11,430 research outputs found
Low field phase diagram of spin-Hall effect in the mesoscopic regime
When a mesoscopic two dimensional four-terminal Hall cross-bar with Rashba
and/or Dresselhaus spin-orbit interaction (SOI) is subjected to a perpendicular
uniform magnetic field , both integer quantum Hall effect (IQHE) and
mesoscopic spin-Hall effect (MSHE) may exist when disorder strength in the
sample is weak. We have calculated the low field "phase diagram" of MSHE in the
plane for disordered samples in the IQHE regime. For weak disorder,
MSHE conductance and its fluctuations vanish identically
on even numbered IQHE plateaus, they have finite values on those odd numbered
plateaus induced by SOI, and they have values and
on those odd numbered plateaus induced by Zeeman energy. For moderate disorder,
the system crosses over into a regime where both and are
finite. A larger disorder drives the system into a chaotic regime where
while is finite. Finally at large disorder both
and vanish. We present the physics behind this ``phase
diagram".Comment: 4 page, 3 figure
Universal spin-Hall conductance fluctuations in two dimensions
We report a theoretical investigation on spin-Hall conductance fluctuation of
disordered four terminal devices in the presence of Rashba or/and Dresselhaus
spin-orbital interactions in two dimensions. As a function of disorder, the
spin-Hall conductance shows ballistic, diffusive and insulating
transport regimes. For given spin-orbit interactions, a universal spin-Hall
conductance fluctuation (USCF) is found in the diffusive regime. The value of
the USCF depends on the spin-orbit coupling , but is independent of
other system parameters. It is also independent of whether Rashba or
Dresselhaus or both spin-orbital interactions are present. When is
comparable to the hopping energy , the USCF is a universal number . The distribution of crosses over from a Gaussian distribution
in the metallic regime to a non-Gaussian distribution in the insulating regime
as the disorder strength is increased.Comment: to be published in Phys. Rev. Lett., 4 figure
Universal quantized spin-Hall conductance fluctuation in graphene
We report a theoretical investigation of quantized spin-Hall conductance
fluctuation of graphene devices in the diffusive regime. Two graphene models
that exhibit quantized spin-Hall effect (QSHE) are analyzed. Model-I is with
unitary symmetry under an external magnetic field but with zero
spin-orbit interaction, . Model-II is with symplectic symmetry where
B=0 but . Extensive numerical calculations indicate that the two
models have exactly the same universal QSHE conductance fluctuation value
regardless of the symmetry. Qualitatively different from the
conventional charge and spin universal conductance distributions, in the
presence of edge states the spin-Hall conductance shows an one-sided log-normal
distribution rather than a Gaussian distribution. Our results strongly suggest
that the quantized spin-Hall conductance fluctuation belongs to a new
universality class
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