Using a van der Waals vertical heterostructure consisting of monolayer graphene, monolayer hBN and NbSe$_2$, we have performed local characterization of induced correlated states in different configurations. At a temperature of 4.6 K, we have shown that both superconductivity and charge density waves can be induced in graphene from NbSe2 by proximity effects. By applying a vertical magnetic field, we imaged the Abrikosov vortex lattice and extracted the coherence length for the proximitized superconducting graphene. We further show that the induced correlated states can be completely blocked by adding a monolayer hBN between the graphene and the NbSe$_2$, which demonstrates the importance of the tunnel barrier and surface conditions between the normal metal and superconductor for the proximity effect.
A topological insulator (TI) interfaced with an s-wave superconductor has been predicted to host an unusual form of superconductivity known as topological superconductivity (TSC). Molecular beam epitaxy (MBE) has been the primary approach in the scalable synthesis of the TI/superconductor heterostructures. Although the growth of epitaxial TI films on s-wave superconductors has been achieved, it remains an outstanding challenge for synthesizing atomically thin TI/superconductor heterostructures, which are critical for engineering the TSC phase. Here, we used MBE to grow Bi2Se3 films with the co…
We study the low-energy electronic structure of heterostructures formed by one sheet of graphene placed on a monolayer of ${\rm NbSe_2}$. We build a continuous low-energy effective model that takes into account the presence of a twist angle between graphene and ${\rm NbSe_2}$, and of spin-orbit coupling and superconducting pairing in ${\rm NbSe_2}$. We obtain the parameters entering the continuous model via ab-initio calculations. We show that despite the large mismatch between the graphene's and ${\rm NbSe_2}$'s lattice constants, due to the large size of the ${\rm NbSe_2}$'s Fermi pockets, t…
Resonant interlayer coupling in NbSe$_2$-graphite epitaxial moir{é} superlattices
SUPA, School of Physics and Astronomy, University of St Andrews（圣安德鲁斯大学物理与天文学学院）；Department of Physics and Astronomy, University of Manchester（曼彻斯特大学物理与天文学系）；Max Planck Institute for Chemical Physics of Solids（马克斯·普朗克固体化学物理研究所）；Physics Study Program, Faculty of Science and Technology, Syarif Hidayatullah State Islamic University Jakarta（雅加达希达亚图拉伊斯兰国立大学科技理学院物理学专业）；Institute for Materials Research, Tohoku University（东北大学材料科学研究所）
Topological superconductors (TSCs) have a full gap in the bulk and gapless surface states consisting of Majorana fermions, which have potential applications in fault-tolerant topological quantum computation. Because TSCs are very rare in nature, an alternative way to study the TSC is to artificially introduce superconductivity into the surface states of a topological insulator (TI) through proximity effect (PE)1-4. Here we report the first experimental realization of the PE induced TSC in Bi2Te3/NbSe2 thin films as demonstrated by the density of states probed using scanning tunneling microscop…
Neutral and charged excitons (trions) in atomically-thin materials offer important capabilities for photonics, from ultrafast photodetectors to highly-efficient light-emitting diodes and lasers. Recent studies of van der Waals (vdW) heterostructures comprised of dissimilar monolayer materials have uncovered a wealth of optical phenomena that are predominantly governed by interlayer interactions. Here, we examine the optical properties in NbSe$_2$ - MoSe$_2$ vdW heterostructures, which provide an important model system to study metal-semiconductor interfaces, a common element in optoelectronics…
Multiple chiral Majorana states in proximitized magnetic topological insulator heterostructures
Universidad Autónoma de Madrid（马德里自治大学）；Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid（马德里自治大学凝聚态物理中心（IFIMAC））；Instituto de Estructura de la Materia IEM-CSIC（CSIC物质结构研究所）；Instituto Nicolás Cabrera, Universidad Autónoma de Madrid（马德里自治大学尼古拉斯·卡布雷拉研究所）
We study the pseudo-spin of electron pair in superconducting transition-metal dichalcogenide monolayers and show that the pseudo-spin affects the electric transport property of lateral heterojunction of the superconducting and metallic monolayers. The pseudo-spins of two electrons forming a Cooper pair are parallel to each other unlike the real spins being anti-parallel. In the lateral heterojunction, the electronic transport with forming a Cooper pair, the Andreev reflection, is suppressed with the Fermi level crossing the valence band near the edge in the metallic monolayer. We numerically i…
Large Field-Free Superconducting Diode Effect with Nonmonotonic Polarity Reversals in NbSe$_2$/CrBr$_3$ Heterostructures
Southern University of Science and Technology（南方科技大学）；International Quantum Academy, and Shenzhen Branch, Hefei National Laboratory（国际量子科学院，合肥国家实验室深圳分院）；Eastern Institute for Advanced Study, Eastern Institute of Technology（宁波东方理工大学（暂名）先进研究院）；State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat‑sen University（中山大学光电信息材料与技术国家重点实验室）
The bilayer heterostructures composed of an ultrathin ferromagnetic metal (FM) and a material hosting strong spin-orbit (SO) coupling are principal resource for SO torque and spin-to-charge conversion nonequilibrium effects in spintronics. We demonstrate how hybridization of wavefunctions of Co layer and a monolayer of transition metal dichalcogenides (TMDs)---such as semiconducting MoSe$_2$ and WSe$_2$ or metallic TaSe$_2$---can lead to dramatic transmutation of electronic and spin structure of Co within some distance away from its interface with TMD, when compared to the bulk of Co or its su…
Modern Superconducting QUantum Interference Devices (SQUIDs) are commonly fabricated from either Al or Nb electrodes, with an in-situ oxidation process to create a weak link between them. However, common problems of such planar nano- and micro-SQUIDs are hysteretic current-voltage curves, and a shallow flux modulation depth. Here, we demonstrate the formation of both Josephson junctions and SQUIDs using a dry transfer technique to stack and deterministically misalign flakes of NbSe$_{2}$; allowing one to overcome these issues. The Josephson dynamics of the resulting twisted NbSe$_{2}$-NbSe$_{2…
Ferroelectric switching control of spin current in graphene proximitized by In$_2$Se$_3$
Institute of Informatics, Slovak Academy of Sciences（斯洛伐克科学院信息学研究所）；Faculty of Physics, University of Belgrade（贝尔格莱德大学物理学院）；Institute of Physics, Pavol Jozef Šafárik University in Košice（科希策帕沃尔·约瑟夫·沙法里克大学物理研究所）；Institute of Physics, University of Silesia in Katowice（卡托维兹西里西亚大学物理研究所）；Institute of Experimental Physics, Slovak Academy of Sciences（斯洛伐克科学院实验物理研究所）；New Technologies Research Centre, University of West Bohemia（西波希米亚大学新技术研究中心）
The combination of two-dimensional (2D) materials into vertical heterostructures has emerged as a promising path to designer quantum materials with exotic properties. Here, we extend this concept from inorganic 2D materials to 2D metal-organic frameworks (MOFs) that offer additional flexibility in realizing designer heterostructures. We successfully fabricate a monolayer 2D Cu-dicyanoanthracene MOF on a 2D van der Waals NbSe$_2$ superconducting substrate. The structural and electronic properties of two different phases of the 2D MOF are characterized by low-temperature scanning tunneling micro…
The proximity effect opens ways to transfer properties from one material into another and is especially important in two-dimensional materials. In van der Waals heterostructures, transition metal dichalcogenides (TMD) can be used to enhance the spin-orbit coupling of graphene leading to the prediction of gate controllable spin-to-charge conversion (SCC). Here, we report for the first time and quantify the SHE in graphene proximitized with WSe$_2$ up to room temperature. Unlike in other graphene/TMD devices, the sole SCC mechanism is the spin Hall effect and no Rashba-Edelstein effect is observ…
Establishing the conditions under which orbital, spin and lattice-pseudospin degrees of freedom are mutually coupled in realistic nonequilibrium conditions is a major goal in the emergent field of graphene spintronics. Here, we use linear-response theory to obtain a unified microscopic description of spin dynamics and coupled spin-charge transport in graphene with an interface-induced Bychkov-Rashba effect. Our method makes use of an SO(5) extension of the familiar inverse-diffuson approach to obtain a quantum kinetic equation for the single-particle density matrix that treats spin and pseudos…
Ultralight mechanical resonators based on low-dimensional materials are well suited as exceptional transducers of minuscule forces or mass changes. However, the low dimensionality also provides a challenge to minimize resistive losses and heating. Here, we report on a novel approach that aims to combine different 2D materials to tackle this challenge. We fabricated a heterostructure mechanical resonator consisting of few layers of niobium diselenide (NbSe$_2$) encapsulated by two graphene sheets. The hybrid membrane shows high quality factors up to 245'000 at low temperatures, comparable to th…
Graphene sandwiched between semiconducting monolayers of ferromagnet Cr$_2$Ge$_2$Te$_6$ and transition-metal dichalcogenide WS$_2$ acquires both spin-orbit (SO), of valley-Zeeman and Rashba types, and exchange couplings. Using first-principles combined with quantum transport calculations, we predict that such doubly proximitized graphene within van der Waals heterostructure will exhibit SO torque driven by unpolarized charge current. This system lacking spin Hall current, putatively considered to be necessary for efficient damping-like (DL) SO torque that plays a key role in magnetization swit…
The ability to imprint a given material property to another through proximity effect in layered two-dimensional materials has opened the way to the creation of designer materials. Here, we use molecular-beam epitaxy (MBE) for a direct synthesis of a superconductor-magnet hybrid heterostructure by combining superconducting niobium diselenide (NbSe$_2$) with the monolayer ferromagnetic chromium tribromide (CrBr$_3$). Using different characterization techniques and density-functional theory (DFT) calculations, we have confirmed that the CrBr$_3$ monolayer retains its ferromagnetic ordering with a…
We investigate the electronic transport property of lateral heterojunctions of semiconducting and metallic transition-metal dichalcogenide monolayers, MoSe$_2$ and NbSe$_2$, respectively. We calculate the electronic transmission probability by using a multi-orbital tight-binding model based on the first-principles band structure. The transmission probability depends on the spin and valley degrees of freedom. This dependence qualitatively changes by the interface structure. The heterostructure with a zig-zag interface preserves the spin and the valley of electron in the transmission process. On…
Orientation-tunable correlated Chern insulating states in chiral twisted double bilayer graphene proximitized by WSe2
Nanjing University（南京大学）；Hefei National Laboratory（合肥国家实验室）；Yangtze Delta Region Academy of Beijing Institute of Technology (Jiaxing)（北京理工大学长三角研究院（嘉兴））；National Institute for Materials Science（国立材料研究所）；Beijing Institute of Technology（北京理工大学）；Nanjing University of Science and Technology（南京理工大学）；Jiangsu Physical Science Research Center（江苏物理科学研究中心）
Gate-tunable synthetic antiferromagnetism with nonrelativistic spin splitting in a graphene/MnS/graphene heterostructure
Institute of Informatics, Slovak Academy of Sciences（斯洛伐克科学院信息学研究所）；Faculty of Physics, University of Belgrade（贝尔格莱德大学物理学院）；Institute of Physics, Pavol Jozef Šafárik University in Košice（科希策帕沃尔·约瑟夫·沙法里克大学物理研究所）；Institute of Experimental Physics, Slovak Academy of Sciences（斯洛伐克科学院实验物理研究所）；New Technologies Research Centre, University of West Bohemia（西波希米亚大学新技术研究中心）
Topological Superconductivity by Engineering Noncollinear Magnetism in Magnet/ Superconductor Heterostructures: A Realistic Prescription for 2D Kitaev Model
提出用邻近 s 波超导体的非共线自旋螺旋构造有效 p_x+p_y 配对，并以 Nb 衬底上的 Mn/Cr 单层验证二维 Kitaev 拓扑超导及稳健 MFEM。
We study the electronic structure of heterostructures formed by a graphene nanoribbon (GNR) and a transition metal dichalcogenides (TMD) monolayer using first-principles. We consider both semiconducting TMDs and metallic TMDs, and different stacking configurations. We find that when the TMD is semiconducting the effects on the band structure of the GNRs are small. In particular the spin-splitting induced by proximity on the GNRs bands is only of the order of few meV irrespective of the stacking configuration. When the TMD is metallic, such as NbSe2, we find that the spin-splitting induced in t…
