Collective spin resonance excitation in the gapped itinerant multipole hidden order phase ofURu2Si2

Abstract

An attractive proposal for the hidden order (HO) in the heavy electron compound URu2Si2 is an itinerant multipole order of high rank. It is due to the pairing of electrons and holes centered on zone center and boundary, respectively in states that have maximally different total angular momentum components. Due to the pairing with commensurate zone boundary ordering vector the translational symmetry is broken and a HO quasiparticle gap opens below the transition temperature THO. Inelastic neutron scattering (INS) has demonstrated that for T < THO the collective magnetic response is dominated by a sharp spin exciton resonance at the ordering vector Q that is reminiscent of spin exciton modes found inside the gap of unconventional superconductors and Kondo insulators. We use an effective two-orbital tight binding model incorporating the crystalline electric field effect to derive closed expressions for quasiparticle bands reconstructed by the multipolar pairing terms. We show that the magnetic response calculated within that model exhibits the salient features of the resonance found in INS. We also use the calculated dynamical susceptibility to explain the low temperature NMR relaxation rate.

Optical and magnetic excitations in the underscreened quasiquartet Kondo lattice

“…Naturally for the itinerant Kondo model the above equation can only be treated numerically using Eqs. (18,25). First we recapitulate the result within the completely localized model without Kondo term but finite inter-site interaction.…”

“…(28,31) using Eqs. (18,25) as in the previous section. It is worthwhile, however, to have at least a qualitative understanding how the criticality condition for induced moment magnetism is modified under the presence of the Kondo screening and resulting 4f quasiparticle itineracy.…”

“…( 16)] and enter as well the physical (cartesian) bare susceptibilities in Eq. (18). The coefficients are determined by the composition…”

“…Likewise, the low-energy charge and spin response as represented by optical conductivity and inelastic neutron scattering (INS) can be qualitatively understood within the mean-field slave boson approach of the Kondo lattices [11][12][13][14], self-consistent perturbation theory [15], and also dynamical mean-field technique [16,17]. In particular the appearance of a collective spin exciton resonance observed in many f -electron materials (possibly superconducting or with hidden order) inside the hybridization gaps or those opened by symmetry breaking may be interpreted within this approach [18][19][20][21].…”

Hidden order and beyond: an experimental-theoretical overview of the multifaceted behavior of URu$_2$Si$_2$

“…Thalmeier et al reviewed the possibilities for an itinerant multipolar order and concluded that in particular the magnetic torque oscillations [36] exclude an (electric) hexadecapolar order parameter and hence proposed an antiferromagnetic E − type triakontadipole due to commensurate nesting over Q 0 [147,149]. Akbari and Thalmeier [150] used the two-orbital tight-binding parametrization of the DFT energy bands made by Rau and Kee [54] to construct a low energy model that describes the sharp spin excitation at Q 0 seen by INS in the framework of an itinerant E − -type triakontadipole which breaks the fourfold rotational symmetry. The orthorhobicity or nematicity that was initially concluded from the magnetic torque measurements has however not been confirmed, eliminating thus the argument in favor of this doubly-degenerate representation (E − ) of the HO parameter.…”