Gate-tunable quantum dot in a high quality single layer MoS2 van der Waals heterostructure

Abstract

We have fabricated an encapsulated monolayer MoS 2 device with metallic ohmic contacts through a prepatterned hBN layer. In the bulk, we observe an electron mobility as high as 3000 cm 2 /Vs at a density of 7 × 10 12 cm −2 at a temperature of 1.7 K. Shubnikov-de Haas oscillations start at magnetic fields as low as 3.3 T. By realizing a single quantum dot gate structure on top of the hBN we are able to confine electrons in MoS 2 and observe the Coulomb blockade effect. By tuning the middle gate voltage we reach a double dot regime where we observe the standard honeycomb pattern in the charge stability diagram.Contrary to graphene, in monolayer molybdenum disulfide (MoS 2 ) inversion symmetry is broken. This, together with the presence of time-reversal symmetry, endows single layer MoS 2 with individually addressable valleys in momentum space at the K and K points in the first Brillouin zone. 1-4 This valley addressability facilitates the momentum state of electrons to be used for novel qubit architectures. Recent theoretical works have been exploring the possibility of using spin and valley states of gate-defined quantum dots in 2D MoS 2 as quantum bits. [5][6][7] In this manuscript, we describe the observation of Coulomb blockade in single and coupled dot in a high quality single layer MoS 2 . The high electronic quality of our monolayer MoS 2 results in the observation of Shubnikov-de Haas oscillations (SdHO) occurring at magnetic fields as low as 3.3 T. The 2DEG in the MoS 2 can be electrostatically depleted below the gate pattern with resistance values exceeding the resistance quantum h/e 2 by orders of magnitude. We observe Coulomb blockade resonances close to pinch-off indicating single electron tunneling in and out of the dot. By adjusting the gate voltages, we are able to tune the electrostatic landscape inside the dot and to form a double dot system within a single dot gate structure. [8][9][10][11] In Fig. 1(a), we show the schematic of a monolayer MoS 2 (∼ 0.7 nm thick) encapsulated between two hexagonal boron nitride (hBN) layers. The measured MoS 2 flake was exfoliated from natural bulk crystal (SPI supplies). The bottom hBN layer is ∼ 30 nm thick and works both as an atomically flat substrate and as a dielectric that isolates the MoS 2 from a graphite backgate. The graphite gate enables us to control electrostatically the electron density in MoS 2 with the voltage V bg . The layers thicknesses were determined by atomic force microscopy (AFM). The top hBN layer (∼50nm thick) has a) Electronic mail: pisonir@phys.ethz.ch been pre-patterned using E-beam lithography and reactive ion etching. 12 This enables us to evaporate metallic contacts (Ti/Au) on top of the MoS 2 layer where the hBN has been etched away, without exposing the channel region to organic residues remaining from the fabrication process. 13 Prior to metal evaporation, the heterostructure has been annealed in forming gas (Ar/H 2 ) at 300 • C for 30 minutes in order to remove most of the organic residues on top of the MoS 2 contact regions a...

Coulomb Blockade in Etched Single- and Few-Layer MoS2 Nanoribbons

“…A first step towards spin based quantum information processing would be demonstration of charge and spin confinement. Signatures of conductance quantization [8,9] and formation of single quantum dot and double quantum dot has been demonstrated in single layer MoS2 [10][11][12] and other TMDC materials [13][14][15]. These confined structures have been created using split-gate technique with top electrostatic gates using either hexagonal-boron nitride (hBN) encapsulated TMDC [8][9][10][11][13][14][15] or atomic layer deposition (ALD) grown gate dielectric [16].…”

Atomistic T -matrix theory of disordered two-dimensional materials: Bound states, spectral properties, quasiparticle scattering, and transport

“…12 is the overall large magnitude of the carrier mobility, µ ∼ 15.000-35.000 cm 2 V −1 s −1 , which exceeds all previously reported experimental values, so far not exceeding µ ∼ 5000 cm 2 V −1 s −1 . 6,107,[109][110][111][112][113][114][115][116][117][118] The large theoretical mobility predicted here is a hallmark of (i) the low defect density used in the calculation which corresponds to high-quality TMDs, 4 and (ii) the absence of the above- mentioned defect charging which leads to a significant reduction of the mobility due to charged-impurity scattering. 101 Both factors are essential for the realization of high-mobility monolayer TMD samples.…”

Effective theory of monolayer TMDC double quantum dots

“…Motivated by recent experimental works [37][38][39][40][41], we have studied and presented the influence of spin-orbit coupling on the low energy properties of a DQD system with spin and valley DOF in the (1, 1) charge configuration. In our analysis we have also explored the possibility of a different spinorbit splitting in each dot and we have included a T -symmetry breaking magnetic field.…”

“…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].…”