Self-Induced Acoustic Transparency in Semiconductor Quantum Films

The stationary current induced by a strong running potential wave in one-dimensional system is studied. Such a wave can result from illumination of a straight quantum wire with special grating or spiral quantum wire by circular-polarized light. The wave drags electrons in the direction correlating with the direction of the system symmetry and polarization of light. In a pure system the wave induces minibands in the accompanied system of reference. We study the effect in the presence of impurity scattering. The current is an interplay between the wave drag and impurity braking. It was found that the drag current is quantized when the Fermi level gets into energy gaps.Two main sources of the stationary photocurrent in homogeneous systems are known: light pressure (photon drag) [1] and photogalvanic [2], [3], [4] or ratchet effect. In the first case photons transmit their momenta to electrons and directly accelerate electrons, in the second case the light serves as an energy source, while the acceleration originates from a third body (impurities, phonons etc.), and the current direction correlates with the polarization of light via material tensors.A related phenomenon is the electron drag by a surface acoustic wave (SAW) [5],[6],[7],[8],[9], [10],[11], [12]. The wavelength of SAW is large as compared with electrons, so the periodicity is less important and electrons are treated as captured into dynamic quantum dots formed by potential minima. The discreteness of electrons leads to the SAW drag quantization. The quantization exists both with and without e-e interaction. If the wave amplitude is weak enough the quantum dots can not keep electrons and the picture fails.In recent papers [13,14] we have studied the electron drag by circular-polarized electromagnetic field in curved quantum wires, particularly, in quantum spirals. In such systems the electric field of a long external electromagnetic wave is converted to an effective short wave propagating along the wire. The wave drags electrons. The effect resembles the travelling-wave tube with the difference that the field remains almost uniform while the acting component of this field projected to the wire has a short wavelength. Besides, the effect takes place in a solid instead of vacuum.We have considered the problem in the limit of weak field. It was also found that strong field bunches electrons in the potential minima, forcing them to move with the phase speed of the wave.It should be emphasized that an effective wave can be produced in different ways, for example in the same way as in the travelling-wave tube, using metallic or dielectric spiral grating and straight quantum wire along the spiral axis. These inhomogeneous dielectric properties pro-duce non-uniformity of local electric field and form the running wave. Such a construction permits to use not an exotic system like semiconductor spiral quantum wire [15,16], but more realistic systems: straight quantum wires together with spiral spacial field modulators. Another more simple design is a double grating...

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“…Current (9) does not depend on the amplitude of a scattering potential. If the amplitude of the wave goes down the current tends to zero.…”

Section: Metallic Casementioning

confidence: 96%

“…A related phenomenon is the electron drag by a surface acoustic wave (SAW) [5], [6], [7], [8], [9], [10], [11], [12]. The wavelength of SAW is large as compared with electrons, so the periodicity is less important and electrons are treated as captured into dynamic quantum dots formed by potential minima.…”

mentioning

confidence: 99%

Stationary drag photocurrent caused by strong effective running wave in quantum wires: Quantization of current

Éntin

Magarill

2010

Phys. Rev. B

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“…A moving array of DQDs with dimensions of ∼ 1 µm can be easily realized by the interference of two SAW beams propagating along the [110] and [11 0] directions, as illustrated in Fig. 2(b) [10,14,17]. The gray scale image in this figure shows a stroboscopic PL micrograph of the DQD array, which propagates along the x = [100] direction with a velocity v DD = √ 2v SAW .…”

Section: Dynamic Quantum Dots -Dqdsmentioning

confidence: 99%

Coherent spin transport by acoustic fields in GaAs quantum wells

Couto

Iikawa

Stotz

et al. 2006

Phys. Status Solidi (c)

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We review processes for long-range spin transport and manipulation in GaAs quantum wells using mobile potentials created by the piezoelectric field of a surface acoustic wave. By reducing spin dephasing mechanisms associated with the spin orbit-coupling, these potentials can coherently transport spins over distances on the order of 100 µm.1 Introduction Quantum information processing using electron spins in semiconductor structures requires the coherent manipulation of spin polarized carriers. For that purpose one needs interaction mechanisms that act efficiently on the spin vectors without reducing the spin coherence time. Advanced applications further require the interaction between two spins in order to realize two-spin gates.Previous studies to control spins in semiconductor nanostructures have focused on two main approaches. The first relies on the use of localized spin systems. Examples are nuclear spins [1,2] or electron spins in quantum dots (QDs). These spin systems are well-isolated from their environment, thus leading to long spin coherence times. The manipulation of electron spins, down to the single spin level, has been achieved by subjecting the spins to external optical, magnetic, or electric fields applied at the QD location [3]. In the case of nuclear spins, control can also be achieved through the interaction with electron spins. A major challenge faced by processes based on confined spins is the controlled coupling between two different spin systems that is required for the formation of two-spin gates. The second approach uses mobile spins and the control of the spin orientation takes place during spin transport via the spin-orbit (so) coupling. This interaction couples the spins to the orbital degrees of freedom, thus making the spins susceptible to applied electric and optic fields. As a result, a moving electron feels an effective magnetic field B int that depends on the electron wave vector as well as on externally applied fields. A well-known proposal is the electrooptical spin analog by Datta and Das [4]. Here, an applied electric field in the direction perpendicular to the movement is used to create the field B int , which rotates the electron spins during transport.In this paper, we review an alternative concept for spin manipulation which combines the main features of the approaches discussed above. It is based on the transport of spins by mobile, but simultaneously confining, potentials produced by the piezoelectric field of a surface acoustic wave (SAW). This concept, which has been introduced in Refs. [5] and [6], is schematically illustrated in Fig. 1. Here, a SAW with a wavelength λ SAW on the order of 1 µm is generated by an interdigital transducer (IDT) deposited on a GaAs quantum well (QW) sample and excited by microwaves [ Fig. 1(a)]. Spin polarized electron-hole pairs are photogenerated within the SAW beam by a circularly polarized laser spot focused on position G. The electrons and holes are captured within the maxima and minima of the SAW piezoelectric potential (Φ SAW ), w...

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“…[36][37][38][39][40] Surface acoustic waves are being used to trap carriers in dynamically created quantum dots, transport these trapped carriers, and store light. [41][42][43][44][45][46][47][48][49] To exploit these nanomechanical deformations, one must have ways to probe and control them. It has been suggested that sideband cooling via optical absorption by QDs buried in nanomechanical structures could bring the structures to the quantum limit.…”

Section: Introductionmentioning

confidence: 99%

Controlling the optics of quantum dots with nanomechanical strain

et al. 2011

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We show how nanomechanical strain can be used to dynamically control the optical response of self-assembled quantum dots embedded in nanomechanical bridges, giving a tool to shift electron and hole levels, manipulate mechanoexciton shape, orientation, fine-structure splitting, and optical transitions, transfer carriers between dots, and interact qubits for quantum processing. Conversely, we show how modulation of the quantum dot optical response can be used to monitor locally an applied nanomechanical strain. Atomistic tight-binding theory is used to describe the response of electrons and holes in a self-assembled quantum dot to applied nanomechanical strain. The internal strain due to the lattice mismatch, the nanomechanical strain, and the internal atomic readjustment to minimize the applied strain must all be accounted for to model correctly the strain effects. Electrons and hole levels and charge distributions can shift together or in opposite directions depending on how the strain is applied. This gives control for tailoring band gaps and optical response. The strain can also be used to transfer electrons and holes between vertically or laterally coupled dots, giving a mechanism for manipulating transition strengths and interacting qubits for quantum information processing. Applied strain can be used to manipulate the fine-structure splitting of mechanoexcitons by distorting electron and hole charge distributions and rotating hole orientation. Most importantly, nanomechanical strain reengineers both the magnitude and phase of the exciton exchange coupling to tune exchange splittings, change the phase of spin mixing, and rotate the polarization of mechanoexcitons, providing phase and energy control of excitons.

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Self-Induced Acoustic Transparency in Semiconductor Quantum Films

Cited by 12 publications

References 25 publications

Stationary drag photocurrent caused by strong effective running wave in quantum wires: Quantization of current

Stationary drag photocurrent caused by strong effective running wave in quantum wires: Quantization of current

Coherent spin transport by acoustic fields in GaAs quantum wells

Controlling the optics of quantum dots with nanomechanical strain

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