Majorana fermions have been predicted to exist at the edge states of a two-dimensional topological superconductor.We fabricated single quintuple layer(QL)Bi2Te3/FeTe heterostructure with the step-flow epitaxy method a...Majorana fermions have been predicted to exist at the edge states of a two-dimensional topological superconductor.We fabricated single quintuple layer(QL)Bi2Te3/FeTe heterostructure with the step-flow epitaxy method and studied the topological properties of this system by using angle-resolved photoemission spectroscopy and scanning tunneling microscopy/spectroscopy.We observed the coexistence of robust superconductivity and edge states on the single QL Bi2Te3 islands which can be potential evidence for topological superconductor.展开更多
As a platform for holding Majorana zero models(MZMs),the two-dimensional planar topological Josephson junction that can be used as carriers for topological quantum computing faces some challenges.One is a combination ...As a platform for holding Majorana zero models(MZMs),the two-dimensional planar topological Josephson junction that can be used as carriers for topological quantum computing faces some challenges.One is a combination of mirror and time-reversal symmetries may make the system hold multiple pairs of MZMs.The other is that a soft gap dominated by a large momentum occurs in a clean system.To solve these problems,asymmetric junction can be introduced.Breaking this symmetry changes the symmetry class from class BDI to class D,and only a single pair of MZMs can be left at the boundary of the system.We numerically study four cases that create an asymmetric system and find out different superconducting pairing potential,different coupling coefficients between two-dimensional electron gases(2DEGs)and two superconducting bulks,different widths of two superconducting bulks make the gap of the system decrease at the optimal value,but make the gap at the minimum value increases.And the zigzag-shape quasi-one-dimensional junction eliminates the large momentum parallel to the junction and enhances the gap at the large momentum.However,the zigzag-shape junction cannot increase the gap at the region of multiple pairs of MZMs in a symmetric system.We show that by combining zigzag-shape junction with different coupling coefficients,the system can maintain a large gap(≈0.2△)in a wide region of the parameter space.展开更多
We performed angle-resolved photoemission spectroscopy studies on a series of FeTe_(1-x)Se_x monolayer films grown on Sr TiO_3.The superconductivity of the films is robust and rather insensitive to the variations of t...We performed angle-resolved photoemission spectroscopy studies on a series of FeTe_(1-x)Se_x monolayer films grown on Sr TiO_3.The superconductivity of the films is robust and rather insensitive to the variations of the band position and effective mass caused by the substitution of Se by Te.However,the band gap between the electron-and hole-like bands at the Brillouin zone center decreases towards band inversion and parity exchange,which drive the system to a nontrivial topological state predicted by theoretical calculations.Our results provide a clear experimental indication that the FeTe_(1-x)Se_x monolayer materials are high-temperature connate topological superconductors in which band topology and superconductivity are integrated intrinsically.展开更多
Topological materials, hosting topological nontrivial electronic band, have attracted widespread attentions. As an application of topology in physics, the discovery and study of topological materials not only enrich t...Topological materials, hosting topological nontrivial electronic band, have attracted widespread attentions. As an application of topology in physics, the discovery and study of topological materials not only enrich the existing theoretical framework of physics, but also provide fertile ground for investigations on low energy excitations, such as Weyl fermions and Majorana fermions, which have not been observed yet as fundamental particles. These quasiparticles with exotic physical properties make topological materials the cutting edge of scientific research and a new favorite of high tech. As a typical example, Majorana fermions, predicted to exist in the edge state of topological superconductors, are proposed to implement topological error-tolerant quantum computers. Thus, the detection of topological superconductivity has become a frontier in condensed matter physics and materials science. Here, we review a way to detect topological superconductivity triggered by the hard point contact: tip-induced superconductivity(TISC) and tip-enhanced superconductivity(TESC). The TISC refers to the superconductivity induced by a non-superconducting tip at the point contact on non-superconducting materials. We take the elaboration of the chief experimental achievement of TISC in topological Dirac semimetal Cd_3As_2 and Weyl semimetal Ta As as key components of this article for detecting topological superconductivity. Moreover, we also briefly introduce the main results of another exotic effect, TESC, in superconducting Au_2Pb and Sr_2RuO_4 single crystals, which are respectively proposed as the candidates of helical topological superconductor and chiral topological superconductor. Related results and the potential mechanism are conducive to improving the comprehension of how to induce and enhance the topological superconductivity.展开更多
Following publication of the original article[1],the following information has been delete from the Acknowledgments section:KTL acknowledges the support of the Croucher Foundation,the Dr.Tai-chin Lo Foundation and the...Following publication of the original article[1],the following information has been delete from the Acknowledgments section:KTL acknowledges the support of the Croucher Foundation,the Dr.Tai-chin Lo Foundation and the HKRGC through grants C6026-16W,C6025-19G,16310219 and 16309718.The following information has been added to the Funding section:K.T.L.acknowledges the support of the Ministry of Science and Technology,China,and Hong Kong Research Grant Council throughGrantsNo.2020YFA0309600,No.RFS2021-6S03,No.C6025-19G,No.AoE/P-701/20,No.16310520,No.16310219,No.16307622,and No.16309718.展开更多
Recently,multifold fermions characterized by band crossings with multifold degeneracy and Fermi surfaces with higher Chern numbers have been discovered experimentally in AlPt(Schroter et al.in Nat Phys 15:759-765,2019...Recently,multifold fermions characterized by band crossings with multifold degeneracy and Fermi surfaces with higher Chern numbers have been discovered experimentally in AlPt(Schroter et al.in Nat Phys 15:759-765,2019)and XSi(X=Rh,Co)(Sanchez et al.in Nature 567:500-505,2019;Rao et al.in Nature 567:496-499,2019;Takane et al.in Phys Rev Lett 122:076402,2019).In this work,we largely expand the family of multifold fermion materials by pointing out that several well-studied noncentrosymmetric superconductors are indeed multifold fermion metals.Importantly,their normal state topological properties,which have been ignored in previous studies,play an important role in the superconducting properties.Taking Li_(2)Pd_(3)B and Li_(2)Pt_(3)B as examples,we found a large number of unconventional degenerate points,such as double spin-1,spin-3/2,Weyl and double Weyl topological band crossing points near the Fermi energy,which result in finite Chern numbers on Fermi surfaces.Long Fermi arc states in Li_(2)Pd_(3)B,originating from the nontrivial band topology were found.Importantly,it has been shown experimentally that Li_(2)Pd_(3)B and Li_(2)Pt_(3)B are fully gapped and gapless superconductors,respectively.By analyzing the possible pairing symmetries,we suggest that Li_(2)Pd_(3)B is a conventional s-wave superconductor or DIII class topological superconductor with Majorana surface states.Li_(2)Pt_(3)B,being gapless,is likely to be a nodal topological superconductor with dispersionless surface Majorana modes.We further identified that several noncentrosymmetric superconductors,such as Mo_(3)Al_(2)C,PdBiSe,Y_(2)C_(3)and La2C_(3),are multifold fermion superconductors.This work calls for a revisit for the study of noncentrosymmtric superconductors which provide platforms for investigating the interplay between superconductivity and topologically nontrivial Fermi surfaces.展开更多
Pursuing new two-dimensional(2D)materials has been a hot topic in materials science,driven by their potential for diverse applications.Recent research has unveiled stable planar hypercoordinate motifs with unconventio...Pursuing new two-dimensional(2D)materials has been a hot topic in materials science,driven by their potential for diverse applications.Recent research has unveiled stable planar hypercoordinate motifs with unconventional geometric arrangements and bonding patterns that facilitate the synthesis of new 2D materials with diverse applications.Among these,yet the design of 2D transition metal systems featuring planar pentacoordinate boron(ppB)is particularly intriguing.Here we address this gap by proposing a novel family of transition metal boride monolayers(MBenes)composed of ppB and heptacoordinate M motifs.The novelty of our MBenes stems from their distinct atomic arrangements and bonding configurations,setting them apart from traditional 2D materials.High-throughput calculations identified 10 stable MBenes(with the stoichiometry of MB,M=Cr,Fe,Co,Ni,Cu,Mo,Pd,Ag,Pt,Au)with exceptional thermodynamic,dynamic,thermal,and mechanical stabilities attributed to strong BB covalent bonds and MB ionic interactions.Notably,five of these MBenes(M=Ni,Pd,Pt,Ag,Au)hold high promise as topological superconducting materials with superconducting transition temperatures of 2.4-5.2 K.This discovery not only enriches the family of topological superconducting materials but also opens new avenues for quantum device development.Meanwhile,FeB monolayer exhibits robust ferromagnetic properties with a high Curie temperature of~750 K,which is particularly significant for spintronics applications.In addition,NiB and CuB MBenes demonstrate extremely low sodium diffusion barriers(about 30 and 90 meV)and high sodium storage capacities(788 and 734 mAh g1,respectively),making them promising anode materials for sodium-ion batteries(SIBs).This study expands the selection of electrode materials for SIBs and mitigates some existing limitations in battery technology.Overall,these findings underscore the multifunctional potential of MBenes,positioning them as transformative materials for quantum computing,spintronics,and energy storage applications.展开更多
With an external in-plane magnetic field, we show the emergence of a topological nodal superconducting phase of the two-dimensional topological surface states. This nodal superconducting phase is protected by the chir...With an external in-plane magnetic field, we show the emergence of a topological nodal superconducting phase of the two-dimensional topological surface states. This nodal superconducting phase is protected by the chiral symmetry with a non-zero magnetic field, and there are corresponding Majorana Fermi arcs(also known as flat band Andreev bound states) connecting the two Majorana nodes along the edges, similar to the case of Weyl semimetal. The topological nodal superconductor is an intermediate phase between two different chiral superconductors, and is stable against the effects of substrates. The two-dimensional effective theory of the nodal superconducting phase also captures the low energy behavior of a three-dimensional lattice model which describes the iron-based superconductor with a thin film geometry. The localizations of the Majorana nodes can be manipulated through external in-plane magnetic fields, which may introduce a non-trivial topological Berry phase between them.展开更多
Topological semimetals,possessing topologically non-trivial band structures,serve as excellent platforms for realizing topological superconductivity through hard point-contact experiments.In this study,we successfully...Topological semimetals,possessing topologically non-trivial band structures,serve as excellent platforms for realizing topological superconductivity through hard point-contact experiments.In this study,we successfully induce superconductivity in the three-dimensional Dirac semimetal,cubic PtBi_(2),using ferromagnetic and paramagnetic tips in hard point contact experiments.The induced superconductivity is proven to be insensitive to ferromagnetism and exhibits unconventional features in the point-contact spectra.The highest superconducting transition temperature(T_(c))reaches approximately 5.1 K,and the T_(c)values are proven to have a positive correlation with the coupling between the tip and the sample.Furthermore,we extend our point-contact experiments to trigonal PtBi_(2),a material possessing a type-ⅠWeyl semimetal band structure and triply degenerate points proximate to the Fermi level.Utilizing both ferromagnetic Ni tips and paramagnetic Ag tips,we successfully enhance superconductivity with a T_(c)of up to 3.0 K in this material.The findings from point-contact measurements reveal that the enhanced superconductivity is compatible with ferromagnetism and the magnetism of the tip can affect the symmetry of the enhanced superconducting state.Given that the lattice structure remains stable under pressure up to 51.2 GPa for cubic PtBi_(2)and 12.9 GPa for trigonal PtBi_(2),the emergent superconducting states observed in these two PtBi_(2)materials could inherit their topological nontrivial nature and be promising candidates for topological superconductor.展开更多
Trigonal PtBi_(2)(γ-PtBi_(2))is a newly discovered polymorphic material with novel topological and superconducting properties[1,2].Due to its non-centrosymmetric structure,γ-PtBi_(2)hosts triply degenerate points an...Trigonal PtBi_(2)(γ-PtBi_(2))is a newly discovered polymorphic material with novel topological and superconducting properties[1,2].Due to its non-centrosymmetric structure,γ-PtBi_(2)hosts triply degenerate points and Weyl fermions[3–6].On the other hand,bulk superconductivity inγ-PtBi_(2)has been observed with a critical temperature Tc up to 0.6 K[7].Recent studies also uncover its surface superconductivity with Tc of 10 K[6,8].Therefore,γ-PtBi_(2),possessing non-trivial electronic topology and superconductivity,is a potential candidate for realizing the Fu-Kane topological superconductivity[6,9,10],which is timely needed to be further studied by low-temperature scanning tunneling microscopy(STM).However,as the first step,STM evidences of the topological surface states inγ-PtB_(2)are still lacking.展开更多
Weyl fermion is a massless Dirac fermion with definite chirality,which has been long pursued since 1929.Though it has not been observed as a fundamental particle in nature,Weyl fermion can be realized as low-energy ex...Weyl fermion is a massless Dirac fermion with definite chirality,which has been long pursued since 1929.Though it has not been observed as a fundamental particle in nature,Weyl fermion can be realized as low-energy excitation around Weyl point in Weyl semimetal,which possesses Weyl fermion cones in the bulk and nontrivial Fermi arc states on the surface. As a firstly discovered Weyl semimetal,Ta As crystal possesses 12 pairs of Weyl points in the momentum space,which are topologically protected against small perturbations. Here,we report for the first time the tip induced superconductivity on Ta As crystal by point contact spectroscopy. The zero bias conductance peak as well as a conductance plateau with double conductance peaks and sharp double dips are observed in the point contact spectra simultaneously,indicating unconventional superconductivity. Our further theoretical study suggests that the induced superconductivity may have nontrivial topology. The present work opens a new route in investigating the novel superconducting states based on Weyl materials.展开更多
The metallic tip-induced superconductivity in normal Weyl semimetal offers a promising platform to study topological superconductivity,which is currently a research focus in condensed matter physics.Here we experiment...The metallic tip-induced superconductivity in normal Weyl semimetal offers a promising platform to study topological superconductivity,which is currently a research focus in condensed matter physics.Here we experimentally uncover that unconventional superconductivity can be induced by hard point contact(PC)method of ferromagnetic tips in Ta As single crystals.The magneto-transport measurements of the ferromagnetic tip-induced superconducting(FTISC)states exhibit the quantum oscillations,which reveal that the superconductivity is induced in the topologically nontrivial Fermi surface of the Weyl semimetal,and show compatibility of ferromagnetism and induced superconductivity.We further measure the point contact spectra(PCS)of tunneling transport for FTISC states which are potentially of nontrivial topology.Considering that the magnetic Weyl semimetal with novel superconductivity is hard to realize in experiment,our results show a new route to investigate the unconventional superconductivity by combining the topological semimetal with ferromagnetism through hard PC method.展开更多
The realization of Majorana zero modes in condensed matter have been attracting enormous interests from fundamental science such as topological quantum computation.Recently iron based superconductors were identified a...The realization of Majorana zero modes in condensed matter have been attracting enormous interests from fundamental science such as topological quantum computation.Recently iron based superconductors were identified as a high-temperature platform for realizing topological superconductivity and Majorana modes.As unconventional superconductors,one of the most important characteristics of them is that they are in the vicinity of magnetic states due to the strong Hund’s coupling in iron atoms.Here we propose that the line defects with missing Te/Se anions in Fe(Se,Te)superconductors provide the realization of intrinsic antiferromagnetic(AFM)chains with Rashba spin-orbit coupling.Against conventional wisdom,Majorana zero modes(MZMs)can be robustly generated at these AFM chain ends.These results can consistently explain the recent experimental observation of zero-energy end states in line defects of monolayer Fe(Te,Se)/SrTiO_(3) by scanning tunneling microscopy(STM)measurements.Our research not only demonstrates an unprecedented interplay among native line defect,emergent magnetism and topological superconductivity but also explores a high-temperature platform for Majorana fermions.展开更多
This article will briefly describe a Majorana platform made of InAs/GaSb(including InAs/(In)GaSb)semiconductor-superconductor heterostructures.A unique advantage of this platform is that the quantum spin Hall edge sta...This article will briefly describe a Majorana platform made of InAs/GaSb(including InAs/(In)GaSb)semiconductor-superconductor heterostructures.A unique advantage of this platform is that the quantum spin Hall edge state realized in inverted InAs/GaSb is a topologically protected spinless single mode,and can be tuned by front-back dual gates.Similar to a number of other platforms the proximity effect of a conventional s-wave superconductor on the helical edge has been proposed to realize Majorana bound state.We will present an introduction to this platform with a focus on the materials and devices aspects and those points that are particularly illustrative.展开更多
Over the past fifteen years,tremendous efforts have been devoted to realizing topological superconductivity in realistic materials and systems,predominately propelled by their promising application potentials in fault...Over the past fifteen years,tremendous efforts have been devoted to realizing topological superconductivity in realistic materials and systems,predominately propelled by their promising application potentials in fault-tolerant quantum information processing.In this article,we attempt to give an overview on some of the main developments in this field,focusing in particular on two-dimensional crystalline superconductors that possess either intrinsic p-wave pairing or nontrivial band topology.We first classify the three different conceptual schemes to achieve topological superconductor(TSC),enabled by real-space superconducting proximity effect,reciprocal-space superconducting proximity effect,and intrinsic TSC.Whereas the first scheme has so far been most extensively explored,the subtle difference between the other two remains to be fully substantiated.We then move on to candidate intrinsic or p-wave superconductors,including Sr2Ru O4,UTe2,Pb3Bi,and graphene-based systems.For TSC systems that rely on proximity effects,the emphases are mainly on the coexistence of superconductivity and nontrivial band topology,as exemplified by transition metal dichalcogenides,cobalt pnictides,and stanene,all in monolayer or few-layer regime.The review completes with discussions on the three dominant tuning schemes of strain,gating,and ferroelectricity in acquiring one or both essential ingredients of the TSC,and optimizations of such tuning capabilities may prove to be decisive in our drive towards braiding of Majorana zero modes and demonstration of topological qubits.展开更多
Type-Ⅱ Dirac semimetals exhibit a unique Fermi surface topology,which allows them to host novel topological superconductivity(TSC).We reveal a novel inter-orbital superconducting state,corresponding to the B_(1u) and...Type-Ⅱ Dirac semimetals exhibit a unique Fermi surface topology,which allows them to host novel topological superconductivity(TSC).We reveal a novel inter-orbital superconducting state,corresponding to the B_(1u) and B_(2u) pairings under the D_(4h) point group.Intriguingly,we find that both first-and second-order TSC coexist in this novel state.It is induced by a dominant inter-orbital attraction and possesses surface helical Majorana cones and hinge Majorana flat bands,spanning the entire z-directed hinge Brillouin zone.Further investigation uncovers that these higher-order hinge modes are robust against the C_(4z) symmetry-breaking perturbation.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61734008 and 11774143)the National Key Research and Development Program of China(Grant Nos.2018YFA0307100,2016YFA0301703,and 2016YFA0300300)+4 种基金the Natural Science Foundation of Guangdong Province,China(Grant Nos.2015A030313840 and 2017A030313033)the State Key Laboratory of Low-Dimensional Quantum Physics(Grant No.KF201602)Technology and Innovation Commission of Shenzhen Municipality,China(Grant Nos.ZDSYS20170303165926217 and JCYJ20170412152334605)Guangdong Provincial Key Laboratory,China(Grant No.2019B121203002)J.-W.M.was partially supported by the Program for Guangdong Introducing Innovative and Entrepreneurial Teams,China(Grant No.2017ZT07C062).
文摘Majorana fermions have been predicted to exist at the edge states of a two-dimensional topological superconductor.We fabricated single quintuple layer(QL)Bi2Te3/FeTe heterostructure with the step-flow epitaxy method and studied the topological properties of this system by using angle-resolved photoemission spectroscopy and scanning tunneling microscopy/spectroscopy.We observed the coexistence of robust superconductivity and edge states on the single QL Bi2Te3 islands which can be potential evidence for topological superconductor.
基金Project supported by the National Natural Science Foundation of China(Grant No.11974271)。
文摘As a platform for holding Majorana zero models(MZMs),the two-dimensional planar topological Josephson junction that can be used as carriers for topological quantum computing faces some challenges.One is a combination of mirror and time-reversal symmetries may make the system hold multiple pairs of MZMs.The other is that a soft gap dominated by a large momentum occurs in a clean system.To solve these problems,asymmetric junction can be introduced.Breaking this symmetry changes the symmetry class from class BDI to class D,and only a single pair of MZMs can be left at the boundary of the system.We numerically study four cases that create an asymmetric system and find out different superconducting pairing potential,different coupling coefficients between two-dimensional electron gases(2DEGs)and two superconducting bulks,different widths of two superconducting bulks make the gap of the system decrease at the optimal value,but make the gap at the minimum value increases.And the zigzag-shape quasi-one-dimensional junction eliminates the large momentum parallel to the junction and enhances the gap at the large momentum.However,the zigzag-shape junction cannot increase the gap at the region of multiple pairs of MZMs in a symmetric system.We show that by combining zigzag-shape junction with different coupling coefficients,the system can maintain a large gap(≈0.2△)in a wide region of the parameter space.
基金supported by grants from the Ministry of Science and Technology of China(2015CB921000,2016YFA0401000,2015CB921301,2016YFA0300300)the National Natural Science Foundation of China(11574371,11274362,1190020,11334012,11274381,11674371)
文摘We performed angle-resolved photoemission spectroscopy studies on a series of FeTe_(1-x)Se_x monolayer films grown on Sr TiO_3.The superconductivity of the films is robust and rather insensitive to the variations of the band position and effective mass caused by the substitution of Se by Te.However,the band gap between the electron-and hole-like bands at the Brillouin zone center decreases towards band inversion and parity exchange,which drive the system to a nontrivial topological state predicted by theoretical calculations.Our results provide a clear experimental indication that the FeTe_(1-x)Se_x monolayer materials are high-temperature connate topological superconductors in which band topology and superconductivity are integrated intrinsically.
基金financially supported by the National Program on Key Basic Research Project(2018YFA0305604 and 2017YFA0303302)National Natural Science Foundation of China(11774008,381/0401210001)+2 种基金the Key Research Program of the Chinese Academy of Sciences(XDPB08-2)the Open Research Fund Program of the State Key Laboratory of Low-Dimensional Quantum Physics,Tsinghua University(KF201703)China Postdoctoral Science Foundation(130/0401130005)
文摘Topological materials, hosting topological nontrivial electronic band, have attracted widespread attentions. As an application of topology in physics, the discovery and study of topological materials not only enrich the existing theoretical framework of physics, but also provide fertile ground for investigations on low energy excitations, such as Weyl fermions and Majorana fermions, which have not been observed yet as fundamental particles. These quasiparticles with exotic physical properties make topological materials the cutting edge of scientific research and a new favorite of high tech. As a typical example, Majorana fermions, predicted to exist in the edge state of topological superconductors, are proposed to implement topological error-tolerant quantum computers. Thus, the detection of topological superconductivity has become a frontier in condensed matter physics and materials science. Here, we review a way to detect topological superconductivity triggered by the hard point contact: tip-induced superconductivity(TISC) and tip-enhanced superconductivity(TESC). The TISC refers to the superconductivity induced by a non-superconducting tip at the point contact on non-superconducting materials. We take the elaboration of the chief experimental achievement of TISC in topological Dirac semimetal Cd_3As_2 and Weyl semimetal Ta As as key components of this article for detecting topological superconductivity. Moreover, we also briefly introduce the main results of another exotic effect, TESC, in superconducting Au_2Pb and Sr_2RuO_4 single crystals, which are respectively proposed as the candidates of helical topological superconductor and chiral topological superconductor. Related results and the potential mechanism are conducive to improving the comprehension of how to induce and enhance the topological superconductivity.
文摘Following publication of the original article[1],the following information has been delete from the Acknowledgments section:KTL acknowledges the support of the Croucher Foundation,the Dr.Tai-chin Lo Foundation and the HKRGC through grants C6026-16W,C6025-19G,16310219 and 16309718.The following information has been added to the Funding section:K.T.L.acknowledges the support of the Ministry of Science and Technology,China,and Hong Kong Research Grant Council throughGrantsNo.2020YFA0309600,No.RFS2021-6S03,No.C6025-19G,No.AoE/P-701/20,No.16310520,No.16310219,No.16307622,and No.16309718.
基金support of the Ministry of Science and Technology,China,and Hong Kong Research Grant Council through Grants No.2020YFA0309600,No.RFS2021-6S03,No.C6025-19G,No.AoE/P-701/20,No.16310520,No.16310219,No.16307622,and No.16309718.
文摘Recently,multifold fermions characterized by band crossings with multifold degeneracy and Fermi surfaces with higher Chern numbers have been discovered experimentally in AlPt(Schroter et al.in Nat Phys 15:759-765,2019)and XSi(X=Rh,Co)(Sanchez et al.in Nature 567:500-505,2019;Rao et al.in Nature 567:496-499,2019;Takane et al.in Phys Rev Lett 122:076402,2019).In this work,we largely expand the family of multifold fermion materials by pointing out that several well-studied noncentrosymmetric superconductors are indeed multifold fermion metals.Importantly,their normal state topological properties,which have been ignored in previous studies,play an important role in the superconducting properties.Taking Li_(2)Pd_(3)B and Li_(2)Pt_(3)B as examples,we found a large number of unconventional degenerate points,such as double spin-1,spin-3/2,Weyl and double Weyl topological band crossing points near the Fermi energy,which result in finite Chern numbers on Fermi surfaces.Long Fermi arc states in Li_(2)Pd_(3)B,originating from the nontrivial band topology were found.Importantly,it has been shown experimentally that Li_(2)Pd_(3)B and Li_(2)Pt_(3)B are fully gapped and gapless superconductors,respectively.By analyzing the possible pairing symmetries,we suggest that Li_(2)Pd_(3)B is a conventional s-wave superconductor or DIII class topological superconductor with Majorana surface states.Li_(2)Pt_(3)B,being gapless,is likely to be a nodal topological superconductor with dispersionless surface Majorana modes.We further identified that several noncentrosymmetric superconductors,such as Mo_(3)Al_(2)C,PdBiSe,Y_(2)C_(3)and La2C_(3),are multifold fermion superconductors.This work calls for a revisit for the study of noncentrosymmtric superconductors which provide platforms for investigating the interplay between superconductivity and topologically nontrivial Fermi surfaces.
基金supported by Research Foundation for Advanced Talents of Inner Mongolia Normal University(2025YJRC005)the National Natural Science Foundation of China(12364038)+5 种基金the“Grassland Talents”project of the Inner Mongolia Autonomous Region(12000-12102613)the Young Science and Technology Talents Cultivation Project of Inner Mongolia University(21200-5223708)the Industrial Technology Innovation Projects of Inner Mongolia Academy of Science and Technology of China(2023JSYD01002)Science and Technology Plan Projects of Inner Mongolia Autonomous Region of China(2023KYPT0012)Key Project Funding from the Inner Mongolia Autonomous Region Natural Science Foundation(2023ZD27)High Level Introduction of Talent Research Start-up Fund(5909002405).
文摘Pursuing new two-dimensional(2D)materials has been a hot topic in materials science,driven by their potential for diverse applications.Recent research has unveiled stable planar hypercoordinate motifs with unconventional geometric arrangements and bonding patterns that facilitate the synthesis of new 2D materials with diverse applications.Among these,yet the design of 2D transition metal systems featuring planar pentacoordinate boron(ppB)is particularly intriguing.Here we address this gap by proposing a novel family of transition metal boride monolayers(MBenes)composed of ppB and heptacoordinate M motifs.The novelty of our MBenes stems from their distinct atomic arrangements and bonding configurations,setting them apart from traditional 2D materials.High-throughput calculations identified 10 stable MBenes(with the stoichiometry of MB,M=Cr,Fe,Co,Ni,Cu,Mo,Pd,Ag,Pt,Au)with exceptional thermodynamic,dynamic,thermal,and mechanical stabilities attributed to strong BB covalent bonds and MB ionic interactions.Notably,five of these MBenes(M=Ni,Pd,Pt,Ag,Au)hold high promise as topological superconducting materials with superconducting transition temperatures of 2.4-5.2 K.This discovery not only enriches the family of topological superconducting materials but also opens new avenues for quantum device development.Meanwhile,FeB monolayer exhibits robust ferromagnetic properties with a high Curie temperature of~750 K,which is particularly significant for spintronics applications.In addition,NiB and CuB MBenes demonstrate extremely low sodium diffusion barriers(about 30 and 90 meV)and high sodium storage capacities(788 and 734 mAh g1,respectively),making them promising anode materials for sodium-ion batteries(SIBs).This study expands the selection of electrode materials for SIBs and mitigates some existing limitations in battery technology.Overall,these findings underscore the multifunctional potential of MBenes,positioning them as transformative materials for quantum computing,spintronics,and energy storage applications.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11804223 (MLL, YW, HZZ, HLC, TYC, XL), 11474061 (XL), and 12174067 (XL))。
文摘With an external in-plane magnetic field, we show the emergence of a topological nodal superconducting phase of the two-dimensional topological surface states. This nodal superconducting phase is protected by the chiral symmetry with a non-zero magnetic field, and there are corresponding Majorana Fermi arcs(also known as flat band Andreev bound states) connecting the two Majorana nodes along the edges, similar to the case of Weyl semimetal. The topological nodal superconductor is an intermediate phase between two different chiral superconductors, and is stable against the effects of substrates. The two-dimensional effective theory of the nodal superconducting phase also captures the low energy behavior of a three-dimensional lattice model which describes the iron-based superconductor with a thin film geometry. The localizations of the Majorana nodes can be manipulated through external in-plane magnetic fields, which may introduce a non-trivial topological Berry phase between them.
基金supported by the National Natural Science Foundation of China[Grant No.12488201(J.W.)]the Innovation Program for Quantum Science and Technology[2021ZD0302403(J.W.)]+2 种基金the National Key R&D Program of the MOST of China[Grant No.2022YFA1602603(M.T.)]the Capacity Building for Sci-Tech Innovation-Fundamental Scientific Research Funds[Grant No.20530290057(H.W.)]the Science and Technology Project of Beijing Municipal Education Commission[KM202010028014(H.W.)].
文摘Topological semimetals,possessing topologically non-trivial band structures,serve as excellent platforms for realizing topological superconductivity through hard point-contact experiments.In this study,we successfully induce superconductivity in the three-dimensional Dirac semimetal,cubic PtBi_(2),using ferromagnetic and paramagnetic tips in hard point contact experiments.The induced superconductivity is proven to be insensitive to ferromagnetism and exhibits unconventional features in the point-contact spectra.The highest superconducting transition temperature(T_(c))reaches approximately 5.1 K,and the T_(c)values are proven to have a positive correlation with the coupling between the tip and the sample.Furthermore,we extend our point-contact experiments to trigonal PtBi_(2),a material possessing a type-ⅠWeyl semimetal band structure and triply degenerate points proximate to the Fermi level.Utilizing both ferromagnetic Ni tips and paramagnetic Ag tips,we successfully enhance superconductivity with a T_(c)of up to 3.0 K in this material.The findings from point-contact measurements reveal that the enhanced superconductivity is compatible with ferromagnetism and the magnetism of the tip can affect the symmetry of the enhanced superconducting state.Given that the lattice structure remains stable under pressure up to 51.2 GPa for cubic PtBi_(2)and 12.9 GPa for trigonal PtBi_(2),the emergent superconducting states observed in these two PtBi_(2)materials could inherit their topological nontrivial nature and be promising candidates for topological superconductor.
基金supported by the National Natural Science Foundation of China(92365201,12234011,12374053,12334003,and 52388201)the Ministry of Science and Technology of the People’s Republic of China(2022YFA1403100 and 2023YFA1406400)+6 种基金the Innovation Program for Quantum Science and Technology(2021ZD0302402)the National Key Research and Development Program of China(2022YFA1403400 and 2020YFA0308800)the Beijing National Laboratory for Condensed Matter Physics(2023BNLCMPKF007)the Beijing Natural Science Foundation(Z210006)supported by the Innovation Program for Quantum Science and Technology(2023ZD0300500)the National Science Fund for Distinguished Young Scholars(12025405)the Beijing Advanced Innovation Center for Future Chip(ICFC),and the Beijing Advanced Innovation Center for Materials Genome Engineering.
文摘Trigonal PtBi_(2)(γ-PtBi_(2))is a newly discovered polymorphic material with novel topological and superconducting properties[1,2].Due to its non-centrosymmetric structure,γ-PtBi_(2)hosts triply degenerate points and Weyl fermions[3–6].On the other hand,bulk superconductivity inγ-PtBi_(2)has been observed with a critical temperature Tc up to 0.6 K[7].Recent studies also uncover its surface superconductivity with Tc of 10 K[6,8].Therefore,γ-PtBi_(2),possessing non-trivial electronic topology and superconductivity,is a potential candidate for realizing the Fu-Kane topological superconductivity[6,9,10],which is timely needed to be further studied by low-temperature scanning tunneling microscopy(STM).However,as the first step,STM evidences of the topological surface states inγ-PtB_(2)are still lacking.
基金financially supported by National Basic Research Program of China (2013CB934600,2012CB927400,2012CB921300,and 2016YFA0301604)the Research Fund for the Doctoral Program of Higher Education (RFDP) of China+2 种基金the Open Project Program of the Pulsed High Magnetic Field Facility (PHMFF2015002)Huazhong University of Science and Technology,Open Research Fund Program of the State Key Laboratory of Low Dimensional Quantum Physicsthe National Natural Science Foundation of China (11474008 and 11574008)
文摘Weyl fermion is a massless Dirac fermion with definite chirality,which has been long pursued since 1929.Though it has not been observed as a fundamental particle in nature,Weyl fermion can be realized as low-energy excitation around Weyl point in Weyl semimetal,which possesses Weyl fermion cones in the bulk and nontrivial Fermi arc states on the surface. As a firstly discovered Weyl semimetal,Ta As crystal possesses 12 pairs of Weyl points in the momentum space,which are topologically protected against small perturbations. Here,we report for the first time the tip induced superconductivity on Ta As crystal by point contact spectroscopy. The zero bias conductance peak as well as a conductance plateau with double conductance peaks and sharp double dips are observed in the point contact spectra simultaneously,indicating unconventional superconductivity. Our further theoretical study suggests that the induced superconductivity may have nontrivial topology. The present work opens a new route in investigating the novel superconducting states based on Weyl materials.
基金financially supported by the National Key R&D Program of China (2018YFA0305604, 2017YFA0303302, and 2016YFA0301604)the National Natural Science Foundation of China (11888101, 11774008, 0401210001, 11574008, 11761161003, 11825401, 11704279, 11774255, U1832214, and 11774007)+3 种基金the Strategic Priority Research Program of Chinese Academy of Sciences (XDB28000000)the Beijing Natural Science Foundation (Z180010)the Key Project of Natural Science Foundation of Tianjin City (17JCZDJC30100)China Postdoctoral Science Foundation (0401130005)
文摘The metallic tip-induced superconductivity in normal Weyl semimetal offers a promising platform to study topological superconductivity,which is currently a research focus in condensed matter physics.Here we experimentally uncover that unconventional superconductivity can be induced by hard point contact(PC)method of ferromagnetic tips in Ta As single crystals.The magneto-transport measurements of the ferromagnetic tip-induced superconducting(FTISC)states exhibit the quantum oscillations,which reveal that the superconductivity is induced in the topologically nontrivial Fermi surface of the Weyl semimetal,and show compatibility of ferromagnetism and induced superconductivity.We further measure the point contact spectra(PCS)of tunneling transport for FTISC states which are potentially of nontrivial topology.Considering that the magnetic Weyl semimetal with novel superconductivity is hard to realize in experiment,our results show a new route to investigate the unconventional superconductivity by combining the topological semimetal with ferromagnetism through hard PC method.
基金funding provided by Shanghai Jiao Tong Universitysupported by the National Natural Science Foundation of China(grant no.12047503)+2 种基金supported by the Ministry of Science and Technology(grant no.2022YFA1403901)the National Natural Science Foundation of China(grant no.NSFC-11888101)the New Cornerstone Foundation.
文摘The realization of Majorana zero modes in condensed matter have been attracting enormous interests from fundamental science such as topological quantum computation.Recently iron based superconductors were identified as a high-temperature platform for realizing topological superconductivity and Majorana modes.As unconventional superconductors,one of the most important characteristics of them is that they are in the vicinity of magnetic states due to the strong Hund’s coupling in iron atoms.Here we propose that the line defects with missing Te/Se anions in Fe(Se,Te)superconductors provide the realization of intrinsic antiferromagnetic(AFM)chains with Rashba spin-orbit coupling.Against conventional wisdom,Majorana zero modes(MZMs)can be robustly generated at these AFM chain ends.These results can consistently explain the recent experimental observation of zero-energy end states in line defects of monolayer Fe(Te,Se)/SrTiO_(3) by scanning tunneling microscopy(STM)measurements.Our research not only demonstrates an unprecedented interplay among native line defect,emergent magnetism and topological superconductivity but also explores a high-temperature platform for Majorana fermions.
基金supported by the National Key Research and Development Program of China(Grant No.2019YFA0308400)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB28000000)。
文摘This article will briefly describe a Majorana platform made of InAs/GaSb(including InAs/(In)GaSb)semiconductor-superconductor heterostructures.A unique advantage of this platform is that the quantum spin Hall edge state realized in inverted InAs/GaSb is a topologically protected spinless single mode,and can be tuned by front-back dual gates.Similar to a number of other platforms the proximity effect of a conventional s-wave superconductor on the helical edge has been proposed to realize Majorana bound state.We will present an introduction to this platform with a focus on the materials and devices aspects and those points that are particularly illustrative.
基金supported by the National Natural Science Foundation of China(Grant Nos.11634011,and 11974323)National Key R&D Program of China(Grant No.2017YFA0303500)+2 种基金Anhui Initiative in Quantum Information Technologies(Grant No.AHY170000)Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB30000000)Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302800)。
文摘Over the past fifteen years,tremendous efforts have been devoted to realizing topological superconductivity in realistic materials and systems,predominately propelled by their promising application potentials in fault-tolerant quantum information processing.In this article,we attempt to give an overview on some of the main developments in this field,focusing in particular on two-dimensional crystalline superconductors that possess either intrinsic p-wave pairing or nontrivial band topology.We first classify the three different conceptual schemes to achieve topological superconductor(TSC),enabled by real-space superconducting proximity effect,reciprocal-space superconducting proximity effect,and intrinsic TSC.Whereas the first scheme has so far been most extensively explored,the subtle difference between the other two remains to be fully substantiated.We then move on to candidate intrinsic or p-wave superconductors,including Sr2Ru O4,UTe2,Pb3Bi,and graphene-based systems.For TSC systems that rely on proximity effects,the emphases are mainly on the coexistence of superconductivity and nontrivial band topology,as exemplified by transition metal dichalcogenides,cobalt pnictides,and stanene,all in monolayer or few-layer regime.The review completes with discussions on the three dominant tuning schemes of strain,gating,and ferroelectricity in acquiring one or both essential ingredients of the TSC,and optimizations of such tuning capabilities may prove to be decisive in our drive towards braiding of Majorana zero modes and demonstration of topological qubits.
基金supported by the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No.XDB33000000)the National Natural Science Foundation of China (Grant Nos.12188101,52188101+3 种基金11974395)the Center for Materials Genomesupported by the National Key R&D Program of China (Grant No.2023YFA1407300)the National Natural Science Foundation of China(Grant No.12047503)。
文摘Type-Ⅱ Dirac semimetals exhibit a unique Fermi surface topology,which allows them to host novel topological superconductivity(TSC).We reveal a novel inter-orbital superconducting state,corresponding to the B_(1u) and B_(2u) pairings under the D_(4h) point group.Intriguingly,we find that both first-and second-order TSC coexist in this novel state.It is induced by a dominant inter-orbital attraction and possesses surface helical Majorana cones and hinge Majorana flat bands,spanning the entire z-directed hinge Brillouin zone.Further investigation uncovers that these higher-order hinge modes are robust against the C_(4z) symmetry-breaking perturbation.
