Camelback-shaped band reconciles heavy electron behavior with weak electronic Coulomb correlations in superconducting TlNi2Se2

TL;DR

This study reveals that TlNi2Se2 exhibits heavy electron behavior due to a van Hove singularity caused by a camelback-shaped band, despite having weak electronic Coulomb correlations, reconciling its heavy effective mass with its weak interactions.

Contribution

The paper demonstrates that a camelback-shaped band near the Fermi level explains heavy electron behavior in TlNi2Se2 without strong correlations, combining spectroscopy and calculations.

Findings

Weak Coulomb correlations with bandwidth renormalization of 1.4.

Presence of a camelback-shaped band near the Fermi level.

Heavy band mass explains large specific heat coefficient.

Abstract

Using high-resolution photoemission spectroscopy and first-principles calculations, we characterize superconducting TlNi$_2$Se$_2$ as a material with weak electronic Coulomb correlations leading to a bandwidth renormalization of 1.4. We identify a camelback-shaped band, whose energetic position strongly depends on the selenium height. While this feature is universal in transition metal pnictides, in TlNi$_2$Se$_2$ it lies in the immediate vicinity of the Fermi level, giving rise to a pronounced van Hove singularity. The resulting heavy band mass resolves the apparent puzzle of a large normal-state specific heat coefficient (Phys. Rev. Lett. 112, 207001) in this weakly correlated compound.