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 $^{87}\rm{Rb}$ 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