arXiv subjects

Ziqing Ye

Publications and source records attributed to Ziqing Ye.

4 recordsLinked to original sources

arXiv2023

Ballistic transport spectroscopy of spin-orbit-coupled bands in monolayer graphene on WSe$_2$

Van der Waals interactions with transition metal dichalcogenides was shown to induce strong spin-orbit coupling (SOC) in graphene, offering great promises to combine large experimental flexibility of graphene with unique tuning capabilities of the SOC that can rotate spin by moving electrons or vice versa. Here, we probe SOC-driven band splitting and electron dynamics in graphene on WSe$_2$ by measuring ballistic transverse magnetic focusing. We found a clear splitting in the first focusing peak whose evolution in charge density and magnetic field is well reproduced by calculations using SOC strength of ~13 meV and no splitting in the second peak that indicates stronger Rashba SOC. A possible suppression of electron-electron scatterings was also found in temperature dependence measurement. Further, we found that Shubnikov-de Haas oscillations exhibit SOC strength of ~3.4 meV, suggesting that it probes different electron dynamics, calling for new theory. Our study demonstrates an interesting possibility to exploit ballistic electron motion pronounced in graphene for emerging spin-orbitronics.

cond-mat.mes-hall↗

arXiv2021

Giant nonlinear Hall effect in twisted WSe$_2$

The recently discovered nonlinear Hall effect (NHE) in a few non-interacting systems provides a novel mechanism to generate second harmonic electrical Hall signals under time-reversal-symmetric conditions. Here, we introduce a new approach to engineering NHE by using twisted moiré structures. We find that the twisted WSe$_2$ bilayer exhibits a NHE when tuning the Fermi level to the moiré flat bands. Near half-filling of the first moiré band, the nonlinear Hall signal shows a sharp peak with the generation efficiency at least two orders of magnitude larger than those in previous experiments. We propose that the giant NHE and diverging generation efficiency originate from a mass-diverging type continuous Mott transition, which is evidenced by resistivity measurements. This work demonstrates not only how interaction effects can couple to Berry curvature dipoles to produce novel quantum phenomena, but also what NHE measurements can provide for developing a new tool to study the quantum criticality.

cond-mat.mes-hall↗

arXiv2020

Negative compressibility in MoS2 capacitance

Large capacitance enhancement is useful for increasing the gate capacitance of field-effect transistors (FETs) to produce low-energy-consuming devices with improved gate controllability. We report strong capacitance enhancement effects in a newly emerged two-dimensional channel material, molybdenum disulfide (MoS2). The enhancement effects are due to strong electron-electron interaction at the low carrier density regime in MoS2. We achieve about 50% capacitance enhancement in monolayer devices and 10% capacitance enhancement in bilayer devices. However, the enhancement effect is not obvious in multilayer (layer number >3) devices. Using the Hartree-Fock approximation, we illustrate the same trend in our inverse compressibility data.

physics.app-ph↗

arXiv2019

Interaction effects and superconductivity signatures in twisted double-bilayer WSe$_2$

Twisted bilayer graphene provides a new two-dimensional platform for studying electron interaction phenomena and flat band properties such as correlated insulator transition, superconductivity and ferromagnetism at certain magic angles. Here, we present strong evidence of correlated insulator states and superconductivity signatures in p-type twisted double-bilayer WSe$_2$. Enhanced interlayer interactions are observed when the twist angle decreases to a few degrees as reflected by the high-order satellites in the electron diffraction patterns taken from the 2H/3R-stacked domains reconstructed from a conventional Moiré superlattice. In contrast to twisted bilayer graphene, there is no specific magic angle for twisted WSe$_2$. The flat band properties are observed at twist angles ranging from 1 to 4 degrees. The highest superconducting transition temperature observed by transport measurement is 6 K. Our work has facilitated future study in the area of flat band related properties in twisted transition metal dichalcogenide layered structures.

cond-mat.mes-hall↗