Evidence of Strong Correlations and Coherence-Incoherence Crossover in the Iron Pnictide Superconductor KFe2As2

TL;DR

This study investigates the normal-state properties of KFe2As2, revealing strong electronic correlations, a coherence-incoherence crossover, and proximity to an orbital-selective Mott transition, supported by experimental measurements and theoretical calculations.

Contribution

It provides new evidence of heavy quasiparticles and a coherence-incoherence crossover in KFe2As2, linking experimental findings with theoretical insights on orbital-selective Mott physics.

Findings

Strong enhancement of Sommerfeld coefficient and Pauli susceptibility

Evidence of a coherence-incoherence crossover due to Hund's coupling

Proximity to an orbital-selective Mott transition

Abstract

Using resistivity, heat-capacity, thermal-expansion, and susceptibility measurements we study the normal-state behavior of KFe2As2. We find that both the Sommerfeld coefficient gamma = 103 mJ mol-1 K-2 and the Pauli susceptibility chi = 4x10-4 are strongly enhanced, which confirm the existence of heavy quasiparticles inferred from previous de Haas-van Alphen and ARPES experiments. We discuss this large enhancement using a Gutzwiller slave-boson mean-field calculation, which reveals the proximity of KFe2As2 to an orbital-selective Mott transition. The temperature dependence of the magnetic susceptibility and the thermal expansion provide strong experimental evidence for the existence of a coherence-incoherence crossover, similar to what is found in heavy fermion and ruthenate compounds, due to Hund's coupling between orbitals.