287 research outputs found
Electronic correlations on a metallic nanosphere
We consider the correlation functions in a gas of electrons moving within a
thin layer on the surface of nanosize sphere. A closed form of expressions for
the RKKY indirect exchange, superconducting Cooper loop and `density-density'
correlation function is obtained. The systematic comparison with planar results
is made, the effects of spherical geometry are outlined. The quantum coherence
of electrons leads to the enhancement of all correlations for the
points--antipodes on the sphere. This effect is lost when the radius of the
sphere exceeds the temperature coherence length.Comment: 5 pages, no figures, to appear in PRB (RC
Effective Hamiltonian of topologically protected qubit in a helical crystal
We study a superlattice formed by tunnel-coupled identical antidots
periodically situated in a two-dimensional topological insulator placed in a
magnetic field. The superlattice spectrum can be controlled by gate electrodes
or by changing the magnetic flux through the antidots. We demonstrate that a
topologically protected qubit appears at the boundary between two regions with
different fluxes. The qubit properties depend on the value of the flux jump on
the boundary and can be controlled by the gate voltage. We derive the effective
Hamiltonian of such a qubit and analyze the dependence of its properties on the
main parameters of the superlattice: the tunnel coupling between antidots, and
the probability of jumps with the spin flip.Comment: 8 pages, 2 figure
New classes of exact solutions of three-dimensional Navier-Stokes equations
New classes of exact solutions of the three-dimensional unsteady
Navier-Stokes equations containing arbitrary functions and parameters are
described. Various periodic and other solutions, which are expressed through
elementary functions are obtained. The general physical interpretation and
classification of solutions is given.Comment: 11 page
Avoided crossings in mesoscopic systems: electron propagation on a non-uniform magnetic cylinder
We consider an electron constrained to move on a surface with revolution
symmetry in the presence of a constant magnetic field parallel to the
surface axis. Depending on and the surface geometry the transverse part of
the spectrum typically exhibits many crossings which change to avoided
crossings if a weak symmetry breaking interaction is introduced. We study the
effect of such perturbations on the quantum propagation. This problem admits a
natural reformulation to which tools from molecular dynamics can be applied. In
turn, this leads to the study of a perturbation theory for the time dependent
Born-Oppenheimer approximation
Bosonization for Wigner-Jordan-like Transformation : Backscattering and Umklapp-processes on Fictitious Lattice
We analyze the asymptotic behavior of the exponential form in the fermionic
density operators as the function of ruling parameter Q. In the particular case
Q=\pi this exponential associates with the Wigner-Jordan transformation for XY
spin chain model. We compare the bosonization approach and the evaluation via
the Toeplitz determinant. The use of Szego-Kac theorem suggests that at Q>\pi/3
the divergent series for intrinsic logarithm provides a bosonized solution and
faster decaying one, found as the logarithm's value on another sheet of the
complex plane. The second solution is revealed as umklapp-process on the
fictitious lattice while originates from backscattering terms in bosonized
density. Our finding preserves in a wide range of fermion filling ratios.Comment: 8 pages, REVTEX, 3 eps figures, accepted to Phys.Rev.
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