Magnetic impurity in a triple-component semimetal

TL;DR

This paper explores how magnetic impurities behave in a triple-component semimetal with a flat band, revealing unique impurity responses and Kondo physics distinct from Dirac or Weyl semimetals.

Contribution

It provides a detailed analysis of impurity effects in a triple-component semimetal, including phase diagram determination and Kondo screening behavior, using multiple theoretical methods.

Findings

Distinct impurity magnetic susceptibility behavior

Modified Kondo screening due to flat band effects

Comparison with Dirac/Weyl semimetals shows unique responses

Abstract

We investigate the effects of a magnetic impurity in a multiband touching fermion system, specifically, a triple-component semimetal with a flat band, which can be realized in a family of transition metal silicides (CoSi family). When the chemical potential coincides with the flat band, it is expected that the impurity response of this system will be very different from that of an ordinary Dirac or Weyl semimetal of which the density of states at the Fermi level vanishes. We first determine the phase diagram within the mean-field approximation. Then, we study the local moment regime by employing two different methods. In the low temperature regime, the Kondo screening is analyzed by the variational wavefunction approach and the impurity contributions to the magnetic susceptibility and heat capacity are obtained, while at higher temperature, we use the equation of motion approach to calculate the occupation number of the impurity site and the impurity magnetic susceptibility. The results are compared and contrasted with those in the usual Fermi liquid and the Dirac/Weyl semimetals.