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1.
The influence of the polarization interactions on the state and phase transitions in magnetic-ordered and dielectric crystals with two interacting order parameters has been investigated. Consideration is given to the case when the interaction in one of the subsystems is considerably weaker than that in the other subsystem. It is demonstrated that the polarization interactions in the weak subsystem can substantially affect the state and the character of phase transitions in the strong subsystem. These interactions can bring about the disordering (formation of the random-field state or the state of spin glass) in the critical region near the second-order phase transition in the main subsystem and also the smearing of the phase transition. At the same time, the polarization interactions can give rise to the ordered and disordered states in the weak subsystem. 相似文献
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The model of linear chains is used to study the lattice softening of A 15-compounds in strong magnetic fields. It is shown that a strong field stabilizes the cubic phase due to the Zeeman energy of the conduction electrons. Experiments are suggested to test our theoretical findings. 相似文献
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A. L. Semenov 《Journal of Experimental and Theoretical Physics》1998,87(4):764-770
A theory is constructed that explains photoinduced phase transitions in a Peierls system being irradiated by light with a
finite width of the optical spectrum and a central frequency close to the upper van Hove singularity of the first kind in
the combined density of electron states. The electron spectrum and the matrix elements of the dipole-moment operator are calculated
by Bogolyubov’s method of canonical transformations. The interaction with the light is described by the Liouville equation
for the density matrix of the electron subsystem in the dipole approximation. The light field is considered a quasimonochromatic
time-independent random process with a Lorentzian spectrum. The derived equations are analyzed for two limits: (1) when the
width of the optical spectrum tends to zero (a monochromatic light field), and (2) when the width of the optical spectrum
is close to the upper limit (a bifurcation point) at which a photoinduced phase transition can still be observed. An existence
criterion for such a transition is obtained, and the main parameters of the transition (the critical points and the size of
the hysteresis loop) are calculated. The broadening of the optical spectrum of the incident light is shown to narrow the range
of values of the central frequency of the light field and to reduce the size of the hysteresis loop. Finally, near the phase
transition point, cavityless optical bistability sets in in the system, with light absorption increasing in the process.
Zh. éksp. Teor. Fiz. 114, 1407–1420 (October 1998) 相似文献
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Cejnar P 《Physical review letters》2003,90(11):112501
Landau theory of phase transitions is applied to quadrupole shapes of rotating atomic nuclei within the interacting boson model (IBM) with cranking. It is shown that the coherent-state method must be generalized to allow for non-Hermitian quadrupole tensors of the coherent-state coefficients, which results in important modifications of the cranking shape-phase diagram compared to previous non-IBM studies of rotating nuclei. The parameter space has two surfaces of the first-order phase transitions and a curve of the second-order phase transition at their intersection. The phase structure of the cranked IBM closely resembles systems with competing superconducting and normal phases. 相似文献
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Elena V. Tartakovskaya 《Journal of magnetism and magnetic materials》2010,322(21):3495-3501
Reorientation phase transitions (RPT) taking place in regular arrays of rectangular submicron-size ferromagnetic particles due to the competition between the external magnetic field of arbitrary direction and internal dipolar fields are analysed in this article. Dipolar interaction between particles is taken into account via real-space calculations of magnetometric demagnetizing factors. Long stripe arrays are also under consideration. I find that the direction of the external magnetic field determines the kind of the phase transition, while the dipolar interaction between particles can significantly change the values of RPT critical field. Calculations were presented for a set of submicron particles/stripe arrays, which were under experimental investigations recently. 相似文献
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By adopting a simplified model of a non-polytropic hard-sphere system where heat capacity depends on the temperature, we demonstrate the importance of non-polytropic effect on the shock-induced phase transitions. We show explicitly that with the increase of the shock strength the perturbed temperature (the temperature after a shock) increases and the vibrational modes are gradually excited, and as a result, shock-induced phase transitions are qualitatively and quantitatively different from the phase transitions observed in a simple polytropic model. The effect on the admissibility (stability) of a shock wave is also analyzed. 相似文献
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Aya S Sasaki Y Araoka F Ema K Ishikawa K Emelyanenko AV Takezoe H 《Physical review letters》2011,106(11):117801
Using specified conditions, we succeeded in observing the isotropic-nematic (Iso-N) liquid crystal phase transition at surfaces followed by that in bulk for the first time. An additional heat anomaly peak was found at a higher temperature side of a main phase transition peak using highly sensitive differential scanning calorimetry (HS-DSC). The peak is pronounced particularly in the cooling process, since the transition starts at surfaces on cooling. The temperature dependence of retardation allows us to safely conclude that the higher temperature peak that appeared in HS-DSC is attributed to the Iso-N transition at surfaces. These measurements also indicate that the surface transition is of first order. These behaviors were theoretically explained by generalized Maier-Saupe theory. 相似文献
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Anissimova S Venkatesan A Shashkin AA Sakr MR Kravchenko SV Klapwijk TM 《Physical review letters》2006,96(4):046409
We measure the thermodynamic magnetization of a low-disordered, strongly correlated two-dimensional electron system in silicon in perpendicular magnetic fields. A new, parameter-free method is used to directly determine the spectrum characteristics (Landé g factor and the cyclotron mass) when the Fermi level lies outside the spectral gaps and the interlevel interactions between quasiparticles are avoided. Intralevel interactions are found to strongly modify the magnetization, without affecting the determined g* and m*. 相似文献
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P. Amann M. Cordin Ch. Braun B. A.J. Lechner A. Menzel E. Bertel C. Franchini R. Zucca J. Redinger M. Baranov S. Diehl 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,75(1):15-22
A quasi-1D system is prepared using the Pt(110) surface as a template. The electronic surface resonance structure is studied by angle-resolved photoemission spectroscopy for the clean surface as well as for different Bromine coverages. A Fermi surface mapping reveals saddle points at the Fermi level in the interior of the surface Brillouin zone. Correspondingly, a maximum in the static response function χ(q, 0) at the connecting vector q is expected. With 1/2Gx < q < 2/3Gx one observes indeed a 3-fold periodicity around defects and a 2-fold periodicity at low temperature for ΘBr = 0.5 ML. Cooling of a defect-free c(2×2)-Br/Pt(110) preparation counter-intuitively results in a loss of long-range order. Motivated by DFT calculations this is attributed to an anomalous order-order phase transition into the (2×1) phase accompanied by intense, strongly anisotropic fluctuations within a temperature range of ~200 K. The peculiar behaviour is rationalised in terms of a competition between inter-adsorbate repulsion and an adsorbate triggered 2kF interaction in the substrate. 相似文献
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We predict the existence of novel first-order phase transitions in a general class of multiqubit cavity systems. Apart from atomic systems, the associated superradiant phase transition should be observable in a variety of solid-state experimental systems, including the technologically important case of interacting quantum dots coupled to an optical cavity mode. 相似文献
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The treatment of the Ising model on a Cayley tree given by Müller-Hartmann and Zittartz is extended in the case of connectivity two to a decorated tree containing additional bonds with an arbitrary coupling constant. The possibility of phase transitions is investigated and discussed. The positions of the singular surfaces, on which continuous order phase transitions take place, are examined as functions of coupling constants and external fields. 相似文献
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Christof Wetterich 《Zeitschrift fur Physik C Particles and Fields》1993,57(3):451-469
We compute the average action for scalar fields in two, three and four dimensions, including the effects of wave function renormalization. A study of the one loop evolution equations for the scale dependence of the average action gives a unified picture of the qualitatively different behaviour in various dimensions for discrete as well as abelian and nonabelian continuous symmetry. The different phases and the phase transitions can be infered from the evolution equation. 相似文献
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A. L. Semenov 《Journal of Experimental and Theoretical Physics》1997,84(6):1171-1176
An electron theory of photoinduced phase transitions and cavityless optical bistability in a light field with a finite optical-spectrum
width is constructed. The Liouville equation for the density matrix is used to derive the existence criteria and calculate
the main characteristics of the given phenomena. Broadening of the optical spectrum is shown to reduce the possibility of
observing critical features (the existence criterion becomes more stringent and the hysteresis-loop area becomes smaller).
Finally, results are compared with experimental data for CdS and amorphous GeS2.
Zh. éksp. Teor. Fiz. 111, 2147–2157 (June 1997) 相似文献
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I.F. Lyuksyutov 《Physics letters. A》1976,56(2):135-136
It is shown that for the case of a strong field coupling in the system of two fields the low temperature phase may be stable in the fluctuation region of the high temperature phase. 相似文献
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It is predicted that an excitonic liquid is formed in a system of spatially separated electrons (e) and holes (h) in a system of two coupled quantum wells. The ground-state energy and the equilibrium density of the excitonic liquid are
calculated as a function of the distance D between the wells. A gas-liquid quantum transition with increasing D is studied. The Berezinskii-Kosterlitz-Thouless transition temperatures at which superfluidity appears in the system are
found (for different D). A quantum Mott metal-insulator transition in an anisotropic double-quantum-well structure is investigated. The region of
existence of crystalline order in a system of spatially separated e and h is studied. Possible experimental manifestations of the predicted effects are discussed.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 8, 526–531 (25 October 1996) 相似文献
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We have investigated the one-dimensional spin-1/2 axial next-nearest-neighbour Ising (ANNNI) model in two orthogonal magnetic
fields at zero temperature. There are four different possible ground state configurations for the ANNNI model in a longitudinal
field, in the thermodynamic limit. The inclusion of a transverse field introduces quantum fluctuations which destroy the existing
spin order along certain critical lines. The effects of the fluctuations in three of the four ordered regions were investigated
using the finite-size scaling technique. The phase boundaries of the ANNNI model in two orthogonal magnetic fields were thus
determined numerically. For certain limits of the Hamiltonian we compared the obtained results with the existing literature
and our results were in good agreement with the results in the existing literature. 相似文献