arXiv subjects

Harsimran Kaur Mann

Publications and source records attributed to Harsimran Kaur Mann.

4 recordsLinked to original sources

arXiv2026

Layer-Polarization-Driven Metal-Insulator Transition in multi-band Graphene Moire' Superlattices

Graphene/hBN moiré superlattices provide a highly tunable platform for exploring emergent quantum phases in low-dimensional systems. Here, we investigate the moiré superlattice formed between hBN and ABA-stacked trilayer graphene (TLG), an inherently multi-band system. We demonstrate that the moiré potential is not merely a perturbation but a tool to hybridize the distinct massless and massive electronic sectors of TLG. By applying a perpendicular displacement field to tune layer polarization, we drive a fundamental reconstruction of the electronic band structure. Specifically, increasing the displacement field evolves the system from a multi-band regime to an effectively single-band regime at low energies, accompanied by a metal--insulator transition at the hole-doped secondary Dirac point. This transition originates from a redistribution of carriers across graphene layers that selectively enhances their coupling to the extrinsic moiré potential. Quantum capacitance measurements provide direct evidence for the suppression of the density of states at the hole-side secondary Dirac point, consistent with gap opening and the emergence of a displacement-field-tuned band gap. Theoretical calculations reproduce these observations and identify layer-selective coupling to the moiré potential as the underlying mechanism. These results demonstrate electrical control of an emergent insulating phase in a low-dimensional moiré system, and highlight that layer polarization and layer-selective coupling in multi-band moiré heterostructures provide a powerful route for engineering topological and correlated phases through band structure reconstruction and electron interactions.

cond-mat.mes-hall↗

arXiv2025

Tunable Band Inversion in Trilayer Graphene

Displacement field control of elecronic bands in low-dimensional systems is a promising route toward engineering emergent quantum phases. Here, we report displacement-field-induced band inversion and modulation of the Berry phase of low-energy quasi particles in high-mobility Bernal-stacked trilayer graphene (TLG). Using quantum oscillations, we track the evolution of the Fermi surface and topological properties of Dirac-like gully bands that emerge under a finite interlayer potential. We observe a striking sequence of transitions: at low displacement field $D$, the gullies are characterized by a Berry phase of $2π$ and large effective mass, indicating massive fermions. As $D$ increases, the Berry phase abruptly shifts to $π$ and the effective mass reaches a minimum, signaling the onset of massless Dirac behavior. At higher $D$, the Berry phase returns to $2π$, and the effective mass increases again, consistent with a band inversion. These findings demonstrate a rare, reversible topological phase transition - massive to massless to massive - driven entirely by an external displacement field. Despite robust theoretical predictions [\textit{Phys. Rev. B} \textbf{87}, 085424 (2013), \textit{Phys. Rev. B} \textbf{87}, 115422 (2013), and \textit{Phys. Rev. B} \textbf{101}, 245411 (2020)], this evolution of the band topology had escaped experimental detection. Our results establish TLG as a tunable platform for nanoscale control of band topology. They establish a means to tune between massive and Dirac-like dispersions dynamically providing a foundation for exploring field-switchable topological phenomena in layered 2D systems.

cond-mat.mes-hall↗

arXiv2024

Optical control of multiple resistance levels in graphene for memristic applications

Neuromorphic computing has emphasized the need for memristors with non-volatile, multiple conductance levels. This paper demonstrates the potential of hexagonal boron nitride (hBN)/graphene heterostructures to act as memristors with multiple resistance states that can be optically tuned using visible light. The number of resistance levels in graphene can be controlled by modulating doping levels, achieved by varying the electric field strength or adjusting the duration of optical illumination. Our measurements show that this photodoping of graphene results from the optical excitation of charge carriers from the nitrogen-vacancy levels of hBN to its conduction band, with these carriers then being transferred to graphene by the gate-induced electric field. We develop a quantitative model to describe our observations. Additionally, utilizing our device architecture, we propose a memristive crossbar array for vector-matrix multiplications.

cond-mat.mes-hall↗

arXiv2024

Controlling Umklapp scattering in bilayer graphene moir'e superlattice

In this Letter, we present experimental findings on electron-electron scattering in a two-dimensional moir'e heterostructure with tunable Fermi wave vector, reciprocal lattice vector, and band gap. We achieve this in high-mobility aligned heterostructures of bilayer graphene (BLG) and hBN. Around half-filling, the primary contribution to the resistance of BLG/hBN aligned superlattices arises from electron-electron Umklapp (Uee) scattering, making the resistance of graphene/hBN moir'e devices significantly larger than that of non-aligned devices (where Uee is forbidden). We quantify the strength of the Uee scattering and find that it follows a universal scaling with Fermi energy and has a non-monotonic dependence on the charge carrier density. The Uee scattering is strongly electric field tunable and affected by layer-polarization of BLG. It has a strong particle-hole asymmetry - the resistance when the chemical potential is in the conduction band is significantly lesser than when it is in the valence band, making the electron-doped regime more practical for potential applications.

cond-mat.mes-hall↗