China Government Project under Grant No CSC-201206340089
文摘We demonstrate the existence of the chirai magnetic effect in a simple lattice model of Weyl semimetal, which is a hallmark of chiral anomaly in the Weyl semimetal, by calculating the anomalous charge current directly. We identify that the uniform external magnetic field can induce a non-dissipative charge current along its direction in Weyl semimetal, even in the absence of an external electric field if the right and left handed Weyl points are separated in energy, and that the anomalous current is proportional to the strength of the magnetic field and the energy separation with a universal coetticient e2/h2, which coincide with the ones predicted on the basis of the field theory treatment. Our results give the possibility to detect these nontrivial electrodynamic phenomena in real materials of Weyl semimetal.
基金Project supported by the National Key R&D Program of China (Grant No. 2022YFA1403700)the National Natural Science Foundation of China (Grant Nos. 12074108 and 12347101)+3 种基金the Chongqing Natural Science Foundation (Grant No. CSTB2022NSCQ-MSX0568)the Fundamental Research Funds for the Central Universities (Grant No. 2023CDJXY048)the Natural Science Foundation of Jiangsu Province(Grant No. BK20230066)the Jiangsu Shuang Chuang Project (Grant No. JSSCTD202209)。
文摘Topological Dirac semimetals are a parent state from which other exotic topological phases of matter, such as Weyl semimetals and topological insulators, can emerge. In this study, we investigate a Dirac semimetal possessing sixfold rotational symmetry and hosting higher-order topological hinge Fermi arc states, which is irradiated by circularly polarized light. Our findings reveal that circularly polarized light splits each Dirac node into a pair of Weyl nodes due to the breaking of time-reversal symmetry, resulting in the realization of the Weyl semimetal phase. This Weyl semimetal phase exhibits rich boundary states, including two-dimensional surface Fermi arc states and hinge Fermi arc states confined to six hinges.Furthermore, by adjusting the incident direction of the circularly polarized light, we can control the degree of tilt of the resulting Weyl cones, enabling the realization of different types of Weyl semimetals.
基金supported by the National Natural Science Foundation of China(Grant No.12104314)the Key Laboratory of Optoelectronic Devices Systems of Ministry of Education and Guangdong Province and Research Foundation of Liaocheng University(Grant No.318052316)。
文摘The advancement of 6G technology relies on the development of high-performance terahertz detectors that can operate at room temperature.These detectors are crucial for Internet of Things(Io T)applications,which require sensitive environmental sensing and efficient reception of 6G signals.One significant research focus is on detection technology with high responsiveness and low equivalent noise power for 6G signals,which experience high losses in the air.To meet the demand for ultra-sensitive detectors in 6G technology,we have employed several techniques.Firstly,we prepared a large area of Weyl-semimetal layer through magnetron sputtering.Secondly,we obtained a high-quality Weyl-semimetal active layer by carefully controlling the annealing conditions.Next,a thin nano-Au layer was introduced as a micro-cavity reflection layer to enhance the device's detection rate.Additionally,we incorporated an electromagnetic induction well to improve carrier confinement and enhance the detection sensitivity.This proposed high-performance terahertz detector,with its potential for industrial production,offers a valuable technical solution for the advancement of 6G technology.
基金support from the National Natural Science Foundation(Grant Nos.62074114,51772220).
文摘It has now become recognized that the electron-phonon coupling(EPC)may play an important role in governing the phonon transport,especially for metallic and semiconducting systems at high carrier concentration.Here we focus on the Weyl semimetals TaAs and NbAs and give a comparative study on their phonon transport properties by explicitly including the EPC in first-principles calculations.It is found that the lattice thermal conductivities of both systems are significantly reduced by the EPC,which is more pronounced for the TaAs compared with the NbAs at the same carrier concentration.Detailed analysis indicates that the TaAs exhibits smaller EPC phonon relaxation time,as characterized by stronger EPC strength which is associated with larger deformation potential constant and Born effective charge.Moreover,we see that the TaAs exhibits obviously larger overlap between the EPC relaxation time and that from intrinsic phonon-phonon scattering,which could further reduce the lattice thermal conduc-tivity.Our work not only highlights the vital importance of EPC in accurately predicting the phonon transport behaviors,but also offers a simple alternative to evaluate the EPC strength of various material systems.
基金supported by the Open Research Fund of Songshan Lake Materials Laboratory(Grant No.2022SLABFN27)National Natural Science Foundation of China(Grant Nos.12274364,and U1932155)+3 种基金Fundamental Research Funds for the Central Universities of China(Grant No.2019kfy XMBZ071)National Key R&D Program of China(Grant No.2022YFA1602602)Guangdong Basic and Applied Basic Research Foundation(Grant No.2022B1515120020)Pioneer and Leading Goose R&D Program of Zhejiang(Grant No.2022SDXHDX0005)。
文摘Topological magnetic Weyl semimetals have been proposed to host controllable chiral domain walls which bear a great prospect in device applications. To exploit them in applications, it is important to have a proper way to tune and manipulate these domain walls. One possible means is through magnetoelastic coupling. The involvement of rare earth in the lately proposed RAl X(R =rare earth, X = Si and Ge) family magnetic Weyl semimetals may provide such a platform. Here we present the transport and thermodynamic properties of Ce Al Ge under hydrostatic pressure. We find that pressure enhances the antiferromagnetic exchange in Ce Al Ge but essentially retains its magnetic structure. A large topological Hall effect with a pronounced loop shape is observed within the magnetically ordered state, and it splits into two regions under pressure. Such an unusual electromagnetic response is inferred to be a consequence of chiral magnetic domain walls. The unprecedented concomitance of its evolution under pressure and the reentrance of antiferromagnetic order strongly suggest the capability of switching on/off this electromagnetic response in noncentrosymmetric magnetic Weyl semimetals via magnetoelastic coupling.