First ESR Detection of Higgs Amplitude Mode and Analysis with Extended Spin-Wave Theory in Dimer System KCuCl$_3$

TL;DR

This paper reports the first detection of the Higgs amplitude mode in KCuCl₃ using high-pressure ESR measurements, supported by extended spin-wave theory analysis, revealing the role of electric dipole via vector spin chirality.

Contribution

First ESR detection of the Higgs amplitude mode in KCuCl₃, with analysis based on extended spin-wave theory incorporating vector spin chirality.

Findings

Detection of Higgs amplitude mode via ESR in KCuCl₃

Role of electric dipole explained by vector spin chirality

Analysis confirms the mode near quantum critical point

Abstract

KCuCl$_3$ is known to show a quantum phase transition from the disordered to antiferromagnetically ordered phases by applying pressure. There is a longitudinal excitation mode (Higgs amplitude mode) in the vicinity of the quantum critical point in the ordered phase. To detect the Higgs amplitude mode, high-pressure ESR measurements are performed in KCuCl$_3$. The experimental data are analyzed by the extended spin-wave theory on the basis of the vector spin chirality. We report the first ESR detection of the Higgs amplitude mode and the important role of the electric dipole described by the vector spin chirality.