3,233 research outputs found
The Structure of the Vortex Liquid at the Surface of a Layered Superconductor
A density-functional approach is used to calculate the inhomogeneous vortex
density distribution in the flux liquid phase at the planar surface of a
layered superconductor, where the external magnetic field is perpendicular to
the superconducting layers and parallel to the surface. The interactions with
image vortices are treated within a mean field approximation as a functional of
the vortex density. Near the freezing transition strong vortex density
fluctuations are found to persist far into the bulk liquid. We also calculate
the height of the Bean-Livingston surface barrier.Comment: 8 pages, RevTeX, 2 figure
Dependence of the BEC transition temperature on interaction strength: a perturbative analysis
We compute the critical temperature T_c of a weakly interacting uniform Bose
gas in the canonical ensemble, extending the criterion of condensation provided
by the counting statistics for the uniform ideal gas. Using ordinary
perturbation theory, we find in first order , where T_c^0 is the transition temperature of the corresponding
ideal Bose gas, a is the scattering length, and is the particle number
density.Comment: 14 pages (RevTeX
Temperature Dependence of the Cu(2) NQR Line Width in YBaCuO
Systematic measurements of the Cu(2) NQR line width were performed in
underdoped YBaCuO samples over the temperature range 4.2 K
K. It was shown that the copper NQR line width monotonically increases
upon lowering temperature in the below-critical region, resembling temperature
behavior of the superconducting gap. The observed dependence is explained by
the fact that the energy of a condensate of sliding charge-current states of
the charge-density-wave type depends on the phase of order parameter.
Calculations show that this dependence appears only at . Quantitative
estimates of the line broadening at agree with the measurement results.Comment: 4 pages, 2 figure
Incipient charge order observed by NMR in the normal state of YBa2Cu3Oy
The pseudogap regime of high-temperature cuprates harbours diverse
manifestations of electronic ordering whose exact nature and universality
remain debated. Here, we show that the short-ranged charge order recently
reported in the normal state of YBa2Cu3Oy corresponds to a truly static
modulation of the charge density. We also show that this modulation impacts on
most electronic properties, that it appears jointly with intra-unit-cell
nematic, but not magnetic, order, and that it exhibits differences with the
charge density wave observed at lower temperatures in high magnetic fields.
These observations prove mostly universal, they place new constraints on the
origin of the charge density wave and they reveal that the charge modulation is
pinned by native defects. Similarities with results in layered metals such as
NbSe2, in which defects nucleate halos of incipient charge density wave at
temperatures above the ordering transition, raise the possibility that
order-parameter fluctuations, but no static order, would be observed in the
normal state of most cuprates if disorder were absent.Comment: Updated version. Free download at Nature Comm. website (doi below
Atomtronics: ultracold atom analogs of electronic devices
Atomtronics focuses on atom analogs of electronic materials, devices and
circuits. A strongly interacting ultracold Bose gas in a lattice potential is
analogous to electrons in solid-state crystalline media. As a consequence of
the band structure, cold atoms in a lattice can exhibit insulator or conductor
properties. P-type and N-type material analogs can be created by introducing
impurity sites into the lattice. Current through an atomtronic wire is
generated by connecting the wire to an atomtronic battery which maintains the
two contacts at different chemical potentials. The design of an atomtronic
diode with a strongly asymmetric current-voltage curve exploits the existence
of superfluid and insulating regimes in the phase diagram. The atomtronic
analog of a bipolar junction transistor exhibits large negative gain. Our
results provide the building blocks for more advanced atomtronic devices and
circuits such as amplifiers, oscillators and fundamental logic gates
Quantized Vortex States of Strongly Interacting Bosons in a Rotating Optical Lattice
Bose gases in rotating optical lattices combine two important topics in
quantum physics: superfluid rotation and strong correlations. In this paper, we
examine square two-dimensional systems at zero temperature comprised of
strongly repulsive bosons with filling factors of less than one atom per
lattice site. The entry of vortices into the system is characterized by jumps
of 2 pi in the phase winding of the condensate wavefunction. A lattice of size
L X L can have at most L-1 quantized vortices in the lowest Bloch band. In
contrast to homogeneous systems, angular momentum is not a good quantum number
since the continuous rotational symmetry is broken by the lattice. Instead, a
quasi-angular momentum captures the discrete rotational symmetry of the system.
Energy level crossings indicative of quantum phase transitions are observed
when the quasi-angular momentum of the ground-state changes.Comment: 12 Pages, 13 Figures, Version
Heavy Quark Production and PDF's Subgroup Report
We present a status report of a variety of projects related to heavy quark
production and parton distributions for the Tevatron Run II.Comment: Latex. 8 pages, 7 eps figures. Contribution to the Physics at Run II
Workshops: QCD and Weak Boson Physic
Thermodynamics of the Spin Luttinger-Liquid in a Model Ladder Material
The phase diagram in temperature and magnetic field of the metal-organic,
two-leg, spin-ladder compound (C5H12N)2CuBr4 is studied by measurements of the
specific heat and the magnetocaloric effect. We demonstrate the presence of an
extended spin Luttinger-liquid phase between two field-induced quantum critical
points and over a broad range of temperature. Based on an ideal spin-ladder
Hamiltonian, comprehensive numerical modelling of the ladder specific heat
yields excellent quantitative agreement with the experimental data across the
complete phase diagram.Comment: 4 pages, 4 figures, updated refs and minor changes to the text,
version accepted for publication in Phys. Rev. Let
- âŠ