J. A. Janik

Gapped itinerant spin excitations account for missing entropy in the hidden-order state of URu 2 Si 2

Gapped itinerant spin excitations account for missing entropy in the hidden-order state of URu 2 Si 2

Itinerant spin excitations near the hidden order transition in URu2Si2

By means of neutron scattering we show that the high temperature precursor to the hidden order state of the heavy fermion superconductor URu(2)Si(2) exhibits heavily damped incommensurate paramagnons whose strong energy dispersion is very similar to that of the long-lived longitudinal f spin excitations that appear below T(0). This suggests that there is a strongly hybridized character to the itinerant excitations observed previously above the hidden order transition. Here we present evidence that the itinerant excitations, like those in chromium, are due to Fermi surface nesting of hole and electron pockets; hence the hidden order phase probably originates from a Fermi surface instability. We identify wavevectors that span nested regions of a f-d hybridized band calculation and that match the neutron spin crossover from incommensurate to commensurate on approach to the hidden order phase.

Impurity-induced singlet breaking in SrCu2(BO3)2

We have performed muon spin relaxation

Doping through the percolation limit in GeNi2−xCoxO4

(\ensuremath{\mu}\mathrm{SR})

Partial Field-Induced Magnetic Order in the Spin-Liquid Kagome Nd{sub 3}Ga{sub 5}SiO{sub 14}

studies on single crystals of

Relief of frustration through spin disorder in multiferroic Ho1- xYxMnO3

\mathrm{Sr}{\mathrm{Cu}}_{2}{(\mathrm{B}{\mathrm{O}}_{3})}_{2}

Dynamic Spin Ice : Pr2Sn2O7

, a quasi-two-dimensional spin system with a spin-singlet ground state. We find evidence for two different muon sites which we associate with muons located adjacent to the two inequivalent O sites. One site, presumably located in the Cu-O-Cu superexchange path, exhibits a large increase in the frequency shift with decreasing temperature which is unaffected by the onset of the singlet ground state, indicating that the muon has perturbed the Cu-Cu interaction and created two quasifree spins. We have also performed

Specific heat of geometrically frustrated and multiferroic R Mn 1 − x Ga x O 3 ( R = Ho , Y )

\ensuremath{\mu}\mathrm{SR}

Spin glass transitions in the absence of chemical disorder for the pyrochlores A2Sb2O7 (A=Mn, Co, Ni)

on single crystals of

Anisotropic superconductivity in bulkCaC6

\mathrm{Sr}{\mathrm{Mg}}_{0.05}{\mathrm{Cu}}_{1.95}{(\mathrm{B}{\mathrm{O}}_{3})}_{2}