Magnetoexciton Transitions Research Articles

Magnetic-field tuning of the intraexcitonic absorption and gain in transition metal dichalcogenides

A systematic microscopic approach combining ab-initio density functional theory with the Dirac-Bloch equations is applied to investigate the intra-excitonic transitions of magneto-excitons in transition metal dichalcogenide monolayers. For the example of hBN-encapsulated $\mathrm{Mo}{\mathrm{S}}_{2}$, the linear optical response and mid-infrared spectra of the pre-excited system are numerically evaluated. It is shown that the transition probability between a subset of the magneto-excitons can be inverted under suitable conditions to display negative absorption, i.e., gain. With the help of an applied magnetic field, the absorption and gain spectra can be tuned over a wide spectral range. Evaluating the Zeeman shift of the excitonic states, effective $g$ factors are deduced that depend on the dielectric environment of the sample under consideration.

量子阱的磁激子跃迁的光吸收谱研究

The internal transitions and absorption spectra of confined magnetoexcitons in GaAs/Ga0.7Al0.3As quantum wells have been theoretically investigated under magnetic fields along the growth direction of the semiconductor heterostructure. The magnetoexciton states are obtained within the effective-mass approximation by using a variational procedure. The trial exciton-envelope wavefunctions are described as hydrogeniclike polynomial functions. The internal transition energies are investigated by studying the allowed magnetoexcitonic transitions using terahertz radiation circularly polarized in the plane of the quantum well. The intraexcitonic magnetoabsorption coefficients are obtained for transitions from 1s-like to 2p^{+-}-like magnetoexciton states as functions of the applied magnetic field.

Positively charged magnetoexciton transitions in a p-doped GaAs/Al0.45Ga0.55As single heterojunction

We report a photoluminescence-detected positively charged exciton (X+) transition from a p-doped GaAs single heterojunction in magnetic fields to 60 T. As the field increased above the quantum limit (10.8 T), the free carrier transition smoothly changes into a neutral exciton (X0) and positively charged exciton (X+) transitions. In comparison to its initial value ∼12 T, the binding energy of the X+ transition is doubled at 58 T. The variation of the X+ binding energy in magnetic fields has B dependency due to an increasing Coulomb interaction within the excitonic complex.

Intra-magnetoexciton transitions in semiconductor quantum wells

AbstractHighly sensitive optically detected resonance experiments have shown that magnetoexcitons in GaAs-(Ga,Al)As semiconductor quantum wells have discrete internal energy levels, with transition energies found in the far-infrared (terahertz) region. Here we are concerned with a theoretical study of the terahertz transitions of light-hole and heavy-hole confined magnetoexcitons in GaAs-(Ga,Al)As quantum wells, under a magnetic field applied in the growth direction of the semiconductor heterostructure. The various magnetoexciton states are obtained in the effective-mass approximation by expanding the corresponding exciton-envelope wave functions in terms of appropriate Gaussian functions. The electron and hole cyclotron resonances and intra-magnetoexciton transitions are theoretically studied by exciting the allowed electron, hole and internal magnetoexcitonic transitions with far-infrared radiation. Theoretical results are obtained for both the intra-magnetoexciton transition energies and oscillator strengths associated with excitations from 1s - like to 2s, 2p±, and 3p±- like magnetoexciton states, and from 2p- to 2s – like exciton states. Present results are in overall agreement with available optically detected resonance measurements and clarifies a number of queries in previous theoretical work.

Magneto-Reflectivity of Gallium Nitride Epilayers

We have used interband magneto-reflectivity to study the band parameters of wurtzite GaN epilayers grown on sapphire. Using magnetic fields up to 57 T, we have observed a series of up to ten magneto-excitonic transitions for the first time. The levels can be fitted with two intersecting magneto-excitonic fans coming from the A and B valence band edges with reduced masses of (0.195 ± 0.01) m0 and (0.180 ± 0.003) m0 respectively. The field dependence of the A-exciton 1s and 2p states gives a reduced mass of (0.180 ± 0.005) m0, and (0.193 ± 0.005) m0 is found with the B-exciton 1s state. The B exciton shows a clear spin splitting at 57 T, whereas no splitting of the A exciton is observed.

Magneto-Reflectivity of Gallium Nitride Epilayers

We have used interband magneto-reflectivity to study the band parameters of wurtzite GaN epilayers grown on sapphire. Using magnetic fields up to 57 T, we have observed a series of up to ten magneto-excitonic transitions for the first time. The levels can be fitted with two intersecting magneto-excitonic fans coming from the A and B valence band edges with reduced masses of (0.195 ± 0.01) m0 and (0.180 ± 0.003) m0 respectively. The field dependence of the A-exciton 1s and 2p states gives a reduced mass of (0.180 ± 0.005) m0, and (0.193 ± 0.005) m0 is found with the B-exciton 1s state. The B exciton shows a clear spin splitting at 57 T, whereas no splitting of the A exciton is observed.

Magnetoexciton quantum beats: influence of Coulomb correlations

We report four-wave-mixing experiments on the magnetoexciton manifold in semiconductor quantum wells using broadband femtosecond pulses. The four-wave-mixing signal exhibits a complex beat structure that reflects the anharmonicity of the magnetoexciton ladder. From spectrally resolved four-wave-mixing experiments, we conclude that the different magnetoexciton transitions are coupled. We discuss the origin of the coupling.

Magnetoluminescence oscillations of a doped (Al,Ga)As/GaAs single heterojunction

We have studied the photoluminescence spectra of a modulation doped (Al,Ga)As/GaAs single heterojunction in magnetic fields to 50 T at 4 K. When an external excitation is introduced to the system, photocreated electrons push the Fermi energy close to the second subband and lead to the formation of a hybridized eigenstate of the second subband (E1) exciton and the first subband (E0) two-dimensional electron state. The conduction-band hybridization enhances nonlinear behavior of magnetoexciton transitions in the optical process. At low fields, the E1 magnetoexciton transition is dominant, because the E1 hole wave-function overlap is larger than that of E0 hole. Beyond the {nu}=2 quantum Hall state, where electron screening becomes negligible, electron-hole attraction is dominant, and holes tend to move to the interface. As a consequence, the photoluminescence oscillator strength switches from the magneto-exciton transition to the lowest-Landau-level subband transition above 13 T. {copyright} {ital 1999} {ital The American Physical Society}

Magneto-optical determination of exciton binding energies in quantum-wire superlattices.

Polarization-resolved photoluminescence excitation spectra of (Al, Ga)As serpentine superlattice quantum-wire arrays have been measured in magnetic fields up to 20 T. In the Faraday configuration we are able to resolve Landau-level-like magnetoexciton transitions in the low-field limit, and to directly determine the exciton binding energy. A maximum enhancement of excitonic binding by 70{percent} is observed in a 160-A-wide quantum wire array as compared to a two-dimensional reference, and the true superlattice character is evidenced by a decreased excitonic binding for a short period (54 A wide) compared to a long period quantum-wire array (160 A wide). {copyright} {ital 1996 The American Physical Society.}

Resonant Raman scattering in GaAsAlAs quantum wells under high magnetic fields

Double Resonant Raman scattering has been observed in GaAs-AlAs Multiquantum Wells under high magnetic fields, when both the incident laser energy and the scattered frequency match simultaneously different magneto-exciton transitions. The results can be explained in terms of exciton-phonon interaction rather than electro- (or hole-) phonon coupling.