43 research outputs found
Vortex Dynamics and the Hall-Anomaly: a Microscopic Analysis
We present a microscopic derivation of the equation of motion for a vortex in
a superconductor. A coherent view on vortex dynamics is obtained, in which {\it
both} hydrodynamics {\it and} the vortex core contribute to the forces acting
on a vortex. The competition between these two provides an interpretation of
the observed sign change in the Hall angle in superconductors with mean free
path of the order of the coherence length in terms of broken
particle-hole symmetry, which is related to details of the microscopic
mechanism of superconductivity.Comment: 12 pages, late
Derivation of the transverse force on a moving vortex in a superfluid
We describe an exact derivation of the total nondissipative transverse force
acting on a quantized vortex moving in a uniform background. The derivation is
valid for neutral boson or fermion superfluids, provided the order parameter is
a complex scalar quantity. The force is determined by the one-particle density
matrix far away from the vortex core, and is found to be the Magnus force
proportional to the superfluid density.Comment: Latex, 6 page
Universal scaling of the Hall resistivity in MgB2 superconductors
The mixed-state Hall resistivity and the longitudinal resistivity in
superconducting MgB2 thin films have been investigated as a function of the
magnetic field over a wide range of current densities from 100 to 10000 A/cm^2.
We observe a universal Hall scaling behavior with a constant exponent of 2.0,
which is independent of the magnetic field, the temperature, and the current
density. This result can be interpreted well within the context of recent
theories.Comment: 4 page
Phase diagram of turbulence in superfluid 3He-B
In superfluid 3He-B mutual-friction damping of vortex-line motion decreases
roughly exponentially with temperature. We record as a function of temperature
and pressure the transition from regular vortex motion at high temperatures to
turbulence at low temperatures. The measurements are performed with
non-invasive NMR techniques, by injecting vortex loops into a long column in
vortex-free rotation. The results display the phase diagram of turbulence at
high flow velocities where the transition from regular to turbulent dynamics is
velocity independent. At the three measured pressures 10.2, 29.0, and 34 bar,
the transition is centered at 0.52--0.59Tc and has a narrow width of 0.06Tc
while at zero pressure turbulence is not observed above 0.45Tc.Comment: To be published in J. Low Temp. Phys. (QFS2004 proceedings
Quasiparticle spectrum of d-wave superconductors in the mixed state: a large Fermi-velocity anisotropy study
The quasiparticle spectrum of a two-dimensional d-wave superconductor in the
mixed state, H_c1 << H << H_c2, is studied for large values of the ``anisotropy
ratio'' alpha_D = v_F/v_Delta. For a square vortex lattice rotated by 45
degrees from the quasiparticle anisotropy axes (and the usual choice of
Franz--Tesanovic singular gauge transformation) we determine essential features
of the band structure asymptotically for large alpha_D, using an effective
one-dimensional model, and compare them to numerical calculations. We find that
several features of the band structure decay to zero exponentially fast for
large alpha_D. Using a different choice of singular gauge transformation, we
obtain a different band structure, but still find qualitative agreement between
the 1D and full 2D calculations. Finally, we distort the square lattice into a
non-Bravais lattice. Both the one- and two-dimensional numerical calculations
of the energy spectra show a gap around zero-energy, with our gauge choice, and
the two excitation spectra agree reasonably well.Comment: 14 pages, 13 figures, revte
Magnetic field effects on the density of states of orthorhombic superconductors
The quasiparticle density of states in a two-dimensional d-wave
superconductor depends on the orientation of the in-plane external magnetic
field H. This is because. in the region of the gap nodes, the Doppler shift due
to the circulating supercurrents around a vortex depend on the direction of H.
For a tetragonal system the induced pattern is four-fold symmetric and, at zero
energy, the density of states exhibits minima along the node directions. But
YBa_2C_3O_{6.95} is orthorhombic because of the chains and the pattern becomes
two-fold symmetric with the position of the minima occuring when H is oriented
along the Fermi velocity at a node on the Fermi surface. The effect of impurity
scattering in the Born and unitary limit is discussed.Comment: 24 pages, 11 Figure
Transition to Superfluid Turbulence
Turbulence in superfluids depends crucially on the dissipative damping in
vortex motion. This is observed in the B phase of superfluid 3He where the
dynamics of quantized vortices changes radically in character as a function of
temperature. An abrupt transition to turbulence is the most peculiar
consequence. As distinct from viscous hydrodynamics, this transition to
turbulence is not governed by the velocity-dependent Reynolds number, but by a
velocity-independent dimensionless parameter 1/q which depends only on the
temperature-dependent mutual friction -- the dissipation which sets in when
vortices move with respect to the normal excitations of the liquid. At large
friction and small values of 1/q < 1 the dynamics is vortex number conserving,
while at low friction and large 1/q > 1 vortices are easily destabilized and
proliferate in number. A new measuring technique was employed to identify this
hydrodynamic transition: the injection of a tight bundle of many small vortex
loops in applied vortex-free flow at relatively high velocities. These vortices
are ejected from a vortex sheet covering the AB interface when a two-phase
sample of 3He-A and 3He-B is set in rotation and the interface becomes unstable
at a critical rotation velocity, triggered by the superfluid Kelvin-Helmholtz
instability.Comment: Short review; to be published in Journal of Low Temperature Physics
(2006
Vortex with Fractional Quantum Numbers in Chiral p-Wave Superconductor
We show that a vortex in a chiral p-wave superconductor, which has the p_{x}+
i p_{y}-wave pairing state and breaks U(1), parity and time reversal symmetry
simultaneously, has fractional charge -{n e}/{4} and fractional angular
momentum -n^{2}/{16} (n; vorticity). This suggests that the vortex could be
anyon and could obey fractional statistics. Electromagnetic property of the
vortex is also discussed and we find that an electric field is induced near the
vortex core.Comment: 10 pages, 3 figures, accepted for publication in Phys. Rev.