arXiv subjects

Oleksiy Roslyak

Publications and source records attributed to Oleksiy Roslyak.

23 records · Page 2Linked to original sources

arXiv2008

Theory of enhanced second-harmonic generation by the quadrupole-dipole hybrid exciton

We report calculated substantial enhancement of the second harmonic generation (SHG) in cuprous oxide crystals resonantly hybridized with an appropriate organic material (DCM2:CA:PS 'solid-state solvent'). The quadrupole origin of the inorganic part of the quadrupole-dipole hybrid provides inversion symmetry breaking and the organic part contributes to the oscillator strength of the hybrid. We show that the enhancement of the SHG, compared to bulk cuprous oxide crystal, is proportional to the ratio of the DCM2 dipole moment and the effective dipole moment of the quadrupole transitions in the cuprous oxide. It is also inversely proportional to the line-width of the hybrid and bulk excitons. The enhancement may be regulated by adjusting the organic blend (mutual concentration of the DCM2 and CA part of the solvent) and pumping conditions(varying the angle of incidence in case of optical pumping or populating the minimum of the lower branch of the hybrid in case of electrical pumping).

cond-mat.mtrl-sci↗

arXiv2007

Theory of enhanced dynamical photo-thermal bi-stability effects in cuprous oxide/organic hybrid heterostructure

We theoretically demonstrate the formation of multiple bi-stability regions in the temperature pattern on the interface between a cuprous oxide quantum well and DCM2:CA:PS organic compound. The Frenkel molecular exciton of the DCM2 is brought into resonance with the $1S$ quadrupole Wannier-Mott exciton in the cuprous oxide by "solvatochromism" with CA. The resulting hybrid is thermalized with surrounding helium bath. This leads to strongly non-linear temperature dependence of the laser field detuning from the quadrupole exciton energy band which is associated with the temperature induced red shift of the Wannier exciton energy. Numerical up and down-scan for the detuning reveals hysteresis-like temperature distribution. The obtained \emph{multiple} bi-stability regions are at least three orders of magnitude bigger ($meV$) than the experimentally observed bi-stability in bulk cuprous oxide ($μeV$). The effective absorption curve exhibits highly asymmetrical behavior for the Frenkel-like (above the $1S$ energy) and Wannier-like (below the $1S$ energy) branches of the hybrid.

cond-mat.mtrl-sci↗

arXiv2007

Evanescent quadrupole polariton

In the work we demonstrate the formation of new type of polariton on the interface between a cuprous oxide slab and a polystyrene micro-sphere placed on the slab. The evanescent field of the resonant whispering gallery mode (WGM) has a substantial gradient, and therefore effectively couples with the quadrupole $1S$ excitons in cuprous oxide. This evanescent polariton has a long life-time ($1.7 ns$), which is determined only by its excitonic component. The polariton lower branch has a well pronounced minimum. This suggests that this excitation can be utilized for BEC. The spatial coherence of the polariton can be improved by assembling the micro-spheres in a linear chain.

cond-mat.mtrl-sci↗

arXiv2007

Polaritons in cuprous oxide perturbed by LA-phonons

We present a comparative analysis of a 'conventional' phonoriton (coherent superposition of exciton-photon-phonon) and a polariton (coherent exciton-photon superposition) 'weakly' coupled to the LA-phonons bath. Depending on duration of the pumping laser field the phonon-induced decoherence results in two distinct types of excitation. Long ($ms$) laser pumping pulses form an 'equilibrium' polariton. The generic feature here is a pronounced photo-thermal bi-stability. i.e. formation of four distinct branches. Transitions between branches can be achieved by excitation energy fluctuations as small as $200 neV$ which may impede BEC of the para-excitons. Short ($μs$) laser pulses create a 'quasi-equilibrium' polariton. In the latter case, for some critical intensity of the laser field we demonstrate possibility of strong luminicence from a highly unstable localized state on the lower polariton branch.

cond-mat.mtrl-sci↗

arXiv2007

Hybridized quadrupole-dipole exciton effects in $Cu_2O$ - Organic Heterostructure

In the present work we discuss resonant hybridization of the $1S$ quadrupole Wannier-Mott exciton (WE) in a $Cu_2O$ quantum well with the Frenkel (FE) dipole exciton in an adjacent layer of organic DCM2:CA:PA. The coupling between excitons is due to interaction between the gradient of electric field induced by DCM2 Frenkel exciton and the quadrupole moment of the $1S$ transition in the cuprous oxide. The specific choice of the organic allows us to use the mechanism of 'solid state solvation' to dynamically tune the WE and FE into resonance during time $\approx 3.3 \: ns$ (comparable with the big life time of the WE) of the 'slow' phase of the solvation. The quadrupole-dipole hybrid utilizes the big oscillator strength of the FE along with the big lifetime of the quadrupole exciton, unlike dipole-dipole hybrid exciton which utilizes big oscillator strength of the FE and big radius of the dipole allowed WE. Due to strong spatial dispersion and big mass of the quadrupole WE the hybridization is not masked by the kinetic energy or the radiative broadening. The lower branch of the hybrid dispersion exhibits a pronounced minimum and may be used in applications. Also we investigate and report noticeable change in the coupling due to a induced 'Stark effect' from the strong local electric field of the FE. We investigated the fine energy structure of the quantum well confined ortho and para excitons in cuprous oxide.

cond-mat.mtrl-sci↗