Nature of the unconventional heavy fermion Kondo state in monolayer CeSiI

TL;DR

This paper investigates the unique heavy-fermion Kondo state in monolayer CeSiI, revealing a multipolar magnetic texture and an unconventional momentum-dependent Kondo screening mechanism through first-principles and novel theoretical methods.

Contribution

It introduces a fractional pseudofermion approach combined with ab initio calculations to analyze the Kondo state in ultrathin CeSiI, highlighting its unconventional magnetic and electronic properties.

Findings

CeSiI exhibits a multipolar magnetic texture with near-zero net moment.

The Kondo-screened state is momentum-dependent and unconventional.

Magnetic exchange interactions influence the heavy-fermion order.

Abstract

CeSiI has been recently isolated in the ultrathin limit, establishing CeSiI as the first intrinsic two-dimensional van der Waals heavy-fermion material up to 85 K. We show that, due to the strong Ce spin-orbit coupling, the local moments develop a multipolar real-space magnetic texture, leading to local pseudospins with a nearly vanishing net moment. To elucidate its Kondo-screened regime, we extract from first principles the parameters of the Kondo lattice model describing this material. We develop a fractional pseudofermion methodology in combination with ab initio calculations to reveal the nature of the Kondo-screened heavy fermion state in CeSiI. Using this formalism, we analyze the competing magnetic interactions leading to a heavy-fermion order as a function of the magnetic exchange between the localized f-electrons and the strength of the Kondo coupling. Our results show that the magnetic exchange interactions promote an unconventional momentum-dependent heavy-fermion Kondo screened phase, establishing the nature of the heavy-fermion behavior of ultrathin CeSiI observed experimentally.