154 research outputs found
High Resolution Study of Spin Excitations in the Shastry-Sutherland Singlet Ground State of SrCu2(BO3)2
High resolution, inelastic neutron scattering measurements on SrCu2(BO3)2
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.Comment: 4 pages, 4 figures. Submitted to PR
Spin Waves in the Ferromagnetic Ground State of the Kagome Staircase System Co3V2O8
Inelastic neutron scattering measurements were performed on single crystal
Co3V2O8 wherein magnetic cobalt ions reside on distinct spine and cross-tie
sites within kagome staircase planes. This system displays a rich magnetic
phase diagram which culminates in a ferromagnetic ground state below Tc~6 K. We
have studied the low-lying magnetic excitations in this phase within the kagome
plane. Despite the complexity of the system at higher temperatures, linear
spin-wave theory describes most of the quantitative detail of the inelastic
neutron measurements. Our results show two spin-wave branches, the higher
energy of which displays finite spin-wave lifetimes well below Tc, and
negligible magnetic exchange coupling between Co moments on the spine sites.Comment: 4 pages and 4 figure
Proximity Effect and Josephson Coupling in the SO(5) Theory of High-Tc Superconductivity
We consider proximity effect coupling in
Superconducting/Antiferromagnetic/Superconducting (S-A-S) sandwiches using the
recently developed SO(5) effective theory of high temperature
superconductivity. We find that, for narrow junctions, the A region acts like a
strong superconductor, and that there is a critical junction thickness which
depends on the effective SO(5) coupling constants and on the phase difference
across the junction, at which the A region undergoes a Freedericksz-like
transition to a state which is intermediate between superconductor and
antiferromagnet. For thick junctions, the current-phase relation is sinusoidal,
as in standard S-N-S and S-I-S junctions, but for thin junctions it shows a
sharp break in slope at the Freedericksz point.Comment: 4 pages, LATEX, 5 eps fig
Microwave Conductivity due to Impurity Scattering in a d-wave Superconductor
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
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.Comment: 5 pages, 4 figure
Frustration and Melting of Colloidal Molecular Crystals
Using numerical simulations we show that a variety of novel colloidal
crystalline states and multi-step melting phenomena occur on square and
triangular two-dimensional periodic substrates. At half-integer fillings
different kinds of frustration effects can be realized. A two-step melting
transition can occur in which individual colloidal molecules initially rotate,
destroying the overall orientational order, followed by the onset of interwell
colloidal hopping, in good agreement with recent experiments.Comment: 6 pages, 3 postscript figures. Procedings of International Conference
on Strongly Coupled Coulomb Systems, Santa Fe, 200
Ginzburg-Landau Theory for a p-Wave Sr_2RuO_4 Superconductor: Vortex Core Structure and Extended London Theory
Based on a two dimensional odd-parity superconducting order parameter for
Sr_2RuO_4 with p-wave symmetry, we investigate the single vortex and vortex
lattice structure of the mixed phase near H_{c1}. Ginzburg-Landau calculations
for a single vortex show a fourfold structure with an orientation depending on
the microscopic Fermi surface properties. The corresponding extended London
theory is developed to determine the vortex lattice structure and we find near
H_{c1} a centered rectangular vortex lattice. As the field is increased from
H_{c1} this lattice continuously deforms until a square vortex lattice is
achieved. In the centered rectangular phase the field distribution, as
measurable through \mu-SR experiments, exhibits a characteristic two peak
structure (similar to that predicted in high temperature and borocarbide
superconductors).Comment: 12 pages, 7 figure
Optical and Thermal-Transport Properties of an Inhomogeneous d-Wave Superconductor
We calculate transport properties of disordered 2D d-wave superconductors
from solutions of the Bogoliubov-de Gennes equations, and show that weak
localization effects give rise to a finite frequency peak in the optical
conductivity similar to that observed in experiments on disordered cuprates. At
low energies, order parameter inhomogeneities induce linear and quadratic
temperature dependencies in microwave and thermal conductivities respectively,
and appear to drive the system towards a quasiparticle insulating phase.Comment: 5 pages,3 figure
Superconducting Vortex with Antiferromagnetic Core
We show that a superconducting vortex in underdoped high T_c superconductors
could have an antiferromagnetic core. This type of vortex configuration arises
as a topological solution in the recently constructed SO(5) nonlinear sigma
model and in Ginzburg-Landau theory with competing antiferromagnetic and
superconducting order parameters. Experimental detection of this type of vortex
by \mu SR and neutron scattering is proposed.Comment: revised version; 4 pages, LaTeX, 3 encapsulated postscript figures,
submitted to Phys. Rev. Let
Spontaneous Quantum Hall Effect in chiral d-density waves
We study the electromagnetic response of a chiral
charge density wave state. Due to parity () and time reversal () violation, Chern-Simons terms emerge in the effective action of the U(1)
gauge field. As a consequence electric and magnetic fields are coupled
providing the possibility of observing the Spontaneous Quantum Hall Effect i.e.
generation of Hall voltage via the sole application of an electric field. We
show how the Chern-Simons terms are induced and discuss the topological origin
of the quantization of Hall conductance.Comment: Published versio
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