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Register a new userS-type Negative Differential Resistance in Semiconducting Transition-Metal Dichalcogenides
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Current-controlled (also known as S-type) negative differential resistance (NDR) is of crucial importance to many emerging applications including neuromorphic computing and high-density memristors integration. However, the experimental realization of S-type NDR based on conventional mechanisms poses demanding requirements on materials, which greatly limits their potential applications. Here, we experimentally identify that semiconducting transition metal dichalcogenides (TMDs) can host a bipolar S-type NDR devices. Theoretical simulations indicate that the origin of the NDR in these devices arises from a thermal feedback mechanism. Furthermore, we demonstrate the potential applications of TMDs based S-type NDR device in signal processing and neuromorphic electronics.
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We present low temperature magneto-photoluminescence experiments which demonstrate the brightening of dark excitons by an in-plane magnetic field $B$ applied to monolayers of different semiconducting transition metal dichalcogenides. For both WSe$_2$ and WS$_2$ monolayers, the dark exciton emission is observed at $sim$50 meV below the bright exciton peak and displays a characteristic doublet structure which intensity is growing with $B^2$, while no magnetic field induced emission peaks appear for MoSe$_2$ monolayer. Our experiments also show that the MoS$_2$ monolayer has a dark exciton ground state with a dark-bright exciton splitting energy of $sim$100 meV.
Nonlinear electrical properties, such as negative differential resistance (NDR), are essential in numerous electrical circuits, including memristors. Several physical origins have been proposed to lead to the NDR phenomena in semiconductor devices in the last more than half a century. Here, we report NDR behavior formation in randomly oriented graphene-like nanostructures up to 37 K and high on-current density up to 10^5 A/cm^2. Our modeling of the current-voltage characteristics, including the self-heating effects, suggests that strong temperature dependence of the low-bias resistance is responsible for the nonlinear electrical behavior. Our findings open opportunities for the practical realization of the on-demand NDR behavior in nanostructures of 2D and 3D material-based devices via heat management in the conducting films and the underlying substrates.
We have observed tunable negative differential resistance (NDR) in scanning tunneling spectroscopy measurements of a double layer of C60 molecules on a metallic surface. Using a simple model we show that the observed NDR behavior is explained by voltage-dependent changes in the tunneling barrier height.
Excitons dominate the optical properties of monolayer transition metal dichalcogenides (TMDs). Besides optically accessible bright exciton states, TMDs exhibit also a multitude of optically forbidden dark excitons. Here, we show that efficient exciton-phonon scattering couples bright and dark states and gives rise to an asymmetric excitonic line shape. The observed asymmetry can be traced back to phonon-induced sidebands that are accompanied by a polaron redshift. We present a joint theory-experiment study investigating the microscopic origin of these sidebands in different TMD materials taking into account intra- and intervalley scattering channels opened by optical and acoustic phonons. The gained insights contribute to a better understanding of the optical fingerprint of these technologically promising nanomaterials.
Due to the Coulomb interaction exciton eignestates in monolayer transitional metal dichalcogenides are coherent superposition of two valleys. The exciton band which couples to the transverse electric mode of light has parabolic dispersion for the center of mass momentum, whereas the one which couples to the transverse magnetic mode has both parabolic and linear components. In this work we present an experimental proposal to observe the signatures of linear component of the dispersion. In particular, it is demonstrated that by pumping the system with linearly polarized light the exciton transport is anisotropic compared to circularly polarized pump. We show that the results persist for moderate level of disorder present in realistic systems. Finally, we demonstrate that similar effects can be obtained for positively detuned exciton-polaritons, in less stringent experimental requirements compared to bare exciton case.
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