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

Abstract

KCuCl3 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 KCuCl3. 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.

Critical behavior of Tan’s contact for bosonic systems with a fixed chemical potential

“…Very recently, Matsumoto et al [60] developed a theoretical description of singlet-triplet transitions in spin gapped magnet KCuCl 3 in the framework of spin-wave theory, and proposed practical formulas for the transition probabilty W, using Fermi's golden rule (see e.g. equation (18) of reference [60]). We surmise that if one uses an effective Hamiltonian similar to equation (2.1) the transition probability from reference [60] can be related to the Tan's contact as in equation (B.1), and hence one will be able to obtain C from measurements of W, using proper normalization of observed quantities.…”

“…equation (18) of reference [60]). We surmise that if one uses an effective Hamiltonian similar to equation (2.1) the transition probability from reference [60] can be related to the Tan's contact as in equation (B.1), and hence one will be able to obtain C from measurements of W, using proper normalization of observed quantities.…”

“…The direct transition between the spin singlet and triplet states is, in principle, forbidden in magnetic dipole transitions. Nonetheless, such transitions have been observed in many spin gapped systems by means of high frequency electron spin resonance measurements [57][58][59][60]. It was shown that, these transitions are, in fact, driven by ac electric fields, and observed electric dipole transitions can be explained by spin dependent polarization.…”

“…It was shown that, these transitions are, in fact, driven by ac electric fields, and observed electric dipole transitions can be explained by spin dependent polarization. Very recently, Matsumoto et al [60] developed a theoretical description of singlet-triplet transitions in spin gapped magnet KCuCl 3 in the framework of spin-wave theory, and proposed practical formulas for the transition probabilty W, using Fermi's golden rule (see e.g. equation (18) of reference [60]).…”