Magnetic Impurity as a Local Probe of the U(1) Quantum Spin Liquid with Spinon Fermi Surface

TL;DR

This paper investigates how a magnetic impurity can serve as a probe to identify a U(1) quantum spin liquid with a spinon Fermi surface by analyzing impurity spectral functions.

Contribution

It introduces a theoretical framework combining slave rotor mean field and gauge field fluctuations to analyze impurity spectral functions in such spin liquids.

Findings

Peaks at Hubbard band edges indicate gauge field fluctuation effects.

Impurity spectral features serve as signatures of U(1) quantum spin liquids.

The approach links impurity spectra to the host's quantum spin liquid state.

Abstract

We solve the problem of a magnetic impurity coupled to a U(1) quantum spin liquid with spinon Fermi surface and compute the impurity spectral function. Using the slave rotor mean field approach combined with gauge field fluctuations, we find that a peak located at the top of the lower Hubbard band and one at the bottom of the upper Hubbard band can emerge in the impurity spectral function. The peaks at the Hubbard band edges arise from the gauge field fluctuations induced spinon chargon binding inside the spinon Kondo screening cloud of the magnetic impurity. For a magnetic impurity embedded in a Mott insulator, our findings suggest that the emergence of a pair of peaks at the Hubbard band edges in the impurity density of states spectra provides strong evidence that the host Mott insulator is a U(1) quantum spin liquid with spinon Fermi surface.