148 research outputs found
Quantum, Multi-Body Effects and Nuclear Reaction Rates in Plasmas
Detailed calculations of the contribution from off-shell effects to the
quasiclassical tunneling of fusing particles are provided. It is shown that
these effects change the Gamow rates of certain nuclear reactions in dense
plasma by several orders of magnitude.Comment: 11 pages; change of content: added clarification of one of the
important steps in the derivatio
Detecting D-Wave Pairing and Collective Modes in Fermionic Condensates with Bragg Scattering
We show how the appearance of d-wave pairing in fermionic condensates
manifests itself in inelastic light scattering. Specifically, we calculate the
Bragg scattering intensity from the dynamic structure factor and the spin
susceptibility, which can be inferred from spin flip Raman transitions. This
information provides a precise tool with which we can identify nontrivial
correlations in the state of the system beyond the information contained in the
density profile imaging alone. Due to the lack of Coulomb effects in neutral
superfluids, this is also an opportunity to observe the Anderson-Bogoliubov
collective mode
Tunable spin transport in CrAs: role of correlation effects
Correlation effects on the electronic structure of half-metallic CrAs in
zinc-blende structure are studied for different substrate lattice constants.
Depending on the substrate the spectral weight of the non-quasiparticle states
might be tuned from a well developed value in the case of InAs substrate to an
almost negligible contribution for the GaAs one. A piezoelectric material that
would allow the change in the substrate lattice parameters opens the
possibility for practical investigations of the switchable (tunable)
non-quasiparticle states. Since the latter are important for the tunneling
magnetoresistance and related phenomena it creates new opportunities in
spintronics.Comment: 12 pages, 3 figures, 2 tables. accepted PRB 71, 1 (2005
Temperature dependent spin susceptibility in a two-dimensional metal
We consider a two-dimensional electron system with Coulomb interaction
between particles at a finite temperature T. We show that the dynamic Kohn
anomaly in the response function at 2K_F leads to a linear-in-T correction to
the spin susceptibility, same as in systems with short-range interaction.
We show that the singularity of the Coulomb interaction at q=0 does not
invalidate the expansion in powers of r_s, but makes the expansion
non-analytic. We argue that the linear temperature dependence is consistent
with the general structure of Landau theory and can be viewed as originating
from the non-analytic component of the Landau function near the Fermi surface.Comment: 4 pages, no figure
Griffiths phase in diluted magnetic semiconductors
We study the effects of disorder in the vicinity of the ferromagnetic
transition in a diluted magnetic semiconductor in the strongly localized
regime. We derive an effective polaron Hamiltonian, which leads to the
Griffiths phase above the ferromagnetic transition point. The Griffiths-McCoy
effects yield non-perturbative contributions to the dynamic susceptibility. We
explicitly derive the long-time susceptibility, which has a pseudo-scaling
form, with the dynamic critical exponent being expressed through the
percolation indices.Comment: 4 pages, final version as publishe
Brownian motion of solitons in a Bose-Einstein Condensate
For the first time, we observed and controlled the Brownian motion of
solitons. We launched solitonic excitations in highly elongated
BECs and showed that a dilute background of impurity atoms in a different
internal state dramatically affects the soliton. With no impurities and in
one-dimension (1-D), these solitons would have an infinite lifetime, a
consequence of integrability. In our experiment, the added impurities scatter
off the much larger soliton, contributing to its Brownian motion and decreasing
its lifetime. We describe the soliton's diffusive behavior using a quasi-1-D
scattering theory of impurity atoms interacting with a soliton, giving
diffusion coefficients consistent with experiment.Comment: 4 figure
Spin-Mediated Mott Excitons
Motivated by recent experiments on Mott insulators, in both iridates and
ultracold atoms, we theoretically study the effects of magnetic order on the
Mott-Hubbard excitons. In particular, we focus on spin-mediated doublon-holon
pairing in Hubbard materials. We use several complementary theoretical
techniques: mean-field theory to describe the spin degrees of freedom, the
self-consistent Born approximation to characterize individual charge
excitations across the Hubbard gap, and the Bethe-Salpeter equation to identify
bound states of doublons and holons. The binding energy of the Hubbard exciton
is found to increase with increasing the N{\'e}el order parameter, while the
exciton mass decreases. We observe that these trends rely significantly on the
retardation of the effective interaction, and require consideration of multiple
effects from changing the magnetic order. Our results are consistent with the
key qualitative trends observed in recent experiments on iridates. Moreover,
the findings could have direct implications on ultracold atom Mott insulators,
where the Hubbard model is the exact description of the system and the
microscopic degrees of freedom can be directly accessed.Comment: 11 pages, 11 figure
Topological superconductivity and Majorana fermions in hybrid structures involving cuprate high-T_c superconductors
The possibility of inducing topological superconductivity with cuprate
high-temperature superconductors (HTSC) is studied for various
heterostructures. We first consider a ballistic planar junction between a HTSC
and a metallic ferromagnet. We assume that inversion symmetry breaking at the
tunnel barrier gives rise to Rashba spin-orbit coupling in the barrier and
allows equal-spin triplet superconductivity to exist in the ferromagnet.
Bogoliubov-de Gennes equations are obtained by explicitly modeling the barrier,
and taking account of the transport anisotropy in the HTSC. By making use of
the self-consistent boundary conditions and solutions for the barrier and HTSC
regions, an effective equation of motion for the ferromagnet is obtained where
Andreev scattering at the barrier is incorporated as a boundary condition for
the ferromagnetic region. For a ferromagnet layer deposited on a (100) facet of
the HTSC, triplet p-wave superconductivity is induced. For the layer deposited
on a (110) facet, the induced gap does not have the p-wave orbital character,
but has an even orbital symmetry and an odd dependence on energy. For the layer
on the (001) facet, an exotic f-wave superconductivity is induced. We also
consider the induced triplet gap in a one-dimensional half-metallic nanowire
deposited on a (001) facet of a HTSC. We find that for a wire axis along the
a-axis, a robust triplet p-wave gap is induced. For a wire oriented 45 degrees
away from the a-axis the induced triplet p-wave gap vanishes. For the
appropriately oriented wire, the induced p-wave gap should give rise to
Majorana fermions at the ends of the half-metallic wire. Based on our result,
topological superconductivity in a semi-conductor nanowire may also be possible
given that it is oriented along the a-axis of the HTSC.Comment: 14 pages, 4 figure
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