Collective excitations from composite orders in Kondo lattice with non-Kramers doublets

TL;DR

This paper investigates the collective excitations, specifically Goldstone modes, in a two-channel Kondo lattice with non-Kramers doublets, revealing their spectra, symmetry properties, and potential for experimental detection.

Contribution

It derives the spectra of Goldstone modes associated with composite orders in the Kondo lattice using the equation of motion and RPA, highlighting their coupling with magnetic and charge excitations.

Findings

Goldstone modes emerge from symmetry breaking in the Kondo lattice.

Spectra of modes depend on the type of composite order and symmetry considerations.

Detection of these modes can identify the underlying composite order parameter.

Abstract

Goldstone modes emerge associated with spontaneous breakdown of the continuous symmetry in the two-channel Kondo lattice, which describes strongly correlated f-electron systems with a non-Kramers doublet at each site. This paper derives the spectra of these collective modes by the equation of motion method together with the random phase approximation. The diagonal composite order breaks the SU(2) channel symmetry, and the symmetry-restoring collective mode couples with magnetic field. On the other hand, the off-diagonal or superconducting composite order breaks the gauge symmetry of conduction electrons, and the collective mode couples with charge excitations near the zone boundary. At half-filling of the conduction bands, the spectra of these two modes become identical by a shift of the momentum, owing to the SO(5) symmetry of the system. The velocity of each Goldstone mode involves not only the Fermi velocity of conduction electrons but amplitude of the mean field as a multiplying factor. Detection of the Goldstone mode should provide a way to identify the composite order parameter.