In this study, an electrostatically induced quantum confinement structure, so-called quantum point contact, has been realized in a p-type trilayer tungsten diselenide-based van der Waals ...heterostructure with modified van der Waals contact method with degenerately doped transition metal dichalcogenide crystals. Clear quantized conductance and pinch-off state through the one-dimensional confinement were observed by dual-gating of split gate electrodes and top gate. Conductance plateaus were observed at a step of e 2/h in addition to quarter plateaus such as 0.25 × 2e 2/h at a finite bias voltage condition indicating the signature of intrinsic spin-polarized quantum point contact.
Stacking of graphene with hexagonal boron nitride (h-BN) can dramatically modify its bands from their usual linear form, opening a series of narrow minigaps that are separated by wider minibands. ...While the resulting spectrum offers strong potential for use in functional (opto)electronic devices, a proper understanding of the dynamics of hot carriers in these bands is a prerequisite for such applications. In this work, we therefore apply a strategy of rapid electrical pulsing to drive carriers in graphene/h-BN heterostructures deep into the dissipative limit of strong electron-phonon coupling. By using electrical gating to move the chemical potential through the "Moiré bands", we demonstrate a cyclical evolution between metallic and semiconducting states. This behavior is captured in a self-consistent model of non-equilibrium transport that considers the competition of electrically driven inter-band tunneling and hot-carrier scattering by strongly non-equilibrium phonons. Overall, our results demonstrate how a treatment of the dynamics of both hot carriers and hot phonons is essential to understanding the properties of functional graphene superlattices.
We use transient electrical measurements to investigate the details of self-heating and charge trapping in graphene transistors encapsulated in hexagonal boron nitride (h-BN) and operated under ...strongly nonequilibrium conditions. Relative to more standard devices fabricated on SiO2 substrates, encapsulation is shown to lead to an enhanced immunity to charge trapping, the influence of which is only apparent under the combined influence of strong gate and drain electric fields. Although the precise source of the trapping remains to be determined, one possibility is that the strong gate field may lower the barriers associated with native defects in the h-BN, allowing them to mediate the capture of energetic carriers from the graphene channel. Self-heating in these devices is identified through the observation of time-dependent variations of the current in graphene and is found to be described by a time constant consistent with expectations for nonequilibrium phonon conduction into the dielectric layers of the device. Overall, our results suggest that h-BN-encapsulated graphene devices provide an excellent system for implementations in which operation under strongly nonequilibrium conditions is desired.
Monolayer materials are strongly affected by their potential fluctuations, which can be induced by an intrinsic corrugation or the surface roughness of the substrate. We compare the effective ...exciton-exciton annihilation (EEA) rate constants of monolayer WS2 on substrates with different surface topographies. We show that the WS2 monolayers on the substrates with atomically flat terraces have small effective EEA rate constants that deviate from the overall tendency and exhibit multiple exciton decay components, which cannot be accounted for by the conventional EEA model. To obtain a correct description, it is important to use a quantized EEA model. The intrinsic EEA rate constants for the flat-terrace substrates determined by this model are comparable to that of hBN-encapsulated monolayer WS2.
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