24 research outputs found
NMR in Superfluid A-like Phase of He Confined in Globally Deformed Aerogel in Tilted Magnetic Field
NMR spectra in superfluid A-like phases confined in axially deformed aerogel
in presence of a magnetic field inclined with respect to deformation axis is
considered. The characteristic features of dipole frequency shift in axially
compressed and axially stretched cases are compared. In particular, it is shown
that in axially stretched aerogel environment the stability region of
coherently spin precessing mode is rather narrow due to the U(1)LIM effect.Comment: 8 pages, 2 figure
Weak antiferromagnetism due to Dzyaloshinskii-Moriya interaction in BaCuOCl
The antiferromagnetic insulating cuprate BaCuOCl contains
folded CuO chains with four magnetic copper ions () per unit cell.
An underlying multiorbital Hubbard model is formulated and the superexchange
theory is developed to derive an effective spin Hamiltonian for this cuprate.
The resulting spin Hamiltonian involves a Dzyaloshinskii-Moriya term and a more
weak symmetric anisotropic exchange term besides the isotropic exchange
interaction. The corresponding Dzyaloshinskii-Moriya vectors of each magnetic
Cu-Cu bond in the chain reveal a well defined spatial order. Both, the
superexchange theory and the complementary group theoretical consideration,
lead to the same conclusion on the character of this order. The analysis of the
ground-state magnetic properties of the derived model leads to the prediction
of an additional noncollinear modulation of the antiferromagnetic structure.
This weak antiferromagnetism is restricted to one of the Cu sublattices.Comment: 13 pages, 1 table, 4 figure
The magnetic ordering in the mixed valence compound beta-Na0.33V2O5
The low-temperature electron spin resonance (ESR) spectra and the static
magnetization data obtained for the stoichiometric single crystals of
-NaVO indicate that this quasi-one-dimensional mixed
valence (V4+/V5+) compound demonstrates at K the phase transition into
the canted antiferromagnetically ordered state. The spontaneous magnetization
of per V ion was found to be oriented along
the two-fold axis of the monoclinic structure, the vector of
antiferromagnetism is aligned with the axis and the Dzyaloshinsky vector is
parallel to the -axis. The experimental data were successfully described in
the frame of the macroscopic spin dynamics and the following values for the
macroscopic parameters of the spin system were obtained: the Dzyaloshinsky
field kOe, the energy gaps of two branches of the spin wave spectrum
GHz and GHz.Comment: 5 pages, 6 figure
Cosmology, Particle Physics and Superfluid 3He
Many direct parallels connect superfluid 3He with the field theories
describing the physical vacuum, gauge fields and elementary fermions.
Superfluid He exhibits a variety of topological defects which can be
detected with single-defect sensitivity. Modern scenarios of defect-mediated
baryogenesis can be simulated by the interaction of the 3He vortices and domain
walls with fermionic quasiparticles. Formation of defects in a
symmetry-breaking phase transition in the early Universe, which could be
responsible for large-scale structure formation and for microwave-background
anisotropy, also may be modelled in the laboratory. This is supported by the
recent observation of vortex formation in neutron-irradiated 3He-B where the
"primordial fireball" is formed in an exothermic nuclear reaction.Comment: Invited talk at LT-21 Conference, 20 pages, 3 figures available at
request, compressed ps file of the camera-ready format with 3 figures is at
ftp://boojum.hut.fi/pub/publications/lowtemp/LTL-96006.ps.g