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A. P. Saiko

Publications and source records attributed to A. P. Saiko.

28 records · Page 2Linked to original sources
arXiv2010

Krylov-Bogoliubov-Mitropolsky Averaging Used to Construct Effective Hamiltonians in the Theory of Strongly Correlated Electron Systems

We show that the Krylov-Bogoliubov-Mitropolsky averaging in the canonical formulation can be used as a method for constructing effective Hamiltonians in the theory of strongly correlated electron systems. As an example, we consider the transition from the Hamiltonians of the Hubbard and Anderson models to the respective Hamiltonians of the t-J and Kondo models. This is a very general method, has several advantages over other methods, and can be used to solve a wide range of problems in the physics of correlated systems.

cond-mat.str-el↗
arXiv2008

Effect of the Bloch-Siegert Shift on the Frequency Responses of Rabi Oscillations in the Case of Nutation Resonance

The dynamics of a two-level spin system dressed by bichromatic radiation is studied under the conditions of double resonance when the frequency of one (microwave) field is equal to the Larmor frequency of the spin system and the frequency of the other (radio-frequency) field ω_{rf} is close to the Rabi frequency ω_{1} in a micro-wave field. It is shown theoretically that Rabi oscillations between dressed-spin states with the frequency εare accompanied by higher-frequency oscillations at frequencies nω_{rf} and nω_{rf}\pm ε, where n = 1, 2, .... The most intense among these are the signals corresponding to n = 1. The counter-rotating (antiresonance) components of the RF field give rise to a shift of the dressed-state energy, i.e., to a frequency shift similar to the Bloch-Siegert shift. In particular, this shift is manifested as the dependence of the Rabi-oscillation frequency εon the sign of the detuning ω{1} -ω{rf} from resonance. In the case of double resonance, the oscillation amplitude is asymmetric; i.e., the amplitude at the sum frequency ω_{rf} +εincreases, while the amplitude at the difference frequency ω_{rf} -εdecreases. The predicted effects are confirmed by observations of the nutation signals of the electron paramagnetic resonance (EPR) of centers in quartz and should be taken into account to realize qubits with a low Rabi frequency in solids.

cond-mat.mtrl-sci↗
arXiv2007

Multiphoton Transitions in a Spin System Driven by Strong Bichromatic Field

EPR transient nutation spectroscopy is used to measure the effective field (Rabi frequency) for multiphoton transitions in a two-level spin system bichromatically driven by a transverse microwave (MW) field and a longitudinal radio-frequency (RF) field. The behavior of the effective field amplitude is examined in the case of a relatively strong MW field, when the derivation of the effective Hamiltonian cannot be reduced to first-order perturbation theory in w_{1} / w_{rf} (w_{1} is the microwave Rabi frequency, w_{rf} is the RF frequency). Experimental results are consistently interpreted by taking into account the contributions of second and third order in w_{1} / w_{rf} evaluated by Krylov-Bogolyubov-Mitropolsky averaging. In the case of inhomogeneously broadened EPR line, the third-order correction modifies the nutation frequency, while the second-order correction gives rise to a change in the nutation amplitude due to a Bloch-Siegert shift.

cond-mat.mtrl-sci↗
arXiv2007

Temperature Hysteresis of Magnetization in Lanthanum Manganite

We propose an explanation for the experimentally observed temperature hysteresis of magnetization in single crystals of lanthanum manganite (La0.8Sr0.2MnO3). The phenomenon is interpreted within the framework of a double-exchange model with allowance for the interaction of the magnetic subsystem with a bistable mode of the tilting-rotational oscillations in the correlated sublattice of MnO6 octahedra.

cond-mat.mtrl-sci↗
arXiv2006

Effective Field and the Bloch-Siegert Shift at Bihromatic Excitation of Multiphoton EPR

The dynamics of multiphoton transitions in a two-level spin system excited by transverse microwave and longitudinal RF fields with the frequencies w_{mw} and w_{rf}, respectively, is analyzed. The effective time-independent Hamiltonian describing the "dressed" spin states of the "spin + bichromatic field" system is obtained by using the Krylov-Bogoliubov-Mitropolsky averaging method. The direct detection of the time behavior of the spin system by the method of nonstationary nutations makes it possible to identify the multiphoton transitions for resonances w_{0} = w_{mw} + rw_{rf} (w_{0} is the central frequency of the EPR line, r = 1, 2), to measure the amplitudes of the effective fields of these transitions, and to determine the features generated by the inhomogeneous broadening of the EPR line. It is shown that the Bloch-Siegert shifts for multiphoton resonances at the inhomogeneous broadening of spectral lines reduce only the nutation amplitude but do not change their frequencies.

cond-mat.mtrl-sci↗
arXiv2004

On Theory of the Phonon Perturbed Superradiance

The paper examines superradiance in impurity crystals in the field of a coherent phonon wave excited by two ultrashort laser pulses via Raman scattering processes at the moment of preparation of the initial state of an ensemble of emitters. It is shown that by varying the power of the excitation pulses and their mutual direction of propagation, one can control the superradiance parameters and extract data on the electron-phonon coupling constant and its anisotropy.

physics.optics↗
arXiv2003

Phenomenological Description of a Giant Temperature Hysteresis of the Ultrasound Velocity and the Internal Friction in Lanthanum Manganite

We propose an explanation for the experimentally observed [JETP Lett. 74, 115 (2001)] giant temperature hysteresis of the ultrasound velocity and the internal friction in single crystals of lanthanum manganite (La0.8Sr0.2MnO3). The effect is interpreted within the framework of a phenomenological model based on the notion of two coexisting sublattices of the oxygen octahedra performing cooperative tilting-rotational oscillations in bistable potential fields.

cond-mat.mtrl-sci↗
arXiv2003

On the Theory of Vibronic Laser

Some aspects of lasing at vibronic transitions in impurity crystals are theoretically studied. The threshold conditions for a vibronic laser are shown to be dependent on the strength of interaction of optical centers with a local vibration, which forms the vibronic spectrum, and the crystal lattice temperature. The theory can be easily generalized to the spectrum containing a structureless phonon sideband and well agrees with the experimental temperature dependence of the output power of a Mg2SiO4:Cr4+ forsterite laser.

physics.optics↗
arXiv2003

On the Theory of Vibronic Superradiance

The Dicke superradiance on vibronic transitions of impurity crystals is considered. It is shown that parameters of the superradiance (duration and intensity of the superradiance pulse and delay times) on each vibronic transition depend on the strength of coupling of electronic states with the intramolecular impurity vibration (responsible for the vibronic structure of the optical spectrum in the form of vibrational replicas of the pure electronic line) and on the crystal temperature through the Debye-Waller factor of the lattice vibrations. Theoretical estimates of the ratios of the time delays, as well as of the superradiance pulse intensities for different vibronic transitions well agree with the results of experimental observations of two-color superradiance in the polar dielectric KCl:O2-. In addition, the theory describes qualitatively correctly the critical temperature dependence of the superradiance effect.

physics.optics↗