Integrabilities of the long-range t-J models with twisted boundary conditions

The effect of uniaxial pressure (X) up to 1 kbar, applied along the three main directions, on the Curie temperature and the dielectric constant ε c of a Pb 5 Ge 3 O 11 single crystal was investigated. The Curie temperature decreases with uniaxial pressure and the coefficient γ i (γ i ≡ ∂T c /∂(X i ) was determined as −6.5, −7.0 and −3.2 K kbar −1 for a-, b-and c-axis respectively. It has been found that uniaxial pressure applied along the c-axis strengthens the second order phase transition but applied along the directions perpendicular to the c-axis it may induce a tricritical point. The critical uniaxial pressure was estimated from the ratio C + /C − against X to be about 2.4 kbar. A tentative description of the mechanism of changes in the phase transition order is given. The phenomenological relation describing γ i is also discussed.

Section: Resultsmentioning

confidence: 99%

Effect of uniaxial pressure on the ferroelectric phase transition in Pb₅Ge₃)₁₁

Koralewski

Molak

1999

“…Excitons and biexcitons (analogous to hydrogen atoms and molecules, respectively) are the best-known examples of such complexes. The trions predicted by Lampert in 1958 [15], the negatively charged exciton (X − : two electrons bound to a hole), and the positively charged exciton (X + : two holes bound to an electron) are much less familiar [16][17][18]. The trion binding energy is substantially increased in a GaAs/Ga 1−x Al x As QW [16,19].…”

Section: Introductionmentioning

confidence: 99%

Electronic structure of donor-impurity complexes in quantum wells

Betancur

Mikhailov

Marín

et al. 1998

The ground state of the two-electron donor-impurity complexes and confined in a quantum well is analysed by using a variational procedure. A model approximation that can be used in the two-electron problem in order to separate the variables is proposed, and it is shown that, for the negative ion and the complex, the electron-electron interaction may be eliminated, in this approximation, by introducing an additional effective charge at a centre of symmetry. The binding energy is calculated as a function of the quantum-well width for different magnetic field strength values, whereas the and dissociation energies are calculated as functions of the spacing between the impurities in the complexes, and for different well widths. The results for the first and the second ionization binding energies as functions of the well width are presented for different separations between impurities. Finally, the scheme that we propose is extremely simple and provides a realistic description of few-particle ground-state electronic structures confined in a quantum well.

“…The network of the domain walls may be affected by applied stress. For instance, such a phenomenon has been observed for axially compressed SrTiO 3 [34]. It seems that under low external pressure the domain walls are released leading to an increase in ε(T, X, y) value.…”

Section: Curie-weiss-type Dependencementioning

confidence: 86%

Flattening of the electric permittivity curve ε(T) of NaNbO₃:yMn single crystals caused by stress application

Molak¹

2001

A DTA test, performed within the 300–700 K range, showed that the series of NaNbO3:yMn single crystals exhibit first-order phase transition known from pure sodium niobate. The introduced Mn dopant lowers the temperature of this phase transition at a rate ΔTP–R/Δ%(Mn) ≈ −15 K wt%−1. The electric permittivity measured at ambient pressure showed a clear Curie–Weiss maximum at this antiferroelectric phase transition. The applied axial compression caused gradual suppression of this anomaly towards step-like characteristics. Flat ε(T, X, y) curves appeared when the axial pressure X exceeded a few hundreds bars. The stress field was calculated around the Mn ions built into the host. It was pointed out that due to this the stress field and external compression are lower than misfit stress estimated for the P–R structural phase transition and any new phase was not induced with dopant manganese ions at the obtained real concentration y level. The recorded ε(T, X, y) characteristics were fitted with a generalized Curie–Weiss formula. It was shown that the molecular field approximation remains valid. Both linear and nonlinear elastic effects were necessary to describe the experimental ε(T, X, y) characteristics.