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1.
A. D. Bozhko A. N. Vasil’ev V. V. Khovailo V. D. Buchel’nikov I. E. Dikshtein S. M. Seletskii V. G. Shavrov 《JETP Letters》1998,67(3):227-232
The phase diagram of the cubic ferromagnetic shape-memory alloy Ni2+x
Mn1−x
Ga is constructed theoretically for the case when the Curie temperature is close to the structural transition temperature.
This diagram agrees well with the experimental data obtained from resistance and magnetic susceptibility measurements. It
is shown that the transition from the paramagnetic cubic phase to the ferromagnetic tetragonal phase can be second-order or
first-order.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 3, 212–216 (10 February 1998) 相似文献
2.
The specific heat of Pb2MgWO6 has been measured in the temperature interval 83–370 K. An anomaly in the specific heat associated with the phase transition
at T
0=312.8K has been discovered. The thermodynamic parameters of the structural phase transition Fm3m-Pmcn have been determined.
Fiz. Tverd. Tela (St. Petersburg) 41, 1686–1688 (September 1999) 相似文献
3.
Nanosecond-resolution absorption spectroscopy at room temperature was used to study the laws governing the creation and evolution
of the primary defect structure in CaF2, SrF2, and BaF2 crystals exposed to an accelerated electron pulse. It is shown that the spectral-kinetic characteristics of self-trapped
excitons created in undamaged parts of the crystal lattice are qualitatively similar. Partial polarization of the absorption
of self-trapped excitons is observed in CaF2. The structure of the transient absorption spectra becomes more complex in the sequence CaF2, SrF2, BaF2 because of the formation of excitons trapped in phase inclusions of homologous cationic impurities. The spectral characteristics
of excitons trapped in undamaged parts of the CaF2 and SrF2 lattice and in their phase inclusions in BaF2 are the same although the latter have a considerably shorter relaxation time. Short-lived (τ⩽100 ns) absorption of unknown defects was observed in the spectral range ⩾5 eV.
Fiz. Tverd. Tela (St. Petersburg) 40, 1228–1234 (July 1998) 相似文献
4.
Yu. E. Lozovik O. L. Berman M. Willander 《Journal of Experimental and Theoretical Physics》1999,88(5):980-986
Instability in a system of interacting quasi-two-dimensional excitons in a type II superlattice of a finite thickness due
to attraction between oppositely-directed excitonic dipoles in neighboring layers has been discovered. A stable system is
that of indirect quasi-two-dimensional biexcitons formed by indirect excitons with dipole moments oriented in opposite directions.
The radius and binding energy of indirect biexcitons has been calculated. A collective spectrum of a system of such biexcitons
with a weak quadrupole interaction between them has been studied. Feasibility of Bose condensation, the density n
s(T) of the superfluid component, and a phase transition to the superfliud state in a low-density system of indirect biexcitons
have been analyzed.
Zh. éksp. Teor. Fiz. 115, 1786–1798 (May 1999) 相似文献
5.
The influence of photoexcited carriers on the dynamics of the absorption spectra of GaAs/AlxGa1−2x
As multilayer quantum wells is investigated experimentally. It is found that at quasiparticle densities all the way up to
1011 cm−2 the saturation of the excitonic absorption is due to both a decrease of oscillator strength and broadening of the excitonic
lines. It is shown that in the case of femtosecond resonance laser exci-tation the decrease of oscillator strength is due
to free electron-hole pairs, while the broadening and energy shift of the excitonic lines are due to the exciton-exciton interaction.
The lifetimes of free electron-hole pairs and excitons (≈65 ps and ≈410 ps, respectively) are determined from the exponential
decrease of the change in the oscillator strength and in the width and energy position of the excitonic lines.
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 3, 139–144 (10 August 1997) 相似文献
6.
V. M. Agranovich S. A. Kiselev Z. G. Soos S. R. Forrest 《Physics of the Solid State》1999,41(5):704-707
We discuss the phase transition to the conducting state in a system of 2D charge-transfer excitons (CTEs) at a donor-acceptor interface. The phase transition arises due to strong dipole-dipole repulsion
between CTEs which stimulates the population of free carriers in higher energy states even at low temperature. We use the
computer simulations with the random distribution of excitons, with finite lifetime explicitly taken into account. The critical
concentration of CTEs and their energy distribution are calculated. We also discuss the possibility of observing the predicted
phenomena.
Fiz. Tverd. Tela (St. Petersburg) 41, 781–784 (May 1999)
Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor. 相似文献
7.
Yu. M. Korchak V. B. Kapustyanyk M. V. Partyka V. P. Rudyk 《Journal of Applied Spectroscopy》2007,74(2):289-294
We have studied the absorption spectra of NH4Al(SO4)2·12H2O crystal hydrates in the visible region of the spectrum, near the low-temperature phase transition at Tc = 76 K. We have shown that the absorption edge in these materials has an exponential shape, following the empirical Urbach’s
rule as a result of exciton-phonon interaction. The relatively strong exciton-phonon interaction is associated with a band
formed by self-localized (self-trapped) excitons. The experimental data obtained support the presence of a phase transition
in the studied ammonium alum at 76 K. We have shown that ammonium aluminum sulfate dodecahydrate crystals are promising materials
for fabricating laser frequency converters.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 258–262, March–April, 2007. 相似文献
8.
S. G. Jabarov D. P. Kozlenko S. E. Kichanov A. V. Belushkin B. N. Savenko R. Z. Mextieva C. Lathe 《Physics of the Solid State》2011,53(11):2300-2304
The crystal structure of lead titanate PbTiO3 was investigated by energy dispersive X-ray diffraction at high pressures up to 4 GPa in a temperature range of 300–950 K.
At the ambient conditions, the PbTiO3 structure is tetragonal with the space group P4mm (ferroelectric phase). A structural phase transition into the cubic phase with a space group Pm[`3]mPm\bar 3m is observed at T = 747 K. It was found that the phase transition temperature decreases upon applying the high pressure with the coefficient
dT
C
/dP = -65 K/GPa. Dependences of parameters and volume of the unit cell on the pressure and temperature was found, and the bulk
modulus and thermal expansion coefficients for the tetragonal and cubic phases of lead titanate have been calculated. 相似文献
9.
E. A. Mulyarov N. N. Sibel’din M. L. Skorikov V. A. Tsvetkov B. Etienne 《JETP Letters》1999,70(9):621-627
Lines corresponding to localized excitonic states formed from “above-barrier” electron and/or hole states (specifically, excitation
lines of excitons formed by an electron localized in a QW and a free heavy hole) have been observed in the photoluminescence
excitation spectra of GaAs/Al0.05Ga0.95As structures with quantum wells (QWs), each containing one single-particle size-quantization level for charge carriers of
each type. A computational method is proposed that permits finding the binding energy and wave functions of excitons in QWs
taking the Coulomb potential into account self-consistently. The computed values of the excitonic transition energies agree
quite well with the experimental results.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 9, 613–619 (10 November 1999) 相似文献
10.
Yu. N. Ovchinnikov 《Journal of Experimental and Theoretical Physics》1997,85(4):818-823
It is shown that near the transition temperature T
c the coefficients of the second and third terms in the expansion of the free energy in powers of H
c2−B (B is the magnetic field induction inside the superconductor) go to zero simultaneously for a value of κ=1 for the Ginzburg-Landau parameter. Thereby the structure of the mixed state near H
c2 for a value of the parameter κ close to unity is determined by the temperature correction to the coefficient for the third power and the coefficient for
the fourth power in the expansion of the free energy in powers of H
c2−B. The values of these coefficients depend on the type of vortex lattice.
Zh. éksp. Teor. Fiz. 112, 1499–1509 (October 1997) 相似文献
11.
We discuss drag effects in a two-layer system of spatially separated electrons and excitons: the entrainment of excitons by
moving electrons, and the entrainment of electrons by moving excitons. For the case of excitons entrained by electrons we
find the drag velocity υ
drag, and for electrons entrained by excitons we compute the induced electric field E
2. These drag effects can be sensitive indicators of the phase state of the excitons and of phase transitions in the exciton
system (to a liquid phase, superfluid state, etc.)
Zh. éksp. Teor. Fiz. 111, 1107–1119 (March 1997) 相似文献
12.
M. V. Radchenko G. V. Lashkarev E. I. Slyn’ko A. P. Malysheva 《Physics of the Solid State》1999,41(10):1604-1607
In the temperature interval 4.2–300K and magnetic fields up to 4 T, we have investigated the electrical, thermal-electrical,
thermal-magnetic, and magnetic properties of single crystals of the solid solution Pb0.8Sn0.2Te. It is shown that an enhancement of its level of structural perfection leads to the appearance of a second structural phase
transition (SPT), and also to an increase in the temperature of the first structural phase transition.
Fiz. Tverd. Tela (St. Petersburg) 41, 1750–1752 (October 1999) 相似文献
13.
The appearance of a new domain structure against the background of the old domain structure is observed in CsDSO4 crystals at 3 °C away from the superionic phase transition. It is established that the appearance of the new domain structure
is accompanied by a gradual increase in the conductivity by 1.5–2 orders of magnitude, and then the conductivity increases
abruptly by another two orders of magnitude at the temperature of the superionic phase transition.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 11, 871–875 (10 June 1996) 相似文献
14.
S. V. Gorbunov K. V. Bautin A. V. Kruzhalov V. Yu. Yakovlev 《Physics of the Solid State》1999,41(4):539-543
Spectra of metastable optical absorption and its relaxation kinetics have been studied in zinc-doped BeO crystals by time-resolved
pulsed absorption spectroscopy. A comparison of the observed induced optical absorption of self-trapped excitons and small-radius
excitons bound to the zinc impurity suggests that their hole components have similar structures and reveals distinctive features
of “forbidden” optical transitions in the electronic components. Metastable optical absorption in Zn+ centers has been discovered. It is shown that the small-radius excitons bound to the zinc impurity form in the hole stages
of thermally stimulated tunneling recombination processes involving Zn+ electronic centers. It has been found that the high recombination probability of the electronic and hole centers created
in BeO-Zn crystals by an electron beam may be due to the high degree of their spatial correlation.
Fiz. Tverd. Tela (St. Petersburg) 41, 601–605 (April 1999) 相似文献
15.
Z. A. Kazei V. V. Snegirev A. S. Andreenko L. P. Kozeeva 《Journal of Experimental and Theoretical Physics》2011,113(2):245-250
The elastic properties of rare-earth cobaltites RBaCo4O7 (R = Y, Tm-Lu) have been experimentally studied in the temperature range of 80–300 K. The strong softening of the Young modulus
ΔE(T)/E
0 ≈ −(0.1–0.2) of cobaltites with Lu and Yb ions has been revealed, which is due to the instability of the crystal structure
upon cooling and is accompanied by an inverse jump at the second-order structural phase transition. The softening of the Young
modulus and the jump at the phase transition decrease by an order of magnitude and the transition temperature T
s and hysteresis ΔT
s increase from a compound with Lu to that with Tm. A large softening of the Young modulus at the structural transition in
Lu- and Yb cobaltites indicates that the corresponding elastic constant goes to zero, whereas this constant in Tm cobaltite
is not a “soft” mode of the phase transition. It has been found that the structural phase transition in Lu- and Yb cobaltites
is accompanied by a large absorption maximum at the phase transition point and an additional maximum in the low-temperature
phase and absorption anomalies in Tm cobaltite is an order of magnitude smaller. 相似文献
16.
M. V. Patrakeev I. A. Leonidov E. B. Mitberg A. A. Lakhtin V. G. Vasiliev V. L. Kozhevnikov K. R. Poeppelmeier 《Ionics》1999,5(5-6):444-449
The equilibrium oxygen content was measured in the model system and important oxygen permeable material La1−xSrxCoO3−δ, where x=0.6, in the temperature range 650–900 °C and oxygen partial pressure range between 10−5 and 1 atm. The data were utilized to obtain changes in the partial entropy and enthalpy of oxygen in the solid as a function
of the oxygen content. It is shown that the initially cubic perovskite undergoes to a phase transition to a tetragonal structure
at δ >0.3. The oxygen permeation of L0.4Sr0.6CoO3−δ at 700–900 °C is found to be controlled by bulk solid state processes. The activation energy equals about 0.8 eV at high
oxygen pressure and small oxygen nonstoichiometry. Increasing oxygen deficiency results in a rapid increase in the activation
energy. In combination with thermodynamic data, these changes can be explained as resulting from the intrinsic spatial inhomogeneouty
in oxygen vacancy distribution which varies both with temperature and oxygen nonstoichiometry. It is shown that, when the
oxygen deficiency increases at constant temperature, the oxygen vacancies form locally ordered microdomains (clusters), which
eventually results in a transition of the cubic perovskite structure to the tetragonal structure. The oxygen ion conductivity
depends strongly on the development of the ordering.
Paper presented at the 6th Euroconference on Solid state Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999. 相似文献
17.
A study has been carried out of the temperature dependences of luminescence spectra on a large number of CdTe/ZnTe structures
differing in average thickness, 〈L
z〉=0.25–4 monolayers (ML), and CdTe layer geometry (continuous, island type). The influence of geometric features in the structure
of ultrathin layers on linewidth, the extent of lateral localization of excitons, their binding energy, and exciton-phonon
coupling is discussed. It is shown that in island structures there is practically no lateral exciton migration. The exciton-phonon
coupling constant in a submonolayer structure has been determined, Γph=53 meV, and it is shown that in structures with larger average thicknesses Γph is considerably smaller. Substantial lateral exciton migration was observed to occur in a quantum well with 〈L
z〉=4 ML, and interaction with acoustic phonons was found to play a noticeable part in transport processes. It has been established
that the depth of the exciton level in a quantum well and structural features of an ultrathin layer significantly affect the
temperature dependences of integrated photoluminescence intensity.
Fiz. Tverd. Tela (St. Petersburg) 41, 717–724 (April 1999) 相似文献
18.
The change in the properties of excitonic states near anticrossing is investigated experimentally. It is shown that the phase
relaxation time of light excitons in a GaAs/AlGaAs symmetric double quantum well increases by a factor of five as a result
of mixing of the energy states of light and heavy excitons.
Pis’ma Zh. éksp. Teor. Fiz. 69, No. 6, 426–430 (25 March 1999) 相似文献
19.
V. V. Kveder V. D. Negrii É. A. Shteinman A. N. Izotov Yu. A. Osip’yan R. K. Nikolaev 《Journal of Experimental and Theoretical Physics》1998,86(2):405-411
Photoluminescence, optical absorption spectra, and photoluminescence excitation spectra were measured on large (2–3 mm), very
pure crystals of fullerene C60 at 5 K. It is shown that the main contribution to the photoluminescence of these crystals is from singlet and triplet excitons
captured on crystal defects. The concentration of these defects does not exceed 1018 cm−23, and the lifetime of triplet excitons on these defects is about 3 ms. It is shown that the symmetry distortion of the C60 molecules at the defects is rather large and causes the oscillator strength of the zero-phonon optical transitions to be
comparable to the most intense optical transitions with the participation of intramolecular vibrations.
Zh. éksp. Teor. Fiz. 113, 734–746 (February 1998) 相似文献
20.
A. V. Mudryi A. V. Karotki M. V. Yakushev R. Martin 《Journal of Applied Spectroscopy》2009,76(2):215-219
Photoluminescence of CuInS2 single crystals grown by both the traveling heater method (THM) and chemical vapor transport (CVT) has been investigated
at 4.2, 78, and 300 K. Intense emission in the near-band-edge region caused by free and bound excitons has been detected for
both types of crystals. Taking into account the energy position of the luminescence line of the ground (n = 1) and first excited (n = 2) states, the binding energy for free A excitons has been estimated to be about 19.7 and 18.5 meV for CuInS2 grown by CVT and THM, respectively.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 2, pp. 232–236, March–April, 2009. 相似文献