818 research outputs found
Integer Quantum Hall Transition and Random SU(N) Rotation
We reduce the problem of integer quantum Hall transition to a random rotation
of an N-dimensional vector by an su(N) algebra, where only N specially selected
generators of the algebra are nonzero. The group-theoretical structure revealed
in this way allows us to obtain a new series of conservation laws for the
equation describing the electron density evolution in the lowest Landau level.
The resulting formalism is particularly well suited to numerical simulations,
allowing us to obtain the critical exponent \nu numerically in a very simple
way. We also suggest that if the number of nonzero generators is much less than
N, the same model, in a certain intermediate time interval, describes
percolating properties of a random incompressible steady two-dimensional flow.
In other words, quantum Hall transition in a very smooth random potential
inherits certain properties of percolation.Comment: 4 pages, 1 figur
Simulation of electron paramagnetic resonance spectra of spin-labeled molecules from replica-exchange molecular dynamics
Energy transport in disordered classical spin chains
We present a numerical study of the diffusion of energy at high temperature in strongly disordered chains of
interacting classical spins evolving deterministically. We find that quenched randomness strongly suppresses
transport with the diffusion constant becoming reduced by several orders of magnitude upon the introduction
of moderate disorder. We have also looked for but not found signs of a classical many-body localization
transition at any nonzero strength of the spin-spin interactions
Towards a statistical theory of transport by strongly-interacting lattice fermions
We present a study of electric transport at high temperature in a model of
strongly interacting spinless fermions without disorder. We use exact
diagonalization to study the statistics of the energy eigenvalues, eigenstates,
and the matrix elements of the current. These suggest that our nonrandom
Hamiltonian behaves like a member of a certain ensemble of Gaussian random
matrices. We calculate the conductivity and examine its
behavior, both in finite size samples and as extrapolated to the thermodynamic
limit. We find that has a prominent non-divergent singularity
at reflecting a power-law long-time tail in the current
autocorrelation function that arises from nonlinear couplings between the
long-wavelength diffusive modes of the energy and particle number
Nernst effect, quasiparticles, and d-density waves in cuprates
We examine the possibility that the large Nernst signal observed in the
pseudogap regime of hole-doped cuprates originates from quasiparticle transport
in a state with d-density wave (DDW) order, proposed by S. Chakravarty et al.
[Phys. Rev. B 63, 094503 (2001)]. We find that the Nernst coefficient can be
moderately enhanced in magnitude by DDW order, and is generally of negative
sign. Thus, the quasiparticles of the DDW state cannot account for the large
and positive Nernst signal observed in the pseudogap phase of the cuprates.
However, the general considerations outlined in this paper may be of broader
relevance, in particular to the recent measurements of Bel et al. in NbSe_2 and
CeCoIn_5 [Phys. Rev. Lett. 91, 066602 (2003); ibid. 92, 217002 (2004)].Comment: 9 pages, 3 figures; published versio
- …