829 research outputs found
Gate tunability of stray-field-induced electron spin precession in a GaAs/InGaAs quantum well below an interdigitated magnetized Fe grating
Time-resolved Faraday rotation is used to measure the coherent electron spin
precession in a GaAs/InGaAs quantum well below an interdigitated magnetized Fe
grating. We show that the electron spin precession frequency can be modified by
applying a gate voltage of opposite polarity to neighboring bars. A tunability
of the precession frequency of 0.5 GHz/V has been observed. Modulating the gate
potential with a gigahertz frequency allows the electron spin precession to be
controlled on a nanosecond timescale
Density dependence of microwave induced magneto-resistance oscillations in a two-dimensional electron gas
We have measured the magneto-resistance of a two-dimensional electron gas
(2DEG) under continuous microwave irradiation as a function of electron density
and mobility tuned with a metallic top-gate. In the entire range of density and
mobility we have investigated, we observe microwave induced oscillations of
large amplitude that are B-periodic. These B-periodic oscillations are
reminiscent of the ones reported by Kukushkin \textit{et al}[1] and which were
attributed to the presence of edge-magneto-plasmons. We have found that the
B-periodicity does not increase linearly with the density in our sample but
shows a plateau in the range (2.4-3) 10^{11}\rm cm^{-2} $. In this regime, the
phase of the B-periodic oscillations is found to shift continuously by two
periods.Comment: 5 pages, 4 figure
Macroscopic Aharonov--Bohm Effect in Type-I Superconductors
In type-I superconducting cylinders bulk superconductivity is destroyed above
the first critical current. Below the second critical current the `type-I mixed
state' displays fluctuation superconductivity which contributes to the total
current. A magnetic flux on the axis of the cylinder can change the second
critical current by as much as 50 percent so that half a flux quantum can
switch the cylinder from normal conduction to superconductivity: the
Aharonov--Bohm effect manifests itself in macroscopically large resistance
changes of the cylinder.Comment: five pages, one figur
Optimized stray-field-induced enhancement of the electron spin precession by buried Fe gates
The magnetic stray field from Fe gates is used to modify the spin precession
frequency of InGaAs/GaAs quantum-well electrons in an external magnetic field.
By using an etching process to position the gates directly in the plane of the
quantum well, the stray-field influence on the spin precession increases
significantly compared with results from previous studies with top-gated
structures. In line with numerical simulations, the stray-field-induced
precession frequency increases as the gap between the ferromagnetic gates is
reduced. The inhomogeneous stray field leads to additional spin dephasing.Comment: 4 pages, 2 figure
Two-subband quantum Hall effect in parabolic quantum wells
The low-temperature magnetoresistance of parabolic quantum wells displays
pronounced minima between integer filling factors. Concomitantly the Hall
effect exhibits overshoots and plateau-like features next to well-defined
ordinary quantum Hall plateaus. These effects set in with the occupation of the
second subband. We discuss our observations in the context of single-particle
Landau fan charts of a two-subband system empirically extended by a density
dependent subband separation and an enhanced spin-splitting g*.Comment: 5 pages, submitte
Bright picosecond x‐rays from intense sub‐picosecond laser‐plasma interactions
Short‐pulse, high‐intensity laser‐plasma interactions are investigated experimentally with temporally and spectrally resolved soft x‐ray diagnostics. The emitted x‐ray spectra from solid targets of various Z are characterized for a range of laser intensities (I<5×1017 W/cm2) and pulse widths (η∼400 fs). With low contrast (105), the x‐ray spectrum in the λ=40–100 Å spectral region is dominated by line emission, and the x‐ray pulse duration is found to be long, τx≳100 ps, characteristic of a long‐scale‐length, low‐density plasma. Bright, picosecond, continuum emission, characteristic of a short‐scalelength, high‐density plasma, is produced only when a high laser contrast (1010) is used. It is demonstrated experimentally that the pulsewidth of laser‐produced x‐ray radiation may be varied down to the picosecond time‐scale by adjusting the incident ultrashort‐pulse laser flux. This controls the peak electron temperature relative to the ionization potential, corresponding to the emitted x‐ray photon energy of interest. The results are found to be consistent with the predictions of a hydrodynamics code coupled to an average atom model only if non‐local thermodynamic equilibrium (NLTE) is assumed. © 1994 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87587/2/473_1.pd
Control of Bright Picosecond X-Ray Emission from Intense Subpicosecond Laser-Plasma Interactions
Using temporally and spectrally resolved diagnostics, we show that the pulse duration of laser-produced soft x rays emitted from solid targets can be controlled, permitting a reduction to as short as a few picoseconds. To enable this control, only a single parameter must be adjusted, namely, the intensity of the high-contrast ultrashort laser pulse (400 fs). These results are found to be in qualitative agreement with a simple model of radiation from a collisionally dominated atomic system
Collapse of ringlike structures in 2DEGs under tilted magnetic fields
In the quantum Hall regime, the longitudinal resistivity plotted
as a density--magnetic-field () diagram displays ringlike structures
due to the crossings of two sets of spin split Landau levels from different
subbands [e.g., Zhang \textit{et al.}, Phys. Rev. Lett. \textbf{95}, 216801
(2005)]. For tilted magnetic fields, some of these ringlike structures "shrink"
as the tilt angle is increased and fully collapse at . Here we theoretically investigate the topology of these structures
via a non-interacting model for the 2DEG. We account for the inter Landau-level
coupling induced by the tilted magnetic field via perturbation theory. This
coupling results in anti-crossings of Landau levels with parallel spins. With
the new energy spectrum, we calculate the corresponding diagram of
the density of states (DOS) near the Fermi level. We argue that the DOS
displays the same topology as in the diagram. For the
ring with filling factor , we find that the anti-crossings make it
shrink for increasing tilt angles and collapse at a large enough angle. Using
effective parameters to fit the data, we find a collapsing
angle . Despite this factor-of-two discrepancy with
the experimental data, our model captures the essential mechanism underlying
the ring collapse.Comment: 3 pages, 2 figures; Proceedings of the PASPS V Conference Held in
August 2008 in Foz do Igua\c{c}u, Brazi
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