Intermittent release of transients in the slow solar wind: 2. In situ evidence

In paper 1, we showed that the Heliospheric Imager (HI) instruments on the pair of NASA STEREO spacecraft can be used to image the streamer belt and, in particular, the variability of the slow solar wind which originates near helmet streamers. The observation of intense intermittent transient outflow by HI implies that the corresponding in situ observations of the slow solar wind and corotating interaction regions (CIRs) should contain many signatures of transients. In the present paper, we compare the HI observations with in situ measurements from the STEREO and ACE spacecraft. Analysis of the solar wind ion, magnetic field, and suprathermal electron flux measurements from the STEREO spacecraft reveals the presence of both closed and partially disconnected interplanetary magnetic field lines permeating the slow solar wind. We predict that one of the transients embedded within the second CIR (CIR‐D in paper 1) should impact the near‐Earth ACE spacecraft. ACE measurements confirm the presence of a transient at the time of CIR passage; the transient signature includes helical magnetic fields and bidirectional suprathermal electrons. On the same day, a strahl electron dropout is observed at STEREO‐B, correlated with the passage of a high plasma beta structure. Unlike ACE, STEREO‐B observes the transient a few hours ahead of the CIR. STEREO‐A, STEREO‐B, and ACE spacecraft observe very different slow solar wind properties ahead of and during the CIR analyzed in this paper, which we associate with the intermittent release of transients

Definitive observation of the dark triplet ground state of charged excitons in high magnetic fields

The ground state of negatively charged excitons (trions) in high magnetic fields is shown to be a dark triplet state, confirming long-standing theoretical predictions. Photoluminescence (PL), reflection, and PL excitation spectroscopy of CdTe quantum wells reveal that the dark triplet trion has lower energy than the singlet trion above 24 Tesla. The singlet-triplet crossover is "hidden" (i.e., the spectral lines themselves do not cross due to different Zeeman energies), but is confirmed by temperature-dependent PL above and below 24 T. The data also show two bright triplet states.Comment: 4 figure

The effect of disorder on the critical temperature of a dilute hard sphere gas

We have performed Path Integral Monte Carlo (PIMC) calculations to determine the effect of quenched disorder on the superfluid density of a dilute 3D hard sphere gas. The disorder was introduced by locating set of hard cylinders randomly inside the simulation cell. Our results indicate that the disorder leaves the superfluid critical temperature basically unchanged. Comparison to experiments of helium in Vycor is made.Comment: 4 pages, 4 figure

Measurement of Rashba and Dresselhaus spin-orbit magnetic fields

Spin-orbit coupling is a manifestation of special relativity. In the reference frame of a moving electron, electric fields transform into magnetic fields, which interact with the electron spin and lift the degeneracy of spin-up and spin-down states. In solid-state systems, the resulting spin-orbit fields are referred to as Dresselhaus or Rashba fields, depending on whether the electric fields originate from bulk or structure inversion asymmetry, respectively. Yet, it remains a challenge to determine the absolute value of both contributions in a single sample. Here we show that both fields can be measured by optically monitoring the angular dependence of the electrons' spin precession on their direction of movement with respect to the crystal lattice. Furthermore, we demonstrate spin resonance induced by the spin-orbit fields. We apply our method to GaAs/InGaAs quantum-well electrons, but it can be used universally to characterise spin-orbit interactions in semiconductors, facilitating the design of spintronic devices

Quantum Computation with Quantum Dots

We propose a new implementation of a universal set of one- and two-qubit gates for quantum computation using the spin states of coupled single-electron quantum dots. Desired operations are effected by the gating of the tunneling barrier between neighboring dots. Several measures of the gate quality are computed within a newly derived spin master equation incorporating decoherence caused by a prototypical magnetic environment. Dot-array experiments which would provide an initial demonstration of the desired non-equilibrium spin dynamics are proposed.Comment: 12 pages, Latex, 2 ps figures. v2: 20 pages (very minor corrections, substantial expansion), submitted to Phys. Rev.

Spin-injection Hall effect in a planar photovoltaic cell

Successful incorporation of the spin degree of freedom in semiconductor technology requires the development of a new paradigm allowing for a scalable, non-destructive electrical detection of the spin-polarization of injected charge carriers as they propagate along the semiconducting channel. In this paper we report the observation of a spin-injection Hall effect (SIHE) which exploits the quantum-relativistic nature of spin-charge transport and which meets all these key requirements on the spin detection. The two-dimensional electron-hole gas photo-voltaic cell we designed to observe the SIHE allows us to develop a quantitative microscopic theory of the phenomenon and to demonstrate its direct application in optoelectronics. We report an experimental realization of a non-magnetic spin-photovoltaic effect via the SIHE, rendering our device an electrical polarimeter which directly converts the degree of circular polarization of light to a voltage signal.Comment: 14 pages, 4 figure

Local field factors in a polarized two-dimensional electron gas

We derive approximate expressions for the static local field factors of a spin polarized two-dimensional electron gas which smoothly interpolate between their small- and large-wavevector asymptotic limits. For the unpolarized electron gas, the proposed analytical expressions reproduce recent diffusion Monte Carlo data. We find that the degree of spin polarization produces important modifications to the local factors of the minority spins, while the local field functions of the majority spins are less affected.Comment: 8 pages, 10 figure