Chiral Second-Sound Collective Modes at the Edge of 2D Systems with a Nontrivial Berry Curvature.

Physical review letters

PubMedID: 28157362

Principi A, Katsnelson MI, Levchenko A. Chiral Second-Sound Collective Modes at the Edge of 2D Systems with a Nontrivial Berry Curvature. Phys Rev Lett. 2017;118(3):036802.
We study the thermal transport in two-dimensional systems with a nontrivial Berry curvature texture. The physical realizations are many; for the sake of definiteness, we consider undoped graphene gapped by the presence of an aligned hexagonal-boron-nitride substrate. The same phenomenology applies, i. e. , to surface states of 3D topological insulators in the presence of a uniform magnetization. We find that chiral valley-polarized second-sound collective modes propagate along the edges of the system. The localization length of the edge modes has a topological origin stemming from the anomalous velocity term in the quasiparticle current. At low temperature, the single-particle contribution to the transverse thermal conductance is exponentially suppressed, and only second-sound modes carry heat along the boundary. A sharp change in the behavior of the thermal Hall conductance, extracted from nonlocal measurements of the temperature along the edge, marks the onset of ballistic heat transport due to second-sound edge modes.