Excitons In Magnetic Field Research Articles

Magneto-absorption spectra of hydrogen-like yellow exciton series in cuprous oxide: excitons in strong magnetic fields

We study the absorption spectra of the yellow excitons in Cu2O in high magnetic fields using polarization-resolved optical absorption measurements with a high frequency resolution. We show that the symmetry of the yellow exciton results in unusual selection rules for the optical absorption of polarized light and that the mixing of ortho- and para- excitons in magnetic field is important. The calculation of the energies of the yellow exciton series in strong and weak magnetic field limits suggests that a broad n = 2 line is comprized by two closely overlapping lines, gives a good fit to experimental data and allows to interpret the complex structure of excitonic levels.

Terahertz‐induced effects on excitons in magnetic field

AbstractTerahertz‐induced intra‐exciton transitions are studied in semiconductor quantum‐well systems under the influence of a constant magnetic field. A systematic description is developed to include carrier–carrier interactions, terahertz transitions, and magnetic‐field effects to the exciton‐correlation dynamics.When a magnetic field is present, the exciton states and energies are changed directly and parametrically via the center‐of‐mass momentum of excitons. The numerical results show that both effects influence the terahertz spectroscopy. Especially, the transition between 1s‐ and 2p‐exciton states is shown to depend strongly on both magnetic field and center‐of‐mass momentum. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Analytical solutions of the Schrödinger equation for a two-dimensional exciton in magnetic field of arbitrary strength

The Feranchuk-Komarov operator method is developed by combining with the Levi-Civita transformation in order to construct analytical solutions of the Schrödinger equation for a two-dimensional exciton in a uniform magnetic field of arbitrary strength. As a result, analytical expressions for the energy of the ground and excited states are obtained with a very high precision of up to four decimal places. Especially, the precision is uniformly stable for the whole range of the magnetic field. This advantage appears due to the consideration of the asymptotic behaviour of the wave-functions in strong magnetic field. The results could be used for various physical analyses and the method used here could also be applied to other atomic systems.

Transient photoluminescence spectroscopy of spin injection dynamics in double quantum wells of diluted magnetic semiconductors

Dynamics of spin injection has been studied in double quantum wells (DQWs) composed of diluted magnetic and non-magnetic semiconductors. Picosecond-transient photoluminescence (PL) of excitons in the DQWs has been measured in magnetic field. In the Cd 1− x Mn x Te-based DQWs, the PL intensity of the magnetic well (MW) excitons decays faster with decreasing barrier width from 12 to 2 nm. This provides the evidence for carrier tunneling from the MW to the non-magnetic well (NW) through the barrier layer. The degree of circular polarization in the transient PL of the NW exciton in magnetic field shows marked evidence for spin injection and rapid spin relaxation in the DQW system. In the Zn 1− y Mn y Se-based DQWs, the degree of circle polarization in the NW exciton PL at 3 T shows a rise with a time constant of 400 ps, while the PL of the MW exciton decays within 50 ps. The observed result is interpreted by the individual spin injection for electrons and holes from the MW to the NW. The results of the transient PL of excitons in the DQWs are compared with the transient absorptions of excitons studied by the pump-and-probe spectroscopy.

Fine structure in the excitonic emission ofInAs∕GaAsquantum dot molecules

The exciton fine structure in self-assembled coupled quantum dots with barriers of varying widths is studied in detail. For narrow barriers we find doublet splittings of the molecule ground state exciton in magnetic field, while for wide barriers in some cases a multiplet of emission lines is observed. Pronounced anticrossings occur in the field dispersion of such a multiplet with details depending on the particular molecule geometry. Strong variations of the fine structure including avoided crossings are observed also for the excited states that arise from the coupling-induced splitting of the quantum dot $s$-shell excitons. Values for the exciton diamagnetic shifts and spin splittings as functions of barrier width are given.

Anomalous diamagnetic shift of excitons in II–VI quantum dots and in indirect short period superlattices

We report recent experimental results of magneto-optical spectroscopy of semiconductor nanostructures in pulsed high magnetic fields. Owing to high magnetic fields that allow high-resolution measurements, many new features were observed concerning electronic and excitonic states confined in the quantum potential. In the photoluminescence from excitons in CdSe/ZnSe quantum dots, it was found that the diamagnetic shift is towards the lower energy (red shift) for a relatively small dot diameter of about 5 nm , and the luminescence intensity decreases with increasing field for these excitons. For larger quantum dots, the diamagnetic shift is a blue shift as in the normal case. The anomalous behavior of excitons in magnetic fields is similar to the case for excitons in GaP/AlP short period superlattices, where the exciton peak shows a prominent decrease in intensity when the field is applied perpendicular to the layers. Both these effects are explained by a model assuming a shrinkage of wave functions of spatially separated electrons and holes.

Interaction potential between dynamic dipoles: Polarized excitons in strong magnetic fields

The interaction potential of a two-dimensional system of excitons with spatially separated electron-hole layers is considered in the strong magnetic field limit. The excitons are assumed to have free dynamics in the $x$-$y$ plane, while being constrained or `polarized' in the $z$ direction. The model simulates semiconductor double layer systems under strong magnetic field normal to the layers. The {\em residual} interaction between excitons exhibits interesting features, arising from the coupling of the center-of-mass and internal degrees of freedom of the exciton in the magnetic field. This coupling induces a dynamical dipole moment proportional to the center-of-mass magnetic moment of the exciton. We show the explicit dependence of the inter-exciton potential matrix elements, and discuss the underlying physics. The unusual features of the interaction potential would be reflected in the collective response and non-equilibrium properties of such system.

Near surface quantum well excitons in magnetic fields

We have demonstrated theoretically and experimentally the strong dielectric enhancement of excitons in near-surface InGaAs/GaAs quantum wells, caused by the abrupt, one order of magnitude, decrease of the dielectric constant at the semiconductor-vacuum interface.

Optical properties and dynamical behavior of localized and bound excitons in Cd1-xMnxTe (x=4%) grown by molecular-beam epitaxy.

An epitaxial ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Te (x=4%) layer has been grown on a CdTe buffer layer on a GaAs substrate by the molecular-beam-epitaxy method. Comparing the photoluminescence (PL) spectra of ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Te with those of CdTe, two peaks in the ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Te PL domain were assigned to localized and bound exciton emissions. The results obtained by PL measurements in magnetic fields up to 40 T support this assignment. The observed temporal energy shifts of the localized and bound exciton emissions can be attributed to localized and bound magnetic polaron formations, respectively. Comparing the temporal behavior of bound excitons in magnetic fields with that of localized excitons, a possible process of the bound magnetic polaron formation is discussed.

Two-dimensional excitons in magnetic fields.

We have obtained the energies and the wave functions for two-dimensional (2D) excitons in magnetic fields for the ground and several excited states, using an exact numerical integration of the Schr\"odinger equation for 2D excitons in a magnetic field. The results of the exact calculation for the ground-state energy and wave functions are in excellent agreement with those of variational and perturbation calculations except at intermediate fields where \ensuremath{\gamma}=(\ensuremath{\Elzxh}${\ensuremath{\omega}}_{c}$/2R) is of order 10. Here, R is the exciton Rydberg unit and ${\ensuremath{\omega}}_{c}$ is the cyclotron frequency of the exciton. Results are presented for the position of the exciton peak and the magnetoabsorption as a function of the field for 2D excitons.

Validity of the Conservation Rule of Nodal Surface Numbers in the Wave Function of Hydrogenic Exciton in Magnetic Field

Magnetoabsorption experiments on the $A$ exciton in InSe have been performed in search of a unified correspondence relation between low and high magnetic field levels of a hydrogenlike state. Results show that the nodal-surface conservation rule of Shinada et al. is a more appropriate representation of this relationship than the so-called noncrossing rule.

Interband Magneto-Optical Transitions in Semiconductors

The optical spectrum of a hydrogen-like exciton in a static uniform magnetic field is studied theoretically on the basis of the adiabatic approximation as a sequel of our series of study. The emphasis of this paper is put on the isotropic excitons rather than anisotropic ones. In §1 and §2 the formulations are given for the hydrogen-like excitons in the magnetic field and the adiabatic approximation, respectively. The results of the calculation are given for the adiabatic potentials, energy levels and optical absorption intensities for m =0 and | m |=1 states for some lower values of n . A way of overcoming the adiabatic approximation will be suggested on the basis of Born's method. It may, however, be difficult to carry out the calculation and the problem is left untouched. Direct comparison with experiment will not be tried in this paper. A qualitative comparison was attempted in another paper.

Oscillatory Magneto-Optical Absorption and Exciton-Phonon Interaction in Thallous Halides

Oscillatory magneto-absorptions due to excitons have been studied in TlCl and TlBr. In zero magnetic field, absorptions due to exciton-phonon quasi-bound state and one and two free-phonon states of exciton quasicontinuum are observed. In magnetic field, members of s exciton series with a subsidiary peak on the high energy side appear. The exciton binding energy is 11.7 meV in TlCl and 9.8 meV in TlBr and the reduced mass is 0.24 4 m 0 in TlCl and 0.23 4 m 0 in TlBr. A direct evidence of exciton polaron effect is obtained by observing the clamping of zero-phonon exciton lines of high quantum number in the vicinity of one free-phonon threshold of 2 s exciton. Above the threshold, absorptions of another series grow as the field increases. They are one-phonon replicas of zero-phonon excitons in magnetic field. The existence of two minima in the conduction band of each halide is suggested.