19 results on '"SPIN polarization"'
Search Results
2. Vacuum Spin LED: First Step towards Vacuum Semiconductor Spintronics.
- Author
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Tereshchenko, Oleg E., Golyashov, Vladimir A., Rusetsky, Vadim S., Kustov, Danil A., Mironov, Andrey V., and Demin, Alexander Yu.
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ELECTRON affinity , *SPINTRONICS , *PHOTOEMISSION , *POLARIZED electrons , *SEMICONDUCTORS , *SPIN polarization - Abstract
Improving the efficiency of spin generation, injection, and detection remains a key challenge for semiconductor spintronics. Electrical injection and optical orientation are two methods of creating spin polarization in semiconductors, which traditionally require specially tailored p-n junctions, tunnel or Schottky barriers. Alternatively, we introduce here a novel concept for spin-polarized electron emission/injection combining the optocoupler principle based on vacuum spin-polarized light-emitting diode (spin VLED) making it possible to measure the free electron beam polarization injected into the III-V heterostructure with quantum wells (QWs) based on the detection of polarized cathodoluminescence (CL). To study the spin-dependent emission/injection, we developed spin VLEDs, which consist of a compact proximity-focused vacuum tube with a spin-polarized electron source (p-GaAs(Cs,O) or Na2KSb) and the spin detector (III-V heterostructure), both activated to a negative electron affinity (NEA) state. The coupling between the photon helicity and the spin angular momentum of the electrons in the photoemission and injection/detection processes is realized without using either magnetic material or a magnetic field. Spin-current detection efficiency in spin VLED is found to be 27% at room temperature. The created vacuum spin LED paves the way for optical generation and spin manipulation in the developing vacuum semiconductor spintronics. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
3. Spin-Filter Devices Based on Resonant Magnetic Tunnel Junctions.
- Author
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Daqiq, Reza
- Subjects
MAGNETIC tunnelling ,RESONANT tunneling ,SPIN-polarized currents ,TUNNEL junctions (Materials science) ,SPIN polarization ,QUANTUM wells ,SPIN-orbit interactions ,SPINTRONICS - Abstract
Spin-polarized currents are investigated in symmetric (asymmetric) resonant magnetic tunnel junctions (S- (A)-RMTJs) including a non-magnetic metal (NM) layer. Charge-diode and spin-diode features are found for the S-RMTJs at definite thicknesses of MgO and NM layers. Owing to the presence of quantum-well states, a full spin polarization can be achieved by proper choice of the thickness of NM layer. The charge and spin currents have increased for the A-RMTJs in comparison to those of the S-RMTJs due to different properties of ferromagnetic electrodes. The present study suggests new spin-filter devices to use in the spintronics field. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
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4. Experimental analysis of the spin–orbit coupling dependence on the drift velocity of a spin packet.
- Author
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Kawahala, N. M., Moraes, F. C. D., Gusev, G. M., Bakarov, A. K., and Hernandez, F. G. G.
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TWO-dimensional electron gas , *VELOCITY , *ELECTRON gas , *SPIN polarization , *SPIN-orbit interactions , *SPINTRONICS , *QUANTUM wells - Abstract
Spin transport was studied in a two-dimensional electron gas hosted in a wide GaAs quantum well occupying two subbands. Using space and time Kerr rotation microscopy to image drifting spin packets under an in-plane accelerating electric field, optical injection and detection of spin polarization were achieved in a pump–probe configuration. The experimental data exhibited high spin mobility and long spin lifetimes allowing us to obtain the spin–orbit fields as a function of the spin velocities. Surprisingly, above moderate electric fields of 0.4 V/cm with velocities higher than 2 µm/ns, we observed a dependence of both bulk and structure-related spin–orbit interactions on the velocity magnitude. A remarkable feature is the increase in the cubic Dresselhaus term to approximately half of the linear coupling when the velocity is raised to 10 µm/ns. In contrast, the Rashba coupling for both subbands decreases to about half of its value in the same range. These results yield new information on the application of drift models in spin–orbit fields and about limitations for the operation of spin transistors. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
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5. Circular photogalvanic spectroscopy of Rashba splitting in 2D hybrid organic–inorganic perovskite multiple quantum wells.
- Author
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Liu, Xiaojie, Chanana, Ashish, Huynh, Uyen, Xue, Fei, Haney, Paul, Blair, Steve, Jiang, Xiaomei, and Vardeny, Z. V.
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QUANTUM wells ,PHOTOCONDUCTIVITY ,ELECTRONIC band structure ,ACTION spectrum ,SPIN polarization ,ELECTROLYTIC corrosion ,PHOTOELECTROCHEMISTRY - Abstract
The two-dimensional (2D) Ruddlesden−Popper organic-inorganic halide perovskites such as (2D)-phenethylammonium lead iodide (2D-PEPI) have layered structure that resembles multiple quantum wells (MQW). The heavy atoms in 2D-PEPI contribute a large spin-orbit coupling that influences the electronic band structure. Upon breaking the inversion symmetry, a spin splitting ('Rashba splitting') occurs in the electronic bands. We have studied the spin splitting in 2D-PEPI single crystals using the circular photogalvanic effect (CPGE). We confirm the existence of Rashba splitting at the electronic band extrema of 35±10 meV, and identify the main inversion symmetry breaking direction perpendicular to the MQW planes. The CPGE action spectrum above the bandgap reveals spin-polarized photocurrent generated by ultrafast relaxation of excited photocarriers separated in momentum space. Whereas the helicity dependent photocurrent with below-gap excitation is due to spin-galvanic effect of the ionized spin-polarized excitons, where spin polarization occurs in the spin-split bands due to asymmetric spin-flip. Hybrid organic-inorganic perovskites (HOIP) have high potential for spintronics applications. Using the circular photogalvanic effect the authors demonstrate the existence of Rashba-splitting in the continuum bands of a 2D layered HOIP that results from inversion symmetry breaking along the growth direction. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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6. Raman Measurements as a Fast and Efficient Technique for Characterisation of TiO2 and Quantum Dots on TiO2 Substrate for Photovoltaic Application.
- Author
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KWASNICKI, P. and INGLOT, M.
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SEMICONDUCTOR nanocrystals , *QUANTUM dots , *QUANTUM wells , *MANUFACTURING processes , *RAMAN microscopy , *MASS production , *COLLOIDAL crystals - Abstract
In this work we focus on the characterization methods allowing fast, cheap, and easy identification of photoanode TiO2 layer as well as quantum dots on the TiO2 surface for photovoltaic application. Application of the colloidal quantum dots material for the production of quantum dots solar cell is a key issue for mass production. At the same time there is a demand for a method to control the production steps for the deposition process for both photoanode and nanomaterial. The method has to be fast and cheap as well as efficient in order to meet the requirements imposed by production processes. For this purpose we propose to use a micro Raman spectroscopy as an efficient method to verify the presence of QDs. In this work we compare the results obtained by scanning electron microscopy with the Raman spectroscopy in theme of the pros and cons of these techniques. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
7. Transport Properties Through Multi-Barrier Magnetic System Containing a “Noncoplanar Defect”.
- Author
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Sahakyan, Avak, Poghosyan, Anahit, Movsesyan, Ruzan, and Kocharian, Armen
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MAGNETIC fields , *COPLANAR waveguides , *QUANTUM wells , *POLARIZATION (Electricity) , *MAGNETIC moments - Abstract
The 1-D nanoscale structures are studied with a potential relief containing magnetic barriers separated by nonmagnetic quantum wells in the absence of exchange interaction between the magnetic moments of adjacent barriers. The considered structure is the sequence of N barriers divided into two “ferromagnetic domains” of the length n and N - n -- 1, both having parallel internal fields. In contrast, the internal field of the nth barrier is not coplanar with respect to the internal fields of the left and/or right “domains.” The degree of spin polarization of an electron wave transmitted through this system is calculated with the assumption that the incident wave is unpolarized with the degree of its polarization equals zero. It is shown that the degree of polarization of the transmitted wave as a function of the impulse exhibits a sequence of sufficiently wide plateaus, which are close to unity. In particular, there are significant deviations from the known spintronics phenomena found earlier in this system such as the valve, filter, and giant magnetoresistance effects. This circumstance provides opportunities for managing the transport properties of the system by varying the noncoplanar degrees of freedom of the system. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
8. Spin Polarization of Carriers in InGaAs Self-Assembled Quantum Rings Inserted in GaAs-AlGaAs Resonant Tunneling Devices.
- Author
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Orsi Gordo, V., Gobato, Y., Galeti, H., Brasil, M., Taylor, D., and Henini, M.
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SPIN polarization ,PHOTOLUMINESCENCE ,ALUMINUM gallium arsenide lasers ,QUANTUM rings ,QUANTUM wells - Abstract
In this work, we have investigated transport and polarization resolved photoluminescence (PL) of n-type GaAs-AlGaAs resonant tunneling diodes (RTDs) containing a layer of InGaAs self-assembled quantum rings (QRs) in the quantum well (QW). All measurements were performed under applied voltage, magnetic fields up to 15 T and using linearly polarized laser excitation. It was observed that the QRs' PL intensity and the circular polarization degree (CPD) oscillate periodically with applied voltage under high magnetic fields at 2 K. Our results demonstrate an effective voltage control of the optical and spin properties of InGaAs QRs inserted into RTDs. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
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9. SPIN-POLARIZED TRANSPORT THROUGH GaAs/AlGaAs PARABOLIC QUANTUM WELL UNDER A UNIFORM MAGNETIC FIELD.
- Author
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WAN, F., JALIL, M. B. A., TAN, S. G., and FUJITA, T.
- Subjects
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POTENTIAL theory (Physics) , *ENERGY-band theory of solids , *QUANTUM wells , *MAGNETIC fields , *PARTICLES (Nuclear physics) - Abstract
We present a GaAs/AlGaAs-based quantum well device capable of achieving an appreciable spin polarization coupled with high electron transmission. Our numerical results indicate that the device is able to achieve a high spin polarization without the need for less commonly used materials with high g-factors required by previously proposed semiconductor-based systems. The electron transmission and spin polarization amplitude of our structure is found to be robust to the length of the parabolic well, which could ease the fabrication of such structures in practical applications. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
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10. Current-Induced Spin Photocurrent in GaAs at Room Temperature.
- Author
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Zhang, Yang, Liu, Yu, Xue, Xiao-Lan, Zeng, Xiao-Lin, Wu, Jing, Shi, Li-Wei, and Chen, Yong-Hai
- Subjects
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AUDITING standards , *SPIN polarization , *GALLIUM arsenide , *ELECTRIC fields , *QUANTUM wells , *TEMPERATURE - Abstract
Circularly polarized photocurrent, observed in p-doped bulk GaAs, varies nonlinearly with the applied bias voltage at room temperature. It has been explored that this phenomenon arises from the current-induced spin polarization in GaAs. In addition, we found that the current-induced spin polarization direction of p-doped bulk GaAs grown in the (001) direction lies in the sample plane and is perpendicular to the applied electric field, which is the same as that in GaAs quantum well. This research indicates that circularly polarized photocurrent is a new optical approach to investigate the current-induced spin polarization at room temperature. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
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11. Spin-Polarized Transport in II—VI Magnetic Resonant-Tunneling Devices.
- Author
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Sánchez, David, Gould, Charles, Schmidt, Georg, and Molenkamp, Laurens W.
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DILUTED magnetic semiconductors , *POLARIZATION (Electricity) , *TUNNEL diodes , *SEMICONDUCTOR diodes , *QUANTUM wells , *MAGNETIC fields - Abstract
In this paper, we investigate electronic transport through II-VI semiconductor resonant-tunneling structures containing diluted magnetic impurities. Due to the exchange interaction between the conduction electrons and the impurities, there arises a giant Zeeman splitting in the presence of a moderately low magnetic field. As a consequence, when the quantum well is magnetically doped, the current-voltage characteristics shows two peaks corresponding to transport for each spin channel. This behavior is experimentally observed and can be reproduced with a simple tunneling model. The model thus allows to analyze other configurations. First, we further increase the magnetic field, which leads to a spin polarization of the electronic current injected from the leads, thus giving rise to a relative change in the current amplitude. We demonstrate that the spin polarization in the emitter can be determined from such a change. Furthermore, in the case of an injector with magnetic impurities, our model shows a large increase in peak amplitude accompanied by a shift of the resonance to higher voltages with increasing fields. We find that this effect arises from a combination of 3-D incident distribution, giant Zeeman splitting, and broad resonance linewidth. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
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12. Spontaneous spin polarization in doped semiconductor quantum wells
- Author
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Pablo Ignacio Tamborenea and L. O. Juri
- Subjects
Physics ,Phase transition ,Condensed Matter - Mesoscale and Nanoscale Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,Spin polarization ,Ciencias Físicas ,Exchange interaction ,FOS: Physical sciences ,semiconductors ,Electron ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Astronomía ,Condensed Matter - Strongly Correlated Electrons ,quantum wells ,Effective mass (solid-state physics) ,Ferromagnetism ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,quantum phase transition ,Fermi gas ,CIENCIAS NATURALES Y EXACTAS ,Quantum well - Abstract
We calculate the critical density of the zero-temperature, first-order ferromagnetic phase transition in n-doped GaAs/AlGaAs quantum wells. We find that the existence of the ferromagnetic transition is dependent upon the choice of well width. We demonstrate rigorously that this dependence is governed by the interplay between different components of the exchange interaction and that there exists an upper limit for the well width beyond which there is no transition. We predict that some narrow quantum wells could exhibit this transition at electron densities lower than the ones that have been considered experimentally thus far. We use a screened Hartree-Fock approximation with a polarization-dependent effective mass, which is adjusted to match the critical density predicted by Monte Carlo calculations for the two-dimensional electron gas., Comment: Submitted to Eur. Phys. Journal B
- Published
- 2005
13. Excitation energy dependence of initial phase shift in Kerr rotation of resident electron spin polarization in a CdTe single quantum well
- Author
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Yan, L. -P., Takamure, T., Kaji, R., Karczewski, G., Takeyama, S., and Adachi, S.
- Subjects
Kerr rotation ,Quantum wells ,spin precession ,CdTe ,spin polarization - Abstract
The generation dynamics of a resident electron spin polarization involve the formation and transformation of the associated optically excited states depending on the excitation photon energy. Initial phase shift in the precession of a resident electron spin polarization gives the important clues to reveal the interplay between the associated excited states and resident electrons. In this work, the excitation energy dependence of the initial phase shift in Kerr rotation of a resident electron spin polarization is investigated in a CdTe/Cd0.85Mg0.15Te single quantum well under a low magnetic field. Through the careful analysis of the spin precession, the excited electron-heavy-hole pairs show unique spin dynamics when the excitation energy is increasing past the neutral exciton resonance. Meanwhile, the negative initial phase shift becomes significantly large in magnitude. The larger initial phase shift and the unique precession traces are caused by the transformation from neutral excitons to negative trions with accompanying the hole spin-flip. The exciton-to-trion transformation time is estimated experimentally to be approximate to 160ps.
- Published
- 2017
14. Spin-orbit coupling and the topology of gases of spin-degenerate cold excitons in photoexcited GaAs-AlGaAs quantum wells
- Author
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Michał Matuszewski, Timothy Chi Hin Liew, Alexey Kavokin, Yuri G. Rubo, and School of Physical and Mathematical Sciences
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Condensed Matter::Quantum Gases ,Physics ,Condensed matter physics ,Spin polarization ,Condensed Matter::Other ,Exciton ,Degenerate energy levels ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Spin–orbit interaction ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Condensed Matter Physics ,Topology ,Electronic, Optical and Magnetic Materials ,Quantum wells ,Quasiparticle ,Excitons ,Quantum well ,Biexciton ,Spin-½ - Abstract
We calculate the spatial structure of four-component spinor systems of mixed bright and dark exciton condensates in coupled quantum wells. The spin-dependent bright-dark exciton conversion and Dresselhaus spin-orbit coupling is found to generate a rich variety of topological elements. By propagating the Gross-Pitaevskii equation in imaginary time, we observe the following: single and multiple polarized vortices; the phase separation of bright and dark excitons; and exotic spatial structures in density and spin polarization. Published version
- Published
- 2012
15. Spin noise spectroscopy in GaAs (110) quantum wells: Access to intrinsic spin lifetimes and equilibrium electron dynamics
- Author
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Dieter Schuh, Georg M. Müller, Michael Oestreich, Werner Wegscheider, Jens Hübner, and Michael Römer
- Subjects
Electron spins ,Quantum well lasers ,Semiconductor systems ,General Physics and Astronomy ,FOS: Physical sciences ,Electrons ,Electron ,Zero field splitting ,N-doped ,Spin dynamics ,Brownian movement ,Probe lasers ,Spin noise spectroscopies ,Spin wave ,Semiconducting indium ,Electron dynamics ,Line widths ,Low temperatures ,ddc:530 ,Spin relaxations ,Semiconducting gallium ,Spin (physics) ,Semiconductor quantum wells ,Nondemolition measurements ,Electron systems ,Physics ,Condensed matter physics ,Spin polarization ,Brownian motions ,Intrinsic spins ,Gallium alloys ,Total momentums ,Spin quantum number ,Dynamics ,Spatially resolved ,Condensed Matter - Other Condensed Matter ,Quantum wells ,Equilibrium conditions ,Semiconductor quantum wires ,Spinplasmonics ,Condensed Matter::Strongly Correlated Electrons ,Dewey Decimal Classification::500 | Naturwissenschaften::530 | Physik ,Quantum spin liquid ,Wells ,Other Condensed Matter (cond-mat.other) - Abstract
In this Letter, the first spin noise spectroscopy measurements in semiconductor systems of reduced effective dimensionality are reported. The nondemolition measurement technique gives access to the otherwise concealed intrinsic, low temperature electron spin relaxation time of n-doped GaAs (110) quantum wells and to the corresponding low temperature anisotropic spin relaxation. The Brownian motion of the electrons within the spin noise probe laser spot becomes manifest in a modification of the spin noise line width. Thereby, the spatially resolved observation of the stochastic spin polarization uniquely allows to study electron dynamics at equilibrium conditions with a vanishing total momentum of the electron system. © 2008 The American Physical Society.
- Published
- 2008
- Full Text
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16. Bidirectional resonant tunneling spin pump
- Author
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Ting, David Z. -Y., Cartoixà Soler, Xavier, and American Physical Society
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Physics ,Spin pumping ,Resonant tunneling ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Spin polarization ,Spin engineering ,Spin polarized scanning tunneling microscopy ,Quantum effects ,Semiconductor device design ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Magnetic semiconductors ,Quantum wells ,Semiconductors ,Electric currents ,Magnetic fields ,Spin transistor ,Spinplasmonics ,Spin Hall effect ,Heterojunctions ,Condensed Matter::Strongly Correlated Electrons ,Rashba effect ,Spin polarized transport - Abstract
We propose a mechanism for achieving bidirectional spin pumping in conventional nonmagnetic semiconductor resonant tunneling heterostructures under zero magnetic field. The device is designed specifically to take advantage of the special spin configuration described by the Rashba effect in asymmetric quantum wells. It induces the simultaneous flow of oppositely spin-polarized current components in opposite directions through spin-dependent resonant tunneling, and can thus generate significant levels of spin current with very little net electrical current across the tunnel structure, a condition characterized by a greater-than-unity current spin polarization. We also present modeling results on temperature dependence and finite device size effects.
- Published
- 2003
17. Polarized interacting exciton gas in quantum wells and bulk semiconductors
- Author
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Carlos Tejedor, Joaquín Fernández-Rossier, Luis Viña, L. Muñoz, Grupo de Nanofísica, and Universidad de Alicante. Departamento de Física Aplicada
- Subjects
Physics ,Condensed Matter::Quantum Gases ,Bulk semiconductors ,Spin polarization ,Condensed matter physics ,Física de la Materia Condensada ,Condensed Matter::Other ,Exciton ,Energy level splitting ,Binding energy ,Condensed Matter (cond-mat) ,Spin polarized exciton gases ,FOS: Physical sciences ,Condensed Matter ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Condensed Matter::Materials Science ,Quantum wells ,Mean field theory ,Exciton binding energies ,Excitation ,Quantum well ,Biexciton - Abstract
We develop a theory to calculate exciton binding energies of both two- and three-dimensional spin polarized exciton gases within a mean field approach. Our method allows the analysis of recent experiments showing the importance of the polarization and intensity of the excitation light on the exciton luminescence of GaAs quantum wells. We study the breaking of the spin degeneracy observed at high exciton density $(5 \ \ 10^{10} cm ^2)$. Energy level splitting betwen spin +1 and spin -1 is shown to be due to many-body inter-excitonic exchange while the spin relaxation time is controlled by intra-exciton exchange., Comment: Revtex, 4 figures sent by fax upon request by e-mail
- Published
- 1996
18. Synchronous Spatial Oscillation of Electron- and Mn-Spin Polarizations in Dilute-Magnetic-Semiconductor Quantum Wells under Spin–Orbit Effective Magnetic Fields
- Author
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Takuma Tsuchiya
- Subjects
Rashba field ,dilute magnetic semiconductors ,General Physics and Astronomy ,FOS: Physical sciences ,Electron ,CdMnTe ,electron-spin precession ,electron-spin polarization ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,s-d interaction ,Physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,Spin polarization ,Condensed matter physics ,Scattering ,Magnetic semiconductor ,Polarization (waves) ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Mn-spin polarization ,Magnetic field ,Monte Carlo method ,quantum wells ,Ferromagnetism ,impurity Overhauser effect ,Condensed Matter::Strongly Correlated Electrons ,Coherence (physics) - Abstract
In semiconductors, spin-orbit effective magnetic fields, i.e., the Rashba and Dresselhaus fields, are used to control electron-spin polarization. This operation, however, destroys the electron-spin coherence, and the spin polarization is limited to the vicinity of a ferromagnetic source electrode. In this paper, we propose the use of dilute magnetic semiconductors to improve the coherence of spatially oscillating electron-spin polarization. In dilute magnetic semiconductors, the electron-spin polarization near the source electrode dynamically induces the local spin polarization of magnetic impurities through s-d spin-flip scattering. This impurity-spin polarization improves, in turn, the coherence of the electron-spin polarization, and this improved electron-spin polarization induces impurity-spin polarization farther in the adjacent region. Because of this positive feedback, the coherent and synchronized spatial oscillations of electron- and impurity-spin polarizations grow cooperatively. A numerical calculation for a CdMnTe quantum well demonstrates the validity of this mechanism., Comment: 30 pages, 6 figures, 1 table
- Published
- 2012
19. Spin splitting in a polarized quasi-two-dimensional exciton gas
- Author
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K. H. Ploog, E. Pérez, Carlos Tejedor, L. Muñoz, Joaquín Fernández-Rossier, Luis Viña, Universidad de Alicante. Departamento de Física Aplicada, and Grupo de Nanofísica
- Subjects
Physics ,Spin polarization ,Condensed matter physics ,Física de la Materia Condensada ,Condensed Matter::Other ,Exciton ,Condensed Matter (cond-mat) ,FOS: Physical sciences ,Condensed Matter ,Zero field splitting ,Polarization (waves) ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Condensed Matter::Materials Science ,Quantum wells ,Spin splitting ,Polarization ,Ultrashort pulse ,Quantum well ,Exciton gas - Abstract
We have observed a large spin splitting between "spin" $+1$ and $-1$ heavy-hole excitons, having unbalanced populations, in undoped GaAs/AlAs quantum wells in the absence of any external magnetic field. Time-resolved photoluminescence spectroscopy, under excitation with circularly polarized light, reveals that, for high excitonic density and short times after the pulsed excitation, the emission from majority excitons lies above that of minority ones. The amount of the splitting, which can be as large as 50% of the binding energy, increases with excitonic density and presents a time evolution closely connected with the degree of polarization of the luminescence. Our results are interpreted on the light of a recently developed model, which shows that, while intra-excitonic exchange interaction is responsible for the spin relaxation processes, exciton-exciton interaction produces a breaking of the spin degeneracy in two-dimensional semiconductors., Revtex, four pages; four figures, postscript file Accepted for publication in Physical Review B (Rapid Commun.)
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