12,671 research outputs found
Hydrostatic and uniaxial pressure dependence of superconducting transition temperature of KFe2As2 single crystals
We present heat capacity, c-axis thermal expansion and pressure dependent,
low field, temperature dependent magnetization for pressures up to ~ 12 kbar,
data for KFe2As2 single crystals. Tc decreases under pressure with dTc/dP ~
-0.10 K/kbar. The inferred uniaxial, c-axis, pressure derivative is positive,
dTc/dpc ~ 0.11 K/kbar. The data are analyzed in comparison with those for
overdoped Fe-based superconductors. Arguments are presented that
superconductivity in KFe2As2 may be different from the other overdoped,
Fe-based materials in the 122 family
A unified approach for exactly solvable potentials in quantum mechanics using shift operators
We present a unified approach for solving and classifying exactly solvable
potentials. Our unified approach encompasses many well-known exactly solvable
potentials. Moreover, the new approach can be used to search systematically for
a new class of solvable potentials.Comment: RevTex, 8 page
Quantum and Classical Spins on the Spatially Distorted Kagome Lattice: Applications to Volborthite
In Volborthite, spin-1/2 moments form a distorted Kagom\'e lattice, of corner
sharing isosceles triangles with exchange constants on two bonds and
on the third bond. We study the properties of such spin systems, and show that
despite the distortion, the lattice retains a great deal of frustration.
Although sub-extensive, the classical ground state degeneracy remains very
large, growing exponentially with the system perimeter. We consider degeneracy
lifting by thermal and quantum fluctuations. To linear (spin wave) order, the
degeneracy is found to stay intact. Two complementary approaches are therefore
introduced, appropriate to low and high temperatures, which point to the same
ordered pattern. In the low temperature limit, an effective chirality
Hamiltonian is derived from non-linear spin waves which predicts a transition
on increasing , from type order to a new
ferrimagnetic {\em striped chirality} order with a doubled unit cell. This is
confirmed by a large-N approximation on the O() model on this lattice. While
the saddle point solution produces a line degeneracy, corrections
select the non-trivial wavevector of the striped chirality state. The quantum
limit of spin 1/2 on this lattice is studied via exact small system
diagonalization and compare well with experimental results at intermediate
temperatures. We suggest that the very low temperature spin frozen state seen
in NMR experiments may be related to the disconnected nature of classical
ground states on this lattice, which leads to a prediction for NMR line shapes.Comment: revised, section V about exact diagonalization is extensively
rewritten, 17 pages, 11 figures, RevTex 4, accepted by Phys. Rev.
Pinning modes and interlayer correlation in high magnetic field bilayer Wigner solids
We report studies of pinning mode resonances in the low total Landau filling
(\nu) Wigner solid of a series of bilayer hole samples with negligible
interlayer tunneling, and with varying interlayer separation d. Comparison of
states with equal layer densities (p,p) to single layer states (p,0) produced
{in situ} by biasing, indicates that there is interlayer quantum correlation in
the solid at small d. Also, the resonance frequency at small d is decreased
just near \nu=1/2 and 2/3, indicating the importance in the solid of
correlations related to those in the fractional quantum Hall effects
Quantum Tomographic Cryptography with a Semiconductor Single Photon Source
In this paper we analyze the security of the so-called quantum tomographic
cryptography with the source producing entangled photons via an experimental
scheme proposed in Phys. Rev. Lett. 92, 37903 (2004). We determine the range of
the experimental parameters for which the protocol is secure against the most
general incoherent attacks
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