Realistic heterointerface model for excitonic states in growth-interrupted GaAs quantum wells

Savona, Vincenzo; Langbein, Wolfgang Werner

doi:10.1103/physrevb.74.075311

Cited by 54 publications

(62 citation statements)

References 47 publications

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“…Such a long dephasing time is likely to be due to radiative decay. 16 We find that in the present experiment using 200 fs pulses ͓see red dashed line in Fig. 2͑a͔͒, the measured ␥ increases approximately linearly with the excitation power, by about ϳ5 eV/ ͑J / cm 2 ͒, significantly more than observed previously in experiments using 2 ps long pulses.…”

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confidence: 56%

“…This sample has been previously investigated 4,7,15 and its properties have been simulated. 16 Here we focus on the fine-structure splitting ͑FSS͒ of the bright exciton into two nondegenerate, orthogonally linearly polarized transitions. 17 The direction of the linear polarization is dictated by the in-plane anisotropy of the localizing structure.…”

mentioning

confidence: 99%

“…One can observe emission from various localized transitions and from a high density of states at the high energy side originating from the next monolayer thickness. The fractional monolayer thickness of the selected sample region leads to a low spectral and spatial density of localized states, 16 enabling us to find a region dominated by a single transition within the focal area both in PL and FWM ͓see black peak in Fig. 2͑a͔͒.…”

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confidence: 99%

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Vectorial four-wave mixing field dynamics from individual excitonic transitions

Kasprzak

Langbein

2008

Phys. Rev. B

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Degenerate four-wave mixing ͑FWM͒ from individual localized excitonic transitions is measured using a dual-polarization extension of heterodyne spectral interferometry. A fine-structure splitting ͑FSS͒ of the localized excitons of 20-80 eV is observed, revealing a spatially anisotropic localization in the quantum well plane, preferentially oriented along the ͓110͔ direction. The ratio of the transition dipole moments of the FSS transitions is in the range 0.7-1.4, with no significant correlation to the FSS. Retrieving both polarization components of the FWM in amplitude and phase we measure the time-resolved polarization state of the exciton after pulsed excitation, showing a coherent evolution oscillating between linear and virtually circular polarization. The polarization of the created FWM state is a result of the initial polarization state created by the first excitation pulse, its free evolution up to the arrival of the second pulse, and its conversion into the FWM controlled by the polarization of the second pulse. DOI: 10.1103/PhysRevB.78.041103 PACS number͑s͒: 78.47.Fg, 78.47.jj, 78.47.jm, 78.47.nj With the recent development of the heterodyne spectral interferometry ͑HSI͒ technique, 1 the measurement of the nonlinear coherent response, e.g., four-wave mixing ͑FWM͒, of individual localized two-level systems has become feasible. Standard FWM experiments 2,3 rely on directional selection of the nonlinear optical response and therefore are not suited for emitters localized to subwavelength regions, like excitons confined in quantum dots. HSI overcomes this limitation by taking advantage of an effective frequency selection of the FWM signal, relying only on the time invariance of the system investigated. HSI has been used to determine broadening mechanisms and measure microscopic dephasing time within finite, inhomogenously broadened ensembles of excitons 4 or transitions experiencing spectral wandering. 5 By applying spectral interferometry, 6 the FWM is retrieved both in amplitude and phase. This permits not only to obtain complete information about the state vector on the Bloch sphere, but also allows the resonant observation of coherent control of excitons on ultrafast time scales.7 By performing delaytime dependent HSI and transforming-in analog to NMR techniques 8,9 -the data into a two-frequency representation R −1,2 ͑ , 1 ͒, one can observe and classify coherent coupling between individual localized excitons. 1 Similar twodimensional techniques are used to investigate many-body interactions in quantum wells 10 and vibrational and electronic coupling in molecules.11 HSI is therefore a powerful tool for coherent characterization, ultrafast coherent control, and manipulation of excitonic qbits.In this work we extend the HSI technique to a dualpolarization scheme ͑DHSI͒, which allows us to simultaneously measure both polarization components of the field in phase and amplitude, completely determining the time or spectrally resolved polarization state of the FWM. A similar technique has been introduced...

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confidence: 56%

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confidence: 99%

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confidence: 99%

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Vectorial four-wave mixing field dynamics from individual excitonic transitions

Kasprzak

Langbein

2008

Phys. Rev. B

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“…We use driven-dissipative GPE to describe the evolution of the polarized polariton fields: where we assumed a parabolic dispersion of polaritons, described by an effective mass m. Interactions between condensed polaritons with parallel and antiparallel spins are described by interaction strengths a 1 and a 2 , respectively. The potential term V 0 represents the disorder in the system, which was modelled by a randomly generated Gauss correlated disorder 35 . The polariton potential is further modified by a blueshift from interaction with the reservoirs, described by strength g R .…”

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confidence: 99%

Dissociation dynamics of singly charged vortices into half-quantum vortex pairs

et al. 2012

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The quest for identification and understanding of fractional vorticity is a major subject of research in the quantum fluids domain, ranging from superconductors, superfluid Helium-3 to cold atoms. In a two-dimensional Bose degenerate gas with a spin degree of freedom, the fundamental topological excitations are fractional vortical entities, called half-quantum vortices. Convincing evidence for the existence of half-quantum vortices was recently provided in spinor polariton condensates. The half-quantum vortices can be regarded as the fundamental structural components of singly charged vortices but, so far, no experimental evidence of this relation has been provided. Here we report on the direct and time-resolved observation of the dynamical process of the dissociation of a singly charged vortex into its primary components, a pair of half-quantum vortices. The physical origin of the observed phenomenology is found in a spatially inhomogeneous static potential that couples the two spin components of the condensate.

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“…The disorder potential was generated using the procedure in ref. 28 to generate a single-layer disorder potential. The potential had an r.m.s.…”

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Observation of the optical spin Hall effect

Leyder¹,

Romanelli²,

Karr³

et al. 2007

Nature Phys

379

347

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The spin Hall effect consists of the generation of a spin current perpendicular to the charge current flow. Thirty-five years after its prediction by Dyakonov and Perel' 1 , it is the focus of experimental and theoretical investigations and constitutes one of the most remarkable effects of spintronics. Owing to scattering and dephasing in electronic gases, it is difficult to observe and has only been demonstrated for the first time a few years ago 2-5 . Recently, three of us have predicted the optical spin Hall effect 6 , which consists of a separation in real space and momentum space of spin-polarized exciton-polaritons generated by a laser in a semiconductor microcavity 7 . The separation takes place owing to a combination of elastic scattering of exciton-polaritons by structural disorder and an effective magnetic field coming from polarization splitting of the polariton states. The excitonic spin current is controlled by the linear polarization of the laser pump. Here, we report the first experimental evidence for this effect and demonstrate propagation of polariton spin currents over 100 µm in a high-quality GaAs/AlGaAs quantum microcavity. By rotating the polarization plane of the exciting light, we were able to switch the directions of the spin currents.The spin carries a quantum bit of information, which makes spin-based devices, also called spintronic devices, extremely promising for quantum-information processing 8 . More specifically, the spin Hall effect (SHE) has recently raised an increasing interest owing to its potentialities in spintronics 2,3 . In a similar way to the Hall effect, in which a magnetic field causes a particle to deviate depending on its charge, the spin Hall effect results in a spin current owing to the spin-dependent scattering of electrons by charged impurities or other defects (extrinsic SHE 1,9 ) or to the spin-orbit effects on the carrier energy dispersion (intrinsic SHE 10,11 ). It leads to a separation in real space and momentum space between spin-up and spin-down electrons and thus enables control of electron spin in semiconductor spintronic devices 12 . Optical 2,3 and electronic 4 measurements of the extrinsic SHE have been reported. Although successfully generated, electronic spin currents are subject to rapid dephasing and decay, mostly due to electron scattering. Recent theoretical studies 5,13 show that the intrinsic SHE is fully suppressed in macroscopic-sized samples because of electron scattering, which directs the system towards equilibrium. The use of neutral particles as carriers for spin currents is an alternative approach that may overcome the problem of dephasing. Here, we demonstrate the spin currents carried by (neutral) exciton-polaritons in a semiconductor microcavity and propagating coherently over 100 µm. We demonstrate for the first time experimentally that the spin currents can be controlled by an optical spin Hall effect (OSHE), which exhibits remarkable analogy to the spin Hall effect.Exciton-polaritons (or polaritons for short) are the 'mixed' exc...

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Realistic heterointerface model for excitonic states in growth-interrupted GaAs quantum wells

Cited by 54 publications

References 47 publications

Vectorial four-wave mixing field dynamics from individual excitonic transitions

Vectorial four-wave mixing field dynamics from individual excitonic transitions

Dissociation dynamics of singly charged vortices into half-quantum vortex pairs

Observation of the optical spin Hall effect

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