1,190 research outputs found
Domain walls in helical magnets
The structure of domain walls determines to a large extent the properties of
magnetic materials, in particular their hardness and switching behavior, it
represents an essential ingredient of spintronics. Common domain walls are of
Bloch and Neel types in which the magnetization rotates around a fixed axis,
giving rise to a one-dimensional magnetization profile. Domain walls in helical
magnets, most relevant in multiferroics, were never studied systematically.
Here we show that domain walls in helical magnets are fundamentally different
from Bloch and Neel walls. They are generically characterized by a
two-dimensional pattern formed by a regular lattice of vortex singularities. In
conical phases vortices carry Berry phase flux giving rise to the anomalous
Hall effect. In multiferroics vortices are charged, allowing to manipulate
magnetic domain walls by electric fields. Our theory allows the interpretation
of magnetic textures observed in helical magnetic structures
Roughening Transition of Interfaces in Disordered Systems
The behavior of interfaces in the presence of both lattice pinning and random
field (RF) or random bond (RB) disorder is studied using scaling arguments and
functional renormalization techniques. For the first time we show that there is
a continuous disorder driven roughening transition from a flat to a rough state
for internal interface dimensions 2<D<4. The critical exponents are calculated
in an \epsilon-expansion. At the transition the interface shows a
superuniversal logarithmic roughness for both RF and RB systems. A transition
does not exist at the upper critical dimension D_c=4. The transition is
expected to be observable in systems with dipolar interactions by tuning the
temperature.Comment: 4 pages, RevTeX, 1 postscript figur
Order and Creep in Flux Lattices and CDWs Pinned by Planar Defects
The influence of randomly distributed point impurities \emph{and} planar
defects on the order and transport in type-II superconductors and related
systems is considered theoretically. For planar defects of identical
orientation the flux line lattice exhibits a new glassy phase dominated by the
planar defects with a finite compressibility, a transverse Meissner effect,
large sample to sample fuctuations of the susceptibility and an exponential
decay of translational long range order. The flux creep resistivity for
currents parallel to the defects is .
Strong disorder enforces an array of dislocations to relax shear strain
Frequency-Temperature Crossover in the Conductivity of Disordered Luttinger Liquids
The temperature () and frequency () dependent conductivity of
weakly disordered Luttinger liquids is calculated in a systematic way both by
perturbation theory and from a finite temperature renormalization group (RG)
treatment to leading order in the disorder strength. Whereas perturbation
theory results in scaling of the conductivity such scaling is
violated in the RG traetment. We also determine the non-linear field dependence
of the conductivity, whose power law scaling is different from that of
temperature and frequency dependence.Comment: 4 pages, 4 figure
A heuristic approach to the weakly interacting Bose gas
Some thermodynamic properties of weakly interacting Bose systems are derived
from dimensional and heuristic arguments and thermodynamic relations, without
resorting to statistical mechanics
Comprehensive study of the critical behavior in the diluted antiferromagnet in a field
We study the critical behavior of the Diluted Antiferromagnet in a Field with
the Tethered Monte Carlo formalism. We compute the critical exponents
(including the elusive hyperscaling violations exponent ). Our results
provide a comprehensive description of the phase transition and clarify the
inconsistencies between previous experimental and theoretical work. To do so,
our method addresses the usual problems of numerical work (large tunneling
barriers and self-averaging violations).Comment: 4 pages, 2 figure
Variable range hopping and quantum creep in one dimension
We study the quantum non linear response to an applied electric field of
a one dimensional pinned charge density wave or Luttinger liquid in presence of
disorder. From an explicit construction of low lying metastable states and of
bounce instanton solutions between them, we demonstrate quantum creep as well as a sharp crossover at towards a linear response
form consistent with variable range hopping arguments, but dependent only on
electronic degrees of freedom
Domain scaling and marginality breaking in the random field Ising model
A scaling description is obtained for the --dimensional random field Ising
model from domains in a bar geometry. Wall roughening removes the marginality
of the case, giving the correlation length in , and for power law behaviour with
, . Here, (lattice, continuum) is one of four rough wall exponents provided by the
theory. The analysis is substantiated by three different numerical techniques
(transfer matrix, Monte Carlo, ground state algorithm). These provide for
strips up to width basic ingredients of the theory, namely free energy,
domain size, and roughening data and exponents.Comment: ReVTeX v3.0, 19 pages plus 19 figures uuencoded in a separate file.
These are self-unpacking via a shell scrip
Effect of nonlocal interactions on the disorder-induced zero-bias anomaly in the Anderson-Hubbard model
To expand the framework available for interpreting experiments on disordered
strongly correlated systems, and in particular to explore further the
strong-coupling zero-bias anomaly found in the Anderson-Hubbard model, we ask
how this anomaly responds to the addition of nonlocal electron-electron
interactions. We use exact diagonalization to calculate the single-particle
density of states of the extended Anderson-Hubbard model. We find that for weak
nonlocal interactions the form of the zero-bias anomaly is qualitatively
unchanged. The energy scale of the anomaly continues to be set by an effective
hopping amplitude renormalized by the nonlocal interaction. At larger values of
the nonlocal interaction strength, however, hopping ceases to be a relevant
energy scale and higher energy features associated with charge correlations
dominate the density of states.Comment: 9 pages, 7 figure
Localized states and interaction induced delocalization in Bose gases with quenched disorder
Very diluted Bose gas placed into a disordered environment falls into a
fragmented localized state. At some critical density the repulsion between
particles overcomes the disorder. The gas transits into a coherent superfluid
state. In this article the geometrical and energetic characteristics of the
localized state at zero temperature and the critical density at which the
quantum phase transition from the localized to the superfluid state proceeds
are found.Comment: 17 pages, 5 figur
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