Epitaxial graphene grown on silicon carbide(Si C/graphene)is a promising solution for achieving a highprecision quantum Hall resistance standard.Previous research mainly focused on the quantum resistance metrology of ...Epitaxial graphene grown on silicon carbide(Si C/graphene)is a promising solution for achieving a highprecision quantum Hall resistance standard.Previous research mainly focused on the quantum resistance metrology of n-type Si C/graphene,while a comprehensive understanding of the quantum resistance metrology behavior of graphene with different doping types is lacking.Here,we fabricated both n-and p-type Si C/graphene devices via polymer-assisted molecular adsorption and conducted systematic magneto-transport measurements in a wide parameter space of carrier density and temperature.It is demonstrated that n-type devices show greater potential for development of quantum resistance metrology compared with p-type devices,as evidenced by their higher carrier mobility,lower critical magnetic field for entering quantized Hall plateaus,and higher robustness of the quantum Hall effect against thermal degeneration.These discrepancies can be reasonably attributed to the weaker scattering from molecular dopants for n-type devices,which is further supported by the analyses on the quantum interference effect in multiple devices.These results enrich our understanding of the charged impurity on electronic transport performance of graphene and,more importantly,provide a useful reference for future development of graphene-based quantum resistance metrology.展开更多
For conductors in the ballistic regime, electron-boundary scattering at the sample edge plays a dominant role in determining the transport performance, giving rise to many intriguing phenomena like low-field negative ...For conductors in the ballistic regime, electron-boundary scattering at the sample edge plays a dominant role in determining the transport performance, giving rise to many intriguing phenomena like low-field negative magnetoresistance effect. We systematically investigate the magneto-transport behaviors of BN-encapsulated graphene devices with narrow channel width W, wherein the bulk mean free path Lmfp can be very large and highly tunable. By comparing the magnetoresistance features and the amplitude of Lmfp in a large parameter space of temperature and carrier density, we reveal that the boundary-scattering-dominated negative magnetoresistance effect can still survive even when the ballistic ratio(Lmfp/W) is as low as 0.15. This striking value is much smaller than the expected value for achieving(quasi-) ballistic transport regime(Lmfp/W ≥ 1), and can be attributed to the ultra-low specularity of the sample edge of our graphene devices. These findings enrich our understanding of the effects of boundary scattering on channel transport, which is of vital importance for future designs of two-dimensional electronic devices with limited lateral sizes.展开更多
As an elemental semiconductor,tellurium has recently attracted intense interest due to its non-trivial band topology,and the resulted intriguing topological transport phenomena.In this study we report systematic elect...As an elemental semiconductor,tellurium has recently attracted intense interest due to its non-trivial band topology,and the resulted intriguing topological transport phenomena.In this study we report systematic electronic transport studies on tellurium flakes grown via a simple vapor deposition process.The sample is self-hole-doped,and exhibits typical weak localization behavior at low temperatures.Substantial negative longitudinal magnetoresistance under parallel magnetic field is observed over a wide temperature region,which is considered to share the same origin with that in tellurium bulk crystals,i.e.,the Weyl points near the top of valence band.However,with lowering temperature the longitudinal magnetoconductivity experiences a transition from parabolic to linear field dependency,differing distinctly from the bulk counterparts.Further analysis reveals that such a modulation of Weyl behaviors in this low-dimensional tellurium structure can be attributed to the enhanced inter-valley scattering at low temperatures.Our results further extend Weyl physics into a low-dimensional semiconductor system,which may find its potential application in designing topological semiconductor devices.展开更多
The reliance on spin-orbit coupling or strong magnetic fields has always posed significant challenges for the mass production and even laboratory realization of most topological materials. Valley-based topological zer...The reliance on spin-orbit coupling or strong magnetic fields has always posed significant challenges for the mass production and even laboratory realization of most topological materials. Valley-based topological zero-line modes have attracted widespread attention due to their substantial advantage of being initially realizable with just an external electric field. However, the uncontrollable nature of electrode alignment and precise fabrication has greatly hindered the advancement in this field. By utilizing minimally twisted bilayer graphene and introducing exchange fields from magnetic substrates, we successfully realize a spin-resolved, electrode-free topological zeroline mode. Further integration of electrodes that do not require alignment considerations significantly enhances the tunability of the system's band structure. Our approach offers a promising new support for the dazzling potential of topological zero-line mode in the realm of low-energy-consumption electronics.展开更多
Nanoclusters consisting of a few atoms have attracted a lot of research interests due to their exotic size-dependent properties. Here, well-ordered two-dimensional Sb cluster superlattice was fabricated on Si substrat...Nanoclusters consisting of a few atoms have attracted a lot of research interests due to their exotic size-dependent properties. Here, well-ordered two-dimensional Sb cluster superlattice was fabricated on Si substrate by a two-step method and characterized by scanning tunneling microscopy. High resolution scanning tunneling microscope measurements revealed the fine structures of the Sb clusters, which consist of several Sb atoms ranging from 2 to 7. Furthermore, the electronic structure of the nanocluster displays the quantized energy-level which is due to the single-electron tunneling effects. We believe that the fabrication of Sb cluster superlattice broadens the species of the cluster superlattice and provides a promising candidate to further explore the novel physical and chemical properties of the semimetal nanocluster.展开更多
We theoretically demonstrate that the electronic second-order topological insulator with robust corner states,having a buckled honeycomb lattice, can be realized in bismuthene by inducing in-plane magnetization. Based...We theoretically demonstrate that the electronic second-order topological insulator with robust corner states,having a buckled honeycomb lattice, can be realized in bismuthene by inducing in-plane magnetization. Based on the sp^(3) Slater–Koster tight-binding model with parameters extracted from first-principles results, we show that spin-helical edge states along zigzag boundaries are gapped out by the in-plane magnetization whereas four robust in-gap electronic corner states at the intersection between two zigzag boundaries arise. By regulating the orientation of in-plane magnetization, we show different position distribution of four corner states with different energies. Nevertheless, it respects some spatial symmetries and thus can protect the higher-order topological phase. Combined with the Kane–Mele model, we discuss the influence of the magnetization orientation on the position distribution of corner states.展开更多
We report the observation of in-plane anisotropic magnetoresistance and planar Hall effect in non-magnetic HfTe_(5) thin layers.The observed anisotropic magnetoresistance as well as its sign is strongly dependent on t...We report the observation of in-plane anisotropic magnetoresistance and planar Hall effect in non-magnetic HfTe_(5) thin layers.The observed anisotropic magnetoresistance as well as its sign is strongly dependent on the critical resistivity anomaly temperature T_(p).Below T_(p),the anisotropic magnetoresistance is negative with large negative magnetoresistance.When the in-plane magnetic field is perpendicular to the current,the negative longitudinal magnetoresistance reaches its maximum.The negative longitudinal magnetoresistance effect in HfTe_(5) thin layers is dramatically different from that induced by the chiral anomaly as observed in Weyl and Dirac semimetals.One potential underlying origin may be attributed to the reduced spin scattering,which arises from the in-plane magnetic field driven coupling between the top and bottom surface states.Our findings provide valuable insights for the anisotropic magnetoresistance effect in topological electronic systems and the device potential of HfTe5 in spintronics and quantum sensing.展开更多
The Weyl semimetal has emerged as a new topologically nontrivial phase of matter,hosting low-energy excitations of massless Weyl fermions.Here,we present a comprehensive study of a type-ⅡWeyl semimetal WP2.Transport ...The Weyl semimetal has emerged as a new topologically nontrivial phase of matter,hosting low-energy excitations of massless Weyl fermions.Here,we present a comprehensive study of a type-ⅡWeyl semimetal WP2.Transport studies show a butterfly-like magnetoresistance at low temperature,reflecting the anisotropy of the electron Fermi surfaces.This four-lobed feature gradually evolves into a two-lobed variant with an increase in temperature,mainly due to the reduced relative contribution of electron Fermi surfaces compared to hole Fermi surfaces for magnetoresistance.Moreover,an angle-dependent Berry phase is also discovered,based on quantum oscillations,which is ascribed to the effective manipulation of extremal Fermi orbits by the magnetic field to feel nearby topological singularities in the momentum space.The revealed topological character and anisotropic Fermi surfaces of the WP2 substantially enrich the physical properties of Weyl semimetals,and show great promises in terms of potential topological electronic and Fermitronic device applications.展开更多
Superconductors with reduced dimensionality have been widely explored for their exotic superconducting behaviors.Especially,at the two-dimensional limit,two-monolayer Pb films with two types of structures provide an i...Superconductors with reduced dimensionality have been widely explored for their exotic superconducting behaviors.Especially,at the two-dimensional limit,two-monolayer Pb films with two types of structures provide an ideal platform to unveil the underlying superconducting mechanism[Science 324,1314(2009)].Here,by combining scanning tunneling microscopy(STM)with the first-principle calculations,we successfully identify that these two types have different atomic lattice structures with varying stacking phases,which further enables us to calculate the phonon spectrum and electron phonon coupling strength of each type.The theoretical calculations are in good agreement with tunneling spectroscopy measurements of the superconducting transition temperatures(T_(c)),which established a correlation between atomic structures and superconductivity.Moreover,it was observed that the higher T_(c)of these two types also possess higher out-of-plane upper critical magnetic fields(Hc2).These findings will provide important new insights into two-dimensional superconductivity at the atomic level.展开更多
Cobalt pnictides have been theoretically proposed to be attractive candi-dates for high-temperature superconductors.Additionally,monolayered CoX(X=As,Sb,Bi)on SrTiO_(3) systems present a potential new platform for rea...Cobalt pnictides have been theoretically proposed to be attractive candi-dates for high-temperature superconductors.Additionally,monolayered CoX(X=As,Sb,Bi)on SrTiO_(3) systems present a potential new platform for realizing topological superconductors in the two-dimensional limit,due to their nontrivial band topology.To this end,we have successfully fabricated high-quality CoBi nanoislands on SrTiO_(3)(001)substrates by molecular beam epitaxy followed by an investigation of their atomic struc-ture and electronic properties via in situ scanning tunneling microscopyl spectroscopy.Beyond the previously predicted lattice with a=b=3.5 A,2×1 dimer row was observed in this study.Furthermore,our results reveal that the topography of CoBi islands is strongly influenced by various growth conditions,such as substrate temperature,the flux ratio between Co and Bi,and the annealing process.This study paves the way for further explorations of the superconductivity and topological properties of cobalt pnictidesystems.展开更多
Exchange bias(EB)is a fundamental phenomenon in widespread information technologies.However,a comprehensive understanding of its microscopic origin remains a great challenge.One key issue in the debate is the role of ...Exchange bias(EB)is a fundamental phenomenon in widespread information technologies.However,a comprehensive understanding of its microscopic origin remains a great challenge.One key issue in the debate is the role of frustration and disorder in the EB mechanism,which motivates the exploration of the EB effect in spin glass(SG)systems.Here,in the SG state of Crdoped Hund's metal CsFe_(2)As_(2),we discover a giant EB effect with a maximum bias field of -2 T,which is almost two orders of magnitude larger than that of traditional alloy SGs.Our results indicate that the giant EB effect should originate from the exchange interactions at the natural boundaries between the tunable ferromagnetic-like(FM)regions around Cr dopants and the SG matrix,via which the FM spins are strongly pinned by the frozen spins in the SG matrix.In addition,the temperaturedependent and cooling-field-dependent EB behaviors could be interpreted well by the SG model with frustrated FM/SG boundaries,which provides an intuitive and explicit understanding of the impact of glassy parameters on the EB effect.All these results suggest that the correlated metals are promising directions for exploring the EB effect in the SG state.展开更多
The superconducting ground state of kagome metals AV_(3)Sb_(5)(where A stands for K,Rb,or Cs)emerges from an exotic charge density wave(CDW)state that potentially breaks both rotational and time reversal symmetries.Ho...The superconducting ground state of kagome metals AV_(3)Sb_(5)(where A stands for K,Rb,or Cs)emerges from an exotic charge density wave(CDW)state that potentially breaks both rotational and time reversal symmetries.However,the specifics of the Cooper pairing mechanism,and the nature of the interplay between these two states remain elusive,largely due to the lack of momentum-space(k-space)superconducting energy gap structure.By implementing Bogoliubov quasiparticle interference(B QPI)imaging,we obtain k-space information on the multiband superconducting gap structureΔ_(SC)^(i)(k)in pristine CsV_(3)Sb_(5).We show that the estimated energy gap on the vanadium d_(xy/x^(2)-y^(2))orbital is anisotropic but nodeless,with a minimal value located near the M point.Interestingly,a comparison ofΔ_(SC)^(i)(k)with the CDW gapΔ_(CDW)^(i)(k)obtained by angle-re solved photoemission spectro scopy(ARPES)reveals direct k-space competition between the se two order parameters,i.e.,the opening of a large(small)CDW gap at a given momentum corresponds to a small(large)superconducting gap.When the long-range CDW order is suppressed by replacing vanadium with titanium,we find a nearly isotropic energy gap on both the V and Sb bands.This information will be critical for identifying the microscopic pairing mechanism and its interplay with intertwined electro nic orders in this kagome superconductor family.展开更多
Ferroelectric resistance switching(RS)devices based on doped HfO_(2) films have drawn extensive attention due to their good complementary metal-oxide-semiconductor transistor(CMOS)compatibility compared with that of c...Ferroelectric resistance switching(RS)devices based on doped HfO_(2) films have drawn extensive attention due to their good complementary metal-oxide-semiconductor transistor(CMOS)compatibility compared with that of conventional perovskite ferroelectrics.However,reported RS characteristics for HfO_(2)-based RS devices contrast sharply with substantially different on/off ratios rangingfrom less than one to four orders of magnitude.展开更多
Nontrivial topological behaviors in superconducting materials provide resourceful ground for the emergence and study of unconventional quantum states.Charge doping by the controlled intercalation of donor atoms is an ...Nontrivial topological behaviors in superconducting materials provide resourceful ground for the emergence and study of unconventional quantum states.Charge doping by the controlled intercalation of donor atoms is an efficient route for enhancing/inducement of superconducting and topological behaviors in layered topological insulators and semimetals.Herein,we enhanced the superconducting temperature of TaSe_(2) by 20-folds(~3 K)through Sn atoms intercalation.Using first-principles calculations,we demonstrated the existence of nontrivial topological features.Sn_(0.5)TaSe_(2) displays topological nodal lines around the K high symmetry point in the Brillouin zone,with drumhead-like shaped surface states protected by inversion symmetry.Altogether,the coexistence of these properties makes Sn_(0.5)TaSe_(2) a potential candidate for topological superconductivity.展开更多
基金supported by the CAS Project for Young Scientists in Basic Research(Grant No.YSBR-046)the National Natural Science Foundation of China(Grant Nos.92165201,11974324,12104435)+4 种基金the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302800)the Anhui Initiative in Quantum Information Technologies(Grant No.AHY170000)Hefei Science Center CAS(Grant No.2020HSC-UE014)the Fundamental Research Funds for the Central Universities(Grant Nos.WK3510000013 and WK2310000104)supported by USTC Tang Scholar。
文摘Epitaxial graphene grown on silicon carbide(Si C/graphene)is a promising solution for achieving a highprecision quantum Hall resistance standard.Previous research mainly focused on the quantum resistance metrology of n-type Si C/graphene,while a comprehensive understanding of the quantum resistance metrology behavior of graphene with different doping types is lacking.Here,we fabricated both n-and p-type Si C/graphene devices via polymer-assisted molecular adsorption and conducted systematic magneto-transport measurements in a wide parameter space of carrier density and temperature.It is demonstrated that n-type devices show greater potential for development of quantum resistance metrology compared with p-type devices,as evidenced by their higher carrier mobility,lower critical magnetic field for entering quantized Hall plateaus,and higher robustness of the quantum Hall effect against thermal degeneration.These discrepancies can be reasonably attributed to the weaker scattering from molecular dopants for n-type devices,which is further supported by the analyses on the quantum interference effect in multiple devices.These results enrich our understanding of the charged impurity on electronic transport performance of graphene and,more importantly,provide a useful reference for future development of graphene-based quantum resistance metrology.
基金supported by the National Natural Science Foundation of China(Grant Nos.92165201 and 11974324)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302800)+3 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDC07010000)the Anhui Initiative in Quantum Information Technologies(Grant No.AHY170000)the Hefei Science Center CAS(Grant No.2020HSC-UE014)the Fundamental Research Funds for the Central Universities(Grant No.WK3510000013)。
文摘For conductors in the ballistic regime, electron-boundary scattering at the sample edge plays a dominant role in determining the transport performance, giving rise to many intriguing phenomena like low-field negative magnetoresistance effect. We systematically investigate the magneto-transport behaviors of BN-encapsulated graphene devices with narrow channel width W, wherein the bulk mean free path Lmfp can be very large and highly tunable. By comparing the magnetoresistance features and the amplitude of Lmfp in a large parameter space of temperature and carrier density, we reveal that the boundary-scattering-dominated negative magnetoresistance effect can still survive even when the ballistic ratio(Lmfp/W) is as low as 0.15. This striking value is much smaller than the expected value for achieving(quasi-) ballistic transport regime(Lmfp/W ≥ 1), and can be attributed to the ultra-low specularity of the sample edge of our graphene devices. These findings enrich our understanding of the effects of boundary scattering on channel transport, which is of vital importance for future designs of two-dimensional electronic devices with limited lateral sizes.
基金Project supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDC07010000)the National Natural Science Foundation of China(Grant Nos.11974324,U1832151,11804326,and 11904001)+2 种基金the National Key Research and Development Program of China(Grant No.2017YFA0403600)the Anhui Initiative Fund in Quantum Information Technologies(Grant No.AHY170000)the Fund from the Hefei Science Center,Chinese Academy of Sciences(Grant No.2020HSC-UE014).
文摘As an elemental semiconductor,tellurium has recently attracted intense interest due to its non-trivial band topology,and the resulted intriguing topological transport phenomena.In this study we report systematic electronic transport studies on tellurium flakes grown via a simple vapor deposition process.The sample is self-hole-doped,and exhibits typical weak localization behavior at low temperatures.Substantial negative longitudinal magnetoresistance under parallel magnetic field is observed over a wide temperature region,which is considered to share the same origin with that in tellurium bulk crystals,i.e.,the Weyl points near the top of valence band.However,with lowering temperature the longitudinal magnetoconductivity experiences a transition from parabolic to linear field dependency,differing distinctly from the bulk counterparts.Further analysis reveals that such a modulation of Weyl behaviors in this low-dimensional tellurium structure can be attributed to the enhanced inter-valley scattering at low temperatures.Our results further extend Weyl physics into a low-dimensional semiconductor system,which may find its potential application in designing topological semiconductor devices.
基金supported by the National Natural Science Foundation of China (Grant Nos.11974327 and 12004369)the Natural Science Basic Research Program of Shanxi Province (Grant No.20210302124252)+1 种基金Anhui Initiative in Quantum Information Technologies (Grant No.AHY170000)the Innovation Program for Quantum Science and Technology (Grant No.2021ZD0302800)。
文摘The reliance on spin-orbit coupling or strong magnetic fields has always posed significant challenges for the mass production and even laboratory realization of most topological materials. Valley-based topological zero-line modes have attracted widespread attention due to their substantial advantage of being initially realizable with just an external electric field. However, the uncontrollable nature of electrode alignment and precise fabrication has greatly hindered the advancement in this field. By utilizing minimally twisted bilayer graphene and introducing exchange fields from magnetic substrates, we successfully realize a spin-resolved, electrode-free topological zeroline mode. Further integration of electrodes that do not require alignment considerations significantly enhances the tunability of the system's band structure. Our approach offers a promising new support for the dazzling potential of topological zero-line mode in the realm of low-energy-consumption electronics.
基金Project supported by the National Key Basic Research Program of China(Grant No.2017YFA0205004)the National Natural Science Foundation of China(Grant Nos.92165201,11474261,and 11634011)+1 种基金the Fundamental Research Funds for the Central Universities(Grant Nos.WK3510000006,and WK3430000003)the Anhui Initiative in Quantum Information Technologies(Grant No.AHY170000)。
文摘Nanoclusters consisting of a few atoms have attracted a lot of research interests due to their exotic size-dependent properties. Here, well-ordered two-dimensional Sb cluster superlattice was fabricated on Si substrate by a two-step method and characterized by scanning tunneling microscopy. High resolution scanning tunneling microscope measurements revealed the fine structures of the Sb clusters, which consist of several Sb atoms ranging from 2 to 7. Furthermore, the electronic structure of the nanocluster displays the quantized energy-level which is due to the single-electron tunneling effects. We believe that the fabrication of Sb cluster superlattice broadens the species of the cluster superlattice and provides a promising candidate to further explore the novel physical and chemical properties of the semimetal nanocluster.
基金financially supported by the Fundamental Research Funds for the Central Universities (Grant Nos. WK3510000010 and WK2030020032)the National Natural Science Foundation of China (Grant Nos. 11974327 and 12004369)the Anhui Initiative in Quantum Information Technologies。
文摘We theoretically demonstrate that the electronic second-order topological insulator with robust corner states,having a buckled honeycomb lattice, can be realized in bismuthene by inducing in-plane magnetization. Based on the sp^(3) Slater–Koster tight-binding model with parameters extracted from first-principles results, we show that spin-helical edge states along zigzag boundaries are gapped out by the in-plane magnetization whereas four robust in-gap electronic corner states at the intersection between two zigzag boundaries arise. By regulating the orientation of in-plane magnetization, we show different position distribution of four corner states with different energies. Nevertheless, it respects some spatial symmetries and thus can protect the higher-order topological phase. Combined with the Kane–Mele model, we discuss the influence of the magnetization orientation on the position distribution of corner states.
基金Supported by the National Key R&D Program(Grant Nos.2017YFB0405703,2017YFA0205004,and 2018YFA0306600)the National Natural Science Foundation of China(Grant Nos.11974327,11474265,11674295,11674024,and 11874193)+2 种基金the Fundamental Research Funds for the Central Universities(Grant Nos.WK2030020032 and WK2340000082)Anhui Initiative in Quantum Information Technologies,and the Shenzhen Fundamental Subject Research Program(Grant No.JCYJ20170817110751776)the USTC Center for Micro and Nanoscale Research and Fabrication。
文摘We report the observation of in-plane anisotropic magnetoresistance and planar Hall effect in non-magnetic HfTe_(5) thin layers.The observed anisotropic magnetoresistance as well as its sign is strongly dependent on the critical resistivity anomaly temperature T_(p).Below T_(p),the anisotropic magnetoresistance is negative with large negative magnetoresistance.When the in-plane magnetic field is perpendicular to the current,the negative longitudinal magnetoresistance reaches its maximum.The negative longitudinal magnetoresistance effect in HfTe_(5) thin layers is dramatically different from that induced by the chiral anomaly as observed in Weyl and Dirac semimetals.One potential underlying origin may be attributed to the reduced spin scattering,which arises from the in-plane magnetic field driven coupling between the top and bottom surface states.Our findings provide valuable insights for the anisotropic magnetoresistance effect in topological electronic systems and the device potential of HfTe5 in spintronics and quantum sensing.
基金Supported by the National Natural Science Foundation of China(Grant Nos.11974324,11804326,U1832151,and 11674296),the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDC07010000)the National Key Research and Development Program of China(Grant No.2017YFA0403600)+4 种基金the Anhui Initiative in Quantum Information Technologies(Grant No.AHY170000)the Hefei Science Center CAS(Grant No.2018HSC-UE014)the Jiangsu Provincial Science Foundation for Youth(Grant No.BK20170821)the National Natural Science Foundation of China for Youth(Grant No.11804160)the Anhui Provincial Natural Science Foundation(Grant No.1708085MF136)。
文摘The Weyl semimetal has emerged as a new topologically nontrivial phase of matter,hosting low-energy excitations of massless Weyl fermions.Here,we present a comprehensive study of a type-ⅡWeyl semimetal WP2.Transport studies show a butterfly-like magnetoresistance at low temperature,reflecting the anisotropy of the electron Fermi surfaces.This four-lobed feature gradually evolves into a two-lobed variant with an increase in temperature,mainly due to the reduced relative contribution of electron Fermi surfaces compared to hole Fermi surfaces for magnetoresistance.Moreover,an angle-dependent Berry phase is also discovered,based on quantum oscillations,which is ascribed to the effective manipulation of extremal Fermi orbits by the magnetic field to feel nearby topological singularities in the momentum space.The revealed topological character and anisotropic Fermi surfaces of the WP2 substantially enrich the physical properties of Weyl semimetals,and show great promises in terms of potential topological electronic and Fermitronic device applications.
基金supported by the National Key Basic Research Program of China(Grant No.2017YFA0205004)the National Natural Science Foundation of China(Grant Nos.92165201,11474261,11634011,and 11974323)+2 种基金the Fundamental Research Funds for the Central Universities(Grant Nos.WK3510000006,and WK3430000003)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302800)the Anhui Initiative in Quantum Information Technologies(Grant No.AHY170000)。
文摘Superconductors with reduced dimensionality have been widely explored for their exotic superconducting behaviors.Especially,at the two-dimensional limit,two-monolayer Pb films with two types of structures provide an ideal platform to unveil the underlying superconducting mechanism[Science 324,1314(2009)].Here,by combining scanning tunneling microscopy(STM)with the first-principle calculations,we successfully identify that these two types have different atomic lattice structures with varying stacking phases,which further enables us to calculate the phonon spectrum and electron phonon coupling strength of each type.The theoretical calculations are in good agreement with tunneling spectroscopy measurements of the superconducting transition temperatures(T_(c)),which established a correlation between atomic structures and superconductivity.Moreover,it was observed that the higher T_(c)of these two types also possess higher out-of-plane upper critical magnetic fields(Hc2).These findings will provide important new insights into two-dimensional superconductivity at the atomic level.
基金supported by the National Natural Science Foundation of China(Nos.12374196,92165201,and 11634011)the Innovation Program for Quantum Science and Technology(No.2021ZD0302800)+2 种基金the CAS Project for Young Scientists in Basic Research(Grant No.YSBR-046)the Fundamental Research Funds for the Central Universities(Grant Nos.WK3510000006and WK3430000003)Anhui Initiative in Quantum Information Technologies(No.AHY170000).
文摘Cobalt pnictides have been theoretically proposed to be attractive candi-dates for high-temperature superconductors.Additionally,monolayered CoX(X=As,Sb,Bi)on SrTiO_(3) systems present a potential new platform for realizing topological superconductors in the two-dimensional limit,due to their nontrivial band topology.To this end,we have successfully fabricated high-quality CoBi nanoislands on SrTiO_(3)(001)substrates by molecular beam epitaxy followed by an investigation of their atomic struc-ture and electronic properties via in situ scanning tunneling microscopyl spectroscopy.Beyond the previously predicted lattice with a=b=3.5 A,2×1 dimer row was observed in this study.Furthermore,our results reveal that the topography of CoBi islands is strongly influenced by various growth conditions,such as substrate temperature,the flux ratio between Co and Bi,and the annealing process.This study paves the way for further explorations of the superconductivity and topological properties of cobalt pnictidesystems.
基金supported by the National Key R&D Program of China(Grant No.2022YFA1602601)the National Natural Science Foundation of China(Grant Nos.12034004,12161160316,and 12325403)+3 种基金the Basic Research Program of the Chinese Academy of Sciences Based on Major Scientific Infrastructures(Grant No.JZHKYPT-2021-08)the CAS Project for Young Scientists in Basic Research(Grant No.YBR-048)the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302800)the Fundamental Research Funds for the Central Universities。
文摘Exchange bias(EB)is a fundamental phenomenon in widespread information technologies.However,a comprehensive understanding of its microscopic origin remains a great challenge.One key issue in the debate is the role of frustration and disorder in the EB mechanism,which motivates the exploration of the EB effect in spin glass(SG)systems.Here,in the SG state of Crdoped Hund's metal CsFe_(2)As_(2),we discover a giant EB effect with a maximum bias field of -2 T,which is almost two orders of magnitude larger than that of traditional alloy SGs.Our results indicate that the giant EB effect should originate from the exchange interactions at the natural boundaries between the tunable ferromagnetic-like(FM)regions around Cr dopants and the SG matrix,via which the FM spins are strongly pinned by the frozen spins in the SG matrix.In addition,the temperaturedependent and cooling-field-dependent EB behaviors could be interpreted well by the SG model with frustrated FM/SG boundaries,which provides an intuitive and explicit understanding of the impact of glassy parameters on the EB effect.All these results suggest that the correlated metals are promising directions for exploring the EB effect in the SG state.
基金supported by the National Key R&D Program of China(Grant Nos.2022YFA1602600,and 2018YFA0305602)the National Natural Science Foundation of China(Grant Nos.11888101,12074364,52273309,and 52261135638)+5 种基金the Innovation Program for Quantum Science and Technology(Grant No.2021ZD0302802)the Basic Research Program of the Chinese Academy of Sciences Based on Major Scientific Infrastructures(Grant No.JZHKYPT-2021-08)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB25000000)the Anhui Initiative in Quantum Information Technologies(Grant No.AHY160000)the Fundamental Research Funds for the Central Universities(Grant Nos.WK3510000012,and WK3510000015)the Major Basic Program of the Natural Science Foundation of Shandong Province(Grant No.ZR2021ZD01)。
文摘The superconducting ground state of kagome metals AV_(3)Sb_(5)(where A stands for K,Rb,or Cs)emerges from an exotic charge density wave(CDW)state that potentially breaks both rotational and time reversal symmetries.However,the specifics of the Cooper pairing mechanism,and the nature of the interplay between these two states remain elusive,largely due to the lack of momentum-space(k-space)superconducting energy gap structure.By implementing Bogoliubov quasiparticle interference(B QPI)imaging,we obtain k-space information on the multiband superconducting gap structureΔ_(SC)^(i)(k)in pristine CsV_(3)Sb_(5).We show that the estimated energy gap on the vanadium d_(xy/x^(2)-y^(2))orbital is anisotropic but nodeless,with a minimal value located near the M point.Interestingly,a comparison ofΔ_(SC)^(i)(k)with the CDW gapΔ_(CDW)^(i)(k)obtained by angle-re solved photoemission spectro scopy(ARPES)reveals direct k-space competition between the se two order parameters,i.e.,the opening of a large(small)CDW gap at a given momentum corresponds to a small(large)superconducting gap.When the long-range CDW order is suppressed by replacing vanadium with titanium,we find a nearly isotropic energy gap on both the V and Sb bands.This information will be critical for identifying the microscopic pairing mechanism and its interplay with intertwined electro nic orders in this kagome superconductor family.
基金financially supported by the National Natural Science Foundation of China(Nos.52125204,52250281,U21A2066,92163210 and 52372128)the National Key Research and Development Program of China(Nos.2022YFB3807602,2019YFA0307900)the Fundamental Research Funds for the Central Universities(No.WK2030000070)。
文摘Ferroelectric resistance switching(RS)devices based on doped HfO_(2) films have drawn extensive attention due to their good complementary metal-oxide-semiconductor transistor(CMOS)compatibility compared with that of conventional perovskite ferroelectrics.However,reported RS characteristics for HfO_(2)-based RS devices contrast sharply with substantially different on/off ratios rangingfrom less than one to four orders of magnitude.
基金the financial support in part by the National Key R&D Program of China(No.2017YFA0303500)the National Natural Science Foundation of China(NSFC)(Nos.U1932201,11574280,and 21727801)+2 种基金NSFC-MAECI(No.51861135202)International Partnership Program of CAS(No.211134KYSB20190063)CAS Collaborative Innovation Program of Hefei Science Center(No.2019HSC-CIP002).
文摘Nontrivial topological behaviors in superconducting materials provide resourceful ground for the emergence and study of unconventional quantum states.Charge doping by the controlled intercalation of donor atoms is an efficient route for enhancing/inducement of superconducting and topological behaviors in layered topological insulators and semimetals.Herein,we enhanced the superconducting temperature of TaSe_(2) by 20-folds(~3 K)through Sn atoms intercalation.Using first-principles calculations,we demonstrated the existence of nontrivial topological features.Sn_(0.5)TaSe_(2) displays topological nodal lines around the K high symmetry point in the Brillouin zone,with drumhead-like shaped surface states protected by inversion symmetry.Altogether,the coexistence of these properties makes Sn_(0.5)TaSe_(2) a potential candidate for topological superconductivity.
