233 research outputs found
Two-dimensional imaging of the spin-orbit effective magnetic field
We report on spatially resolved measurements of the spin-orbit effective
magnetic field in a GaAs/InGaAs quantum-well. Biased gate electrodes lead to an
electric-field distribution in which the quantum-well electrons move according
to the local orientation and magnitude of the electric field. This motion
induces Rashba and Dresselhaus effective magnetic fields. The projection of the
sum of these fields onto an external magnetic field is monitored locally by
measuring the electron spin-precession frequency using time-resolved Faraday
rotation. A comparison with simulations shows good agreement with the
experimental data.Comment: 6 pages, 4 figure
Spin-orbit interaction and spin relaxation in a two-dimensional electron gas
Using time-resolved Faraday rotation, the drift-induced spin-orbit Field of a
two-dimensional electron gas in an InGaAs quantum well is measured. Including
measurements of the electron mobility, the Dresselhaus and Rashba coefficients
are determined as a function of temperature between 10 and 80 K. By comparing
the relative size of these terms with a measured in-plane anisotropy of the
spin dephasing rate, the D'yakonv-Perel' contribution to spin dephasing is
estimated. The measured dephasing rate is significantly larger than this, which
can only partially be explained by an inhomogeneous g-factor.Comment: 6 pages, 5 figure
Mode Spectroscopy and Level Coupling in Ballistic Electron Waveguides
A tunable quantum point contact with modes occupied in both transverse
directions is studied by magnetotransport experiments. We use conductance
quantization of the one-dimensional subbands as a tool to determine the mode
spectrum. A magnetic field applied along the direction of the current flow
couples the modes. This can be described by an extension of the Darwin-Fock
model. Anticrossings are observed as a function of the magnetic field, but not
for zero field or perpendicular field directions, indicating coupling of the
subbands due to nonparabolicity in the electrical confinement.Comment: 4 pages, 3 figure
Penetration depth study of the type-I superconductor PdTe2
Superconductivity in the topological non-trivial Dirac semimetal PdTe was
recently shown to be type-I. We here report measurements of the relative
magnetic penetration depth, , on several single crystals using
a high precision tunnel diode oscillator technique. The temperature variation
follows an exponential function for ,
consistent with a fully-gapped superconducting state and weak or moderately
coupling superconductivity. By fitting the data we extract a -value of ~nm. The normalized superfluid density is in good
agreement with the computed curve for a type-I superconductor with nonlocal
electrodynamics. Small steps are observed in , which
possibly relates to a locally lower due to defects in the single
crystalline sample. single crystalline sample.Comment: 13 pages, including 5 figure
Long-Lived Spin Coherence States
We study evolution of electron spin coherence having non-homogeneous
direction of spin polarization vector in semiconductor heterostructures. It is
found that the electron spin relaxation time due to the D'yakonov-Perel'
relaxation mechanism essentially depends on the initial spin polarization
distribution. This effect has its origin in the coherent spin precession of
electrons diffusing in the same direction. We predict a long spin relaxation
time of a novel structure: a spin coherence standing wave and discuss its
experimental realization
Voltage control of nuclear spin in ferromagnetic Schottky diodes
We employ optical pump-probe spectroscopy to investigate the voltage
dependence of spontaneous electron and nuclear spin polarizations in hybrid
MnAs/n-GaAs and Fe/n-GaAs Schottky diodes. Through the hyperfine interaction,
nuclear spin polarization that is imprinted by the ferromagnet acts on
conduction electron spins as an effective magnetic field. We demonstrate tuning
of this nuclear field from <0.05 to 2.4 kG by varying a small bias voltage
across the MnAs device. In addition, a connection is observed between the diode
turn-on and the onset of imprinted nuclear polarization, while traditional
dynamic nuclear polarization exhibits relatively little voltage dependence.Comment: Submitted to Physical Review B Rapid Communications. 15 pages, 3
figure
Effect of Spin-Orbit Interaction and In-Plane Magnetic Field on the Conductance of a Quasi-One-Dimensional System
We study the effect of spin-orbit interaction and in-plane effective magnetic
field on the conductance of a quasi-one-dimensional ballistic electron system.
The effective magnetic field includes the externally applied field, as well as
the field due to polarized nuclear spins. The interplay of the spin-orbit
interaction with effective magnetic field significantly modifies the band
structure, producing additional sub-band extrema and energy gaps, introducing
the dependence of the sub-band energies on the field direction. We generalize
the Landauer formula at finite temperatures to incorporate these special
features of the dispersion relation. The obtained formula describes the
conductance of a ballistic conductor with an arbitrary dispersion relation.Comment: will appear in Physical Review
Two-subband electron transport in nonideal quantum wells
Electron transport in nonideal quantum wells (QW) with large-scale variations
of energy levels is studied when two subbands are occupied. Although the mean
fluctuations of these two levels are screened by the in-plane redistribution of
electrons, the energies of both levels remain nonuniform over the plane. The
effect of random inhomogeneities on the classical transport is studied within
the framework of a local response approach for weak disorder. Both short-range
and small-angle scattering mechanisms are considered. Magnetotransport
characteristics and the modulation of the effective conductivity by transverse
voltage are evaluated for different kinds of confinement potentials (hard wall
QW, parabolic QW, and stepped QW).Comment: 10 pages, 6 figure
Magnetic-Field-Induced Hybridization of Electron Subbands in a Coupled Double Quantum Well
We employ a magnetocapacitance technique to study the spectrum of the soft
two-subband (or double-layer) electron system in a parabolic quantum well with
a narrow tunnel barrier in the centre. In this system unbalanced by gate
depletion, at temperatures T\agt 30 mK we observe two sets of quantum
oscillations: one originates from the upper electron subband in the
closer-to-the-gate part of the well and the other indicates the existence of
common gaps in the spectrum at integer fillings. For the lowest filling factors
and , both the common gap presence down to the point of one- to
two-subband transition and their non-trivial magnetic field dependences point
to magnetic-field-induced hybridization of electron subbands.Comment: Major changes, added one more figure, the latest version to be
published in JETP Let
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