Evidence for ground state coherence in a two-dimensional Kondo lattice

TL;DR

This study provides experimental evidence of a coherent magnetic ground state in a two-dimensional Kondo lattice formed by a TaSe2 heterobilayer, revealing unique electronic resonances and magnetic interactions at ultra-low temperatures.

Contribution

It demonstrates the existence of a coherent ground state in 2D TMD-based Kondo lattices using STM/STS, supported by theoretical calculations, highlighting magnetic order rather than full Kondo screening.

Findings

Detection of symmetric electronic resonances indicating coherence.

Resonance energy separation varies non-linearly with magnetic field.

Evidence suggests magnetic order mediated by conduction electrons.

Abstract

Kondo lattices are ideal testbeds for the exploration of heavy-fermion quantum phases of matter. While our understanding of Kondo lattices has traditionally relied on complex bulk f-electron systems, transition metal dichalcogenide heterobilayers have recently emerged as simple, accessible and tunable 2D Kondo lattice platforms where, however, their ground state remains to be established. Here we present evidence of a coherent ground state in the 1T/1H-TaSe2 heterobilayer by means of scanning tunneling microscopy/spectroscopy at 340 mK. Our measurements reveal the existence of two symmetric electronic resonances around the Fermi energy, a hallmark of coherence in the spin lattice. Spectroscopic imaging locates both resonances at the central Ta atom of the charge density wave of the 1T phase, where the localized magnetic moment is held. Furthermore, the evolution of the electronic structure with the magnetic field reveals a non-linear increase of the energy separation between the electronic resonances. Aided by ab initio and auxiliary-fermion mean-field calculations, we demonstrate that this behavior is inconsistent with a fully screened Kondo lattice, and suggests a ground state with magnetic order mediated by conduction electrons. The manifestation of magnetic coherence in TMD-based 2D Kondo lattices enables the exploration of magnetic quantum criticality, Kondo breakdown transitions and unconventional superconductivity in the strict two-dimensional limit.