Negative differential conductance(NDC)serves as a crucial characteristic that reveals various underlying physics and transport process in hybrid superconducting devices.We report the observation of gate-tunable NDC ou...Negative differential conductance(NDC)serves as a crucial characteristic that reveals various underlying physics and transport process in hybrid superconducting devices.We report the observation of gate-tunable NDC outside the superconducting energy gap on two types of hybrid semiconductor–superconductor devices,i.e.,normal metal–superconducting nanowire–normal metal and normal metal–superconducting nanowire–superconductor devices.Specifically,we study the dependence of the NDCs on back-gate voltage and magnetic field.When the back-gate voltage decreases,these NDCs weaken and evolve into positive differential conductance dips;and meanwhile they move away from the superconducting gap towards high bias voltage,and disappear eventually.In addition,with the increase of magnetic field,the NDCs/dips follow the evolution of the superconducting gap,and disappear when the gap closes.We interpret these observations and reach a good agreement by combining the Blonder–Tinkham–Klapwijk(BTK)model and the critical supercurrent effect in the nanowire,which we call the BTK-supercurrent model.Our results provide an in-depth understanding of the tunneling transport in hybrid semiconductor–superconductor devices.展开更多
Recently,a contact-resistance-measurement method was developed to detect the minigap,hence the Andreev bound states(ABSs),in Josephson junctions constructed on the surface of three-dimensional topological insulators(3...Recently,a contact-resistance-measurement method was developed to detect the minigap,hence the Andreev bound states(ABSs),in Josephson junctions constructed on the surface of three-dimensional topological insulators(3D TIs).In this work,we further generalize that method to the circumstance with radio frequency(rf)irradiation.We find that with the increase of the rf power,the measured minigap becomes broadened and extends to higher energies in a way similar to the rf power dependence of the outer border of the Shapiro step region.We show that the corresponding data of contact resistance under rf irradiation can be well interpreted by using the resistively shunted Josephson junction(RSJ)model and the Blonder–Tinkham–Klapwijk(BTK)theory.Our findings could be useful when using the contact-resistancemeasurement method to study the Majorana-related physics in topological insulator-based Josephson junctions under rf irradiation.展开更多
Twisting two layers into a magic angle(MA) of ~1.1°is found essential to create low energy flat bands and the resulting correlated insulating,superconducting,and magnetic phases in twisted bilayer graphene(TBG).W...Twisting two layers into a magic angle(MA) of ~1.1°is found essential to create low energy flat bands and the resulting correlated insulating,superconducting,and magnetic phases in twisted bilayer graphene(TBG).While most of previous works focus on revealing these emergent states in MA-TBG,a study of the twist angle dependence,which helps to map an evolution of these phases,is yet less explored.Here,we report a magnetotransport study on one non-magic angle TBG device,whose twist angle θ changes from 1.25° at one end to 1.43°at the other.For θ=1.25° we observe an emergence of topological insulating states at hole side with a sequence of Chern number |C|=4-|v|,where v is the number of electrons(holes) in moire unite cell.When θ> 1.25°,the Chern insulator from flat band disappears and evolves into fractal Hofstadter butterfly quantum Hall insulator where magnetic flux in one moire unite cell matters.Our observations will stimulate further theoretical and experimental investigations on the relationship between electron interactions and non-trivial band topology.展开更多
Introduction of spin-orbit coupling(SOC)in a Josephson junction(JJ)gives rise to unusual Josephson effects.We investigate JJs based on a newly discovered heterodimensional superlattice V_(5)S_(8) with a special form o...Introduction of spin-orbit coupling(SOC)in a Josephson junction(JJ)gives rise to unusual Josephson effects.We investigate JJs based on a newly discovered heterodimensional superlattice V_(5)S_(8) with a special form of SOC.The unique homointerface of our JJs enables elimination of extrinsic effects due to interfaces and disorder.We observe asymmetric Fraunhofer patterns with respect to both the perpendicular magnetic field and the current.The asymmetry is influenced by an in-plane magnetic field.Analysis of the pattern points to a nontrivial spatial distribution of the Josephson current that is intrinsic to the SOC in V_(5)S_(8).展开更多
Recently, a Corbino-geometry type of Josephson junction constructed on the surface of topological insulators has been proposed for hosting and braiding Majorana zero modes. As a first step to test this proposal, we su...Recently, a Corbino-geometry type of Josephson junction constructed on the surface of topological insulators has been proposed for hosting and braiding Majorana zero modes. As a first step to test this proposal, we successfully fabricated Corbino-geometry Josephson junctions(JJs) on the surface of Bi_(2)Te_(3) flakes. Ac Josephson effect with fractional Shapiro steps was observed in the Corbino-geometry JJs while the flux in the junction area was quantized. By analyzing the experimental data using the resistively shunted Josephson junction model, we found that the Corbino-geometry JJs exhibit a skewed current-phase relation due to its high transparency. The results suggest that Corbino-geometry JJs constructed on the surface of topological insulators may provide a promising platform for studying Majorana-related physics.展开更多
We report on magnetoresistance, Hall effect, and quantum Shubnikov–de Haas oscillation(SdH) experiments in NbIrTe4 single crystals, which was recently predicted to be a type-II Weyl semimetal. NbIrTe4 manifests a non...We report on magnetoresistance, Hall effect, and quantum Shubnikov–de Haas oscillation(SdH) experiments in NbIrTe4 single crystals, which was recently predicted to be a type-II Weyl semimetal. NbIrTe4 manifests a non-saturating and parabolic magnetoresistance at low temperatures. The magneto-transport measurements show that NbIrTe4 is a multiband system. The analysis of the SdH oscillations reveals four distinct oscillation frequencies. Combined with the density-functional theory calculations, we show that they come from two types of Fermi surfaces: electron pocket E1 and hole pocket H2.展开更多
Solid-state quantum computation station belongs to the group 2 of manipulation of quantum state in the Synergetic Extreme Condition User Facility. Here we will first outline the research background, aspects, and objec...Solid-state quantum computation station belongs to the group 2 of manipulation of quantum state in the Synergetic Extreme Condition User Facility. Here we will first outline the research background, aspects, and objectives of the station, followed by a discussion of the recent scientific as well as technological progress in this field based on similar experimental facilities to be constructed in the station. Finally, a brief summary and research perspective will be presented.展开更多
We studied anomalous Josephson effect(AJE) in Josephson trijunctions fabricated on Bi_(2)Se_(3), and found that the AJE in T-shaped trijunctions significantly alters the Majorana phase diagram of the trijunctions, whe...We studied anomalous Josephson effect(AJE) in Josephson trijunctions fabricated on Bi_(2)Se_(3), and found that the AJE in T-shaped trijunctions significantly alters the Majorana phase diagram of the trijunctions, when an in-plane magnetic field is applied parallel to two of the three single junctions. Such a phenomenon in topological insulator-based Josephson trijunction provides unambiguous evidence for the existence of AJE in the system, and may provide an additional knob for controlling the Majorana bound states in the Fu–Kane scheme of topological quantum computation.展开更多
二维过渡金属硫族化合物(transition metal dichalcogenides, TMDCs)是继石墨烯之后的新型范德瓦耳斯材料,由于其天然的二维特性以及强自旋轨道耦合作用(spin-orbital coupling, SOC),导致诸如金属-绝缘体转变、电荷密度波(charge densi...二维过渡金属硫族化合物(transition metal dichalcogenides, TMDCs)是继石墨烯之后的新型范德瓦耳斯材料,由于其天然的二维特性以及强自旋轨道耦合作用(spin-orbital coupling, SOC),导致诸如金属-绝缘体转变、电荷密度波(charge density wave, CDW)、能谷电子学、非常规超导电性等新颖物理性质的出现,使得这类材料成为研究低维量子物理的又一理想平台.其中能谷电子学与拓扑超导已经成为近年来凝聚态物理前沿研究的热点方向.本文在综述TMDCs材料的结构与基本物理性质的基础上,重点介绍了最近发展的用于生长原子层厚度的TMDCs材料的熔盐辅助化学气相沉积方法、在Se掺杂的MoSexTe2-x薄膜中实现的Td相到1T′相再到2H相的结构相变与超导增强现象,以及在少层Td-MoTe2中发现的非对称性SOC作用引起的类伊辛超导现象.最后,展望了TMDCs材料的潜在应用与可能存在的拓扑超导.展开更多
基金the National Key Research and Development Program of China(Grant Nos.2022YFA1403400 and 2017YFA0304700)the National Natural Science Foundation of China(Grant Nos.12074417,92065203,92065106,61974138,11774405,11527806,and 12104489)+3 种基金the Strategic Priority Research Program B of Chinese Academy of Sciences(Grant Nos.XDB28000000 and XDB33000000)the Synergetic Extreme Condition User Facility sponsored by the National Development and Reform Commissionthe Innovation Program for Quantum Science and Technology(2021ZD0302600)the support from Youth Innovation Promotion Association,Chinese Academy of Sciences(Grant Nos.2017156 and Y2021043).
文摘Negative differential conductance(NDC)serves as a crucial characteristic that reveals various underlying physics and transport process in hybrid superconducting devices.We report the observation of gate-tunable NDC outside the superconducting energy gap on two types of hybrid semiconductor–superconductor devices,i.e.,normal metal–superconducting nanowire–normal metal and normal metal–superconducting nanowire–superconductor devices.Specifically,we study the dependence of the NDCs on back-gate voltage and magnetic field.When the back-gate voltage decreases,these NDCs weaken and evolve into positive differential conductance dips;and meanwhile they move away from the superconducting gap towards high bias voltage,and disappear eventually.In addition,with the increase of magnetic field,the NDCs/dips follow the evolution of the superconducting gap,and disappear when the gap closes.We interpret these observations and reach a good agreement by combining the Blonder–Tinkham–Klapwijk(BTK)model and the critical supercurrent effect in the nanowire,which we call the BTK-supercurrent model.Our results provide an in-depth understanding of the tunneling transport in hybrid semiconductor–superconductor devices.
基金Project supported by the National Basic Research Program of China(Grant Nos.2016YFA0300601,2017YFA0304700,and 2015CB921402)the National Natural Science Foundation China(Grant Nos.11527806,91221203,11174357,91421303,and 11774405)+1 种基金the Strategic Priority Research Program B of the Chinese Academy of Sciences(Grant Nos.XDB07010100 and XDB28000000)the Beijing Municipal Science&Technology Commission,China(Grant No.Z191100007219008)
文摘Recently,a contact-resistance-measurement method was developed to detect the minigap,hence the Andreev bound states(ABSs),in Josephson junctions constructed on the surface of three-dimensional topological insulators(3D TIs).In this work,we further generalize that method to the circumstance with radio frequency(rf)irradiation.We find that with the increase of the rf power,the measured minigap becomes broadened and extends to higher energies in a way similar to the rf power dependence of the outer border of the Shapiro step region.We show that the corresponding data of contact resistance under rf irradiation can be well interpreted by using the resistively shunted Josephson junction(RSJ)model and the Blonder–Tinkham–Klapwijk(BTK)theory.Our findings could be useful when using the contact-resistancemeasurement method to study the Majorana-related physics in topological insulator-based Josephson junctions under rf irradiation.
基金National Key R&D program(Grant No.2020YFA0309604)the National Natural Science Foundation of China(Grant Nos.61888102,11834017,and 12074413)+7 种基金the Strategic Priority Research Program of CAS(Grant Nos.XDB30000000 and XDB33000000)the Key-Area Research and Development Program of Guangdong Province(Grant No.2020B0101340001)Research Program of Beijing Academy of Quantum Information Sciences(Grant No.Y18G11)the start-up grant of ShanghaiTech UniversityNational Key R&D Program(Grant No.2020YFA0309601)Elemental Strategy Initiative conducted by the MEXT,Japan(Grant No.JPMXP0112101001)JSPS KAKENHI(Grant No.JP20H00354)CREST(JPMJCR15F3),JST。
文摘Twisting two layers into a magic angle(MA) of ~1.1°is found essential to create low energy flat bands and the resulting correlated insulating,superconducting,and magnetic phases in twisted bilayer graphene(TBG).While most of previous works focus on revealing these emergent states in MA-TBG,a study of the twist angle dependence,which helps to map an evolution of these phases,is yet less explored.Here,we report a magnetotransport study on one non-magic angle TBG device,whose twist angle θ changes from 1.25° at one end to 1.43°at the other.For θ=1.25° we observe an emergence of topological insulating states at hole side with a sequence of Chern number |C|=4-|v|,where v is the number of electrons(holes) in moire unite cell.When θ> 1.25°,the Chern insulator from flat band disappears and evolves into fractal Hofstadter butterfly quantum Hall insulator where magnetic flux in one moire unite cell matters.Our observations will stimulate further theoretical and experimental investigations on the relationship between electron interactions and non-trivial band topology.
基金Project supported by the National Key Basic Research Program of China(Grant No.2016YFA0300600)the National Natural Science Foundation of China(Grant Nos.11574005 and 11774009)。
文摘Introduction of spin-orbit coupling(SOC)in a Josephson junction(JJ)gives rise to unusual Josephson effects.We investigate JJs based on a newly discovered heterodimensional superlattice V_(5)S_(8) with a special form of SOC.The unique homointerface of our JJs enables elimination of extrinsic effects due to interfaces and disorder.We observe asymmetric Fraunhofer patterns with respect to both the perpendicular magnetic field and the current.The asymmetry is influenced by an in-plane magnetic field.Analysis of the pattern points to a nontrivial spatial distribution of the Josephson current that is intrinsic to the SOC in V_(5)S_(8).
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 92065203, 11527806, 12074417, 11874406, 11774405, and E2J1141)the National Basic Research Program of China (Grant Nos. 2016YFA0300601, 2017YFA0304700, and 2015CB921402)+2 种基金the Strategic Priority Research Program B of the Chinese Academy of Sciences (Grant Nos. XDB33010300, DB28000000, and XDB07010100)the Innovation Program for Quantum Science and Technology (Grant No. 2021ZD302600)Synergetic Extreme Condition User Facility (SECUF) sponsored by the National Development and Reform Commission, China。
文摘Recently, a Corbino-geometry type of Josephson junction constructed on the surface of topological insulators has been proposed for hosting and braiding Majorana zero modes. As a first step to test this proposal, we successfully fabricated Corbino-geometry Josephson junctions(JJs) on the surface of Bi_(2)Te_(3) flakes. Ac Josephson effect with fractional Shapiro steps was observed in the Corbino-geometry JJs while the flux in the junction area was quantized. By analyzing the experimental data using the resistively shunted Josephson junction model, we found that the Corbino-geometry JJs exhibit a skewed current-phase relation due to its high transparency. The results suggest that Corbino-geometry JJs constructed on the surface of topological insulators may provide a promising platform for studying Majorana-related physics.
基金Supported by the National Basic Research Program of China under Grant Nos 2015CB921101 and 2016YFA0300600the National Natural Science Foundation of China under Grant No 11874406+2 种基金the Singapore National Research Foundation under Grant No NRF-NRFF2013-08the Tier 2 MOE2016-T2-2-153the A*Star QTE Programme
文摘We report on magnetoresistance, Hall effect, and quantum Shubnikov–de Haas oscillation(SdH) experiments in NbIrTe4 single crystals, which was recently predicted to be a type-II Weyl semimetal. NbIrTe4 manifests a non-saturating and parabolic magnetoresistance at low temperatures. The magneto-transport measurements show that NbIrTe4 is a multiband system. The analysis of the SdH oscillations reveals four distinct oscillation frequencies. Combined with the density-functional theory calculations, we show that they come from two types of Fermi surfaces: electron pocket E1 and hole pocket H2.
文摘Solid-state quantum computation station belongs to the group 2 of manipulation of quantum state in the Synergetic Extreme Condition User Facility. Here we will first outline the research background, aspects, and objectives of the station, followed by a discussion of the recent scientific as well as technological progress in this field based on similar experimental facilities to be constructed in the station. Finally, a brief summary and research perspective will be presented.
基金supported by the National Basic Research Program of China (Grant Nos. 2016YFA0300601, 2017YFA0304700, and 2015CB921402)the National Natural Science Foundation of China (Grant Nos. 11527806, 92065203, 12074417, 11874406, and 11774405)+2 种基金the Beijing Academy of Quantum Information Sciences (Grant No. Y18G08)the Strategic Priority Research Program B of Chinese Academy of Sciences (Grant Nos. XDB33010300, XDB28000000, and XDB07010100)the Synergetic Extreme Condition User Facility sponsored by the National Development and Reform Commission。
文摘We studied anomalous Josephson effect(AJE) in Josephson trijunctions fabricated on Bi_(2)Se_(3), and found that the AJE in T-shaped trijunctions significantly alters the Majorana phase diagram of the trijunctions, when an in-plane magnetic field is applied parallel to two of the three single junctions. Such a phenomenon in topological insulator-based Josephson trijunction provides unambiguous evidence for the existence of AJE in the system, and may provide an additional knob for controlling the Majorana bound states in the Fu–Kane scheme of topological quantum computation.
文摘二维过渡金属硫族化合物(transition metal dichalcogenides, TMDCs)是继石墨烯之后的新型范德瓦耳斯材料,由于其天然的二维特性以及强自旋轨道耦合作用(spin-orbital coupling, SOC),导致诸如金属-绝缘体转变、电荷密度波(charge density wave, CDW)、能谷电子学、非常规超导电性等新颖物理性质的出现,使得这类材料成为研究低维量子物理的又一理想平台.其中能谷电子学与拓扑超导已经成为近年来凝聚态物理前沿研究的热点方向.本文在综述TMDCs材料的结构与基本物理性质的基础上,重点介绍了最近发展的用于生长原子层厚度的TMDCs材料的熔盐辅助化学气相沉积方法、在Se掺杂的MoSexTe2-x薄膜中实现的Td相到1T′相再到2H相的结构相变与超导增强现象,以及在少层Td-MoTe2中发现的非对称性SOC作用引起的类伊辛超导现象.最后,展望了TMDCs材料的潜在应用与可能存在的拓扑超导.
