40 research outputs found
Phase fluctuations of s-wave superconductors on a lattice
Based on an attractive Hubbard model on a lattice with up to second
neighbor hopping we derive an effective Hamiltonian for phase fluctuations. The
superconducting gap is assumed to have s-wave symmetry. The effective
Hamiltonian we finally arrive at is of the extended XY type. While it correctly
reduces to a simple XY in the continuum limit, in the general case, it contains
higher neighbor interaction in spin space. An important feature of our
Hamiltonian is that it gives a much larger fluctuation region between the
Berezinskii-Kosterlitz-Thouless transition temperature identified with
for superconducting and the mean field transition temperature identified with
the pseudogap temperature.Comment: 3 figure
Hidden Symmetries of Electronic Transport in a Disordered One-Dimensional Lattice
Correlated, or extended, impurities play an important role in the transport
properties of dirty metals. Here, we examine, in the framework of a
tight-binding lattice, the transmission of a single electron through an array
of correlated impurities. In particular we show that particles transmit through
an impurity array in identical fashion, regardless of the direction of
transversal. The demonstration of this fact is straightforward in the continuum
limit, but requires a detailed proof for the discrete lattice. We also briefly
demonstrate and discuss the time evolution of these scattering states, to
delineate regions (in time and space) where the aforementioned symmetry is
violated
Quantum mechanics of spin transfer in coupled electron-spin chains
The manner in which spin-polarized electrons interact with a magnetized thin
film is currently described by a semi-classical approach. This in turn provides
our present understanding of the spin transfer, or spin torque phenomenon.
However, spin is an intrinsically quantum mechanical quantity. Here, we make
the first strides towards a fully quantum mechanical description of spin
transfer through spin currents interacting with a Heisenberg-coupled spin
chain. Because of quantum entanglement, this requires a formalism based on the
density matrix approach. Our description illustrates how individual spins in
the chain time-evolve as a result of spin transfer.Comment: 4 pages, 3 (colour) figure
Wiedemann-Franz violation in the vortex state of a d-wave superconductor
We show that the Wiedemann-Franz law is violated in the vortex state of a
d-wave superconductor at zero temperature. We use a semiclassical approach,
which includes the Doppler shift on the quasiparticles as well as the Andreev
scattering from a random distribution of vortices. We also show that the vertex
corrections to the electrical conductivity due to the anisotropy of impurity
scattering become unimportant in the presence of a sufficiently large magnetic
field.Comment: To be published in Physica C as a proceeding of M2S-HTSC Rio 200
Electron and Spin Transport in the Presence of a Complex Absorbing Potential
We examine the impact of a complex absorbing potential on electron transport both in the continuum and on a lattice. This requires the use of non-Hermitian Hamiltonians; the required formalism is briefly outlined. The lattice formulation allows us to study the interesting problem of an electron interacting with a stationary spin and the subsequent time evolution of the electron and spin properties as the electron is absorbed after the initial interaction. Remarkably, the properties of the localized spin are affected “at a distance” by the interaction of the (now entangled) electron with a complex potential