W. C. Wu

Quantum critical metamagnetism of Sr3Ru2O7 under hydrostatic pressure

Using ac susceptibility, we have determined the pressure dependence of the metamagnetic critical endpoint temperature T⊃* for a field applied in the ab plane in the itinerant metamagnet Sr3Ru2O 7. We find that T⊃* falls monotonically to zero as pressure increases, producing a quantum critical endpoint (QCEP) at P c~13.6±0.2kbar. New features are observed near the QCEP-the slope of T⊃* versus pressure changes at ~12.8 kbar, and weak subsidiary maxima appear on either side of the main susceptibility peak at pressures near Pc-indicating that some new physics comes into play near the QCEP. Clear signatures of a nematic phase, however, that were seen in field-angle tuning of T⊃* are not observed. As T⊃* is suppressed by pressure, the metamagnetic peak in the susceptibility remains sharp as a function of an applied magnetic field. As a function of temperature, however, the peak becomes broad with only a very weak maximum, suggesting that, near the QCEP, the uniform magnetization density is not the order parameter for the metamagnetic transition.

Quantized hydrodynamic model and the dynamic structure factor for a trapped Bose gas

We quantize the recent hydrodynamic analysis of Stringari for the low-energy collective modes of a trapped Bose gas at T=0. This is based on the time-dependent Gross-Pitaevskii equation, but omits the kinetic energy of the density fluctuations. We diagonalize the hydrodynamic Hamiltonian in terms of the normal modes associated with the amplitude and phase of the inhomogeneous Bose order parameter. These normal modes provide a convenient basis for calculating observable quantities. As applications, we calculate the depletion of the condensate at T=0 as well as the inelastic light-scattering cross section S(q,\ensuremath{\omega}) from low-energy condensate fluctuations. The latter involves a sum over all normal modes, with a weight proportional to the square of the q Fourier component of the density fluctuation associated with a given mode. Finally, we show how the Thomas-Fermi hydrodynamic description can be derived starting from the coupled Bogoliubov equations. \textcopyright{} 1996 The American Physical Society.

Spin-State Transition in the Fe Pnictides

We report an Fe Kβ x-ray emission spectroscopy study of local magnetic moments in the rare-earth doped iron pnictide Ca(1-x)RE(x)Fe(2)As(2) (RE = La, Pr, and Nd). In all samples studied the size of the Fe local moment is found to decrease significantly with temperature and goes from ∼ 0.9 μ(B) at T = 300 K to ∼ 0.45 μ(B) at T = 70 K. In the collapsed tetragonal phase of Nd- and Pr-doped samples (T<70 K) the local moment is quenched, while the moment remains unchanged for the La-doped sample, which does not show lattice collapse. Our results show that Ca(1-x)RE(x)Fe(2)As(2) (RE = Pr and Nd) exhibits a spin-state transition and provide direct evidence for a nonmagnetic Fe(2+) ion in the collapsed tetragonal phase; spin state as predicted by Yildirim. We argue that the gradual change of the spin state over a wide temperature range reveals the importance of multiorbital physics, in particular the competition between the crystal field split Fe 3d orbitals and the Hunds rule coupling.

Gap-function symmetry and spin dynamics in electron-doped cuprate superconductors

An antiferromagnetic (AF) spin fluctuation induced pairing model is proposed for the electron-doped cuprate superconductors. It suggests that, similar to the hole-doped side, the superconducting gap function is monotonic d(x)(2)-y(2) wave and explains why the observed gap function has a nonmonotonic d(x)(2)-y(2)-wave behavior when an AF order is taken into account. Dynamical spin susceptibility is calculated and shown to be in good agreement with the experiment. This gives a strong support to the proposed model.

Transport and the order parameter of superconducting Sr2RuO4

Recent experiments make it appear more likely that the order parameter of the unconventional superconductor

Vortices in a rotating Bose-Einstein condensate under extreme elongation in a harmonic plus quartic trap

{\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}

Two-band model of Raman scattering on electron-doped high- Tc superconductors

has a spin-triplet f-wave symmetry. We study ultrasonic absorption and thermal conductivity of superconducting

Universal zero-frequency Raman slope in a d-wave superconductor

{\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}

Pseudospin orders in the supersolid phases in binary Rydberg-dressed Bose-Einstein condensates

and fit to the recent data for various f-wave candidates. It is shown that only

Quantum crystals in a trapped Rydberg-dressed Bose-Einstein condensate

{f}_{{x}^{2}\ensuremath{-}{y}^{2}}