195 research outputs found
Reply to Comment on "Strongly Correlated Fractional Quantum Hall Line Junctions"
In two recent articles [PRL 90, 026802 (2003); PRB 69, 085307 (2004)], we
developed a transport theory for an extended tunnel junction between two
interacting fractional-quantum-Hall edge channels, obtaining analytical results
for the conductance. Ponomarenko and Averin (PA) have expressed disagreement
with our theoretical approach and question the validity of our results
(cond-mat/0602532). Here we show why PA's critique is unwarranted.Comment: 1 page, no figures, RevTex
Heat transport of clean spin-ladders coupled to phonons: Umklapp scattering and drag
We study the low-temperature heat transport in clean two-leg spin ladder
compounds coupled to three-dimensional phonons. We argue that the very large
heat conductivities observed in such systems can be traced back to the
existence of approximate symmetries and corresponding weakly violated
conservation laws of the effective (gapful) low--energy model, namely
pseudo-momenta. Depending on the ratios of spin gaps and Debye energy and on
the temperature, the magnetic contribution to the heat conductivity can be
positive or negative, and exhibit an activated or anti-activated behavior. In
most regimes, the magnetic heat conductivity is dominated by the spin-phonon
drag: the excitations of the two subsystems have almost the same drift
velocity, and this allows for an estimate of the ratio of the magnetic and
phononic contributions to the heat conductivity.Comment: revised version, 8 pages, 3 figures, added appendi
Large thermomagnetic effects in weakly disordered Heisenberg chains
The interplay of different scattering mechanisms can lead to novel effects in
transport. We show theoretically that the interplay of weak impurity and
Umklapp scattering in spin-1/2 chains leads to a pronounced dip in the magnetic
field dependence of the thermal conductivity at a magnetic field . In sufficiently clean samples, the reduction of the magnetic
contribution to heat transport can easily become larger than 50% and the effect
is predicted to exist even in samples with a large exchange coupling, J >> B,
where the field-induced magnetization is small. Qualitatively, our theory might
explain dips at observed in recent heat transport measurements on
copper pyrazine dinitrate, but a fully quantitative description is not possible
within our model.Comment: 5 pages, 2 figure
Coulomb Drag for Strongly Localized Electrons: Pumping Mechanism
The mutual influence of two layers with strongly loclized electrons is
exercised through the random Coulomb shifts of site energies in one layer
caused by electron hops in the other layer. We trace how these shifts give rise
to a voltage drop in the passive layer, when a current is passed through the
active layer. We find that the microscopic origin of drag lies in the time
correlations of the occupation numbers of the sites involved in a hop. These
correlations are neglected within the conventional Miller-Abrahams scheme for
calculating the hopping resistance.Comment: 5 pages, 3 figure
Magnetothermal transport in the spin-1/2 chains of copper pyrazine dinitrate
We present experiments on the thermal transport in the spin-1/2 chain
compound copper pyrazine dinitrate Cu(C_4 H_4 N_2)(NO_3)_2. The heat
conductivity shows a surprisingly strong dependence on the applied magnetic
field B, characterized at low temperatures by two main features. The first one
appearing at low B is a characteristic dip located at mu_B B ~ k_B T, that may
arise from Umklapp scattering. The second one is a plateau-like feature in the
quantum critical regime, mu_B |B-B_c| < k_B T, where B_c is the saturation
field at T=0. The latter feature clearly points towards a momentum and field
independent mean free path of the spin excitations, contrary to theoretical
expectations.Comment: 4 pages, 4 figure
Subharmonic Generation in Quantum Systems
We show how the classical-quantum correspondence permits long-lived
subharmonic motion in a quantum system driven by a periodic force.
Exponentially small deviations from exact subharmonicity are due to coherent
tunneling between quantized vortex tubes which surround classical elliptic
periodic orbits.Comment: 11 pages + 5 figures (available upon request), Revtex 3.0,
NSF-ITP-93-4
Quarter-Filled Honeycomb Lattice with a Quantized Hall Conductance
We study a generic two-dimensional hopping model on a honeycomb lattice with
strong spin-orbit coupling, without the requirement that the half-filled
lattice be a Topological Insulator. For quarter-(or three-quarter) filling, we
show that a state with a quantized Hall conductance generically arises in the
presence of a Zeeman field of sufficient strength. We discuss the influence of
Hubbard interactions and argue that spontaneous ferromagnetism (which breaks
time-reversal) will occur, leading to a quantized anomalous Hall effect.Comment: 4 pages, 3 figure
Effective Drag Between Strongly Inhomogeneous Layers: Exact Results and Applications
We generalize Dykhne's calculation of the effective resistance of a 2D
two-component medium to the case of frictional drag between the two parallel
two-component layers. The resulting exact expression for the effective
transresistance, , is analyzed in the limits when the resistances
and transresistances of the constituting components are strongly different -
situation generic for the vicinity of the {\em classical} (percolative)
metal-insulator transition (MIT). On the basis of this analysis we conclude
that the evolution of across the MIT is determined by the type
of correlation between the components, constituting the 2D layers. Depending on
this correlation, in the case of two electron layers, changes
either monotonically or exhibits a sharp maximum. For electron-hole layers
is negative and exhibits a sharp minimum at the
MIT.Comment: 7 pages, 3 figure
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