Electrical control of charged carriers and excitons in atomically thin materials

Abstract

Electrical confinement and manipulation of charge carriers in semiconducting nanostructures are essential for realizing functional quantum electronic devices. The unique band structure of atomically thin transition metal dichalcogenides (TMDs) offers a new route towards realizing novel 2D quantum electronic devices, such as valleytronic devices and valley-spin qubits . 2D TMDs also provide a platform for novel quantum optoelectronic devices due to their large exciton binding energy. However, controlled confinement and manipulation of electronic and excitonic excitations in TMD nanostructures have been technically challenging due to the prevailing disorder in the material, preventing accurate experimental control of local confinement and tunnel couplings. Here we demonstrate a novel method for creating high-quality heterostructures composed of atomically thin materials that allows for efficient electrical control of excitations. Specifically, we demonstrate quantum transport in the gate-defined, quantum-confined region, observing spin-valley locked quantized conductance in quantum point contacts. We also realize gate-controlled Coulomb blockade associated with confinement of electrons and demonstrate electrical control over charged excitons with tunable local confinement potentials and tunnel couplings. Our work provides a basis for novel quantum opto-electronic devices based on manipulation of charged carriers and excitons.

Wigner crystals in two-dimensional transition-metal dichalcogenides: Spin physics and readout

“…The confinement is characterized by the trapping frequency ω and V int denotes the two-body interaction potential. In TMDs, the former may be induced by strain [28,29] or defined via local gates [30] and the latter is usually modeled by the Keldysh potential [31],…”

Spin-valley system in a gated MoS2-monolayer quantum dot

“…The area of application of monolayer materials for construction of electronic nanodevices is currently under strong development [1,[7][8][9][10][11][12]. Methods for building devices based on gated TMDC monolayers or nanotubes become increasingly advanced [13][14][15][16][17], opening the possibility of utilizing the spin and valley index of electrons controlled therein. In particular, it is shown by recent results with electrostatic quantum dots (QDs) with a gated MoS 2 -nanoribbon-QD measured by a single electron transport [18,19], or tunable TMDC spintronic devices, where spin or valley polarized currents emerge in TMDC monolayer proximitized by nearby ferromagnetic [20][21][22][23][24].…”

Effective theory of monolayer TMDC double quantum dots

“…In the case ∆ < 0, the results are analogous, but the ground state is |n + . Regarding the experimental situation, the few available experiments indicate U ≈ 2 meV for QDs created in WSe 2 [37] and MoS 2 [39][40][41] with QD radii around 100 nm. On the other hand, the theory predicts 2∆ to be about 3 meV for MoS 2 and larger for other compounds [7,52].…”

“…However, recently there has been a significant progress in the fabrication process of nanostructures in TMDCs. This has enabled the creation of single QDs on monolayer [37,41] or trilayer TMDCs [40], double QD experiments with tunable coupling strength between the dots [39,41] and the observation of gatecontrolled Coulomb blockade effect [37][38][39][40][41].…”

“…Theoretical investigation of QDs in TMDCs started with QDs in gated nanoribbons [27] and the magnetic field dependence of the single-electron spectrum [7] and it now includes studies of valley hybridisation [28], flake QDs of triangular and hexagonal shape and nanoribbons [29,30], the valley Zeeman effect [31], optical control of a spin-valley qubit [32], spin-degenerate regimes for small QDs in a magnetic field [33], spin relaxation [34], electric control of a spin-valley qubit [35] and a model of valley qubit [36]. On the experimental side, gating monolayer TMDCs is not straightforward [38,40] and low material quality has hindered the exper imental study of the intrinsic properties of these mat erials for a long time. However, recently there has been a significant progress in the fabrication process of nanostructures in TMDCs.…”