Abstract
Graphene and its multilayers offer a great opportunity to study electron-electron (e-e) interactions due to the absence of the energy gap and the layer number-dependent band structures that enables a systematic study of the effect in the same material family with different electronic bands. In the very low range of carrier density and with ultrahigh mobility, e-e interactions present a strong effect in graphene and its multilayers including reshaping Dirac cones in monolayer graphene and inducing broken symmetry states in bilayer graphene. Notably, a phase transition with increasingly large Tc (the bilayer-like subband gap will vanish for temperatures T > Tc) in suspended graphene multilayers will occur. As part of this project, suspended graphene multilayers with dual gates are fabricated to experimentally investigate the effect of a perpendicular electric field on the phase transition. On the other hand, e-e interactions can also be studied effectively between closely spaced but electrically isolated electron systems when the current applied in one (active) layer induces voltage in the second (passive) layer, which offers one of the most sensitive probes of interaction in two-dimensional van der Waals (vdW) systems. In recent studies, only monolayer graphene and bilayer graphene with hBN as insulating spacer have been studied in such drag systems. In this project, vdW heterostructures composed of two graphene layers separated by and aligned with hexagonal boron nitride (hBN) are prepared to study the effect of moire superlattice induced between graphene and hBN on interlayer e-e interactions.
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