Exciton-polaritons In Quantum Wells Research Articles

Whispering-Gallery Quantum-Well Exciton Polaritons in an Indium Gallium Arsenide Microdisk Cavity.

Despite appealing high-symmetry properties that enable strong spatial confinement and ultrahigh-Q, optical whispering-gallery modes of spherical and circular resonators have been absent from the field of quantum-well exciton polaritons. Here we observe whispering-gallery exciton polaritons in a gallium arsenide microdisk cavity filled with indium gallium arsenide quantum wells, the test bed materials of polaritonics. Strong coupling is evidenced in photoluminescence and resonant spectroscopy accessed through concomitant confocal microscopy and near-field optical techniques. Excitonic and optical resonances are tuned by varying temperature and disk radius, revealing Rabi splittings between 5 and 10meV. A dedicated analytical quantum model for such circular whispering-gallery polaritons is developed, which reproduces the measured values. At high power, lasing is observed and accompanied by a blueshift of the emission consistent with the regime of polariton lasing. With experimental methods and theory now established, whispering-gallery-mode polaritons in round dielectric resonators appear as a new viable platform toward low loss polaritonics.

Magnetic-field interaction of spatially confined quantum-well exciton-polaritons

We report on pronounced magneto-optical effects of trapped polariton modes in a single InGaAs quantum well microresonator with a lithographically defined modulation of the cavity length. In our optical polariton traps with diameters ranging from 1 to 10 μm, a confinement potential of 7.5 meV is achieved. In magnetic-field dependent experiments, a diamagnetic shift and a Zeeman splitting of the trap-modes are observed which confirms that the polaritonic nature of the quantized emission modes are preserved even for traps as small as 1 μm. Furthermore, focusing on theoretical estimates using a simple model, we have identified a clear correlation between the polaritons' magnetic response and their excitonic fraction, corresponding to the Hopfield coefficients of the composite particles.

Zeeman splitting and diamagnetic shift of spatially confined quantum-well exciton polaritons in an external magnetic field

We report on pronounced magneto-optical effects of spatially confined polariton modes in an InGaAs quantum-well microcavity. The polaritons were trapped by a lithographically modulated cavity length. In contrast to etched structures suffering from nonradiative recombination, this approach allows for a gentle modification of the dielectric properties and results in a confinement potential of 7.5 meV. In the presence of an external magnetic field, a diamagnetic shift and Zeeman splitting of the quantized modes were observed for different trap diameters, ranging from 1 to 10 \ensuremath{\mu}m. This confirms that the polaritonic properties of the emission modes are preserved even for small traps. Moreover, a clear correlation between the magnetic response and the excitonic fraction of the polaritons was identified by magnetic field--dependent measurements.

Theory of Propagation and Scattering of Exciton-Polaritons in Quantum Wells

A novel semi-classical theory of exciton-polaritons in quantum wells (QWs) is presented. Time-resolved coherent optical spectra of QWs are described by the light coupling with ensembles of localized quantum dot-like exciton states. The ratio between reflection and resonant Rayleigh scattering (RRS) intensity gives a direct measure of the density of these excitonic dots. Good agreement with experimental data for time-resolved angle-dependent reflection and RRS from a GaAs single QW is achieved.

45° REFLECTOMETRY OF SEMICONDUCTOR QUANTUM WELLS

We have applied the 45° reflectometry for the first time to study exciton-polaritons in quantum wells. The 45° reflectometry is a new polarization-modulation technique, which is based on the measurement of the difference [Formula: see text] between the p-polarization reflectivity (Rp) and the squared s-polarization reflectivity [Formula: see text] at an angle of incidence of 45°. We show that [Formula: see text] spectra may provide qualitatively new information on the exciton-polariton modes in a quantum well. These optical spectra turn out to be very sensitive to the zeros of the dielectric function along the quantum-well growth direction and, therefore, allow to identify the resonances associated with the Z exciton-polariton mode. We demonstrate that 45° reflectometry could be a powerful tool for studying Z exciton-polariton modes in near-surface quantum wells, which are difficult to observe in simple spectra of reflectivity Rp

Picosecond dynamics of resonantly-excited excitons in GaAs quantum wells

We have simultaneously investigated various processes contributing to the initial dynamics of resonantly-excited excitons in quantum wells. A unified analysis of the results provides quantitative information on different scattering rates and exciton recombination rate. Our results clearly show the important role of enhanced recombination of exciton-polaritons in quantum wells and provide new insights into the initial dynamics of excitons.

Electric field dependence of the propagation of quantum-well exciton polaritons in a waveguide structure

Electric field dependence of the propagation of quantum-well exciton polaritons in a waveguide structure is investigated with an interferometric technique and discussed on the basis of electric-field-dependent spatial-dispersion relations. Two-dimensional enhancement of photon-exciton interaction gives rise to an increase in the longitudinal-transverse splitting energy of quantum-well exciton, five times as large as that of three-dimensional bulk exciton. This enlargement characterizes the quantum-confinement effect on exciton polaritons in a waveguide structure. The 1S oscillator strength of relevant quantum-well exciton is 0.4 that amounts ot 40% of the total oscillator strength of the quantum-well exciton.

Electric-field induced phase modulation of quantum-well exciton polaritons in a guided-wave structure

Electric-field dependence of optical phases of quantum-well exciton polaritons in a guided-wave structures is investigated by an interferometric technique and discussed on the basis of electric-field-dependent spatial-dispersion relations. Two-dimensional enhancement of photon-exciton interaction gives rise to an increase in the energy splitting between longitudinal and transverse excitons, which is found to be 5 times as large as that of three-dimensional bulk exciton.

Quantum-well exciton polariton emission from multi-quantum-well wire structures

The radiative decay of quantum-well exciton (QWE) polaritons in microstructured Al 0.3 Ga 0.7 As - GaAs multi-quantum wells (MQW) has been studied by photoluminescence spectroscopy. Periodic wire structures with lateral periodicities a = 250–500 nm and lateral widths t = 100–200 nm have been fabricated by plasma etching. The thickness of the QWs was 13 nm. In the QW wire samples the free-exciton photoluminescence was strongly reduced and the QWE polariton emission was observed as a maximum peaked at a 3 meV higher energy than the free QWE transition. In samples which had only a microstructured cladding layer, the free-exciton photoluminescence was dominant in the spectrum and the QWE polariton emission was observed as a shoulder on the high-energy side of the free QWE transition. In addition, two transitions at the low energy side of the free QWE photoluminescence were present in the microstructured samples, which were related to etching induced states.