Determination of topological edge quantum numbers of fractional quantum Hall phases by thermal conductance measurements
Saurabh Kumar Srivastav, Ravi Kumar, Christian Spånslätt, Kenji Watanabe, Takashi Taniguchi, A. D. Mirlin, Yuval Gefen, Anindya Das
Abstract
Abstract To determine the topological quantum numbers of fractional quantum Hall (FQH) states hosting counter-propagating (CP) downstream ( N d ) and upstream ( N u ) edge modes, it is pivotal to study quantized transport both in the presence and absence of edge mode equilibration. While reaching the non-equilibrated regime is challenging for charge transport, we target here the thermal Hall conductance G Q , which is purely governed by edge quantum numbers N d and N u . Our experimental setup is realized with a hexagonal boron nitride (hBN) encapsulated graphite gated single layer graphene device. For temperatures up to 35 mK, our measured G Q at ν = 2/3 and 3/5 (with CP modes) match the quantized values of non-equilibrated regime ( N d + N u ) κ 0 T , where κ 0 T is a quanta of G Q . With increasing temperature, G Q decreases and eventually takes the value of the equilibrated regime ∣ N d − N u ∣ κ 0 T . By contrast, at ν = 1/3 and 2/5 (without CP modes), G Q remains robustly quantized at N d κ 0 T independent of the temperature. Thus, measuring the quantized values of G Q in two regimes, we determine the edge quantum numbers, which opens a new route for finding the topological order of exotic non-Abelian FQH states.