119 research outputs found
Ambivalence of the anisotropy of the vortex lattice in an anisotropic type-II superconductor
We present a geometry-based discussion of possible vortex configurations in
the mixed state of anisotropic type-II superconductors. It is shown that, if
energy considerations assign six nearest neighbors to each vortex, two distinct
modifications of the vortex lattice are possible. It is expected that certain
conditions lead to a first order phase transition from one modification of the
vortex lattice to the other upon varying the external magnetic field.Comment: 3 pages, 2 figure
Thermal conductivity of anisotropic and frustrated spin-1/2 chains
We analyze the thermal conductivity of anisotropic and frustrated spin-1/2
chains using analytical and numerical techniques. This includes mean-field
theory based on the Jordan-Wigner transformation, bosonization, and exact
diagonalization of systems with N<=18 sites. We present results for the
temperature dependence of the zero-frequency weight of the conductivity for
several values of the anisotropy \Delta. In the gapless regime, we show that
the mean-field theory compares well to known results and that the
low-temperature limit is correctly described by bosonization. In the
antiferromagnetic and ferromagnetic gapped regime, we analyze the temperature
dependence of the thermal conductivity numerically. The convergence of the
finite-size data is remarkably good in the ferromagnetic case. Finally, we
apply our numerical method and mean-field theory to the frustrated chain where
we find a good agreement of these two approaches on finite systems. Our
numerical data do not yield evidence for a diverging thermal conductivity in
the thermodynamic limit in case of the antiferromagnetic gapped regime of the
frustrated chain.Comment: 4 pages REVTeX4 including 6 figures; published version, main
modification: added emphasis that the data of our Fig. 3 point to a vanishing
of the thermal Drude weight in the thermodynamic limit in this cas
Asymmetric Heat Flow in Mesoscopic Magnetic System
The characteristics of heat flow in a coupled magnetic system are studied.
The coupled system is composed of a gapped chain and a gapless chain. The
system size is assumed to be quite small so that the mean free path is
comparable to it. When the parameter set of the temperatures of reservoirs is
exchanged, the characteristics of heat flow are studied with the Keldysh Green
function technique. The asymmetry of current is found in the presence of a
local equilibrium process at the contact between the magnetic systems. The
present setup is realistic and such an effect will be observed in real
experiments. We also discuss the simple phenomenological explanation to obtain
the asymmetry.Comment: 13 pages, 3 figure
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