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Search for the Photo-Induced Hidden Phase in Inorganic and Organic Systems

100%
Koshihara S., Onda K., Okimoto Y., Ishikawa T.
Acta Physica Polonica A
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2012
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vol. 121
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issue 2
328-331
EN
We review the dynamical behavior of strongly electron-lattice (orbital) coupled system induced by photo-excitation of fs laser pulse. By virtue of the femtosecond (fs) spectroscopy and picosecond (ps) time-resolved X-ray diffraction measurements, we demonstrate that the photo-irradiation creates new ordered state so called as "hidden phase" which can never be realized under thermo-equilibrium condition. This exotic phase commonly plays the key role for realizing the gigantic photo-induced changes in optical properties of inorganic and organic electron-lattice strongly coupled systems.
2
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Bond-Selective Excitation and Following Displacement of Ge Atoms in GeTe/Sb_{2}Te_{3} Superlattice

100%
Makino K., Tominaga J., Kolobov A., Fons P., Hase M.
Acta Physica Polonica A
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2012
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vol. 121
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issue 2
336-339
EN
Phase change random access memory devices made from chalcogenides compounds, such as Ge_{2}Sb_{2}Te_{5}, have attracted much attention because of their high-speed read-write and low power consumption capabilities. The phase change in Ge_{2}Sb_{2}Te_{5} is thought to be characterized by the displacement of Ge atoms, accompanying relaxation of surrounding Sb and Te atoms. Here we examine a new approach, that is the manipulation of Ge-Te bonds using linearly-polarized femtosecond near-infrared optical pulses. As a result, p-polarized pump pulses are found to be more effective in inducing the precursor of phase change, probably due to the atomic arrangements along the unique axis of the superlattice structure.
3
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Phonon Effects on the Weak Measurement of Charge States in Quantum Dots with a Quantum Point Contact

100%
Marcinowski Ł., Krzyżosiak M.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
640-643
EN
We study theoretically the process of a weak measurement of charge states in a double quantum dot performed by coupling to a quantum point contact. We focus on the interplay of the measurement process with phonon-induced dephasing of delocalized superpositions of electron states and compare the time scales relevant for the dynamics of the open system and for the measurement process: the decoherence rate, the localization rate of the state conditioned on the measurement outcome and the time scale on which information on the system state is gained in the process of the measurement.
4
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Electron States, Phonon-Assisted Relaxation and Tunneling in Self-Assembled Quantum Dot Molecules in an Electric Field

100%
Gawarecki K., Machnikowski P.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
637-639
EN
We present a theoretical analysis of the phonon-assisted relaxation in a system composed of two self-assembled vertically stacked quantum dots. We construct realistic model, which takes into account the geometry and strain distribution in the system. We calculate phonon-assisted relaxation rates between the two lowest states (in one- and two-electron cases). The relaxation rates and energy levels are studied as a function of external (axial) electric field and geometry of the structure (dot sizes). We show that the relaxation times can be as low as 1 ps but efficient relaxation occurs only for very finely tuned dots.
5
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Phonon-Assisted Tunneling of an Electron in a Strained Self-Assembled Quantum Dot Molecule

100%
Pochwała M., Machnikowski P.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1285-1291
EN
We calculate phonon-assisted relaxation rates in a self-assembled quantum dot molecule. The calculation is based on wave functions obtained within an envelope function approach, including strain effects. The single-phonon relaxation is shown to be efficient for separations between the dots around 10 nm when, in addition, the dots are brought close to resonance.
6
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Lattice Thermal Conductivity of GaAs

100%
Ataullah Ansari M., Ashokan V., Indu B., Kumar R.
Acta Physica Polonica A
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2012
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vol. 121
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issue 3
639-646
EN
A new approach to evaluate the relaxation times of various collision events responsible for thermal transport has been reported through which various deficiencies of earlier models of lattice thermal conductivity have been resolved. These investigations involve the evaluation of the phonon Green functions via a non-perturbative approach. The new expressions of relaxation times expressions for scattering of phonons by boundaries, atomic impurities, phonon-phonon scattering, electron-phonon scattering are the new features of the theory. The lattice thermal conductivity of three samples of GaAs has been analyzed on the basis of modified Callaway model and fairly good agreement between theory and experimental observations has been reported.
7
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Second-Order Resonant Polaron in a Self-Assembled Quantum Dot

100%
Kaczmarkiewicz P., Machnikowski P.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1139-1144
EN
We calculate numerically the spectrum of a polaron in a quantum dot in the region of resonance with two-phonon states. We show that the experimental data can be reproduced by a model that does not depend on any adjustable parameters.
8
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Vibronic Magnetoelectric Effects in the Bi-Based Multiferroics

100%
Konsin P., Sorkin B.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
243-244
EN
The detailed magneto-electron-lattice (vibronic) theory of ferroelectricity in the Bi-based multiferroics (BiFeO₃ etc.) is developed further. The vibronic admixture of the empty oxygen 2p states to the Bi 6s lone electron pair state leads to ferroelectricity. These interactions are the driving and restoring forces of the structural phase transformations of the Bi-based multiferroics. The free energy of the BiFeO₃-type multiferroics with the ferroelectric and the G-type antiferromagnetic phase transitions are derived. The Zeeman splitting and spin-transversal optical phonon couplings are also important.
9
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Optical Absorption and Raman Scattering Studies of Few-Layer Epitaxial Graphene Grown on 4H-SiC Substrates

88%
Grodecki K., Drabińska A., Bożek R., Wysmołek A., Korona K., Strupiński W., Borysiuk J., Stępniewski R., Baranowski J.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
835-837
EN
Optical absorption and Raman scattering studies of few-layer epitaxial graphene obtained by high temperature annealing of carbon terminated face of 4H-SiC(000-1) on-axis substrates are presented. Changing the pressure and annealing time, different stages of the graphene formation were achieved. Optical absorption measurements enabled us to establish average number of graphene layers covering the SiC substrate. Raman scattering experiments showed that integrated intensity of the characteristic 2D peak positively correlated with the number of graphene layers deposited on the SiC substrate. The spectral width of the 2D peak was found to decrease with the number of the deposited graphene layers.
10
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Influence of Pressure on the Electron-Phonon Interaction in Superconductors

88%
Orendáč M., Gabáni S., Pristáš G., Gažo E., Shitsevalova N., Flachbart K.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
1039-1041
EN
The electron-phonon interaction is a very important and ubiquitous process in solids, affecting almost all their physical properties. In metals, where the relaxation processes depend on both electrons and phonons, all thermodynamic and transport properties are dictated by the electron-phonon interaction. A very strong manifestation of the electron-phonon interaction is related with the superconducting state. Here we report the effect of high pressure on the transport electron-phonon interaction, λ_{tr}, in superconducting systems such as YB_6 (T_c ≈ 7.5 K), Pb (T_c ≈7.2 K), Nb bulk or thin film (T_c ≈9.2 K), and in LaB_6 in which superconductivity was not yet observed. The expected pressure effect should correspond to the theoretically predicted negative pressure effect on T_c (except for Nb thin film and LaB_6). To determine the influence of pressure on λ_{tr}, we utilized the Bloch-Grüneisen fit (denoted also as "thermal spectroscopy") of the precise temperature dependence of resistivity measurements in the normal state up to a pressure of 2.8 GPa. Based on this fit the observed negative pressure effect on λ_{tr} values, dλ_{tr}/dp, are as follows: dλ_{tr}/dp ≈-0.045 GPa^{-1} for YB_6, dλ_{tr}/dp ≈-0.13 GPa^{-1} for Pb, dλ_{tr}/dp ≈-0.019 GPa^{-1} or -0.028 GPa^{-1} for Nb bulk or thin film, respectively, and dλ_{tr}/dp ≈-0.003 GPa^{-1} for LaB_6.
11
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Thermodynamic Characteristics of 1D Structures

63%
Jaćimovski S., Raković D.
Acta Physica Polonica A
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2011
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vol. 120
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issue 2
231-233
EN
In this paper 1D crystal lattice is analyzed within harmonic approximation, with one atom per elementary cell and nearest neighbor interaction included. For this type of crystal lattice dispersion relations are well known. Thermodynamic functions (specific heat and phonon thermal conductivity) are calculated via phonon density of states given in exact form. Thermodynamic variables are calculated for a whole temperature range. In limiting cases of low and high temperatures these thermodynamic variables can be found in analytic forms. For thermal conductivity the results of Callaway model for exact phonon density of states are compared with the results of Callaway model for Debye approximation of phonon density of states.
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