Rotational Quantum Impurities in a Metal: Stability of the 2-Channel Kondo Fixed Point in a Magnetic Field

TL;DR

This paper investigates the stability of the two-channel Kondo fixed point in a three-level quantum impurity system within a metal, especially under magnetic fields, and relates findings to experimental spectra.

Contribution

It demonstrates the robustness of the 2CK fixed point against level splitting and connects theoretical analysis to experimental dI/dV spectra in quantum point contacts.

Findings

2CK fixed point remains stable over a wide parameter range

Level splitting affects the Kondo behavior in predictable ways

Theoretical results explain experimental spectra in quantum point contacts

Abstract

A three-level system with partially broken SU(3) symmetry immersed in a metal, comprised of a unique non-interacting ground state and two-fold degenerate excited states, exhibits a stable two-channel Kondo fixed point within a wide range of parameters, as has been shown in previous work. Such systems can, for instance, be realized by protons dissolved in a metal and bound in the interstitial space of the host lattice, where the degeneracy of excited rotational states is guaranteed by the space inversion symmetry of the lattice. We analyze the robustness of the 2CK fixed point with respect to a level splitting of the excited states and discuss how this may explain the behavior of the well-known dI/dV spectra measured by Ralph and Buhrman on ultrasmall quantum point contacts in a magnetic field.