77 research outputs found
Zeeman splitting of shallow donors in GaN
The Zeeman splitting of the donor spectra in cubic- and hexagonal-GaN are
studied using an effective mass theory approach. Soft-core pseudopotentials
were used to describe the chemical shift of the different substitutional
dopants. The donor ground states calculated range from 29.5 to 33.7 meV, with
typically 1 meV higher binding in the hexagonal phase. Carbon is found to
produce the largest donor binding energy. The ionization levels and excited
states are in excellent agreement with Hall and optical measurements, and
suggest the presence of residual C in recent experiments.Comment: REVTEX file - 2 figure
Spin Hall and longitudinal conductivity of a conserved spin current in two dimensional heavy-hole gases
The spin Hall and longitudinal conductivity of a 2D heavy-hole gas with {\it
k}-cubic Rashba and Dresselhaus spin-orbit interaction is studied in the ac
frequency domain. Using Kubo linear-response theory and a recently proposed
definition for the (conserved) spin current operator suitable for spin-3/2
holes, it is shown that the spin conductivity tensor exhibit very
distinguishable features from those obtained with the standard definition of
the spin current. This is due to a significant contribution of the spin-torque
term arisen from the alternative definition of spin current which strongly
affects the magnitude and the sign of the dynamic spin current. In the dc (free
of disorder) limit, the spin Hall conductivity for only (or dominant) {\it
k}-cubic Rashba coupling is , whereas
for only (or dominant) {\it k}-cubic
Dresselhaus coupling. Such anisotropic response is understood in terms of the
absence of mapping the {\it k}-cubic Rashba Dresselhaus
Hamiltonians. This asymmetry is also responsible for the non-vanishing dc spin
Hall conductivity () when the Rashba and
Dresselhaus parameters have the same strength, in contrast with its
corresponding case for electrons. These results are of relevance to validate
the alternative definition of spin-current through measurements in the
frequency domain of the spin accumulation and/or spin currents in 2D hole
gases.Comment: 12 pages, 6 figures; typos added; Recommendations from referees
added. Title change
Zero field spin splitting in AlSb/InAs/AlSb quantum wells induced by surface proximity effects
InAs quantum well heterostructures are of considerable interest for
mesoscopic device applications such as scanning probe and magnetic recording
sensors, which require the channel to be close to the surface. Here we report
on magnetotransport measurements of AlSb/InAs/AlSb Hall bars at a shallow depth
of 20 nm. Analysis of the observed Shubnikov-de Haas oscillations and modeling
show that spin splitting energies in excess of 2.3 meV occur at zero magnetic
field. We conclude that the spin-splitting results from the Rashba effect due
to the band bending in the quantum well. This is caused by substantial electron
transfer from the surface to the quantum well and becomes significant when the
quantum well is located near the surface.Comment: 14 pages, 2 figures. (To be published in APL
Spin and charge optical conductivities in spin-orbit coupled systems
We study the frequency dependent spin- and charge- conductivity tensors of a
two-dimensional electron gas (2DEG) with Rashba and Dresselhaus spin-orbit
interaction. We show that the angular anisotropy of the spin-splitting energy
induced by the interplay between the Rashba and Dresselhaus couplings gives
rise to a characteristic spectral behavior of the spin and charge response
which is significantly different from that of pure Rashba or Dresselhaus case.
Such new spectral structures open the possibility for control of the optical
response by applying an external bias and/or by adjusting the light frequency.
In addition, it is shown that the relative strength of the spin-orbit coupling
parameters can be obtained through optical probing.Comment: 13 pages, 4 figures. Revised versio
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