145 research outputs found
Symmetry-restoring quantum phase transition in a two-dimensional spinor condensate
Bose Einstein condensates of spin-1 atoms are known to exist in two different
phases, both having spontaneously broken spin-rotation symmetry, a
ferromagnetic and a polar condensate. Here we show that in two spatial
dimensions it is possible to achieve a quantum phase transition from a polar
condensate into a singlet phase symmetric under rotations in spin space. This
can be done by using particle density as a tuning parameter. Starting from the
polar phase at high density the system can be tuned into a strong-coupling
intermediate-density point where the phase transition into a symmetric phase
takes place. By further reducing the particle density the symmetric phase can
be continuously deformed into a Bose-Einstein condensate of singlet atomic
pairs. We calculate the region of the parameter space where such a molecular
phase is stable against collapse.Comment: 5 pages, 1 Figure + Supplemen
Decoherence induced by magnetic impurities in quantum Hall system
Scattering by magnetic impurities is known to destroy coherence of electron
motion in metals and semiconductors. We investigate the decoherence introduced
in a single act of electron scattering by a magnetic impurity in a quantum Hall
system. To this end we introduce a fictitious nonunitary scattering matrix
for electrons that reproduces the exactly calculated scattering
probabilities. The strength of decoherence is identified by the deviation of
eigenvalues of the product from unity. Using
the fictitious scattering matrix, we estimate the width of the metallic region
at the quantum Hall effect inter-plateau transition and its dependence on the
exchange coupling strength and the degree of polarization of magnetic
impurities.Comment: 13 pages, 4 figure
Thermal and electrical quantum Hall effects in ferromagnet-topological insulator-ferromagnet junction
We present the theoretical description for a class of experimental setups
that measure quantum Hall coefficients in ferromagnet-topological
insulator-ferromagnet (FM-TI-FM) junctions. We predict that varying the
magnetization direction in ferromagnets, one can change the induced Hall
voltage and transverse temperature gradient from the maximal values,
corresponding to the quantized Hall coefficients, down to their complete
suppression to zero. We provide detailed analysis of thermal and electrical
Hall resistances as functions of the magnetization directions in ferromagnets,
the spin-scattering time in TI, and geometrical positions of FM leads and
measurement contacts.Comment: 6 pages, 6 figures. This is an extended version of arXiv:1401.4986.
The theoretical approach is refined. New results concerning various
experimental geometries are presente
- …