829,674 research outputs found
Thermal Conductivity of Spin-1/2 Chains
We study the low-temperature transport properties of clean one-dimensional
spin-1/2 chains coupled to phonons. Due to the presence of approximate
conservation laws, the heat current decays very slowly giving rise to an
exponentially large heat conductivity, . As a result of an
interplay of Umklapp scattering and spinon-phonon coupling, the characteristic
energy scale turns out to be of order , where is
the Debye energy, rather than the magnetic exchange interaction -- in
agreement with recent measurements in SrCuO compounds. A large magnetic field
strongly affects the heat transport by two distinct mechanisms. First, it
induces a LINEAR spinon--phonon coupling, which alters the nature of the fixed point: the elementary excitations of the system are COMPOSITE
SPINON-PHONON objects. Second, the change of the magnetization and the
corresponding change of the wave vector of the spinons strongly affects the way
in which various Umklapp processes can relax the heat current, leading to a
characteristic fractal--like spiky behavior of when plotted as a
function of magnetization at fixed T.Comment: 16 pages, RevTex4, 2 figures included; revised refs. and some useful
comments on experimental relevance. On July 12 2005, added an appendix
correcting an error in the form of the phonon propagator. The main result is
unchange
Transport properties of non-equilibrium systems under the application of light: Photo-induced quantum Hall insulators without Landau levels
In this paper, we study transport properties of non-equilibrium systems under
the application of light in many-terminal measurements, using the Floquet
picture. We propose and demonstrate that the quantum transport properties can
be controlled in materials such as graphene and topological insulators, via the
application of light. Remarkably, under the application of off-resonant light,
topological transport properties can be induced; these systems exhibits quantum
Hall effects in the absence of a magnetic field with a near quantization of the
Hall conductance, realizing so-called quantum Hall systems without Landau
levels first proposed by Haldane.Comment: Updated to include the detailed explanation of formalism to study the
non-equilibrium transpor
Origin of Intrinsic Josephson Coupling in the Cuprates and Its Relation to Order Parameter Symmetry: An Incoherent Hopping Model
Experiments on the cuprate superconductors demonstrate that these materials
may be viewed as a stack of Josephson junctions along the c-direction. In this
paper, we present a model which describes this intrinsic Josephson coupling in
terms of incoherent quasiparticle hopping along the c-axis arising from
wave-function overlap, impurity-assisted hopping, and boson-assisted hopping.
We use this model to compute the magnitude and temperature T dependence of the
resulting Josephson critical current j_c (T) for s- and d-wave superconductors.
Contrary to other approaches, d-wave pairing in this model is compatible with
an intrinsic Josephson effect at all hole concentrations and leads to j_c (T)
\propto T at low T. By parameterizing our theory with c-axis resistivity data
from YBCO, we estimate j_c (T) for optimally doped and underdoped members of
this family. Our estimates suggest that further experiments on this compound
would be of great help in elucidating the validity of our model in general and
the pairing symmetry in particular. We also discuss the implications of our
model for LSCO and BSCCO.Comment: 28 pages, REVTEX, 5 compressed PostScript figures. Substantially
expanded and revised from the earlier version. To appear in Physica
- …