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1.
We have investigated the Einstein relation in n-channel inversion layers on A3IIB2V semiconductors at low temperatures on the basis of a newly derived dispersion relation of the carriers under arbitrary magnetic quantization for the general case which occurs from the consideration of the anisotropies of the band parameters within the frame work of k · p formalism. It is found by incorporating both the effects of electron spin and broadening of Landau levels, using n-Cd3As2 as an example, that the theoretical formulation is in qualitative agreement with the suggested experimental method of determining the Einstein relation in degenerate semiconductors having arbitrary dispersion law. In addition, the corresponding well-known results for bulk specimens of two band Kane model both in the presence and absence of magnetic quantization, are also obtained from the generalized expressions as special cases. 相似文献
2.
A. Peláiz-Barranco I. González-Carmenate F. Calderón-Piñar 《Solid State Communications》2005,134(8):519-522
The relaxor behaviour of the (Pb0.8Ba0.2)[(Zn1/3Nb2/3)0.7Ti0.3]O3 ferroelectric ceramic is presented. A strong dispersion of the maximum of the dielectric permittivity (ε′) below the transition temperature (Tm) is observed, which shift towards higher temperatures with increasing frequency. There is a strong deviation from the Curie-Weiss law. The results are fitted by using the Volger-Fulcher relationship, showing typical behaviour of a spin glass system. The hysteresis loops suggest relaxor behaviour. 相似文献
3.
4.
J.M. de Araújo F.A. da Costa F.D. Nobre 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(4):661-667
A spin-1 model, appropriated to study the competition between bilinear (J
ij
S
i
S
j
) and biquadratic (K
ij
S
i
2
S
j
2) random interactions, both of them with zero mean, is investigated. The interactions are infinite-ranged and the replica
method is employed. Within the replica-symmetric assumption, the system presents two phases, namely, paramagnetic and spin-glass,
separated by a continuous transition line. The stability analysis of the replica-symmetric solution yields, besides the usual
instability associated with the spin-glass ordering, a new phase due to the random biquadratic couplings between the spins.
Received 18 May 1999 and Received in final form 20 October 1999 相似文献
5.
S. Uji J.S. Brooks M. Chaparala L. Seger T. Szabo M. Tokumoto N. Kinoshita T. Kinoshita Y. Tanaka H. Anzai 《Solid State Communications》1996,100(12):825-830
De Haas-van Alphen (dHvA) oscillations in the two dimensional organic conductor α-(BEDT-TTF)2KHg(SCN)4 have been measured by a canti-lever technique at high magnetic fields up to 30 T. The wave shape of the dHvA oscillations undergoes a drastic change around the transition field BK (24 T). The effective mass shifts 1.5 m0 in the density wave phase (B<BK) to 1.65 m0 in the normal metallic phase (B>BK). Based on the simulation, we have determined that the primary cause of the characteristic field dependence of the wave shape is the change in the effective mass. 相似文献
6.
7.
K. P. Ghatak N. Chattopadhyay M. Mondal 《Applied Physics A: Materials Science & Processing》1987,44(4):305-312
An attempt is made to study the Einstein relations for the diffusivity-mobility ratios of the carriers in n-channel inversion layers on ternary chalcopyrite semiconductors under both weak and strong electric field limits, taking n-channel inversion layers on CdGeAs2 as an example. It is found, on the basis of newly derived 2D E-ks dispersion relations of the conduction electrons for both the limits by considering the various types of anisotropies in the energy band, that the ratios increase with increasing surface electric fields for both the limits and the theoretical results are in qualitative agreement with the suggested experimental method of determining the Einstein relation in degenerate semiconductors having arbitrary dispersion law. The corresponding well-known results for isotropic twoband Kane model are also obtained from the expressions derived. 相似文献
8.
详细论述Si/SiGe量子级联激光器的工作原理,通过对比找到一组合适的Si,Ge和SiGe合金的能带参数,进而应用6×6 k·p方法计算了不同阱宽、不同Ge组分Si/Si1-xGex/Si量子阱价带量子化的空穴能级本征值及其色散关系,分析Si/Si1-xGex/Si量子阱空穴态能级间距随阱宽和组分的变化规律,最后应用计算结果讨论了Si/SiGe量子级联激光器有源区的能带设计,有益于优化Si /SiGe量子级联激光器结构.
关键词:
硅锗材料
量子级联激光器
子带跃迁
k·p方法')" href="#">k·p方法 相似文献
9.
10.
Dispersion of second-order nonlinear optical coefficient 总被引:2,自引:0,他引:2
J. Seres 《Applied physics. B, Lasers and optics》2001,73(7):705-709
A simple, approximate relation between the dispersion of the second-order nonlinear optical (SNLO) coefficient and first-order
susceptibility has been derived using the well-known results of density-matrix calculation of quantum-mechanical theory. A
new tensor of SNLO coefficient has been defined, which retains symmetries when the input beams are in the spectral range of
transparency while the generated beam can also be in the spectral range of absorption. The validity of the relation has been
checked for three ferroelectric crystals, KTP, LiNbO3 and KNbO3, which are transparent in the visible and near infrared, and for two semiconductors, GaP and GaAs, which absorb in the visible.
Contrary to Miller’s law, the presented relation is in good agreement with measurements.
Received: 8 February 2001 / Revised version: 2 July 2001 / Published online: 10 October 2001 相似文献
11.
A.E. Allahverdyan Th.M. Nieuwenhuizen D.B. Saakian 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(2):317-335
In a p-spin interaction spherical spin-glass model both the spins and the couplings are allowed to change with time. The spins are
coupled to a heat bath with temperature T, while the coupling constants are coupled to a bath having temperature TJ. In an adiabatic limit (where relaxation time of the couplings is much larger that of the spins) we construct a generalized
two-temperature thermodynamics. It involves entropies of the spins and the coupling constants. The application for spin-glass
systems leads to a standard replica theory with a non-vanishing number of replicas, n=T/T
J
. For p>2 there occur at low temperatures two different glassy phases, depending on the value of n. The obtained first-order transitions have positive latent heat, and positive discontinuity of the total entropy. This is
an essentially non-equilibrium effect. The dynamical phase transition exists only for n<1. For p=2 correlation of the disorder (leading to a non-zero n) removes the known marginal stability of the spin glass phase. If the observation time is very large there occurs no finite-temperature
spin glass phase. In this case there are analogies with the non-equilibrium (aging) dynamics. A generalized fluctuation-dissipation
relation is derived.
Received 12 July 1999 and Received in final form 8 December 1999 相似文献
12.
S. De Toro Arias X. Waintal J.-L. Pichard 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(1):149-158
The interplay between the quantum interferences responsible for one particle localization over a length L1, and the partial dephasing induced by a local interaction of strength U with another particle leading to partial delocalization over a length L
2
> L
1
, is illustrated by a study of the motion of two particles put close to each other at the initial time. Localization is reached
in two steps. First, before the time t1 necessary to propagate over L1, the interaction slows down the ballistic motion. On the contrary, after t1 the interaction favors a very slow delocalization, characterized by a spreading of the center of mass, until L2 is reached. This slow motion is related to the absence of quantum chaos in this one dimensional model, the interaction being
only able to induce weaker chaos with critical spectral statistics. Under appropriate initial conditions, the motion remains
invariant under the duality transformation mapping the behavior at small U onto the behavior at large U.
Received 24 August 1998 相似文献
13.
Neutron and x-ray diffraction studies of Sb2S3 indicate extensive diffuse scattering in the plane perpendicular to the chain axis of polymer-like (Sb4S6)
n
molecules. The crystal structure of the paraelectric phase is said to be orthorhombic with space group D
2h
16
with four molecules per unit cell. The observed diffuse scattering may be due to static disorder or some dynamical effects.
In this paper the authors have examined the possible dynamical origin by recourse to lattice dynamical studies. Dispersion
relation of phonons along the three symmetry directionsa*,b* andc* is evaluated based on a lattice dynamical model incorporating Coulomb, covalent and a Born-Mayer-like short range interactions.
Group theoretical analysis based on the group of neutral elements of crystal sites (GNES) was essential in order to examine
and aid in the numerical computations. The group theoretical technique involving GNES extended to ‘pseudo-molecular’ systems
is also discussed in this context.
The phonon dispersion relation shows that there are rather flat TA-TO branches of very low frequency in thea andc directions which may give rise to diffuse scattering. The branches along theb-axis are quite dissimilar to those alonga andc axes because of anisotropy. Variation of the potential parameters leads to instability of the lowest TA-TO branch. This is
suggestive of a temperatures or pressure-dependent phase transition. However since these modes are optically ‘silent’ one
needs to carry out either high resolution neutron scattering or ultrasonic studies to confirm various aspects of the theoretical
studies. 相似文献
14.
V. Chaplain C. Allain J.P. Hulin 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(2):225-231
An analytical model is presented to describe the dispersion of tracers in a power-law fluid flowing through a statistically
homogeneous and isotropic porous medium. The model is an extension of Saffman's approach to the case of non-Newtonian fluids.
It is shown that an effective viscosity depending on the pressure gradient and on the characteristics of the fluid, must be
introduced to satisfy Darcy's law. An analytical expression of the longitudinal dispersivity is given as a function of the Peclet number Pe and of the power-law index n that characterizes the dependence of the viscosity on the shear rate . As the flow velocity increases the dispersivity obeys an asymptotic power law: . This asymptotic regime is achieved at moderate Peclet numbers with strongly non-Newtonian fluids and on the contrary at very large values when n goes to 1 ( for n=0.9). This reflects the cross-over from a scaling behaviour for towards a logarithmic behaviour predicted for Newtonian fluids (n=1).
Received: 22 July 1997 / Revised and Accepted: 2 July 1998 相似文献
15.
The linewidth ΔH pp and spin-Hamiltonian parameters under temperature and high hydrostatic pressure by X-band continuous wave electron paramagnetic resonance in the K3H(SO4)2 crystal were studied. Spin-Hamiltonian parameters, direction cosines and coordination of Mn2+ ion were determined at room temperature. The pressure at 300?MPa leads to the change of hydrogen bond potential and the transition from double well to single well potential moves about 10?K towards a higher temperature. 相似文献
16.
The microwave dielectric and magnetic properties of Pb(Fe2/3W1/3)O3 multiferroic ceramics were investigated. A dielectric dispersion occurring in the frequency range 100 MHz-3 GHz and in a broad temperature range showed itself to be a powerful tool to detect magnetostrictive effects. The experimental results revealed the following remarkable features: the temperature dependence of fR (characteristic frequency) and the dielectric strength Δε (characteristic of the dispersion) enabled us to identify not only the para-ferroelectric (TC≈180 K) but also the para-antiferromagnetic (TN≈340 K) phase transitions, while magnetic measurements revealed the para-antiferromagnetic ordering and a weak superexchange interaction (TN2∼15 K). Additionally, both characterizations confirmed the existence of structural or magnetic instabilities around 250 K. 相似文献
17.
B Bednarska-BolekZ Ciunik R Jakubas G BatorP Ciapa?a 《Journal of Physics and Chemistry of Solids》2002,63(3):507-518
New triethylammonium salts: [(C2H5)3NH]SbCl6 (TCA) and [(C2H5)3NH]SbCl6·1/2[(C2H5)3NH]Cl (TCAT) have been synthesized. The compounds crystallise in monoclinic symmetry: space groups P21/n and P21/c, for TCA at 293 K and TCAT at 100 K, respectively. The crystal structure of [(C2H5)3NH]SbCl6 consists of discrete ionic pairs—triethylammonium cations and hexachloroantimonate anions—linked via the bifurcated N-H?Cl hydrogen bonds. The crystal structure of [(C2H5)3NH]SbCl6·1/2[(C2H5)3NH]Cl is composed of three symmetrically independent triethylammonium cations, chlorine anion and two symmetrically independent hexachloroantimonate anions. TCA undergoes a structural phase transition at 336 K (on heating) into the orthorhombic C222 space group, whereas TCAT reveals a structural phase transition at 332 K. The phase transitions are of the first order type. TCA shows a ferroelastic domain structure below 336 K. Differential scanning calorimetry, dilatometric, dielectric dispersion and Raman scattering measurements have been used to study the phase transition mechanisms in these triethylammonium salts. 相似文献
18.
K.M. Frahm 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(2):371-378
The localization length L2 of two interacting particles in a one-dimensional disordered system is studied for very large system sizes by an efficient
and accurate variant of the Green function method. The numerical results (at the band center) can be well described by the
functional form L
2
=L
1
[0.5+c(U) L
1
] where L1 is the one-particle localization length and the coefficient depends on the strength U of the on-site Hubbard interaction. The Breit-Wigner width or equivalently the (inverse) life time of non-interacting pair
states is analytically calculated for small disorder and taking into account the energy dependence of the one-particle localization
length. This provides a consistent theoretical explanation of the numerically found U-dependence of c(U).
Received 16 September 1998 相似文献
19.
S. Leenhardt O. Sorlin M.G. Porquet F. Azaiez J.C. Angélique M. Belleguic C. Borcea C. Bourgeois J.M. Daugas C. Donzaud I. Deloncle J. Duprat A. Gillibert S. Grévy D. Guillemaud-Mueller J. Kiener M. Lewitowicz S.M. Lukyanov F. Marie N.A. Orr Yu.-E. Penionzhkevich F. de Oliveira Santos F. Pougheon M.G. Saint-Laurent W. Shuying Yu. Sobolev J.S. Winfield 《The European Physical Journal A - Hadrons and Nuclei》2002,14(1):1-5
The reduced transition probability B(E2: 01
+→ 2+) of 72Zn has been measured for the first time by Coulomb excitation at intermediate energy. The result B(E2: 01
+→ 2+) = 1740±210 e2fm4, corresponds to the deformation parameter β2 of 0.23, in close agreement with expectations derived from the neighboring nucleus 73Zn. A discussion of the evolution of the N = 40 sub-shell closure as a function of Z is presented.
Received: 19 December 2001 / Accepted: 14 March 2002 相似文献
20.
M. Potthoff W. Nolting 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(4):555-568
The correlation-driven transition from a paramagnetic metal to a paramagnetic Mott-Hubbard insulator is studied within the
half-filled Hubbard model for a thin-film geometry. We consider simple-cubic films with different low-index surfaces and film
thickness d ranging from d=1 (two-dimensional) up to d=8. Using the dynamical mean-field theory, the lattice (film) problem is self-consistently mapped onto a set of d single-impurity Anderson models which are indirectly coupled via the respective baths of conduction electrons. The impurity models are solved at zero temperature using the exact-diagonalization
algorithm. We investigate the layer and thickness dependence of the electronic structure in the low-energy regime. Effects
due to the finite film thickness are found to be the more pronounced the lower is the film-surface coordination number. For
the comparatively open sc(111) geometry we find a strong layer dependence of the quasi-particle weight while it is much less
pronounced for the sc(110) and the sc(100) film geometries. For a given geometry and thickness d there is a unique critical interaction strength U
c2
(d) at which all effective masses diverge and there is a unique strength U
c1
(d) where the insulating solution disappears. U
c2
(d) and U
c1
(d) gradually increase with increasing thickness eventually approaching their bulk values. A simple analytical argument explains
the complete geometry and thickness dependence of Uc2. Uc1 is found to scale linearly with Uc2.
Received 19 August 1998 相似文献