Wiedemann-Franz law in a non-Fermi liquid and Majorana central charge: Thermoelectric transport in a two-channel Kondo system

Abstract

Quantum dot devices allow one to access the critical point of the two-channel Kondo model. The effective critical theory involves a free Majorana fermion quasiparticle localized on the dot. As a consequence, this critical point shows both the phenomenon of non-Fermi-liquid physics and fractionalization. Although a violation of the Wiedemann-Franz law is often considered to be a sign of non-Fermi-liquid systems, we show by exact calculations that it holds at the critical point, thereby providing a counterexample to this lore. Furthermore, we show that the fractionalized Majorana character of the critical point can be unambiguously detected from the heat conductance, opening the door to a direct experimental measurement of the elusive Majorana central charge c = 1 2 .