arXiv subjects

Kaining Yang

Publications and source records attributed to Kaining Yang.

6 recordsLinked to original sources

arXiv2026

Hilbert-space selected switch of helical edges in an artificial quantum Hall insulator

Quantum Hall effects (QHE) host one-dimensional topologically-protected edge channels, which can serve as an essential ingredient in exotic quantum electronic systems. Yet the manual reconstruction of Landau-level topology, by electrostatic confinement or symmetry breaking, remains experimentally challenging. Here, we show that interfacial charge transfer in between CrOCl and large-angle twisted bilayer graphene offsets the two otherwise decoupled Dirac Landau-level ladders in each graphene layer, creating a new sequence of composite filling configurations. At charge neutrality, the composited $(+2,-2)$ state involves only the zeroth Landau levels and becomes fully insulating, with longitudinal resistance reaching the G$\Omega$ regime. By contrast, higher composite zero-filling quantum Hall states, including $(+6,-6)$ and $(+10,-10)$, retain counter-propagating helical edge channels and exhibit pronounced non-local transport, reaching up to $50\%$ of the local response. We attribute such switching-behavior to the Landau-spinor Hilbert space -- as the filling is reduced from $(+6,-6)$ to $(+2,-2)$, the orthogonal $N=\pm1$ orbital components are removed, eliminating the edge-compatible channel and gapping both bulk and boundary transport. The interaction nature of the observed gapped sates was further examined both experimentally and theoretically. Our results suggest that charge transfer provides a direct route to engineer artificial quantum Hall insulators, opening possibilities for wavefunction-selective control of helical edge modes.

cond-mat.mes-hall↗

arXiv2026

An AI-driven robotic system for two-dimensional hetero-assemblies

Nanomaterials stacked on-demand, such as rotationally assembled two-dimensional (2D) van der Waals (vdW) layered compounds, provides a versatile platform for quantum simulation and the exploration of exotic electronic phases. Currently, however, such nanoassemblies remain largely confined to inefficiency, manually operated process, limiting their potential for probing emergent physical phenomena. There is a pressing need in the field for high-precision, automated assembling techniques, especially for the scalable fabrication of 2D twistronic heterostructures. Here, we present an intelligent automation system dedicated to the fabrication of van der Waals stacks, following the state-of-the-art protocol for dry transfer of exfoliated 2D materials. The system further employs metadata generated from each automated stacking procedure to perform reinforcement learning, thereby continuously bettering its performances. As a concrete demonstration, we fabricate twisted bilayer graphene (TBLG) -- known for its challenging preparation -- and exhibit its unconventional superconductivity near the magic angle. Our work may pave the way for high-throughput fabrication of low-dimensional nanomaterials including twistronic heterostructures, where integrating data mining and artificial intelligence can accelerate the discovery of novel physical phenomena.

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arXiv2025

A two-dimensional semiconductor-semimetal drag hybrid

Lateral charge transport of a two-dimensional (2D) electronic system can be much influenced by feeding a current into another closely spaced 2D conductor, known as the Coulomb drag phenomenon -- a powerful probe of electron-electron interactions and collective excitations. Yet the materials compatible for such investigations remain limited to date. Especially, gapped 2D semiconductors with inherently large correlations over a broad gate range have been rarely accessible at low temperatures. Here, we show the emergence of a large drag response (drag resistance $R_{\text{drag}}$ at the order of k$\Omega$, with a passive-to-active drag ratio up to $\sim$ 0.6) in a semiconductor-semimetal hybrid, realized in a graphene-MoS$_{2}$ heterostructure isolated by an ultrathin 3 nm hexagonal boron nitride (h-BN) dielectric. We observe a crossover of $T$ to $T^{2}$ dependence of $R_{\text{drag}}$, separated by a characteristic temperature $T_{d} \sim E_{F}/k_{F}d$ ($d$ being the interlayer distance), in echo with the presence of a metal-insulator transition in the semiconducting MoS$_{2}$. Interestingly, the current nanostructure allows the decoupling of intralayer interaction-driven drag response by varying density in one layer with that in the other layer kept constant. A large Wigner-Seitz radius $r_{s}$ ($>$ 10 within the density range of 1 to $4 \times 10^{12}~\mathrm{cm}^{-2}$) in the massive Schr\"odinger carriers in MoS$_{2}$ is thus identified to dominate the quadratic dependence of total carriers in the drag system, while the massless Dirac carriers in graphene induce negligible drag responses as a function of carrier density. Our findings establish semiconductor-semimetal hybrid as a platform for studying unique interaction physics in Coulomb drag systems.

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arXiv2022

Synergistic correlated states and nontrivial topology in coupled graphene-insulator heterostructures

In this work, we study the synergistic correlated states in two distinct types of interacting electronic systems coupled by interlayer Coulomb interactions. We propose that this scenario can be realized in a type of Coulomb-coupled graphene-insulator heterostructures with gate tunable band alignment. We find that, by virtue of the interlayer Coulomb coupling between the interacting electrons in the two layers, electronic states that cannot be revealed in either individual layer would emerge in a cooperative and synergistic manner. Specifically, as a result of the band alignment, charge carriers can be transferred between graphene and the substrate under the control of gate voltages, which can yield a long-wavelength electronic crystal at the surface of the substrate. This electronic crystal exerts a superlattice Coulomb potential on the Dirac electrons in graphene, which generates subbands with reduced non-interacting Fermi velocity. As a result, $e$-$e$ Coulomb interactions within graphene would play a more important role, giving rise to a gapped Dirac state at the charge neutrality point, accompanied by interaction-enhanced Fermi velocity. Moreover, the superlattice potential can give rise to topologically nontrivial subband structures which are tunable by superlattice's constant and anisotropy. Reciprocally, the electronic crystal formed in the substrate can be substantially stabilized in such coupled bilayer heterostructure by virtue of the cooperative interlayer Coulomb coupling. We further perform high-throughput first principles calculations to identify a number of promising insulating materials as candidate substrates for graphene to demonstrate these effects.

cond-mat.mes-hall↗

arXiv2021

Realization of graphene logics in an exciton-enhanced insulating phase

For two decades, two-dimensional carbon species, including graphene, have been the core of research in pursuing next-generation logic applications beyond the silicon technology. Yet the opening of a gap in a controllable range of doping, whilst keeping high conductance outside of this gapped state, has remained a grand challenge in them thus far. Here we show that, by bringing Bernal-stacked bilayer graphene in contact with an anti-ferromagnetic insulator CrOCl, a strong insulating behavior is observed in a wide range of positive total electron doping $n_\mathrm{tot}$ and effective displacement field $D_\mathrm{eff}$ at low temperatures. Transport measurements further prove that such an insulating phase can be well described by the picture of an inter-layer excitonic state in bilayer graphene owing to electron-hole interactions. The consequential over 1 $\mathrm{G\Omega}$ excitonic insulator can be readily killed by tuning $D_\mathrm{eff}$ and/or $n_\mathrm{tot}$, and the system recovers to a high mobility graphene with a sheet resistance of less than 100 $\mathrm{\Omega}$. It thus yields transistors with "ON-OFF" ratios reaching 10$^{7}$, and a CMOS-like graphene logic inverter is demonstrated. Our findings of the robust insulating phase in bilayer graphene may be a leap forward to fertilize the future carbon computing.

cond-mat.mes-hall↗

arXiv2021

Quantum Hall phase in graphene engineered by interfacial charge coupling

Quantum Hall effect (QHE), the ground to construct modern conceptual electronic systems with emerging physics, is often much influenced by the interplay between the host two-dimensional electron gases and the substrate, sometimes predicted to exhibit exotic topological states. Yet the understanding of the underlying physics and the controllable engineering of this paradigm of interaction remain challenging. Here we demonstrate the observation of an unusual QHE, which differs markedly from the known picture, in graphene samples in contact with an anti-ferromagnetic insulator CrOCl equipped with dual gates. Owing to the peculiar interfacial coupling, Landau levels in monolayer graphene remain intact at negative filling fractions, but largely deviated for the positive gate-doping range. The latter QHE phase even presents in the limit of zero magnetic field, with the consequential Landau quantization following a parabolic relation between the displacement field $D$ and the magnetic field $B$. This characteristic prevails up to 100 K in a sufficiently wide effective doping range from 0 to 10$^{13}$ cm$^{-2}$. Our findings thus open up new routes for manipulating the quantum electronic states, which may find applications in such as quantum metrology.

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