The search of a p-type metal contact on MoS2 has remained inconclusive, with high work function metals such as Au, Ni, and Pt showing n-type behavior and mixed reports of n as well as p-type behavior for Pd. In this work, we report quantitative Schottky barrier heights for Au and Pd contacts to MoS2 obtained by analysing low temperature transistor characteristics and contact resistance data obtained using the transfer length method. Both Au and Pd exhibit n-type behavior on multilayer as well as monolayer MoS2 transistors with Schottky barrier heights of 0.126 eV and 0.4 eV, and contact resistances of 42 Ω.mm and 18 × 104 Ω.mm respectively. Scanning photocurrent spectroscopy data is in agreement with the resulting energy band alignment in Au-MoS2-Pd devices further reinforcing the observation that the Fermi-level is pinned in the upper half of MoS2 bandgap.

While photons in free space barely interact, matter can mediate interactions between them resulting in optical nonlinearities. Such interactions at the single-quantum level result in an on-site photon repulsion [1, 2], crucial for photon-based quantum information processing and for realizing strongly interacting many-body states of light [3][4][5][6][7]. Here, we report repulsive dipole-dipole interactions between electric field tuneable, localized interlayer excitons in MoSe 2 /WSe 2 heterobilayer. The presence of a single, localized exciton with an out-of-plane, non-oscillating dipole moment increases the energy of the second excitation by ∼ 2 meV -an order of magnitude larger than the emission linewidth and corresponding to an inter-dipole distance of ∼ 5 nm. At higher excitation power, multi-exciton complexes appear at systematically higher energies. The magnetic field dependence of the emission polarization is consistent with spin-valley singlet nature of the dipolar molecular state. Our finding is an important step towards the creation of excitonic few-and many-body states such as dipolar crystals with spin-valley spinor in van der Waals (vdW) heterostructures.Optical response in atomically thin layered semiconductors is determined by excitons and other excitonic complexes such as trions and biexcitons which are strongly bound due to increased Coulomb interactions in truly 2D limit [5,9]. In addition, due to the type-II band alignment in heterobilayer of MoSe 2 /WSe 2 , an interlayer exciton comprising of an electron in the MoSe 2 layer and hole in the WSe 2 layer is found to be stable and long-lived [4,10,11,13]. As shown in Fig. 1a, due to the spatial separation of electron and hole, the interlayer exciton carries a static, out-of-plane electric dipole moment which allows for the tuning of its energy by an external electric field (E). The orientation of this dipole is fixed by the ordering of MoSe 2 and WSe 2 layers and hence leads to a repulsive interaction between interlayer excitons. arXiv:1910.08139v1 [cond-mat.mes-hall] 17 Oct 2019 10 µm WSe2 MoSe2 a b c U d-d on-site E x E x -+ Mo W Se ℎ + − Electric field Figure 1: Interlayer exciton dipoles in WSe 2 /MoSe 2 heterostructure. a, A schematic showing the interlayer exciton in WSe 2 -MoSe 2 heterobilayer under an external electric field E. Due to the type-II band alignment, electron and hole are separated in MoSe 2 and WSe 2 , respectively, forming a permanent out-ofplane dipole. The dipole energy red-shifts (blue-shifts) when E is parallel (anti-parallel) to the direction of dipole. b, Energy diagram of localized interlayer exciton and biexciton in a potential well. The energy of biexciton is raised up by on-site dipole-dipole interaction U on−site dd . c, An optical image of WSe 2 /MoSe 2 heterobilayer with graphite bottom gate. Monolayer WSe 2 (MoSe 2 ) is depicted in orange (yellow) dashed line. The final device has graphite bottom and top gates with h-BN as dielectric on both sides.This dipolar interaction is potentially interesting for inducing e...

Superlattice in graphene generates extra Dirac points in the band structure and their number depends on the superlattice potential strength. Here, we have created a lateral superlattice in a graphene device with a tunable barrier height using a combination of two gates. In this Letter, we demonstrate the use of lateral superlattice to modify the band structure of graphene leading to the emergence of new Dirac cones. This controlled modification of the band structure persists up to 100 K.

Quantum entanglement is a fundamental phenomenon which, on the one hand, reveals deep connections between quantum mechanics, gravity and the space-time [1, 2]; on the other hand, has practical applications as a key resource in quantum information processing [3]. While it is routinely achieved in photon-atom ensembles [4], entanglement involving the solid-state [5-7] or macroscopic objects [8] remains challenging albeit promising for both fundamental physics and technological applications. Here, we report entanglement between collective, chiral vibrations in two-dimensional (2D) WSe 2 host -chiral phonons (CPs) -and single-photons emitted from quantum dots [9-13] (QDs) present in it. CPs which carry angular momentum were recently observed in WSe 2 and are a distinguishing feature of the underlying honeycomb lattice [14, 15]. The entanglement results from a "which-way" scattering process, involving an optical excitation in a QD and doubly-degenerate CPs, which takes place via two indistinguishable paths. Our unveiling of entanglement involving a macroscopic, collective excitation together with strong interaction between CPs and QDs in 2D materials opens up ways for phonon-driven entanglement of QDs and engineering chiral or non-reciprocal interactions at the single-photon level.Two dimensional (2D) materials with a honeycomb lattice, such as graphene and WSe 2 , have degenerate, low energy electronic states which exhibit handedness. In the momentum space, this arXiv:1808.09984v1 [cond-mat.mes-hall]

Control and manipulation of single charges and their internal degrees of freedom, such as spins, is a fundamental goal of nanoscience with promising technological applications. Recently, atomically thin semiconductors such as WSe 2 have emerged as a platform for valleytronics, offering rich possibilities for optical, magnetic and electrical control of the valley index [1, 2]. While progress has been made in controlling valley index of ensemble of charge carriers [3-5], valley control of individual charges, crucial for valleytronics, remains unexplored. Here, we provide unambiguous evidence for localized holes with net spin in optically active WSe 2 quantum dots (QDs) and control their spin-valley state with the helicity of the excitation laser under small magnetic field. We estimate a lower bound on the valley lifetime of a single charge in QD from recombination time to be ∼ nanoseconds. Remarkably, neutral QDs do not exhibit such a control, demonstrating the role of excess charge in prolonging the valley lifetime. Our work extends the field of 2D valleytronics to the level of single spin-valley, relevant for quantum information and sensing applications.Localized single spins in solid-state have been widely studied for quantum information technology, spintronics and quantum sensing [6,7], in addition to serving as a versatile playground for exploring many-body physics [8]. With the rise of semiconducting van der Waals (vdW) materials having direct band gap such as group VI-B transition metal dichalcogenides (TMDs), a arXiv:1810.01887v1 [cond-mat.mes-hall]