Time filter

Source Type

Podlesny I.V.,Moldova Academy of Sciences | Moskalenko S.A.,Moldova Academy of Sciences | Hakioglu T.,Bilkent University | Hakioglu T.,Institute of Theoretical and Applied Physics | And 2 more authors.
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2013

The Landau quantization of the two-dimensional (2D) heavy holes, its influence on the energy spectrum of 2D magnetoexcitons, as well as their optical orientation are studied. The Hamiltonian of the heavy holes is written in two-band model taking into account the Rashba spin-orbit coupling (RSOC) with two spin projections, but with nonparabolic dispersion law and third-order chirality terms. The most Landau levels, except three with m=0,1,2, are characterized by two quantum numbers m-3 and m for m≥3 for two spin projections correspondingly. The difference between them is determined by the third-order chirality. Four lowest Landau levels (LLLs) for heavy holes were combined with two LLLs for conduction electron, which were taken the same as they were deduced by Rashba in his theory of spin-orbit coupling (SOC) based on the initial parabolic dispersion law and first-order chirality terms. As a result of these combinations eight 2D magnetoexciton states were formed. Their energy spectrum and the selection rules for the quantum transitions from the ground state of the crystal to exciton states were determined. On this base such optical orientation effects as spin polarization and magnetoexciton alignment are discussed. The continuous transformation of the shake-up (SU) into the shake-down (SD) recombination lines is explained on the base of nonmonotonous dependence of the heavy hole Landau quantization levels as a function of applied magnetic field. © 2013 Elsevier B.V. All rights reserved.


Hakioglu T.,Bilkent University | Hakioglu T.,Institute of Theoretical and Applied Physics | Liberman M.A.,Uppsala University | Moskalenko S.A.,Moldova Academy of Sciences | Podlesny I.V.,Moldova Academy of Sciences
Journal of Physics Condensed Matter | Year: 2011

The influence of the Rashba spinorbit coupling(RSOC) on the two-dimensional (2D) electrons and holes in a strong perpendicular magnetic field leads to different results for the Landau quantization in different spin projections. In the Landau gauge the unidimensional wave vector describing the free motion in one in-plane direction is the same for both spin projections, whereas the numbers of Landau quantization levels are different. For an electron in an s-type conduction band they differ by one, as was established earlier by Rashba(1960 Fiz. Tverd. Tela2 1224), whereas for heavy holes in a p-type valence band influenced by the 2D symmetry of the layer they differ by three. The shifts and the rearrangements of the 2D hole Landau quantization levels on the energy scale are much larger in comparison with the case of conduction electron Landau levels. This is due to the strong influence of the magnetic field on the RSOC parameter. At sufficiently large values of this parameter the shifts and rearrangements are comparable with the hole cyclotron energy. There are two lowest spin-split Landau levels for electrons as well as four lowest ones for holes in the case of small RSOC parameters. They give rise to eight lowest energy bands of the 2D magnetoexcitons, as well as of the band-to-band quantum transitions. It is shown that three of them are dipole-active, three are quadrupole-active and two are forbidden. The optical orientation under the influence of circularly polarized light leads to optical alignment of the magnetoexcitons with different orbital momentum projections in the direction of the external magnetic field. © 2011 IOP Publishing Ltd.


Hakioglu T.,Bilkent University | Hakioglu T.,Institute of Theoretical and Applied Physics | Ozgun E.,Bilkent University
Solid State Communications | Year: 2011

It is already well known that radiative interband interaction in the excitonic normal liquid in semiconducting double quantum wells is responsible for a negligible splitting between the energies of the dark and bright excitons enabling us to consider a four fold spin degeneracy. This has also lead many workers to naively consider the same degeneracy in studying the condensate. On the other hand, the non-perturbative aspects of this interaction in the condensed phase, e.g. its consequences on the order parameter and the darkbright mixture in the ground state have not been explored. In this work, we demonstrate that the ground state concentrations of the dark and the bright exciton condensates are dramatically different beyond a sharp interband coupling threshold where the contribution of the bright component in the ground state vanishes. This shows that the effect of the radiative interband interaction on the condensate is nonperturbative. We also observe in the free energy a discontinuous derivative with respect to the layer separation at the entrance to the condensed phase, indicating a strong critical Casimir force. An estimate of its strength shows that it is measurable. Measuring the Casimir force is challenging, but at the same time it has a conclusive power about the presence of the long sought for condensed phase. © 2011 Elsevier Ltd. All rights reserved.


Hakioglu T.,Bilkent University | Hakioglu T.,Institute of Theoretical and Applied Physics | Ozgun E.,Bilkent University | Gunay M.,Bilkent University
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2014

An exciton condensate is a vast playground in studying a number of symmetries that are of high interest in the recent developments in topological condensed matter physics. In double quantum wells (DQWs) they pose highly nonconventional properties due to the pairing of non-identical fermions with a spin dependent order parameter. Here, we demonstrate a new feature in these systems: the robustness of the ground state to weak external magnetic field and the appearance of the artificial spinor gauge fields beyond a critical field strength where negative energy pair-breaking quasi particle excitations, i.e. de-excitation pockets (DX-pockets), are created in certain k regions. The DX-pockets are the Kramers symmetry broken analogs of the negative energy pockets examined in the 1960s by Sarma. They respect a disk or a shell-topology in k-space or a mixture between them depending on the magnetic field strength and the electron-hole density mismatch. The Berry connection between the artificial spinor gauge field and the TKNN number is made. This field describes a collection of pure spin vortices in real space when the magnetic field has only inplane components. © 2014 Elsevier B.V. All rights reserved.


Hakioglu T.,Bilkent University | Hakioglu T.,Institute of Theoretical and Applied Physics | Ozgun E.,Bilkent University | Gunay M.,Bilkent University
Applied Physics Letters | Year: 2014

Free energy signatures related to the measurement of an emergent force (≈10-9N) due to the exciton condensate (EC) in Double Quantum Wells are predicted and experiments are proposed to measure the effects. The EC-force is attractive and reminiscent of the Casimir force between two perfect metallic plates, but also distinctively different from it by its driving mechanism and dependence on the parameters of the condensate. The proposed experiments are based on a recent experimental work on a driven micromechanical oscillator. Conclusive observations of EC in recent experiments also provide a strong promise for the observation of the EC-force. © 2014 AIP Publishing LLC.

Loading Institute of Theoretical and Applied Physics collaborators
Loading Institute of Theoretical and Applied Physics collaborators