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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Valkov V. V., Valkova T. A.
Заглавие : Application of indefinite metric for transition to bose description of Su(3) hamiltonians - excitation spectrum of spin nematics
Место публикации : Zhurnal Eksperimentalnoi Teor. Fiz. - 1991. - Vol. 99, Is. 6. - P.1881-1897. - ISSN 0044-4510
Примечания : Cited References: 37
Предметные рубрики: BIQUADRATIC EXCHANGE
PHASE-TRANSITIONS
DIAGRAM TECHNIQUE
MAGNETISM
FIELD
STATE
Аннотация: A procedure is developed for a correct transition to the Bose representation for quantum SU(3) Hamiltonians. The analysis is carried out for a spin nematic by applying the indefinite metric formalism and pseudo-Hubbard operators. An important aspect of the theory is that the finiteness of the number of physical states is taken into account. This is attained by introducing and consistently taking into account the metric operator for which purpose a simple expression in terms of Bose operators is suggested. It is shown that in this approach the quantum Bose analog of the Hamiltonian is an Hermitian operator. This circumstance removes a number of principle contradictions which appeared previously on application of the Bose analog of the Hamiltonian derived by virtually identifying the Hubbard and pseudo-Hubbard operators and ignoring the finiteness of the number of physical states. The integral equations defining the chief characteristics of the system are obtained and solved analytically for the spin-nematic state of a magnet with S = 1 and by taking into account anharmonic effects. This permits one to write down in nonlinear theory explicit expressions for the two branches of the quantum excitation spectrum. The character of the renormalization of the spectrum parameters due to the presence of zero-point quantum oscillations is studied. The renormalization of the critical field on transition of the system from the spin nematic state is calculated analytically.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bondarenko I. N., Gekht R. S., Ponomarev V. I.
Заглавие : Magnetic transitions in layered triangular antiferromagnets
Место публикации : Phys. Lett. A: ELSEVIER SCIENCE BV, 1996. - Vol. 222, Is. 4. - P269-274. - ISSN 0375-9601, DOI 10.1016/0375-9601(96)00635-4
Примечания : Cited References: 22
Предметные рубрики: HEISENBERG-ANTIFERROMAGNET
PHASE-TRANSITION
VBR2
SYSTEMS
FIELD
VCL2
Ключевые слова (''Своб.индексиров.''): triangular antiferromagnets--quantum and thermal fluctuations--successive phase transitions--quantum and thermal fluctuations--successive phase transitions--triangular antiferromagnets
Аннотация: Magnetic states and phase transitions of the layered triangular antiferromagnets in an applied field are studied. It is shown that in compounds like VBr2 and VCl2 quantum effects change the ground state structure and cause successive phase transitions as the magnetic field increases. Coplanar structures of different spin configuration are realized far from the saturation field and a noncoplanar structure of umbrella-type configuration is realized near this field. The ground-state phase diagram is constructed, and a finite region of fields where the collinear phase is also possible is indicated.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aronov I. E., Berman G. P., Campbell D. K., Dudiy S. V.
Заглавие : Wigner function description of ac transport through a two-dimensional quantum point contact
Разночтения заглавия :авие SCOPUS: Wigner function description of a.c. transport through a two-dimensional quantum point contact
Место публикации : J. Phys.: Condens. Matter: IOP PUBLISHING LTD, 1997. - Vol. 9, Is. 24. - P.5089-5103. - ISSN 0953-8984, DOI 10.1088/0953-8984/9/24/009
Примечания : Cited References: 45
Предметные рубрики: QUANTIZED CONDUCTANCE
BALLISTIC-RESISTANCE
CONSTRICTION
CAPACITANCE
ADMITTANCE
ELECTRONS
SYSTEMS
FIELD
PUMP
Аннотация: We have calculated the admittance of a two-dimensional quantum point contact (QPC) using a novel variant of the Wigner distribution function (WDF) formalism. In the semiclassical approximation, a Boltzmann-like equation is derived for the partial WDF describing both propagating and non-propagating electron modes in an effective potential generated by the adiabatic QPC. We show that this quantum kinetic approach leads to the well known stepwise behaviour of the real part of the admittance (the conductance), and of the imaginary part of the admittance (the emittance), in agreement with the latest results derived by Christen and Buttiker, which is determined by the number of propagating electron modes. It is shown that the emittance is sensitive to the geometry of the QPC, and can be controlled by the gate voltage. We have established that the emittance has contributions corresponding to both quantum inductance and quantum capacitance. Stepwise oscillations in the quantum inductance are determined by the harmonic mean of the velocities for the propagating modes, whereas the quantum capacitance is a significant mesoscopic manifestation of the nonpropagating (reflecting) modes.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Alekseev K. N., Erementchouk M. V., Kusmartsev F. V.
Заглавие : Direct-current generation due to wave mixing in semiconductors
Место публикации : Europhys. Lett. - 1999. - Vol. 47, Is. 5. - P.595-600. - ISSN 0295-5075, DOI 10.1209/epl/i1999-00430-0
Примечания : Cited References: 34
Предметные рубрики: BLOCH OSCILLATOR
SUPERLATTICES
PHOTOCURRENT
TRANSPORT
FREQUENCY
FIELD
RECTIFIERS
EMISSION
CHAOS
GAAS
Аннотация: We describe an effect of the generation of direct current which may arise in semiconductors or semiconductor microstructures due to a mixing of coherent electromagnetic radiations of commensurate frequencies. The effect is, in essence, due to a nonparabolicity of the electron energy bands and is stronger in systems where this nonparabolicity is greater. We have made exact calculations in the framework of the Kane model, applicable to narrow-gap semiconductors and the tight-binding model which we employ for a description of a semiconductor superlattice.
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Pankrats A. I., Petrakovskii G. A., Popov M. A., Sablina K. A., Prozorova L. A., Sosin S. S., Szimczak G., Szimczak R., Baran M.
Заглавие : New magnetic states in copper metaborate CuB2O4
Место публикации : JETP Letters. - 2003. - Vol. 78, Is. 9. - P.569-573. - ISSN 0021-3640, DOI 10.1134/1.1641486
Примечания : Cited References: 15
Предметные рубрики: SOLITON LATTICE
FIELD
Аннотация: The static and resonance properties of copper metaborate CuB2O4 were experimentally studied in a magnetic field applied in the crystal tetragonal plane. The field-induced second-order phase transition to a weakly ferromagnetic state was observed in the temperature range 10-20 K. The low-field state is characterized by the absence of spontaneous moment, and it represents, presumably, a long-period helicoid. At temperatures below 2 K, two sequential first-order phase transitions were observed. They were accompanied by jumps in resonance absorption with a hysteresis upon changing field-scan direction. These transitions can be caused by the transformation of the incommensurate spin structure into the helicoidal states with periods commensurate with the lattice translation period. (C) 2003 MAIK "Nauka / Interperiodica".
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Shaikhutdinov K. A., Balaev D. A., Popkov S. I., Petrov M. I.
Заглавие : Transport and magnetic properties of Y3/4Lu1/4Ba2Cu3O7+Y3Fe5O12 composites representing a Josephson-type superconductor-ferrimagnet-superconductor weak-link network
Разночтения заглавия :авие SCOPUS: Transport and Magnetic Properties of Y3/4Lu1/4Ba 2Cu3O7 + Y3Fe5O 12 Composites Representing a Josephson-Type Superconductor-Ferrimagnet-Superconductor Weak-Link Network
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2003. - Vol. 45, Is. 10. - P1866-1873. - ISSN 1063-7834, DOI 10.1134/1.1620087
Примечания : Cited References: 36
Предметные рубрики: RESISTIVE PROPERTIES
JUNCTION NETWORK
SYSTEM
TRANSITION
CURRENTS
VOLTAGE
STATE
FIELD
Аннотация: Y3/4Lu1/4Ba2Cu3O7 + Y3Fe5O12 composites with different volume ratios of the starting components were synthesized. The composites model an S-F-S Josephson junction network, where S stands for a superconductor and F, for a ferrimagnet. A study of the transport characteristics of the composites revealed that the temperature behavior of the electrical resistivity rho(T) below the superconducting transition point T-C is different in two regions separated by a temperature T-m. Below T-m, the current-voltage characteristics of the composites are nonlinear, while in the interval from T-C to T-m the values of rho(T) do not depend on the transport current j and magnetic field H. This behavior of rho(T, j ) and rho(T, H) is assigned to specific features of the tunneling of superconducting carriers through the ferrimagnetic layers separating HTSC grains in the composite. Magnetic measurements showed the diamagnetic response of HTSC grains to be lower in composites with a ferrimagnet. (C) 2003 MAIK "Nauka / Interperiodica".
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Popov M. A., Petrakovskii G. A., Zinenko V. I.
Заглавие : Magnetic properties of copper metaborate: Two-parameter phenomenological model
Разночтения заглавия :авие SCOPUS: Magnetic Properties of Copper Metaborate: Two-Parameter Phenomenological Model
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2004. - Vol. 46, Is. 3. - P491-497. - ISSN 1063-7834, DOI 10.1134/1.1687867
Примечания : Cited References: 9
Предметные рубрики: SOLITON LATTICE
CUB2O4
FIELD
Аннотация: Symmetry analysis is performed for the magnetic subsystem of copper metaborate, and a phenomenological model is proposed with two two-component order parameters that correspond to ferromagnetism and antiferromagnetism vectors lying in the tetragonal plane of this crystal. Owing to the I (4) over bar 2d space group of symmetry of this crystal, the thermodynamic potential contains the Lifshitz invariant having the form of an antisymmetric product of the order parameters and their spatial derivatives. Analysis of this model shows that the temperatures of ordering in the magnetic subsystem and of the formation of a spiral structure in it can be different. This fact allows numerical calculation of the temperature dependences of the spiral wave vector, magnetization, and intensities of first- and third-order magnetic satellites in the incommensurate phase that arise in neutron elastic scattering, as well as the field dependence of the magnetization. The experimental data, including a magnetic-field-temperature phase diagram, are satisfactorily described. The parameters of the phenomenological thermodynamic potential of the magnetic subsystem of copper metaborate are estimated. (C) 2004 MAIK "Nauka / Interperiodica".
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Bayukov O. A., Abd-Elmeguid M. M., Ivanova N. B., Kazak N. V., Ovchinnikov S. G., Rudenko V. V.
Заглавие : Mossbauer effect study in Fe1-xVxBO3 solid solutions
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2004. - Vol. 46, Is. 6. - P1088-1094. - ISSN 1063-7834, DOI 10.1134/1.1767250
Примечания : Cited References: 28. - One of the authors (M.M. A.-E.) would like to thank the Deutsche Forschungsgemeinschaft for financial support (SFB 608). This study was supported by the Russian Foundation for Basic Research (project no. 03-02-16286) and the federal program “Integration” (project no. Б0017)
Предметные рубрики: MAGNETO-OPTICAL PROPERTIES
FEBO3 SINGLE-CRYSTALS
FERRIC BORATE
CALCITE STRUCTURE
IRON BORATE
TEMPERATURE
FIELD
SPECTRA
FE3BO6
CRBO3
Аннотация: The Mossbauer effect in the Fe1 - xVxBO3 solid solutions has been measured at 130 and 300 K. The Fe0.05V0.95BO3 composition was studied in the interval 4.2-300 K. The experimental data obtained are described in terms of the model of a dilute magnetic insulator in which atoms of the first coordination sphere provide a major contribution to the hyperfine field at iron nucleus sites. It was found that, at low temperatures, the field H-hf is generated primarily by the iron ion itself and depends only weakly on substitution. The hyperfine interaction parameters in the discrete configuration series 6Fe, 5Fe1V, 4Fe2V, 3Fe3V, and 2Fe4V were determined. The magnitude of the isomer shift suggests that iron in the crystal resides in the trivalent state. (C) 2004 MAIK "Nauka/Interperiodica".
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Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Aver'yanov E. M.
Заглавие : Correlation of the molecular structure of discotic nematic liquid crystals with their orientational order and specific features of the nematic-isotropic phase transition
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2004. - Vol. 46, Is. 8. - P1554-1559. - ISSN 1063-7834, DOI 10.1134/1.1788794
Примечания : Cited References: 32
Предметные рубрики: MONTE-CARLO
ANISOTROPIC SYSTEMS
COMPUTER-SIMULATION
BEHAVIOR
TRIPHENYLENE
DISCOGEN
MESOGEN
FIELD
Аннотация: The orientational order parameter S of molecules in high-temperature discotic nematic liquid-crystal phases of triphenylene derivatives is investigated as a function of the length of side flexible molecular chains at different temperatures. It is established that the orientational order parameters S in the range of the transition from the nematic phase to the isotropic liquid phase (the N-D-I transition) are smaller than those predicted from the molecular-statistical theory and computer simulation. It is shown that the N-D-I transition is close to both the isolated Landau point and the tricritical point (regardless of the chemical structure of the molecules and the anisotropy of dispersion intermolecular interactions). Consistent explanations are offered for a number of experimental findings, such as the anomalously small changes in the enthalpy and entropy upon the N-D-I transition (as compared to those revealed upon the N-I transition in calamitic nematic liquid crystals), the anomalously strong response of the isotropic phase of discotic nematic liquid crystals to external fields (thermodynamically conjugate to the order parameter S) and the long relaxation times of this response, and the formation of cybotactic discotic molecular clusters in the isotropic phase in the vicinity of the N-D-I transition. (C) 2004 MAIK "Nauka / Interperiodica".
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Erkaev N. V., Shaidurov V. A., Semenov V. S., Langmayr D., Biernat H. K.
Заглавие : Peculiarities of Alfven wave propagation along a nonuniform magnetic flux tube
Место публикации : Phys. Plasmas: AMER INST PHYSICS, 2005. - Vol. 12, Is. 1. - Ст.12905. - ISSN 1070-664X, DOI 10.1063/1.1833392
Примечания : Cited References: 18
Предметные рубрики: HYDROMAGNETIC-WAVES
TRANSFER EVENTS
FIELD
SLOW
Ключевые слова (''Своб.индексиров.''): algebra--approximation theory--boundary conditions--electric conductivity--electric field effects--integral equations--magnetic flux--magnetohydrodynamics--perturbation techniques--polarization--vectors--velocity measurement--alfven wave propagation--axial symmetry--magnetic flux tubes--magnetosonic pulses--wave propagation
Аннотация: Within the framework of the assumption of large azimuthal wave numbers, the equations for Alfven and slow magnetosonic waves are obtained using frozen-in material coordinates. These equations are specified for the case of a nonuniform magnetic field with axial symmetry. Assuming a meridional polarization of the magnetic field and velocity perturbations, the effects of Alfven wave propagation are analyzed which are related to geometric characteristics of a nonuniform magnetic field: (a) A finite curvature radius of the magnetic field lines and (b) convergence of magnetic field lines. The interaction between the Alfven and magnetosonic waves is found to be strongly dependent on the curvature radius of the magnetic tube and the local plasma beta parameter. The electric field amplitude and the length scale of a wave front are found to increase very strongly in the course of the Alfven wave propagation along a converging magnetic flux tube. Also studied is a temporal decrease of the wave perturbations which is caused by dissipation at the conducting boundary. (C) 2005 American Institute of Physics.
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