Collective spin resonance excitation in the gapped itinerant multipole hidden order phase of URu2Si2

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 T_HO. Inelastic neutron scattering (INS) has demonstrated that for T<T_HO 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.Comment: 13 pages, 8 figure

Gap function of hexagonal pnictide superconductor SrPtAs from quasiparticle interference spectrum

The pnictide superconductor SrPtAs has a hexagonal layered structure containing inversion symmetry. It is formed by stacking two inequivalent PtAs layers separated by Sr layers. The former have no local (in-plane) inversion symmetry and therefore a (layer-) staggered Rashba spin orbit coupling appears which splits the three Kramers degenerate bands into six quasi-2D bands. The symmetry of the superconducting state of SrPtAs is unknown. Three candidates, spin-singlet $A_{1g}$ and $E_g$ as well as triplet $A_{2u}$ states have been proposed. We predict the quasiparticle interference (QPI) spectrum for these gap functions in t-matrix Born approximation. We show that distinct differences in the pattern of characteristic QPI wave vectors appear. These results may be important to determine the gap symmetry of SrPtAs by STM-QPI method.Comment: 5 pages, 4 figure

Inelastic magnetic scattering effect on LDOS of topological insulators

Magnetic ions such as Fe, Mn and Co with localized spins may be adsorbed on the surface of topological insulators like \Bi. They form scattering centers for the helical surface states which have a Dirac cone dispersion as long as the local spins are disordered. However, the local density of states (LDOS) may be severely modified by the formation of bound states. Commonly only elastic scattering due to normal and exchange potentials of the adatom is assumed. Magnetization measurements show, however, that considerable magnetic single ion anisotropies exist which lead to a splitting of the local impurity spin states resulting in a singlet ground state. Therefore inelastic scattering processes of helical Dirac electrons become possible as described by a dynamical local self energy of second order in the exchange interaction. The self energy influences bound state formation and leads to significant new anomalies in the LDOS at low energies and low temperatures which we calculate within T-matrix approach. We propose that they may be used for spectroscopy of local impurity spin states by appropriate tuning of chemical potential and magnetic field.Comment: 10 pages, 9 figures; published version; Fig.9b and five references adde

Multiorbital and hybridization effects in the quasiparticle interference of triplet superconductor Sr2RuO4

The tetragonal compound Sr2RuO4 exhibits a chiral p-wave superconducting (SC) state of its three t2g-type conduction bands. The characteristics of unconventional gap structure are known from experiment, in particular field-angle resolved specific heat measurements and from microscopic theories. A rotated extremal structure on the main active SC band with respect to the nodal gaps on the passive bands was concluded. We propose that this gap structure can be further specified by applying the STM- quasiparticle interference (QPI) method. We calculate the QPI spectrum within a three band and chiral three gap model and give closed analytical expressions. We show that as function of bias voltage the chiral three gap model will lead to characteristic changes in QPI that may be identified and may be used for more quantitative gap determination of the chiral gap structure.Comment: 9 pages, 5 figure

Dynamics of Quantum Coherence and Quantum Fisher Information After Sudden Quench

The dynamics of relative entropy and $l_{1}$-norm of coherence, as well as, the Wigner-Yanase-skew and quantum Fisher information are studied for a time-dependent coupled XY spin chain in presence of a time-dependent transverse magnetic field. Independent of the initial state of the system and while the relative entropy of coherence, $l_{1}$-norm of coherence, and quantum Fisher information are incapable, surprisingly, the dynamic Wigner-Yanase-skew information can truly spotlight the equilibrium critical point. We also observe that when the system is quenched to the critical point, these quantities show suppressions and revivals. Moreover, the first suppression (revival) time scales linearly with the system size and its scaling ratio is unique for all quenches independent to the initial phase. This is the promised universality of the first suppression (revival) time.Comment: 8 pages, 8 figures; to appear in Phys. Rev.

Field induced spin exciton doublet splitting in d_{x^2-y^2}-wave 115-heavy electron superconductors

We investigate the spin-exciton modes in the superconducting d_{x^2-y^2} state of CeMIn_5 heavy fermion compounds found at the antiferromagnetic wave vector by inelastic neutron scattering. We present a theoretical model that explains the field dependence for both field directions. We show that the recently observed splitting of the spin exciton doublet in CeCoIn_5 into two non-degenerate modes for in-plane field appears naturally in this model. This is due to the spin anisotropy of g- factors and quasiparticle interactions which lead to different resonant conditions for the dynamic susceptibility components. We predict that the splitting of the spin resonance doublet becomes strongly nonlinear for larger fields when the energy of both split components decreases. For field along the tetragonal axis no splitting but only a broadening of the resonance is found in agreement with experiment.Comment: 8 pages, 5 figure

Full t-matrix approach to quasiparticle interference in non-centrosymmetric superconductors

We develop the full t-matrix theory of quasiparticle interference (QPI) for non-centrosymmetric (NCS) superconductors with Rashba spin-orbit coupling. We give a closed solution for the QPI spectrum for arbitrary combination and strength of nonmagnetic (Vc) and magnetic (Vm) impurity scattering potentials in terms of integrated normal and anomalous Green's functions. The theory is applied to a realistic 2D model of the Ce-based 131- type heavy fermion superconductors. We discuss the QPI dependence on frequency, composition and strength of scattering and compare with Born approximation results. We show that the QPI pattern is remarkably stable against changes in the scattering model and can therefore give reliable information on the properties of Rashba-split Fermi surface sheets and in particular on the accidental nodal position of the mixed singlet-triplet gap function in NCS superconductors.Comment: 12 pages, 7 figure

Spin Exciton Formation inside the Hidden Order Phase of CeB6

The heavy fermion metal CeB6 exhibits hidden order of antiferroquadrupolar (AFQ) type below T_Q=3.2K and subsequent antiferromagnetic (AFM) order at T_N=2.3K. It was interpreted as ordering of the quadrupole and dipole moments of a $\Gamma_8$ quartet of localised Ce $4f^1$ electrons. This established picture has been profoundly shaken by recent inelastic neutron scattering (G. Friemel et al., arXiv:1111.4151) that found the evolution of a feedback spin exciton resonance within the hidden order phase at the AFQ wave vector which is stabilized by the AFM order. We develop an alternative theory based on a fourfold degenerate Anderson lattice model, including both order parameters as particle-hole condensates of itinerant heavy quasiparticles. This explains in a natural way the appearance of the spin exciton resonance and the momentum dependence of its spectral weight, in particular around the AFQ vector and its rapid disappearance in the disordered phase. Analogies to the feedback effect in unconventional heavy fermion superconductors are pointed out.Comment: 5 pages, 3 figure

Disordered Kitaev chain with long-range pairing: Loschmidt echo revivals and dynamical phase transitions

We explore the dynamics of long-range Kitaev chain by varying pairing interaction exponent, $\alpha$. It is well known that distinctive characteristics on the nonequilibrium dynamics of a closed quantum system are closely related to the equilibrium phase transitions. Specifically, the return probability of the system to its initial state (Loschmidt echo), in the finite size system, is expected to exhibit very nice periodicity after a sudden quench to a quantum critical point. Where the periodicity of the revivals scales inversely with the maximum of the group velocity. We show that, contrary to expectations, the periodicity of the return probability breaks for a sudden quench to the non-trivial quantum critical point. Further, We find that, the periodicity of return probability scales inversely with the group velocity at the gap closing point for a quench to the trivial critical point of truly long-range pairing case, $\alpha < 1$. In addition, analyzing the effect of averaging quenched disorder shows that the revivals in the short range pairing cases are more robust against disorder than that of the long rang pairing case. We also study the effect of disorder on the non-analyticities of rate function of the return probability which introduced as a witness of the dynamical phase transition. We exhibit that, the non-analyticities in the rate function of return probability are washed out in the presence of strong disorders.Comment: 13+ pages, 8 figures, new results adde