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Register a new userResonant optical control of the electrically-induced spin polarization by periodic excitation
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We show that the electron spin polarization generated by an electrical current may have its direction controlled and magnitude amplified by periodic optical excitation. The electrical and optical spin control methods were combined and implemented in a two-dimensional electron gas. By Kerr rotation in an external transverse magnetic field, we demonstrate unexpected long-lived coherent spin oscillations of the current-induced signal in a system with large spin-orbit interaction. Using a single linearly polarized pulse for spin manipulation and detection, we found a strong dependence on the pulse optical power and sample temperature indicating the relevance of the hole spin in the electron spin initialization. The signal was mapped in a Hall bar as function of the position relative to the injection contact. Finally, the presence of an in-plane spin polarization was directly verified by rotating the experimental geometry.
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The precise adjustment of the polariton condensate flow under incoherent excitation conditions is an indispensable prerequisite for polariton-based logic gate operations. In this report, an all-optical approach for steering the motion of a polariton condensate using only non-resonant excitation is demonstrated. We create arbitrarily shaped functional potentials by means of a spatial light modulator, which allow for tailoring the condensate state and guiding a propagating condensate along reconfigurable pathways. Additional numerical simulations confirm the experimental observations and elucidate the interaction effects between background carriers and polariton condensates.
We investigate interactions between electrons and nuclear spins by using the resistance (Rxx) peak which develops near filling factor n = 2/3 as a probe. By temporarily tuning n to a different value, ntemp, with a gate, the Rxx peak is shown to relax quickly on both sides of ntemp = 1. This is due to enhanced nuclear spin relaxation by Skyrmions, and demonstrates the dominant role of nuclear spin in the transport anomaly near n = 2/3. We also observe an additional enhancement in the nuclear spin relaxation around n = 1/2 and 3/2, which suggests a Fermi sea of partially-polarized composite fermions.
We have studied the current through a carbon nanotube quantum dot with one ferromagnetic and one normal-metal lead. For the values of gate voltage at which the normal lead is resonant with the single available non-degenerate energy level on the dot, we observe a pronounced decrease in the current for one bias direction. We show that this rectification is spin-dependent, and that it stems from the interplay between the spin accumulation and the Coulomb blockade on the quantum dot. Our results imply that the current is spin-polarized for one direction of the bias, and that the degree of spin polarization is fully and precisely tunable using the gate and bias voltages. As the operation of this spin diode does not require high magnetic fields or optics, it could be used as a building block for electrically controlled spintronic devices.
The spin-split states subject to Rashba spin-orbit coupling in two-dimensional systems have long been accepted as pointing inplane and perpendicular to the corresponding wave vectors. This is in general true for free electron model, but exceptions do exist elsewhere. Within the tight-binding model, we unveil the unusual upstanding behavior of those Rashba spins around $bar{K}$ and $bar{K}^{prime}$ points in honeycomb lattices. Our calculation (i) explains the recent experiment of the Tl/Si(111)-$(1times1)$ surface alloy [Phys. Rev. Lett. textbf{102}, 096805 (2009)], where abrupt upstanding spin states near $bar{K}$ are observed, and (ii) predicts an electrically reversible out-of-plane surface spin polarization.
It is widely recognized that a physical system can only respond to a periodic driving significantly when the driving frequency matches the normal mode frequency of the system, which leads to resonance. Off-resonant phenomena are rarely considered because of the difficulty to realize strong coupling between physical systems and off-resonant waves. Here we examine the response of a magnetic system to squeezed light and surprisingly find that the magnons are maximally excited when the effective driving frequency is several orders of magnitude larger than the resonant frequency. The generated magnons are squeezed which brings the advantage of tunable squeezing through an external magnetic field. Furthermore, we demonstrate that such off-resonant quasi-particle excitation is universal in all the hybrid systems in which the coherent and parametric interaction of bosons exists and that it is purely a quantum effect, which is rooted in the quantum fluctuations of particles in the squeezed vacuum. Our findings may provide an unconventional route to study off-resonant phenomena and may further benefit the use of hybrid matter-light systems in continuous variable quantum information.
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