Physics (Internal)

Flavor-Hall effect and nonlocal charge transport in graphene

This event is part of the Condensed Matter Theory Seminar Series.

Abstract:The properties of charge carriers in ideal graphene system are governed by a number of
symmetries, including time-reversal symmetry, inversion symmetry, and particle-hole symmetry.
In a realistic setting, some or all of these symmetries can be naturally broken: magnetic
field breaks time-reversal symmetry, strain of the graphene sheet breaks the inversion
symmetry, while the particle-hole symmetry is broken by Coulomb interactions and free-particle
effects such as the next-nearest-neighbor hopping. Such symmetry breaking can
lead to energy splitting of the two valleys. We show that the resulting imbalance of the Hall
conductivities leads to valley-Hall effect, similar to the spin-Hall effect, but with the valley
playing the role of spin. In the regime of slow inter-valley relaxation, the valley-Hall effect
manifests itself in non-local charge transport. Remarkably, the non-local response can occur
in both classical and quantized Hall transport regimes. We show that the nonlocal response
can be used as a diagnostic for different types of symmetry breaking at the Dirac point.
In addition, our study provides an explanation of recent experiments of Manchester group,
in which pronounced non-locality of transport in macroscopic graphene samples subject to
magnetic field has been observed.