In this article we briefly review new quantum functional compounds primarily based on our recent works. We will highlight the effects of pressures on both materials synthesis and quantum tuning. The contents include ...In this article we briefly review new quantum functional compounds primarily based on our recent works. We will highlight the effects of pressures on both materials synthesis and quantum tuning. The contents include （I） ＂111＂-type iron based super- conducting system, （II） pressure induced superconductivity in topological insulators and （II/） the new diluted magnetic semi- conductors with decoupled spin charge doping.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
In this contribution results from different disciplines of science were compared to show their intimate interweaving with each other having in common the golden ratio <i><span style="font-family:Verdana;...In this contribution results from different disciplines of science were compared to show their intimate interweaving with each other having in common the golden ratio <i><span style="font-family:Verdana;">φ</span></i><span style="font-family:Verdana;"> respectively its fifth power </span><i><span style="font-family:Verdana;">φ</span></i><sup><span style="font-family:Verdana;">5</span></sup><span style="font-family:Verdana;">. The research fields cover model calculations of statistical physics associated with phase transitions, the quantum probability of two particles, new physics of everything suggested by the information relativity theory (</span><i><span style="font-family:Verdana;">IRT</span></i><span style="font-family:Verdana;">) including explanations of cosmological relevance, the </span><i><span style="font-family:Verdana;">ε</span></i><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">-</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">infinity theory, superconductivity, and the </span><i><span style="font-family:Verdana;">Tammes</span></i><span style="font-family:Verdana;"> problem of the largest diameter of </span><i><span style="font-family:Verdana;">N</span></i><span style="font-family:Verdana;"> non-overlapping circles on the surface of a sphere with its connection to viral morphology and crystallography. Finally, </span><i><span style="font-family:Verdana;">Fibo</span><span style="font-family:Verdana;">nacci</span></i><span style="font-family:Verdana;"> anyons proposed for topological quantum</span><span style="font-family:Verdana;"> computation (</span><i><span style="font-family:Verdana;">TQC</span></i><span style="font-family:Verdana;">) were briefly described in comparison to the recently formulated reverse </span><i><span style="font-family:Verdana;">Fibonacci</span></i><span style="font-family:Verdana;"> approach using the </span><span style="font-family:Verdana;"><em>Jani</em></span></s展开更多
Inducing or enhancing superconductivity in topological materials is an important route toward topological superconductivity.Reducing the thickness of transition metal dichalcogenides(e.g.WTe2 and MoTe2)has provided an...Inducing or enhancing superconductivity in topological materials is an important route toward topological superconductivity.Reducing the thickness of transition metal dichalcogenides(e.g.WTe2 and MoTe2)has provided an important pathway to engineer superconductivity in topological matters.However,such monolayer sample is difficult to obtain,unstable in air,and with extremely low Tc.Here we report an experimentally convenient approach to control the interlayer coupling to achieve tailored topological properties,enhanced superconductivity and good sample stability through organic-cation intercalation of the Weyl semimetals MoTe2 and WTe2.The as-formed organic-inorganic hybrid crystals are weak topological insulators with enhanced Tc of 7.0 K for intercalated MoTe2(0.25 K for pristine crystal)and2.3 K for intercalated WTe2(2.8 times compared to monolayer WTe2).Such organic-cation intercalation method can be readily applied to many other layered crystals,providing a new pathway for manipulating their electronic,topological and superconducting properties.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
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
Recently,the coexistence of topology and superconductivity has garnered considerable attention.Specifically,the dimensionality of these materials is crucial for the realization of topological quantum computation.Howev...Recently,the coexistence of topology and superconductivity has garnered considerable attention.Specifically,the dimensionality of these materials is crucial for the realization of topological quantum computation.However,the naturally grown materials,especially with one-dimensional feature that exhibits the coexistence of topology and superconductivity,still face challenges in terms of experimental realization and scalability,which hinders the fundamental research development and the potential to revolutionize quantum computing.Here,we report the first experimental synthesis of quasi-one-dimensional InNbS_(2)nanoribbons that exhibit the coexistence of topological order and superconductivity via a chemical vapor transport method.Especially,the inplane upper critical field of InNbS_(2)nanoribbons exceeds the Pauli paramagnetic limit by more than 2.2 times,which can be attributed to the enhanced spin-orbit coupling and the weakened interlayer interaction between the NbS_(2)layers induced by the insertion of In atoms,making InNbS_(2)exhibit spin-momentum locking similar to that of monolayer NbS_(2).Moreover,for the first time,we report the superconducting diode effect in a quasi-one-dimensional superconductor system without any inherent geometric imperfections.The measured maximum efficiency is manifested as 14%,observed atμ0H≈±60 mT,and we propose that the superconducting diode effect can potentially be attributed to the presence of the nontrivial topological band.Our work provides a platform for studying exotic phenomena in condensed matter physics and potential applications in quantum computing and quantum information processing.展开更多
PtTe2 and PtSe2 with trigonal structure have attracted extensive research interests since the discovery of type-II Dirac fermions in the bulk crystals. The evolution of the electronic structure from bulk 3D topologica...PtTe2 and PtSe2 with trigonal structure have attracted extensive research interests since the discovery of type-II Dirac fermions in the bulk crystals. The evolution of the electronic structure from bulk 3D topological semimetal to 2D atomic thin films is an important scientific question. While a transition from 3D type-II Dirac semimetal in the bulk to 2D semiconductor in monolayer(ML) film has been reported for PtSe2, so far the evolution of electronic structure of atomically thin PtTe2 films still remains unexplored.Here we report a systematic angle-resolved photoemission spectroscopy(ARPES) study of the electronic structure of high quality PtTe2 films grown by molecular beam epitaxy with thickness from 2 ML to 6 ML.ARPES measurements show that PtTe2 films still remain metallic even down to 2 ML thickness, which is in sharp contrast to the semiconducting property of few layer PtSe2 films. Moreover, a transition from 2D metal to 3D type-II Dirac semimetal occurs at film thickness of 4–6 ML. In addition, Spin-ARPES measurements reveal helical spin textures induced by local Rashba effect in the bulk PtTe2 crystal, suggesting that similar hidden spin is also expected in few monolayer PtTe2 films. Our work reveals the transition from2D metal to 3D topological semimetal and provides new opportunities for investigating metallic 2D films with local Rashba effect.展开更多
The origin of superconductivity observed at the point contact between the normal metal tip and the topological material remains uncertain due to the potential presence of superconducting elements or allotropes impurit...The origin of superconductivity observed at the point contact between the normal metal tip and the topological material remains uncertain due to the potential presence of superconducting elements or allotropes impurities.It is imperative to seek out a topological material entirely free of superconducting impurities and induce superconductivity between it and normal tips to verify the source of the induced superconductivity.Here,we report the observation of superconductivity up to 9 K induced at point contacts between normal metal tips and the topological material grey arsenic,which is free of superconductivity.The determined temperature dependencies of superconducting gapsΔ(T)deviate from the Bardeen-Cooper-Schriefer(BCS)superconductivity law,exhibiting abnormal behavior.Furthermore,the highly anisotropic upper critical field H_(c2)(T)suggests the anisotropy of the projected interfacial Fermi surface.By tuning the junction resistance,we obtained a negative correlation between the superconducting gapΔand the efective barrier height Z,which validates the interfacial coupling strength as a key factor in the observed tip-induced superconductivity.These experimental results provide guidance for the relevant theory about tip-induced superconductivity on topological materials.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
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
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
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
New two-dimensional systems such as the surfaces of topological insulators （TIs） and graphene offer the possibility of experimentally investigating situations considered exotic just a decade ago. These situations in...New two-dimensional systems such as the surfaces of topological insulators （TIs） and graphene offer the possibility of experimentally investigating situations considered exotic just a decade ago. These situations include the quantum phase transition of the chiral type in electronic systems with a relativistic spectrum. Phonon-mediated （conventional） pairing in the Dirac semimetal appearing on the surface of a TI causes a transition into a chiral superconducting state, and exciton condensation in these gapless systems has long been envisioned in the physics of narrow-band semiconductors. Starting from the microscopic Dirac Hamiltonian with local attraction or repulsion, the Bardeen- Cooper-Schrieffer type of Gaussian approximation is developed in the framework of functional integrals. It is shown that owing to an ultrarelativistic dispersion relation, there is a quantum critical point governing the zero-temperature transition to a superconducting state or the exciton condensed state. Quantum transitions having critical exponents differ greatly from conventional ones and belong to the chiral universality class. We discuss the application of these results to recent experiments in which surface superconductivity was found in TIs and estimate the feasibility of phonon pairing.展开更多
基金supported by the National Natural Science Foundation of China and Ministry of Science and Technology(MOST)
文摘In this article we briefly review new quantum functional compounds primarily based on our recent works. We will highlight the effects of pressures on both materials synthesis and quantum tuning. The contents include （I） ＂111＂-type iron based super- conducting system, （II） pressure induced superconductivity in topological insulators and （II/） the new diluted magnetic semi- conductors with decoupled spin charge doping.
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.
文摘In this contribution results from different disciplines of science were compared to show their intimate interweaving with each other having in common the golden ratio <i><span style="font-family:Verdana;">φ</span></i><span style="font-family:Verdana;"> respectively its fifth power </span><i><span style="font-family:Verdana;">φ</span></i><sup><span style="font-family:Verdana;">5</span></sup><span style="font-family:Verdana;">. The research fields cover model calculations of statistical physics associated with phase transitions, the quantum probability of two particles, new physics of everything suggested by the information relativity theory (</span><i><span style="font-family:Verdana;">IRT</span></i><span style="font-family:Verdana;">) including explanations of cosmological relevance, the </span><i><span style="font-family:Verdana;">ε</span></i><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">-</span></span></span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">infinity theory, superconductivity, and the </span><i><span style="font-family:Verdana;">Tammes</span></i><span style="font-family:Verdana;"> problem of the largest diameter of </span><i><span style="font-family:Verdana;">N</span></i><span style="font-family:Verdana;"> non-overlapping circles on the surface of a sphere with its connection to viral morphology and crystallography. Finally, </span><i><span style="font-family:Verdana;">Fibo</span><span style="font-family:Verdana;">nacci</span></i><span style="font-family:Verdana;"> anyons proposed for topological quantum</span><span style="font-family:Verdana;"> computation (</span><i><span style="font-family:Verdana;">TQC</span></i><span style="font-family:Verdana;">) were briefly described in comparison to the recently formulated reverse </span><i><span style="font-family:Verdana;">Fibonacci</span></i><span style="font-family:Verdana;"> approach using the </span><span style="font-family:Verdana;"><em>Jani</em></span></s
基金supported by the National Natural Science Foundation of China(11725418,21975140)Ministry of Science and Technology of China(2016YFA0301004,2016YFA0301001 and2015CB921001)+1 种基金the Basic Science Center Program of NSFC(51788104)Beijing Advanced Innovation Center for Future Chip(ICFC).
文摘Inducing or enhancing superconductivity in topological materials is an important route toward topological superconductivity.Reducing the thickness of transition metal dichalcogenides(e.g.WTe2 and MoTe2)has provided an important pathway to engineer superconductivity in topological matters.However,such monolayer sample is difficult to obtain,unstable in air,and with extremely low Tc.Here we report an experimentally convenient approach to control the interlayer coupling to achieve tailored topological properties,enhanced superconductivity and good sample stability through organic-cation intercalation of the Weyl semimetals MoTe2 and WTe2.The as-formed organic-inorganic hybrid crystals are weak topological insulators with enhanced Tc of 7.0 K for intercalated MoTe2(0.25 K for pristine crystal)and2.3 K for intercalated WTe2(2.8 times compared to monolayer WTe2).Such organic-cation intercalation method can be readily applied to many other layered crystals,providing a new pathway for manipulating their electronic,topological and superconducting properties.
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supported by Innovation Program for Quantum Science and Technology(No.2021ZD0302800)the National Natural Science Foundation of China(Nos.52373309 and 12374177)+1 种基金University of Macao Start-up research grant(No.SRG2023-00057-IAPME)National Synchrotron Radiation Laboratory(No.KY2060000177).
文摘Recently,the coexistence of topology and superconductivity has garnered considerable attention.Specifically,the dimensionality of these materials is crucial for the realization of topological quantum computation.However,the naturally grown materials,especially with one-dimensional feature that exhibits the coexistence of topology and superconductivity,still face challenges in terms of experimental realization and scalability,which hinders the fundamental research development and the potential to revolutionize quantum computing.Here,we report the first experimental synthesis of quasi-one-dimensional InNbS_(2)nanoribbons that exhibit the coexistence of topological order and superconductivity via a chemical vapor transport method.Especially,the inplane upper critical field of InNbS_(2)nanoribbons exceeds the Pauli paramagnetic limit by more than 2.2 times,which can be attributed to the enhanced spin-orbit coupling and the weakened interlayer interaction between the NbS_(2)layers induced by the insertion of In atoms,making InNbS_(2)exhibit spin-momentum locking similar to that of monolayer NbS_(2).Moreover,for the first time,we report the superconducting diode effect in a quasi-one-dimensional superconductor system without any inherent geometric imperfections.The measured maximum efficiency is manifested as 14%,observed atμ0H≈±60 mT,and we propose that the superconducting diode effect can potentially be attributed to the presence of the nontrivial topological band.Our work provides a platform for studying exotic phenomena in condensed matter physics and potential applications in quantum computing and quantum information processing.
基金supported by the National Natural Science Foundation of China(11725418 and 11334006)the National Basic Research Program of China(2016YFA0301004,2016YFA0301001,and 2015CB921001)+1 种基金Science Challenge Project(TZ2016004)Beijing Advanced Innovation Center for Future Chip(ICFC)
文摘PtTe2 and PtSe2 with trigonal structure have attracted extensive research interests since the discovery of type-II Dirac fermions in the bulk crystals. The evolution of the electronic structure from bulk 3D topological semimetal to 2D atomic thin films is an important scientific question. While a transition from 3D type-II Dirac semimetal in the bulk to 2D semiconductor in monolayer(ML) film has been reported for PtSe2, so far the evolution of electronic structure of atomically thin PtTe2 films still remains unexplored.Here we report a systematic angle-resolved photoemission spectroscopy(ARPES) study of the electronic structure of high quality PtTe2 films grown by molecular beam epitaxy with thickness from 2 ML to 6 ML.ARPES measurements show that PtTe2 films still remain metallic even down to 2 ML thickness, which is in sharp contrast to the semiconducting property of few layer PtSe2 films. Moreover, a transition from 2D metal to 3D type-II Dirac semimetal occurs at film thickness of 4–6 ML. In addition, Spin-ARPES measurements reveal helical spin textures induced by local Rashba effect in the bulk PtTe2 crystal, suggesting that similar hidden spin is also expected in few monolayer PtTe2 films. Our work reveals the transition from2D metal to 3D topological semimetal and provides new opportunities for investigating metallic 2D films with local Rashba effect.
基金supported by the National Key R&D Program of China(Grant Nos.2022YFA1403203,2017YFA0302904,2017YFA0303201,2018YFA0305602,and 2016YFA0300604)the National Natural Science Foundation of China(Grant Nos.12074002,11574372,11674331,11804379,11874417,and 92265104)+4 种基金the National Basic Research Program of China(Grant No.2015CB921303)the“Strategic Priority Research Program(B)”of the Chinese Academy of Sciences(Grant Nos.XDB07020300,XDB07020100,and XDB33030100)the Recruitment Program for Leading Talent Team of Anhui Province(2019-16)the Major Basic Program of Natural Science Foundation of Shandong Province(Grant No.ZR2021ZD01)supported by the High Magnetic Field Laboratory of Anhui Province,China。
文摘The origin of superconductivity observed at the point contact between the normal metal tip and the topological material remains uncertain due to the potential presence of superconducting elements or allotropes impurities.It is imperative to seek out a topological material entirely free of superconducting impurities and induce superconductivity between it and normal tips to verify the source of the induced superconductivity.Here,we report the observation of superconductivity up to 9 K induced at point contacts between normal metal tips and the topological material grey arsenic,which is free of superconductivity.The determined temperature dependencies of superconducting gapsΔ(T)deviate from the Bardeen-Cooper-Schriefer(BCS)superconductivity law,exhibiting abnormal behavior.Furthermore,the highly anisotropic upper critical field H_(c2)(T)suggests the anisotropy of the projected interfacial Fermi surface.By tuning the junction resistance,we obtained a negative correlation between the superconducting gapΔand the efective barrier height Z,which validates the interfacial coupling strength as a key factor in the observed tip-induced superconductivity.These experimental results provide guidance for the relevant theory about tip-induced superconductivity on topological materials.
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.
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Acknowledgements We are indebted to C. W. Luo, J. J. Lin, and W. B. Jian for explaining the details of their experiments, and T. Maniv and M. Lewkowicz for valuable discussions. The work of D. Li and B. Rosenstein was supported by the NSC of Taiwan, China, Grant No. 98-2112-M-009-014-MY3, and the MOE ATU program. The work of D. Li was also supported by the National Natural Science Foundation of China （Grant No. 11274018）. B. Rosenstein was grateful to the School of Physics of Peking University for its hospitality.
文摘New two-dimensional systems such as the surfaces of topological insulators （TIs） and graphene offer the possibility of experimentally investigating situations considered exotic just a decade ago. These situations include the quantum phase transition of the chiral type in electronic systems with a relativistic spectrum. Phonon-mediated （conventional） pairing in the Dirac semimetal appearing on the surface of a TI causes a transition into a chiral superconducting state, and exciton condensation in these gapless systems has long been envisioned in the physics of narrow-band semiconductors. Starting from the microscopic Dirac Hamiltonian with local attraction or repulsion, the Bardeen- Cooper-Schrieffer type of Gaussian approximation is developed in the framework of functional integrals. It is shown that owing to an ultrarelativistic dispersion relation, there is a quantum critical point governing the zero-temperature transition to a superconducting state or the exciton condensed state. Quantum transitions having critical exponents differ greatly from conventional ones and belong to the chiral universality class. We discuss the application of these results to recent experiments in which surface superconductivity was found in TIs and estimate the feasibility of phonon pairing.
