A. J. Berlinsky

VORTEX STATE IN A D-WAVE SUPERCONDUCTOR

We discuss the physics of the vortex state in a {ital d}-wave superconductor, using the phenomenological Ginzburg-Landau theory, where many unusual phenomena arise from the small admixture of the {ital s}-wave component induced by spatial variations in the dominant {ital d} wave. Properties of an isolated vortex and of the Abrikosov vortex lattice are studied by means of analytic and numerical methods. An isolated vortex has a considerable structure, with four {open_quote}{open_quote}extra{close_quote}{close_quote} nodes in the {ital s}-wave order parameter symmerically placed around the core and an amplitude forming a four-lobe profile decaying as 1/{ital r}{sup 2} at large distances. The supercurrent and magnetic-field distributions are also calculated. The Abrikosov lattice is in general oblique with the precise shape determined by the magnetic field and {ital s}-{ital d} mixing parameter {epsilon}{sub {ital v}}. The magnetic-field distribution in the Abrikosov state has two nonequivalent saddle points resulting in the prediction of a double peak line shape in {mu}SR and NMR experiments as a test of a {ital d}-wave symmetry. Detailed comparison is made with existing experimental data and experiments are proposed to test for the predicted effects. {copyright} {ital 1996 The American Physical Society.}

Impurity scattering and localization in d-wave superconductors.

Strong evidence is presented for the localization of low-energy quasiparticle states in disordered

High-resolution study of spin excitations in the singlet ground state of SrCu2(BO3)2.

d

Microwave conductivity due to impurity scattering in ad-wave superconductor

-wave superconductors. Within the framework of the Bogoliubov-de Gennes (BdG) theory applied to the extended Hubbard model with a finite concentration of nonmagnetic impurities, we carry out a fully self-consistent numerical diagonalization of the BdG equations on finite clusters containing up to 50\ifmmode\times\else\texttimes\fi{}50 sites. Localized states are identified by probing their sensitivity to the boundary conditions and by analyzing the finite-size dependence of inverse participation ratios.

Ordering and spin waves in Na Ni O 2 : A stacked quantum ferromagnet

High-resolution, inelastic neutron scattering measurements on SrCu2(BO3)2, a realization of the Shastry-Sutherland model for two-dimensional Heisenberg antiferromagnets, reveal the dispersion of the three single triplet excitations continuously across the (H,0) direction within its tetragonal basal plane. These measurements also show distinct Q dependencies for the single and multiple triplet excitations, and that these excitations are largely dispersionless perpendicular to this plane. The temperature dependence of the intensities of these excitations is well described as the complement of the dc susceptibility of SrCu2(BO3)2.

Spin-lattice relaxation in the mixed state of YBa 2 Cu 3 O 7 − δ and Doppler-shifted d − wave quasiparticles

The self-consistent t-matrix approximation for impurity scattering in unconventional superconductors is used to interpret recent measurements of the temperature and frequency dependence of the microwave conductivity of YBCO crystals below 20K. In this theory, the conductivity is expressed in terms of a fequency dependent single particle self-energy, determined by the impurity scattering phase shift which is small for weak (Born) scattering and approaches

Spin-lattice relaxation in the mixed state of YBaCuO: Can we see Doppler-shifted d-wave quasiparticles?

\pi / 2

TWIN BOUNDARIES IN D-WAVE SUPERCONDUCTORS

for unitary scattering. Inverting this process, microwave conductivity data are used to extract an effective single-particle self-energy and obtain insight into the nature of the operative scattering processes. It is found that the effective self-energy is well approximated by a constant plus a linear term in frequency with a small positive slope for thermal quasiparticle energies below 20K. Possible physical origins of this form of self-energy are discussed.

Computer simulations of flux pinning and flux flow in two dimensions

Neutron scattering measurements on powder

Minimizers of the Lawrence-Doniach energy in the small-coupling limit : finite width samples in a parallel field

\mathrm{Na}\mathrm{Ni}{\mathrm{O}}_{2}