T. Takimoto

Signatures of hidden-order symmetry in torque oscillations, elastic constant anomalies, and field-induced moments in URu2Si2

We discuss the conclusions on the symmetry of hidden order (HO) in URu2Si2 that may be drawn from recent torque experiments in rotating magnetic field by Okazaki et al. [1]. They are very sensitive to changes in the magnetic susceptibility induced by HO. We show that the observed twofold angular torque oscillations give evidence that hidden order has degenerate E- type (yz,zx) symmetry where both components are realised. The oscillations have the wrong characteristics or are absent for the 1D nontrivial representations like quadrupolar B1 (x^2-y^2) and B2 (xy) type HO or hexadecapolar A2(xy(x^2-y^2)) type HO. Therefore they may be excluded as candidates for hidden order. We also predict the field-angular variation of possible field-induced Bragg peaks based on underlying E-type order parameter and discuss the expected elastic constant anomalies.

Triplet Cooper Pair Formation by Anomalous Spin Fluctuations in Non-centrosymmetric Superconductors

A microscopic theory for the spin triplet Cooper pairing in non-centrosymmetric superconductors like CePt 3 Si and CeTSi 3 (T = Rh, Ir) is presented. The lack of inversion symmetry leads to new anomalous spin fluctuations which stabilize the triplet part in addition to the singlet part originating from the centrosymmetric spin fluctuations. It is shown that both parts have similar nontrivial momentum dependence of A 1 type. Therefore the mixed singlet-triplet gap function has accidental line nodes on both Fermi surface sheets which are stable as function of temperature. This gap function explains the salient features of CePt 3 Si and CeTSi 3 superconductors.

Anomalous Spin Response in Non-centrosymmetric Compounds

We examine static spin susceptibilities χ αβ ( q ) of spin components S α and S β in the non-centrosymmetric tetragonal system. The anomalous susceptibility, which vanish in centrosymmetric systems, remains showing a momentum dependence like χ x x ( q )-χ y y ( q )∼ q x 2 - q y 2 and χ x y ( q )+χ y x ( q )∼ q x q y . A characteristic property of the non-centrosymmetric system is the non-vanishing anomalous susceptibility, whose momentum dependence is not invariant to some symmetry operations of the system. As the direct probe of the anomalous spin susceptibility, we propose a polarized neutron scattering experiment, especially, around an ordering wave vector.

Theory of induced quadrupolar order in tetragonal YbRu2Ge2

The tetragonal compound

Characteristic feature of dynamical susceptibility in noncentrosymmetric system

\mathrm{Yb}{\mathrm{Ru}}_{2}{\mathrm{Ge}}_{2}

Self-consistent renormalization theory of spin fluctuations in paramagnetic spinel LiV2O4

exhibits a nonmagnetic transition at

Multipolar Order and Superconductivity in f-Electron Compounds

{T}_{0}=10.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}

Low-energy spin fluctuations in the metallic spinel compound LiV2O4

and a magnetic transition at

Ferromagnetism and electronic structure of TmB2

{T}_{1}=6.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}

Low-temperature electrical resistivity in paramagnetic spinel LiV2O4

in zero magnetic field. We present a model for this material based on a quasiquartet of