共查询到20条相似文献,搜索用时 31 毫秒
1.
M. Hinczewski A. N. Berker 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(4):461-472
The anisotropic d=3 tJ model is studied by
renormalization-group theory, yielding the evolution of the system
as interplane coupling is varied from the isotropic
three-dimensional to quasi-two-dimensional regimes.
Finite-temperature phase diagrams, chemical potential shifts, and
in-plane and interplane kinetic energies and antiferromagnetic
correlations are calculated for the entire range of electron
densities. We find that the novel τ phase, seen in earlier
studies of the isotropic d=3 tJ model, persists even for
strong anisotropy. While the τ phase appears at low
temperatures at 30–35% hole doping away from 〈
ni〉=1, at smaller hole dopings we see a complex lamellar
structure of antiferromagnetic and disordered regions, with a
suppressed chemical potential shift, a possible marker of
incommensurate ordering in the form of microscopic stripes. An
investigation of the renormalization-group flows for the isotropic
two-dimensional tJ model also shows a clear pre-signature of the
τ phase, which in fact appears with finite transition
temperatures upon addition of the smallest interplane coupling. 相似文献
2.
J. Sjakste V. Tyuterev N. Vast 《Applied Physics A: Materials Science & Processing》2007,86(3):301-307
Interactions between excited electrons and short-wavelength (intervalley) phonons in GaAs are studied using density functional
theory for the conduction bands, and density functional perturbation theory for phonon frequencies and matrix elements of
the electron–phonon interaction. We have calculated the deformation potentials (DPs) and the average intervalley scattering
time 〈τ〉. The integration of the scattering probabilities over all possible final states in the Brillouin zone has been performed
without any ad hoc assumption about the behavior of the electron–phonon matrix elements nor the topology of the conduction
band. For transitions from the L point to Γ valley (within the first conduction band), we find 〈τ〉L to be 1.5 ps at 300 K, in good agreement with time-resolved photoluminescence experiment. We discuss the difference between
our calculated DPs, and effective parameters used in Monte Carlo simulations of optical and transport properties of semiconductors.
The latter are based on Conwell’s model, in which electron–phonon interaction is described by one single constant and a parabolic
model is used for conduction bands. We deduce the effective DP from our 〈τ〉, and compare it to our calculated DPs. We conclude
that only effective DPs obtained from a full calculation of 〈τ〉 are relevant parameters for Monte Carlo simulations.
PACS 71.10-w; 72.10.Di; 71.55.Eq 相似文献
3.
L. G. Mamsurova N. G. Trusevich K. S. Pigalskiy N. B. Butko A. A. Vishnev 《Bulletin of the Russian Academy of Sciences: Physics》2011,75(8):1136-1139
It was proven experimentally that the structural disordering inherent to fine-grained high-temper- ature YBa2Cu3O
y
superconductors (with an average grain size of 〈D〉 < 2 μm) leads to a reduction of the level of hole doping and the creation of features inherent to the pseudogap state (antiferromagnetic
correlations and the lowered density of states at the Fermi level) even in samples with optimum oxygen content y ≈ 6.92. 相似文献
4.
M. N. Khlopkin 《JETP Letters》1999,69(1):26-30
The specific heat of a V3Si single crystal (T
c=17 K, H
c2=20 T) in magnetic fields up to 8 T isinvestigated experimentally for three orientations of the field relative to the crystallographic
directions — H∥〈001〉, H∥〈110〉, and H∥〈111〉. Both the upper critical magnetic field and the specific heat of the mixed state are observed to depend on the orientation
of the magnetic field relative to the crystallographic directions (anisotropy): The critical field reaches its maximum value
and the specific heat its minimum value in a field along the 〈001〉 direction. The anisotropy scale in both phenomena increases
as the magnetic field and reaches 3% in a 6 T field. The interrelationship of the upper critical field anisotropy and the
specific-heat anisotropy in type-II superconductors is studied. It is shown that the anisotropy of the specific heat in the
mixed state in weak fields can serve as a criterion for nontrivial pairing.
Pis’ma Zh. éksp. Teor. Fiz. 69, No. 1, 26–29 (10 January 1999) 相似文献
5.
Experimental studies of the dielectric properties in the nematic and isotropic phases of 4-cyanophenyl-4′-n-octylbenzoate
(8CPB) have been performed in the frequency range from 50 kHz to 100 MHz. The relaxation process related to the rotation around
the short molecular axis has been analysed. The results obtained have revealed that in the vicinity of the I-N phase transition,
the molecular subdiffusional rotation process occurs. It is connected with the pretransitional effects which are observed
both in the static and dynamic dielectric measurements. On the basis of the temperature dependence of the relaxation time
in the nematic and isotropic phases, the orientational order parameter 〈P2〉 has been determined. The values of 〈P2〉 obtained in this way have been compared with those evaluated from the measurements of the polarized electronic absorption
of the dichroic dye, dissolved as guest probe in the mesogenic host. 相似文献
6.
B. J. Madhu H. S. Jayanna S. Asokan 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,71(1):21-25
The compositional dependence of thermal properties, such as glass transition temperature (Tg), non-reversing enthalpy change (ΔHNR) and the specific heat capacity change (ΔCp) of melt quenched Ge7Se93-xSbx (21 ≤ x ≤ 31) glasses, has been studied using alternating differential scanning calorimetry (ADSC) which is analogous to
modulated differential scanning calorimetry (MDSC). The glass transition temperature, Tg, which is a measure of global connectivity of the glass, has been found to increase with the addition of
Sb. In addition, a change in slope has been observed in the composition dependence of Tg at an average coordination 〈r〉 = 2.40. The experimentally observed compositional variation of glass transition temperature,
has been compared with the theoretical predictions from the
stochastic agglomeration theory (SAT) and has been found to be consistent. Further, a narrow thermally reversing window is
seen in the compositional variation of the relaxation enthalpy (ΔHNR), which is centered around 〈r〉 = 2.40. The change in specific heat capacity (ΔCp) at Tg is also found to exhibit a distinct minima at 〈r〉 = 2.40, suggesting that the structural rearrangements for the liquid in
the glass transition region are minimized around 〈r〉 = 2.4. 相似文献
7.
D. M. Shukurova A. S. Orekhov B. Z. Sharipov V. V. Klechkovskaya T. S. Kamilov 《Technical Physics》2011,56(10):1423-1428
The current-voltage characteristics of Mn4Si7-Si〈Mn〉-Mn4Si7 and Mn4Si7-Si〈Mn〉-M photodiodes are studied experimentally. The current passage mechanism under illumination with hν ≥ E
g
is considered. The role of a contact to Mn4Si7 in the provision of high photosensitivity under illumination of the base by light with hν ≥ 1.14 eV at low temperatures, 77–220 K, is analyzed. From electrical measurements, electron microscopic data for the Mn4Si7-Si〈Mn〉 interface, and photocurrent-voltage characteristics, a band diagram under the conditions of photocurrent passage is
constructed. The high low-temperature photosensitivity of the diodes (I
ph/I
d ≥ 109) is explained by the impact-ionization-induced modulation of the base conductivity and injection amplification of holes in
the transition layer. 相似文献
8.
The effect of doping CdIn2S4 single crystals by copper (3 mol %) on their X-ray dosimetric characteristics is investigated. It is found that the characteristic
X-ray conductivity of CdIn2S4〈Cu〉 single crystals increases 3–16 times compared with undoped CdIn2S4 at effective radiation hardness V
a = 25−50 keV and dose rate E = 0.75−78.05 R/min. Moreover, the persistence of the crystal characteristics completely disappears and the supply voltage
of a CdIn2S4〈Cu〉 X-ray detector decreases fivefold. The dependence of the steady X-ray-induced current in CdIn2S4〈Cu〉 on the X-ray dose is described as ΔI
E, 0 ∝ E
α, where 0.6 ≤ α ≤ 1.8. 相似文献
9.
The interpretation of the violation of Bell-Clauser-Horne inequalities is revisited, in relation with the notion of extension of QM predictions to unmeasurable correlations. Such extensions are compatible with QM predictions in many cases, in particular for observables with compatibility relations
described by tree graphs. This implies classical representability of any set of correlations 〈A
i
〉, 〈B〉, 〈A
i
B〉, and the equivalence of the Bell-Clauser-Horne inequalities to a non void intersection between the ranges of values for
the unmeasurable correlation 〈A
1
A
2〉 associated to different choices for B. The same analysis applies to the Hardy model and to the “perfect correlations” discussed by Greenberger, Horne, Shimony
and Zeilinger. In all the cases, the dependence of an unmeasurable correlation on a set of variables allowing for a classical
representation is the only basis for arguments about violations of locality and causality. 相似文献
10.
Wenwei Ge Hong Liu Xiangyong Zhao Xiaobing Li Xiaoming Pan Di Lin Haiqing Xu Xiangping Jiang Haosu Luo 《Applied Physics A: Materials Science & Processing》2009,95(3):761-767
In this paper, a single crystal of 0.96Na0.5Bi0.5TiO3-0.04BaTiO3 with dimensions of Φ 30×10 mm was grown by the top-seeded-solution growth method. X-ray powder diffraction results show that the as-grown crystal
possesses the rhombohedral perovskite-type structure. The dielectric, piezoelectric and electrical conductivity properties
were systematically investigated with 〈001〉, 〈110〉 and 〈111〉 oriented crystal samples. The room-temperature dielectric constants
for the 〈001〉, 〈110〉 and 〈111〉 oriented crystal samples are found to be 650, 740 and 400 at 1 kHz. The (T
m, ε
m) values of the dielectric temperature spectra are almost independent of the crystal orientations; they are (306°C, 3718),
(305°C, 3613) and (307°C, 3600) at 1 kHz for the 〈001〉, 〈110〉 and 〈111〉 oriented crystal. The optimum poling conditions were
obtained by investigating the piezoelectric constants d
33 as a function of poling temperature and poling electric field. For the 〈001〉 and 〈110〉 crystal samples, the maximum d
33 values of 146 and 117 pC/N are obtained when a poling electric field of 3.5 kV/mm and a poling temperature of 80°C were applied
during the poling process. The as-grown 0.96Na0.5Bi0.5TiO3-0.04BaTiO3 crystal possesses a relatively large dc electrical conductivity, especially at higher temperature, having a value of 1.98×10−11 Ω−1⋅m−1 and 3.95×10−9 Ω−1⋅m−1 at 25°C and 150°C for the 〈001〉 oriented crystal sample. 相似文献
11.
The depolarisation ratio for the Raman-active phenyl stretching mode has been measured over the whole of the mesophase range,
and the orientational order parameters deduced, in the uniaxial nematic liquid crystal octylcyanobiphenyl (8CB). Linearly
polarised light was incident normally on a homogeneously aligned sample and a χ2 minimisation routine performed on the 360° depolarisation ratio profile. The order parameters 〈P
200〉 and 〈P
400〉 , together with the differential polarisability ratio, r , are used as fitting parameters and measured as a function of temperature. Interestingly, we show that the value for r , conventionally measured in the isotropic phase and assumed to remain constant, has a clear temperature dependence, ranging
from -0.032±0.008 in the isotropic phase through to -0.245±0.015 at the nematic-to-smectic A phase transition. The measured
order parameters 〈P
200〉 and 〈P
400〉 varied from 0.35- 0.55±0.02 and 0.180- 0.245±0.02 , respectively, across the 8 ° C wide nematic phase range. The values of both 〈P
200〉 and 〈P
400〉 are in excellent agreement with theory, but it is noteworthy that 〈P
400〉 shows a much better quantitative match than has been reported in previous work. Crucially the temperature dependence of
r is shown to be a contributing factor in the low 〈P
400〉 values that have been conventionally reported from Raman scattering measurements. The potential for fitting the entire angular
depolarisation ratio distribution in liquid crystalline systems that are described by more order parameters, specifically
biaxial materials, is discussed. 相似文献
12.
The damage spreading of the Ising model on the 3–12 lattice with competing Glauber and Kawasaki dynamics is studied. The difference
between the two kinds of nearest-neighboring spin interactions (interaction between two 12-gons, or interaction between a
12-gon and a triangle) are considered in the Hamiltonian. It is shown that the ratio of the interaction strengthF between the two kinds of interactions plays an important role in determining the critical temperature Td of phase transition from frozen to chaotic. Two methods are used to introduce the bond dilution on the Ising model on the
3–12 lattice: regular and random. The maximum of the average damage spreading 〈D〉max can approach values lower than 0.5 in both cases and the reason can be attributed to the ’survivors’ among the spins. We
have also, for the first time, presented the phase diagram of the mixed G-K dynamics in the 3–12 lattice which shows what
happens when going from pure Glauber to pure Kawasaki 相似文献
13.
Measurements have been made of the Hall coefficientR of some alloys of silver in palladium over the temperature range 1°K to 120°K. The alloys contain between ∼1 and ∼10 at.-%
silver. Values ofR were also obtained at room temperature and these were in good agreement with earlier published work. The values ofR are negative in all the alloys, and |R| increases both on reducing the temperature and increasing the silver concentration,c. Below ∼10°K, |R| becomes independent of temperature but shows a linear dependence onc, increasing by a factor of 2.5 over the concentration range measured.
This increase is too great to be accounted for in terms of band structure changes alone, so we have examined the effects of
anisotropic impurity scattering. To a first approximation it can be shown thatR is proportional to an anisotropy parameterA, defined asA=〈τ
2(k)〉/〈τ(k)〉2, whereτ(k) represents the relaxation time of an electron in a statek, and 〈〉 is an average over the Fermi surface. In palladium we assume that the majority of the current is carried by the s-electrons.
In the presence of silver impurities these electrons can be scattered into s-states or d-states with relaxation times given
byτ
ss
α1/c(1−c) andτ
sd
α1/c
2(1−c) respectively. FollowingPlate we have assumed thatτ
ss is isotropic and thatτ
sd is anisotropic, leading to an overall anisotropic relaxation time for impurity scattering. We then find the parameterA increases approximately linearly with silver content, in accordance with our experimental results. 相似文献
14.
Mario Rabinowitz 《International Journal of Theoretical Physics》2009,48(3):706-722
Discrepancies and accords between quantum (QM) and classical mechanics (CM) related to expectation values and periods are
generally found for both the harmonic oscillator (SHO) and a free particle in a box (FPB), which may apply generally. These
indicate non-locality is expected throughout QM. The FPB energy states violate the Correspondence Principle. Previously unexpected
accords are found and proven that 〈x
2〉
CM
=〈x
2〉
QM
and τ
CM
=τ
QMb
(beat period i.e. beats between the phases for adjoining energy states) for the SHO for all quantum numbers, n. However, for the FPB the beat periods differ at small n. It is shown that a particle’s velocity in an infinite square well varies, no matter how wide the box, nor how far the particle
is from the walls. The quantum free particle variances share an indirect commonality with the Aharonov-Bohm and Aharonov-Casher
effects in that there is a quantum action in the absence of a force. The concept of an “Expectation Value over a Partial Well
Width” is introduced. This paper raises the question as to whether these inconsistencies are undetectable, or can be empirically
ascertained. These inherent variances may need to be fixed, or nature is manifestly more non-classical than expected. 相似文献
15.
G. L. Bochek V. I. Kulibaba N. I. Maslov V. D. Ovchinnik S. M. Potin 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2011,5(4):650-654
To determine the possibility of technological use of coherent Bremsstrahlung beams the photonuclear transmutation doping of
silicon by aluminum upon γ-quantum irradiation from the aligned single-crystal target was studied. An increase in aluminum
concentration by approximately ten times was obtained upon γ-radiation of silicon from the crystalline target aligned by the
crystallographic axis 〈111〉 along the direction of the electron beam with the energy of 1200 MeV. The orientation effect of
an increase in the yield of γ-radiation from silicon and tungsten crystals in the range of energies of accelerated electrons
of 300–1200 MeV was examined. This result is essential for the estimation of a possible minimum energy of electrons at which
the use of the orientation effect is reasonable. 相似文献
16.
D. M. Sedrakyan D. A. Badalyan V. M. Gasparyan A. Zh. Khachatryan 《Journal of Experimental and Theoretical Physics》1997,84(2):317-321
We find the dependence of the ensemble-averaged resistance, 〈ρ
L〉, of a one-dimensional chain consisting of periodically spaced random delta-function potentials of the chain length L, the incident-electron energy, and the chain disorder parameter w. We show that generally the 〈ρ
L〉 vs L dependence can be written as a sum of three exponential functions, two of which tend to zero as L℩∞. Hence the asymptotic expression for 〈ρ
L〉 is always an exponential function of L. Such an expression for 〈ρ
L〉 means that the electronic states are indeed localized and makes it possible (which is important) to find the dependence
of the localization radius on the incident-electron energy and the force with which an electron interacts with the sites of
the chain. We also derive a recurrence representation for 〈ρ
L〉, which proves convenient in numerical calculations.
Zh. éksp. Teor. Fiz. 111, 575–584 (February 1997) 相似文献
17.
A. S. Barabash 《Physics of Atomic Nuclei》2010,73(1):162-178
The present status of double-beta-decay experiments (including the search for 2β
+, ECβ
+, and ECEC processes) are reviewed. The results of the most sensitive experiments are discussed. Average and recommended half-life
values for two-neutrino double-beta decay are presented. Conservative upper limits on effective Majorana neutrino mass and
the coupling constant of the Majoron to the neutrino are established as 〈m
ν
〉 < 0.75 eV and 〈g
ee
〉 < 1.9 × 10−4, respectively. Proposals for future double-betadecay experiments with a sensitivity for the 〈m
ν
〉 at the level of 0.01–0.1 eV are considered. 相似文献
18.
L. R. Nie D. C. Mei 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(4):475-481
The properties of the underdamped Josephson junction subjected to
colored noises were investigated with large and small phase
difference (φ). For the case of the large φ, we found
numerically that: (i) the probability distribution function of
φ exhibits monostability → bistability → monostability
transitions as the autocorrelation rate (λ) of a colored
noise increases; (ii) in the bistability region the multiplicative
noise drives the phase difference to turn over periodically; (iii)
the slope K of the linear response of the junction potential
difference (〈V 〉) can be somewhat reduced by means of tuning an
optimal λ; (iv) the amplitude of φ in response to
external sinusoidal signals changes with λ. For the case of
small φ, after deriving the analytical expressions of the
potential difference amplitude (〈V 〉max) and the K in the
presence of a dichotomous noise, we found nonmonotonic behavior of
〈V 〉max and the slope K as a function of λ. 相似文献
19.
Xue-Fen Xu 《International Journal of Theoretical Physics》2010,49(7):1446-1451
In a preceding paper (Fan and Lv in J. Math. Phys. 50:102108, 2009), the phase-space integration corresponding to the straight line characteristic of two different real parameters λ,τ over the Wigner operator (i.e. the Radon transformation) leads to pure-state density operator |u〉
λ,τ
λ,τ
〈u|, where |u〉
λ,τ
is just the coordinate-momentum intermediate representation. In this work we show that generalized Radon transformation of
the Wigner operator yields multimode density operator of continuum variables. This provides us with a new approach for obtaining
multimode entangled state representation. The Weyl ordering of the Wigner operator is used in our discussions. 相似文献
20.
We demonstrate that all liquids in supercritical region may exist in two qualitatively different states: solid-like and gas-like.
Solid-like to gas-like crossover corresponds to the condition τ ≈ τ0, where τ is liquid relaxation time and τ0 is the minimum period of transverse waves. This condition corresponds to the loss of shear stiffness of a liquid at all frequencies
and defines a new narrow crossover zone on the phase diagram. We show that the intersection of this zone corresponds to the
disappearance of high-frequency sound, qualitative changes of diffusion and viscous flow, increase in particle thermal speed
to half of the speed of sound and reduction of the specific heat at constant volume to 2k
B per particle. The new crossover is universal: it separates two liquid states at arbitrarily high pressure and temperature,
and even exists in systems where liquid-gas transition and the critical point are absent overall. 相似文献