Title: Investigating 2D heterostructures using electrical transport and alternate probes
Date & Time: July 24th , 2026 (Friday) & 3:00-4:30PM
Venue: SV Narasaiah Auditorium, IAP
Abstract: The recent development of moiré materials has provided an exceptional platform for exploring strongly correlated and topological electronic phases with unprecedented tunability. These systems exhibit a rich interplay between electronic interactions, symmetry breaking, topology, and band structure engineering, giving rise various unconventional transport phenomena. Our work primarily aims to develop and utilize transport-based experimental probes to uncover electronic structure and interaction effects beyond conventional linear-response measurements as discussed below.
First, the quintessential linear electrical transport is conducted in twisted triple bilayer graphene (tTBG). Owing to the reduced sensitivity of twist-angle variations in these multilayer structures, they serve as an ideal platform for investigating multiband electronic phenomena. An anomalous Hall response was observed near the charge neutrality point (CNP). Unlike the conventional Hall response, where the sign reversal of Hall resistance directly reflects a change in charge carriers, an unprecedented opposite carrier-type transition near filling factor 1 is observed. This unconventional behaviour originates from the intricate multiband electronic structure. In addition, we observed multiple Fermi surface reconstructions across the density range, manifested through Lifshitz transitions and reset-like behaviour in the transport response.
To answer the question: if the reconstruction of the Fermi surface is intrinsic to the moiré system itself or induced by the presence of an external magnetic field (B), a framework for mapping the evolution using complementary linear and nonlinear (NL) transport measurements is employed in the second work. Linear transport under finite B and nonlinear transport under zero B conducted in twisted bilayer graphene (tBG) captured the same underlying electronic reconstruction, demonstrating the observed behaviour is intrinsic to the system rather than field induced. This work established nonlinear transport as a B-field free probe for investigating correlated and topological phenomena in moiré materials.
Unlike the equilibrium conditions in the previous work, the last part employs very high DC current to drive graphene systems in nonequilibrium transport regime. Interplay of high current densities, carrier density and magnetic field reveals nontrivial nonlinear current voltage (I-V) response with strong presence of negative differential resistance (NDR).
In summary, this thesis demonstrates that electrical transport, when extended beyond the conventional linear-response regime, provides a powerful window into the complex electronic landscape of moiré van der Waals materials. Through complementary linear, nonlinear, and high-bias measurements, it reveals multiband electronic reconstruction, intrinsic zero-field correlated phenomena, and emergent nonequilibrium transport signatures, thereby expanding the experimental toolbox for studying quantum materials.
Refreshments will be given after the colloquium .