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
Recently discovered Ising superconductors have garnered considerable interest due to their anomalously large in-plane upper critical fields(B_(c2)). However, the requisite strong spin-orbital coupling in the Ising pai...Recently discovered Ising superconductors have garnered considerable interest due to their anomalously large in-plane upper critical fields(B_(c2)). However, the requisite strong spin-orbital coupling in the Ising pairing mechanism generally renders these superconductors heavy-element dominant with notably low superconducting transition temperatures(Tc). Here, based on the Migdal-Eliashberg theory and the mean-field Bogoliubov-de Gennes Hamiltonian, we demonstrate a significant enhancement of Ising superconductivity in monolayer NbSe_(2) through surface fluorination, as evidenced by concomitant improvements in Tcand Bc_(2). This enhancement arises from three predominant factors. Firstly, fluorine atoms symmetrically and stably adhere to both sides of the monolayer NbSe_(2), thereby maintaining the out-of-plane mirror symmetry and locking carrier spins out-of-plane.Secondly, fluorination suppresses the charge density wave in monolayer NbSe_(2) and induces a van Hove singularity in the vicinity of the Fermi level, leading to a marked increase in the number of carriers and, consequently, strengthening the electron-phonon coupling(EPC). Lastly, the appearance of fluorine-related, low-frequency phonon modes further augments the EPC. Our findings suggest a promising avenue to elevate Tcin two-dimensional Ising superconductors without compromising their Ising pairing.展开更多
Understanding and control of many-body collective phenomena such as charge density wave(CDW)and superconductivity in atomically thin crystals remains a hot topic in material science.Here,using first-principles calcula...Understanding and control of many-body collective phenomena such as charge density wave(CDW)and superconductivity in atomically thin crystals remains a hot topic in material science.Here,using first-principles calculations,we find that 1T-HfTe_(2)possessing no CDWs in the bulk form,unexpectedly shows a stable 2×2 CDW order in the monolayer form,which can be attributed to the enhancement of electron–phonon coupling(EPC)in the monolayer.Meanwhile,the CDW induces a metal-to-insulator transition in monolayer 1T-HfTe_(2)through the accompanying lattice distortion.Remarkably,Ising superconductivity with a significantly enhanced in-plane critical field can emerge in centrosymmetric monolayer 1T-HfTe_(2)after the CDW is suppressed by electron doping.The Ising paring is revealed to be protected by the spin–orbital locking without the participation of the inversion symmetry breaking which is a must for conventional 2H-NbSe2-like Ising superconductors.Our results open a new window for designing and controlling novel quantum states in two-dimensional(2D)matter.展开更多
Recently, the layered transition metal dichalcogenide 1 T MoTe2 has attracted considerable attention due to its non-saturating magnetoresistance, type-II Weyl semimetal properties, superconductivity, and potential can...Recently, the layered transition metal dichalcogenide 1 T MoTe2 has attracted considerable attention due to its non-saturating magnetoresistance, type-II Weyl semimetal properties, superconductivity, and potential candidate for twodimensional（2 D） topological insulator in the single-and few-layer limit. Here in this work, we perform systematic transport measurements on thin flakes of MoTe2 prepared by mechanical exfoliation. We find that MoTe2 flakes are superconducting and have an onset superconducting transition temperature Tc up to 5.3 K, which significantly exceeds that of its bulk counterpart. The in-plane upper critical field(Hc2||) is much higher than the Pauli paramagnetic limit, implying that the MoTe2 flakes have Zeeman-protected Ising superconductivity. Furthermore, the Tc and Hc2|| can be tuned by up to 320 mK and 400 mT by applying a gate voltage. Our result indicates that MoTe2 flake is a good candidate for studying exotic superconductivity with nontrivial topological properties.展开更多
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.
基金supported by the National Natural Science Foundation of China (Grant Nos. 12274013, 11874079)and the Independent Research Project of Medical Engineering Laboratory of Chinese PLA General Hospital (Grant No. 2022SYSZZKY10)+5 种基金Wujun Shi was supported by the Science and Technology Commission of Shanghai Municipality (STCSM) (Grant No. 22ZR1441800)Yong Xu and Wenhui Duan were supported by the Basic Science Center Project of NSFC (Grant No. 52388201)the National Natural Science Foundation of China (Grant No. 12334003)the National Science Fund for Distinguished Young Scholars (Grant No. 12025405)the Beijing Advanced Innovation Center for Future Chip (ICFC)the Beijing Advanced Innovation Center for Materials Genome Engineering。
文摘Recently discovered Ising superconductors have garnered considerable interest due to their anomalously large in-plane upper critical fields(B_(c2)). However, the requisite strong spin-orbital coupling in the Ising pairing mechanism generally renders these superconductors heavy-element dominant with notably low superconducting transition temperatures(Tc). Here, based on the Migdal-Eliashberg theory and the mean-field Bogoliubov-de Gennes Hamiltonian, we demonstrate a significant enhancement of Ising superconductivity in monolayer NbSe_(2) through surface fluorination, as evidenced by concomitant improvements in Tcand Bc_(2). This enhancement arises from three predominant factors. Firstly, fluorine atoms symmetrically and stably adhere to both sides of the monolayer NbSe_(2), thereby maintaining the out-of-plane mirror symmetry and locking carrier spins out-of-plane.Secondly, fluorination suppresses the charge density wave in monolayer NbSe_(2) and induces a van Hove singularity in the vicinity of the Fermi level, leading to a marked increase in the number of carriers and, consequently, strengthening the electron-phonon coupling(EPC). Lastly, the appearance of fluorine-related, low-frequency phonon modes further augments the EPC. Our findings suggest a promising avenue to elevate Tcin two-dimensional Ising superconductors without compromising their Ising pairing.
基金supported by the National Natural Science Foundation of China(Nos.12274013 and 11874079)the open research fund program of the State key laboratory of low dimensional quantum physics(No.KF202103)the Independent Research Project of Medical Engineering Laboratory of Chinese PLA General Hospital(No.2022SYSZZKY10).
文摘Understanding and control of many-body collective phenomena such as charge density wave(CDW)and superconductivity in atomically thin crystals remains a hot topic in material science.Here,using first-principles calculations,we find that 1T-HfTe_(2)possessing no CDWs in the bulk form,unexpectedly shows a stable 2×2 CDW order in the monolayer form,which can be attributed to the enhancement of electron–phonon coupling(EPC)in the monolayer.Meanwhile,the CDW induces a metal-to-insulator transition in monolayer 1T-HfTe_(2)through the accompanying lattice distortion.Remarkably,Ising superconductivity with a significantly enhanced in-plane critical field can emerge in centrosymmetric monolayer 1T-HfTe_(2)after the CDW is suppressed by electron doping.The Ising paring is revealed to be protected by the spin–orbital locking without the participation of the inversion symmetry breaking which is a must for conventional 2H-NbSe2-like Ising superconductors.Our results open a new window for designing and controlling novel quantum states in two-dimensional(2D)matter.
基金Project supported by the Guangdong Innovative and Entrepreneurial Research Team Program,China(Grant No.2016ZT06D348)the National Natural Science Foundation of China(Grant No.11874193)the Shenzhen Fundamental Subject Research Program,China(Grant Nos.JCYJ20170817110751776 and JCYJ20170307105434022)
文摘Recently, the layered transition metal dichalcogenide 1 T MoTe2 has attracted considerable attention due to its non-saturating magnetoresistance, type-II Weyl semimetal properties, superconductivity, and potential candidate for twodimensional（2 D） topological insulator in the single-and few-layer limit. Here in this work, we perform systematic transport measurements on thin flakes of MoTe2 prepared by mechanical exfoliation. We find that MoTe2 flakes are superconducting and have an onset superconducting transition temperature Tc up to 5.3 K, which significantly exceeds that of its bulk counterpart. The in-plane upper critical field(Hc2||) is much higher than the Pauli paramagnetic limit, implying that the MoTe2 flakes have Zeeman-protected Ising superconductivity. Furthermore, the Tc and Hc2|| can be tuned by up to 320 mK and 400 mT by applying a gate voltage. Our result indicates that MoTe2 flake is a good candidate for studying exotic superconductivity with nontrivial topological properties.
