D. K. Loginov

Exciton polaritons in quantum wells in a transverse magnetic field

This paper reports on a study of the exciton polariton region in reflection spectra of wide CdTe/CdZnTe quantum wells (with well width exceeding by far the exciton Bohr radius) measured in Voigt geometry in a magnetic field. In a magnetic field, forbidden exciton lines were observed to appear for each exciton quantization level. The exciton diamagnetic shift constant has been observed to decrease noticeably with increasing number of the quantum confined level. A comparison of calculated with experimental spectra reveals a growth of the exciton translational mass with increasing magnetic field. It has been shown that both the growth of mass and the decrease of the diamagnetic shift can be traced to mixing of exciton internal with translational motion states.

Interference of polariton waves in structures with wide GaAs/AlGaAs quantum wells

The optical reflection spectra of semiconductor GaAs/AlGaAs structures with wide quantum wells are studied experimentally. A theoretical analysis of the spectra is performed in terms of the exciton-polariton model in the approximation of quantum confinement of the exciton center of mass with regard to the contributions of both heavy and light excitons to the crystal polarization. The applicability range of the theory of the center-of-mass confinement for GaAs/AlGaAs heterostructures is estimated. It is established that, for quantum wells more than 180 nm wide, the interference effects observed in the reflection spectra of polariton waves are reproduced, to a good accuracy, by theoretical calculations based on the quantum confinement of the exciton center of mass. For quantum-well widths less than 150 nm, the experimental results are described better by the model of quantum confinement of electrons and holes.

Magnetic-field-induced polariton effects in light reflection spectra of structures with wide exciton quantum wells

A theoretical model has been developed to describe the behavior of exciton polaritons in a wide quantum well for structures with the zinc blende symmetry in a transverse magnetic field (the Voigt geometry). The model takes into account the mixing of the 1s-1s and 1s-2p states of heavy excitons by the magnetic field and makes it possible to explain and quantitatively describe the activation of optically inactive states in the reflection spectra and the magnetic-field-induced increase in the translational mass of the exciton. The quantitative calculations of the spectra have been preformed using typical parameters for CdTe/ZnCdTe quantum-well structures.

Enhancement of the longitudinal magnetic moment of the exciton due to its motion

A new physical phenomenon has been found, namely a giant enhancement of the exciton magnetic moment due to its motion. This phenomenon was observed in GaAs, CdTe and ZnSe based quantum wells with QW widths much larger than the exciton Bohr radius. Consequently, it is relevant to any crystal with zinc blende structure.

Experimental determination of dead layer thickness for excitons in a wide GaAs/AlGaAs quantum well

The thickness of the GaAs “dead layer” in the GaAs/AlGaAs heterostructure has been directly measured. The widths of the dead layer obtained in the experiment are compared with the values for the same material interfacing with the external medium which were found earlier, as well as with theoretical predictions made by different authors.

Stabilized High-Temperature Hexagonal Phase in Copper Halide Nanocrystals

Low-temperature (T = 4.2–77 K) absorption spectra of CuCl and CuBr nanocrystals in photochromic glass matrixes are studied. A fine structure of exciton absorption bands (Z3 band for CuCl and Z12 band for CuBr) is discovered and studied as a function of nanocrystal size. It is suggested that the high-energy part of the absorption band is due to the high-temperature hexagonal β phase being stabilized in very small samples; a transition to the stable cubic phase with increasing nanocrystal size is demonstrated.

Motional enhancement of the exciton magnetic moment

This paper overviews our recent results on the magneto-optics of excitons in wide quantum wells, when the well width is much larger than the exciton Bohr radius. We have demonstrated that the magnetic moment of the exciton increases by an order of magnitude due to its motion along the magnetic field. The effect was observed for a set of quantum well structures with different well widths and based on various semiconductor compounds. The reason for this effect is mixing of the excitons center-of-mass motion and the internal motion of electron and hole in the exciton.

Reduction of exciton mass by uniaxial stress in GaAs/AlGaAs quantum wells

D. K. Loginov, P. S. Grigoryev, E. V. Ubiyvovk, Yu. P. Efimov, S. A. Eliseev, V. A. Lovtcius, Yu. P. Petrov, and I. V. Ignatiev Spin Optics Laboratory, St. Petersburg State University, 198504 St. Petersburg, Russia Department of Physics, St. Petersburg State University, 198504 St. Petersburg, Russia Resource Center “Nanophotonics”, St. Petersburg State University, 198504 St. Petersburg, Russia (Dated: May 11, 2015)

Decrease of heavy-hole exciton mass induced by uniaxial stress in GaAs/AlGaAs quantum well

D. K. Loginov, P. S. Grigoryev, E. V. Ubiyvovk, Yu. P. Efimov, S. A. Eliseev, V. A. Lovtcius, Yu. P. Petrov, and I. V. Ignatiev Spin Optics Laboratory, St. Petersburg State University, 198504 St. Petersburg, Russia Department of Physics, St. Petersburg State University, 198504 St. Petersburg, Russia Resource Center “Nanophotonics”, St. Petersburg State University, 198504 St. Petersburg, Russia (Dated: May 11, 2015)