Thermoelectricity of moir\'e heavy fermions in MoTe2/WSe2 bilayers

TL;DR

This study provides the first comprehensive thermoelectric measurements of moiré heavy fermions in MoTe2/WSe2 bilayers, revealing entropy changes during Kondo lattice formation and breakdown, and highlighting discrepancies with semiclassical models.

Contribution

It introduces quantitative thermoelectric measurements to moiré heavy fermion systems, uncovering entropy signatures associated with Kondo physics and phase transitions.

Findings

Sign change in Seebeck coefficient near Kondo coherence temperature

Observation of entropy accumulation during Kondo singlet breakdown

Discrepancies with semiclassical Mott relation in thermoelectric behavior

Abstract

Tunable Kondo lattice and heavy fermion physics have been recently reported in moir\'e materials, but most of the studies have focused on the electrical and magnetic properties. Quantitative thermoelectric measurements, which can reveal entropic information of the heavy fermions, have yet to be achieved. Here, we report a comprehensive thermoelectric study on the moir\'e heavy fermion phase realized in hole-doped angle-aligned MoTe2/WSe2 bilayers. By electrically gating the material to the Kondo lattice region of the phase diagram, we observe a sign change in the Seebeck coefficient near the Kondo coherence temperature, where the heavy fermion phase with an electron-like Fermi surface evolves into an itinerant Fermi liquid with a hole-like Fermi surface. We compare the results with the semiclassical Mott relation and discuss the observed discrepancies. In addition to the thermal dissociation of Kondo singlets in the heavy Fermi liquid, a sign change accompanied by a strong peak in the Seebeck coefficient is also observed near a Zeeman breakdown of the Kondo singlets, signaling an entropy accumulation. Our results provide entropic information on both the formation and breakdown of heavy fermions in moir\'e semiconductors.