1,792,663 research outputs found
Spin noise in quantum dot ensembles
We study theoretically spin fluctuations of resident electrons or holes in
singly charged quantum dots. The effects of external magnetic field and
effective fields caused by the interaction of electron and nuclei spins are
analyzed. The fluctuations of spin Faraday, Kerr and ellipticity signals
revealing the spin noise of resident charge carriers are calculated for the
continuous wave probing at the singlet trion resonance.Comment: 8 pages, 4 figure
Resonant Fibonacci Quantum Well Structures
We propose a resonant one-dimensional quasicrystal, namely, a multiple
quantum well (MQW) structure satisfying the Fibonacci-chain rule with the
golden ratio between the long and short inter-well distances. The resonant
Bragg condition is generalized from the periodic to Fibonacci MQWs. A
dispersion equation for exciton-polaritons is derived in the two-wave
approximation, the effective allowed and forbidden bands are found. The
reflection spectra from the proposed structures are calculated as a function of
the well number and detuning from the Bragg condition.Comment: 5 pages, 3 figures, submitted to Phys. Rev.
Properties of 1D two-barrier quantum pump with harmonically oscillating barriers
We study a one-dimensional quantum pump composed of two oscillating
delta-functional barriers. The linear and non-linear regimes are considered.
The harmonic signal applied to any or both barriers causes the stationary
current. The direction and value of the current depend on the frequency,
distance between barriers, value of stationary and oscillating parts of barrier
potential and the phase shift between alternating voltages.Comment: 7 pages, 8 figure
Special mandrel permits uniform welding of out-of-round tubing
Clamp holds irregularly shaped pieces in lathe chuck without damage and eliminates excessive time in selecting optimum mounting. Interchangeable jaws ride in standard jaw slots but swivel so that the jaw face bears evenly against the workpiece regardless of contour. The jaws can be used on both engine and turret lathes
Detection of methane on Kuiper Belt Object (50000) Quaoar
The near-infrared spectrum of (50000) Quaoar obtained at the Keck Observatory
shows distinct absorption features of crystalline water ice, solid methane and
ethane, and possibly other higher order hydrocarbons. Quaoar is only the fifth
Kuiper belt object on which volatile ices have been detected. The small amount
of methane on an otherwise water ice dominated surface suggests that Quaoar is
a transition object between the dominant volatile-poor small Kuiper belt
objects (KBOs) and the few volatile-rich large KBOs such as Pluto and Eris.Comment: 8 pages, 2 figures, accepted for publication in ApJ
Quantum diffusion of dipole-oriented indirect excitons in coupled quantum wells
A model for diffusion of statistically-degenerate excitons in (coupled)
quantum wells is proposed and analysed. Within a microscopic approach, we
derive a quantum diffusion equation, calculate and estimate the self-diffusion
coefficient for excitons in quantum wells and derive a modified Einstein
relation adapted to statistically-degenerated quasi-two-dimensional bosons. It
is also shown that the dipole-dipole interaction of indirect excitons
effectively screens long-range-correlated disorder in quantum wells. Numerical
calculations are given for indirect excitons in GaAs/AlGaAs coupled quantum
wells.Comment: To appear in Europhysics Letter
Spin and valley-orbit splittings in SiGe/Si heterostructures
Spin and valley-orbit splittings are calculated in SiGe/Si/SiGe quantum wells
(QWs) by using the tight-binding approach. In accordance with the symmetry
considerations an existence of spin splitting of electronic states in perfect
QWs with an odd number of Si atomic planes is microscopically demonstrated. The
spin splitting oscillates with QW width and these oscillations related to the
inter-valley reflection of an electron wave from the interfaces. It is shown
that the splittings under study can efficiently be described by an extended
envelope-function approach taking into account the spin- and valley-dependent
interface mixing. The obtained results provide a theoretical base to the
experimentally observed electron spin relaxation times in SiGe/Si/SiGe QWs.Comment: 10 pages, 5 figure
Thermal Fluctuations of the Electric Field in the Presence of Carrier Drift
We consider a semiconductor in a non-equilibrium steady state, with a dc
current. On top of the stationary carrier motion there are fluctuations. It is
shown that the stationary motion of the carriers (i.e., their drift) can have a
profound effect on the electromagnetic field fluctuations in the bulk of the
sample as well as outside it, close to the surface (evanescent waves in the
near field). The effect is particularly pronounced near the plasma frequency.
This is because drift leads to a significant modification of the dispersion
relation for the bulk and surface plasmons.Comment: Comments are welcom
- …