Anomalous Local Fermi Liquid in $f^{2}$-Singlet Configuration: Impurity Model for Heavy-Electron System UPt_3

TL;DR

This paper demonstrates through numerical methods that a specific impurity model with a singlet ground state exhibits an anomalous Fermi liquid behavior, explaining peculiar experimental observations in UPt_3.

Contribution

It introduces a new impurity model for heavy-electron systems that explains anomalous Fermi liquid behavior observed in UPt_3, highlighting anisotropic Fermi liquid corrections.

Findings

Static magnetic susceptibility remains uncorrelated.

NMR relaxation rate is enhanced proportionally to the square of the mass enhancement.

The Korringa-Shiba relation is broken.

Abstract

It is shown by the Wilson numerical renormalization group method that a strongly correlated impurity with a crystalline-electric-field singlet ground state in the f^2-configuration exhibits an anomalous local Fermi liquid state in which the static magnetic susceptibility remains an uncorrelated value while the NMR relaxation rate is enhanced in proportion to the square of the mass enhancement factor. Namely, the Korringa-Shiba relation is apparently broken. This feature closely matches the anomalous behaviors observed in UPt_3, i.e., the coexistence of an unenhanced value of the Knight shift due to quasiparticles contribution (the decrease across the superconducting transition) and the enhanced relaxation rate of NMR. Such an anomalous Fermi liquid behavior suggests that the Fermi liquid corrections for the susceptibility are highly anisotropic.