967 research outputs found
Random anisotropy disorder in superfluid 3He-A in aerogel
The anisotropic superfluid 3He-A in aerogel provides an interesting example
of a system with continuous symmetry in the presence of random anisotropy
disorder. Recent NMR experiments allow us to discuss two regimes of the
orientational disorder, which have different NMR properties. One of them, the
(s)-state, is identified as the pure Larkin-Imry-Ma state. The structure of
another state, the (f)-state, is not very clear: probably it is the
Larkin-Imry-Ma state contaminated by the network of the topological defects
pinned by aerogel.Comment: JETP Lett. style, 6 pages, no figures, discussion extended,
references added, version to be published in JETP Letter
Stable Spin Precession at one Half of Equilibrium Magnetization in Superfluid 3He-B
New stable modes of spin precession have been observed in superfluid 3He-B.
These dynamical order parameter states include precession with a magnetization
S=pS_{eq} which is different from the equilibrium value S_{eq}. We have
identified modes with p=1, 1/2 and \approx 0. The p=1/2 mode is the second
member of phase correlated states of a spin superfluid. The new states can be
excited in the temperature range 1-T/T_c \lesssim 0.02 where the energy
barriers between the different local minima of the spin-orbit energy are small.
They are stable in CW NMR due to low dissipation close to T_c.Comment: submitted to Physical Review Letters, 4 pages, revtex, 4 Figures in
ftp://boojum.hut.fi/pub/publications/lowtemp/LTL-96005.p
Spin dynamics in the regime of hopping conductivity
We consider spin dynamics in the impurity band of a semiconductor with
spin-split spectrum. Due to the splitting, phonon-assisted hops from one
impurity to another are accompanied by rotation of the electron spin, which
leads to spin relaxation. The system is strongly inhomogeneous because of
exponential variation of hopping times. However, at very small couplings an
electron diffuses over a distance exceeding the characteristic scale of the
inhomogeneity during the time of spin relaxation, so one can introduce an
averaged spin relaxation rate. At larger values of coupling the system is
effectively divided into two subsystems: the one where relaxation is very fast
and another one where relaxation is rather slow. In this case, spin decays due
to escape of the electrons from one subsystem to another. As a result, the spin
dynamics is non-exponential and hardly depends on spin-orbit coupling
Linear magnetoresistance in compensated graphene bilayer
We report a nonsaturating linear magnetoresistance in charge-compensated
bilayer graphene in a temperature range from 1.5 to 150 K. The observed linear
magnetoresistance disappears away from charge neutrality ruling out the
traditional explanation of the effect in terms of the classical random resistor
network model. We show that experimental results qualitatively agree with a
phenomenological two-fluid model taking into account electron-hole
recombination and finite-size sample geometry
Orbital glass and spin glass states of 3He-A in aerogel
Glass states of superfluid A-like phase of 3He in aerogel induced by random
orientations of aerogel strands are investigated theoretically and
experimentally. In anisotropic aerogel with stretching deformation two glass
phases are observed. Both phases represent the anisotropic glass of the orbital
ferromagnetic vector l -- the orbital glass (OG). The phases differ by the spin
structure: the spin nematic vector d can be either in the ordered spin nematic
(SN) state or in the disordered spin-glass (SG) state. The first phase (OG-SN)
is formed under conventional cooling from normal 3He. The second phase (OG-SG)
is metastable, being obtained by cooling through the superfluid transition
temperature, when large enough resonant continuous radio-frequency excitation
are applied. NMR signature of different phases allows us to measure the
parameter of the global anisotropy of the orbital glass induced by deformation.Comment: 7 pages, 6 figures, Submitted to Pis'ma v ZhETF (JETP Letters
Phonons in magnon superfluid and symmetry breaking field
Recent experiments [1],[2] which measured the spectrum of the Goldstone
collective mode of coherently precessing state in 3He-B are discussed using the
presentation of the coherent spin precession in terms of the Bose-Einstein
condensation of magnons. The mass in the spectrum of the Goldstone boson --
phonon in the superfluid magnon liquid -- is induced by the symmetry breaking
field, which is played by the RF magnetic fieldComment: 2 pages, JETP Letters style, no figures, version accepted in JETP
Letter
Generalized Neighbor-Interaction Models Induced by Nonlinear Lattices
It is shown that the tight-binding approximation of the nonlinear
Schr\"odinger equation with a periodic linear potential and periodic in space
nonlinearity coefficient gives rise to a number of nonlinear lattices with
complex, both linear and nonlinear, neighbor interactions. The obtained
lattices present non-standard possibilities, among which we mention a
quasi-linear regime, where the pulse dynamics obeys essentially the linear
Schr{\"o}dinger equation. We analyze the properties of such models both in
connection with their modulational stability, as well as in regard to the
existence and stability of their localized solitary wave solutions
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