arXiv subjects

Lingyuan Lyu

Publications and source records attributed to Lingyuan Lyu.

3 recordsLinked to original sources

arXiv2026

Dynamic twisting and imaging of moiré crystals

Moiré superlattices in stacked 2D crystals are powerful platforms for engineering correlated and topological quantum phases, with twisted graphene and transition metal dichalcogenides (TMDs) as prominent examples. Their angle-sensitive band structures enable rich tunability; however, conventional tear-and-stack methods fix the angle at assembly, limiting systematic exploration of angle-dependent phenomena. Here, we present a scanning-probe-based manipulation scheme that enables in situ, continuous post-fabrication twist control using nanostructured metal rotors. We demonstrate reproducible angle tuning and direct moiré imaging across three platforms: graphene, hBN, and encapsulated, air-sensitive MoTe2. Quantitative piezoresponse force microscopy (PFM) analysis confirms sub-degree precision with minimal induced heterostrain, preserving sample quality even in the marginally twisted regime. Crucially, the device architecture maintains open access to the active region, allowing optical, scanning-probe, and transport measurements. This work enables single-device mapping of the angular phase diagram of moiré materials, including the twisted TMD homobilayers.

cond-mat.mes-hall↗

arXiv2025

3D microwave imaging of a van der Waals heterostructure

Van der Waals (vdW) heterostructures offer a tunable platform for the realization of emergent phenomena in layered electron systems. While scanning probe microscopy techniques have proven useful for the characterization of surface states and 2D crystals, the subsurface imaging of quantum phenomena in multi-layer systems presents a significant challenge. In 3D heterostructures, states that occupy different planes can simultaneously contribute to the signal detected by the microscope probe, which complicates image analysis and interpretation. Here we present a quantum imaging technique that offers a glimpse into the third dimension by resolving states out of plane: it extracts the charge density landscape of individual atomic planes inside a vdW heterostructure, layer by layer. As a proof-of-concept, we perform layer-resolved imaging of quantum Hall states and charge disorder in double-layer graphene using milliKelvin microwave impedance microscopy. Here the discrete energy spectrum of the top layer enables transmission of microwaves through gapped states, thus opening direct access to quantum phases in the subsurface layer. Resolving how charge is distributed out-of-plane offers a direct probe of interlayer screening, revealing signatures of negative quantum capacitance driven by many-body correlations. At the same time, we extract key features of the band structure and thermodynamics, including gap sizes. Notably, by imaging the charge distribution on different atomic planes beneath the surface, we shed light on the roles of surface impurities and screening on the stability of fractional quantum Hall states. We also show that the uppermost graphene layer can serve as a top gate: This unlocks access to a wide range of phenomena that require displacement field control, from fractional Chern insulators in Moiré superlattices to correlated states in multilayer graphene.

cond-mat.mes-hall↗

arXiv2022

Approaching intrinsic threshold breakdown voltage and ultra-high gain in graphite/InSe Schottky photodetector

Realizing both ultra-low breakdown voltage and ultra-high gain has been one of the major challenges in the development of high-performance avalanche photodetector. Here, we report that an ultra-high avalanche gain of 3*10^5 can be realized in the graphite/InSe Schottky photodetector at a breakdown voltage down to 5.5 V. Remarkably, the threshold breakdown voltage can be further reduced down to 1.8 V by raising the operating temperature, approaching the theoretical limit of 1.5E_g/e with E_g the band gap of semiconductor. We develop a two-dimensional impact ionization model and uncover that observation of high gain at low breakdown voltage arises from reduced dimensionality of electron-phonon (e-ph) scattering in the layered InSe flake. Our findings open up a promising avenue for developing novel weak-light detectors with low energy consumption and high sensitivity.

physics.app-ph↗