- 标题
- 摘要
- 关键词
- 实验方案
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Spatial Separation of Carrier Spin by the Valley Hall Effect in Monolayer WSe <sub/>2</sub> Transistors
摘要： We investigate the valley Hall effect (VHE) in monolayer WSe2 field-effect transistors using optical Kerr rotation measurements at 20 K. While studies of the VHE have so far focused on n-doped MoS2, we observe the VHE in WSe2 in both the n- and p-doping regimes. Hole doping enables access to the large spin-splitting of the valence band of this material. The Kerr rotation measurements probe the spatial distribution of the valley carrier imbalance induced by the VHE. Under current flow, we observe distinct spin-valley polarization along the edges of the transistor channel. From analysis of the magnitude of the Kerr rotation, we infer a spin-valley density of 44 spins/μm, integrated over the edge region in the p-doped regime. Assuming a spin diffusion length less than 0.1 μm, this corresponds to a spin-valley polarization of the holes exceeding 1%.
关键词： magneto-optical Kerr effect,Tungsten diselenide,valleytronics,spintronics
更新于2025-09-23 15:23:52
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Topological valley pumping in Weyl semimetals
摘要： We investigate the topological pumping effect in Weyl semimetals, subject to the modulation of two ac electric fields along y and z directions, respectively. We show that the pumping effect originates from the anomalous velocity related to the Berry curvature. The direction of the pumping current is dependent on the chirality of the Weyl fermions. While the total particle current is vanishing because the Weyl points of opposite chirality always come in pairs in Weyl semimetals, the pump gives rise to a net chirality current or valley current. The noiseless valley current generated can be useful in valleytronic applications.
关键词： Valleytronics,Chirality,Topological pumping effect,Valley current,Weyl semimetal
更新于2025-09-23 15:23:52
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Low-frequency spectroscopy for quantum multilevel systems
摘要： A periodically driven quantum system with avoided level crossing experiences both nonadiabatic transitions and wave-function phase changes. These result in coherent interference fringes in the system’s occupation probabilities. For qubits, with repelling energy levels, such interference, named after Landau-Zener-Stückelberg-Majorana, displays arc-shaped resonance lines. In the case of a multilevel system with an avoided level crossing of the two lower levels, we demonstrate that the shape of the resonances can change from convex arcs to concave heart-shaped and harp-shaped resonance lines. Indeed, the whole energy spectrum determines the shape of such resonance fringes and this also provides insight into the slow-frequency system spectroscopy. As a particular example, we consider this for valley-orbit silicon quantum dots, which are important for the emerging field of valleytronics.
关键词： valley-orbit silicon quantum dots,valleytronics,low-frequency spectroscopy,quantum multilevel systems,Landau-Zener-Stückelberg-Majorana interference
更新于2025-09-23 15:21:21
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Toward Valleya??Coupled Spin Qubits
摘要： The bid for scalable physical qubits has attracted many possible candidate platforms. In particular, spin-based qubits in solid-state form factors are attractive as they could potentially benefit from processes similar to those used for conventional semiconductor processing. However, material control is a significant challenge for solid-state spin qubits as residual spins from substrate, dielectric, electrodes, or contaminants from processing contribute to spin decoherence. In the recent decade, valleytronics has seen a revival due to the discovery of valley-coupled spins in monolayer transition metal dichalcogenides. Such valley-coupled spins are protected by inversion asymmetry and time reversal symmetry and are promising candidates for robust qubits. In this report, the progress toward building such qubits is presented. Following an introduction to the key attractions in fabricating such qubits, an up-to-date brief is provided for the status of each key step, highlighting advancements made and/or outstanding work to be done. This report concludes with a perspective on future development highlighting major remaining milestones toward scalable spin-valley qubits.
关键词： valleytronics,qubits,quantum information,transition metal dichalcogenides,quantum dots
更新于2025-09-23 15:21:01
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Chiral phonons in two-dimensional materials
摘要： There has been growing interest in investigating chiral phonons since they are theoretically found and experimentally verified recently. In a magnetic system with time inversion symmetry breaking, phonon can have nonzero angular momentum, which makes a correction to the gyromagnetic ratio measured in the Einstein-de Haas Effect. Though total phonon angular momentum is zero in a nonmagnetic two-dimensional (2D) hexagonal system with space inversion symmetry breaking, phonons at high symmetry points of the Brillouin zone can have nonzero phonon angular momentum, which means they are chiral phonons. Chiral phonons decide selection rules in the electronic intervalley scattering, which has been experimentally verified in tungsten-diselenide monolayers very recently (Science 359, 579 (2018)). In this review, after a brief introduction of related background and some basic concepts, we mainly report recent progress of phonon angular momentum in magnetic systems and chiral phonon in nonmagnetic systems. We also review known experiments in verifications of the phonon chirality and finally conclude with an outlook of future developments.
关键词： two-dimensional materials,chiral phonons,phonon Hall effect,valleytronics,Einstein-de Haas Effect,phonon angular momentum
更新于2025-09-10 09:29:36
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Room Temperature Valley Polarization and Coherence in Transition Metal Dichalcogenide-Graphene van der Waals Heterostructures
摘要： Van der Waals heterostructures made of graphene and transition metal dichalcogenides (TMD) are an emerging platform for opto-electronic, -spintronic and -valleytronic devices that could benefit from (i) strong light-matter interactions and spin-valley locking in TMDs and (ii) exceptional electron and spin transport in graphene. The operation of such devices requires significant valley polarization and valley coherence, ideally up to room temperature. Here, using a comprehensive Mueller polarimetry analysis, we report artifact-free room temperature degrees of valley polarization up to 40 % and, remarkably, of valley coherence up to 20 % in monolayer tungsten disulfide (WS2)/graphene heterostructures. At a temperature of 20 K, we measure a record degree of valley coherence of 60 %, a value that exceeds the degree of valley polarization (50 %) and indicates that our samples are minimally affected by pure dephasing processes. Valley contrasts have been particularly elusive in molybdenum diselenide (MoSe2), even at cryogenic temperatures. Upon interfacing monolayer MoSe2 with graphene, the room temperature degrees of valley polarization and coherence are as high as 14 % and 20 %, respectively. Our results are discussed in light of recent reports of highly efficient interlayer exciton and carrier transfer in TMD/graphene heterostructures and hold promise for room temperature chiral light-matter interactions and opto-valleytronic devices.
关键词： Mueller polarimetry,spin-valley locking,Transition metal dichalcogenides,graphene,chiral optics,opto-valleytronics,excitons
更新于2025-09-10 09:29:36
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Electrically tunable valleytronics in quantum anomalous Hall insulating transition metal trihalides
摘要： We propose a different scheme for achieving valley splitting using an electric ?eld in the materials with inversion symmetry but without time-reversal symmetry, and apply this scheme to two-dimensional transition metal trihalides VX3 (X = Cl, Br). Based on ab initio calculations and the tight-binding model, we ?nd few layer VX3 can be readily tuned from intrinsic quantum anomalous Hall insulators to quantum valley Hall insulators by external electric ?elds. Especially, the electric-?eld-induced valley splitting of the bilayer VX3 is extremely large, about two orders of magnitude higher than that induced by a magnetic ?eld in the state-of-the-art valleytronic materials (e.g., MoS2 and WSe2). We further reveal rich topological phases of few layer VX3 and valley-polarized states at the phase boundary. These ?ndings may motivate further topology and valleytronics related researches in low-dimensional transition metal compounds.
关键词： quantum valley Hall insulators,valleytronics,quantum anomalous Hall insulators,transition metal trihalides,electric ?eld,topological phases
更新于2025-09-09 09:28:46
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Designing multidirectional energy splitters and topological valley supernetworks
摘要： Using group theoretic and topological concepts, together with tunneling phenomena, we geometrically design interfacial wave networks that contain splitters which partition energy in two, three, four, or five directions. This enriches the valleytronics literature that has, so far, been limited to two-directional splitters. Additionally, we describe a design paradigm that gives greater detail about the relative transmission along outgoing leads, away from a junction; previously, only the negligible transmission leads were predictable. We utilize semianalytic numerical simulations, as opposed to finite element methods, to clearly illustrate all of these features with highly resolved edge states. As a consequence of this theory, networks, with directionality tunable by geometry, ideal for applications such as beam-splitters, switches, and filters are created. Coupling these networks that contain multidirectional energy-splitters culminates in the realization of a topological supernetwork.
关键词： multidirectional energy splitters,valleytronics,topological valley supernetworks,group theoretic,tunneling phenomena,topological concepts
更新于2025-09-04 15:30:14
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[IEEE 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2018) - Nagoya (2018.9.9-2018.9.14)] 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Terahertz Quasiparticle Acceleration: From Electron-Hole Collisions To Lightwave Valleytronics
摘要： Intense lightwaves can accelerate quasiparticles inside solids. This strong-field light-matter interaction results in the emission of high-harmonic or high-order sideband radiation. While the former process relies on a complex coupling between simultaneously driven interband polarization and intraband currents, high-order sidebands originate from a ballistic acceleration of the quasiparticles within the bands. This mechanism allows for the implementation of a quasiparticle collider in order to study those entities in close analogy to conventional collision experiments. Accelerating electrons and holes in a monolayer of transition metal dichalcogenides extends this scheme to internal quantum degrees of freedom. Our experiments show a lightwave-induced switching of the valley pseudospin, paving the way to ultimately fast valleytronics.
关键词： valley pseudospin,terahertz,high-harmonic generation,lightwave valleytronics,electron-hole collisions,quasiparticle acceleration,high-order sideband radiation,transition metal dichalcogenides
更新于2025-09-04 15:30:14