共查询到20条相似文献,搜索用时 31 毫秒
1.
Prabir K. Mukherjee 《Journal of Physics and Chemistry of Solids》2011,72(9):1066-1069
A model free energy has been constructed to describe the RIV-RIII rotator phase transition in alkanes in terms of the elastic strains and order parameter. The conditions for the RIV-RIII phase transition are discussed. From the free energy, the order parameter and the elastic strains are determined. The model free energy describes the first or second order character of the RIV-RIII transition depending on the strength of the coupling. The elastic properties in the vicinity of the RIV-RIII transition are discussed on the basis of a free energy expansion. The temperature dependence of the elastic constants is calculated on both sides of the transition. The coupling between the order parameter and elastic stains is shown to have a crucial influence on the phase behavior and the order of the transition. 相似文献
2.
The k-linear intravalence and intraconduction band coupling terms along the 〈111〉 directions are shown to explain the anomalously large strength of the E′1 structure relative to E′1 + Δ′1 and also the large energy separation between them. Quantitative agreement between theory and experiment is obtained using intraband coupling values calculated from k · p perturbation theory. 相似文献
3.
The Al Kα excited M4,5N4,5N4,5 Auger spectrum of Ba has been measured from the metallic sample evaporated on a Ag substrate. The spectrum has been decomposed into individual line components after the background subtraction. The decomposed spectrum has been compared with the theoretical spectrum calculated for the 4d?2 final state configuration in the mixed coupling scheme applying jj-coupling for the initial state and intermediate coupling for the final state. The most prominent structure of the spectrum shows the two 4d-hole coupling, but the structure which is caused by the Auger transitions M,45N2,3V has also been observed. The screening of the core holes in Ba metal seems to be produced by (5d6s) electrons. The simple excited atom model HF-calculations give an Auger kinetic energy shift (metal-free atom) of 16.7 eV, which is comparable to the experimental value 14–18 eV. 相似文献
4.
H. Aksela J. Väyrynen S. Aksela 《Journal of Electron Spectroscopy and Related Phenomena》1979,16(3):339-350
High resolution M4,5N4,5N4,5 Auger electron spectra from Sb4 and Te2 vapours have been measured using electron impact excitation. The spectra have been decomposed into line components and relative intensities and energies of the components are compared with calculated intensities and energies. The calculations have been done for these molecular samples using the free-atom calculation model involving initially filled shells. The calculations have been treated in the mixed coupling scheme using jj coupling for initial state and intermediate coupling for the final state. The experimental results agree well with the calculated values, indicating that the molecular effects on the relative intensities and energies are very small for these core level transitions. The clear molecular effects are found in the broadening of lines and in the kinetic energy shifts due to extra-atomic relaxation effects. 相似文献
5.
A. V. Ognev A. S. Samardak Yu. D. Vorob’ev L. A. Chebotkevich 《Physics of the Solid State》2004,46(6):1084-1087
The effect of isothermal annealing on the magnetic anisotropy, bilinear and biquadratic exchange coupling energies, and domain structure of Co/Cu/Co trilayer fiilms with dCo=6 nm and dCu=1.0 and 2.1 nm prepared by magnetron sputtering has been studied. It is shown that, under isothermal annealing, the biquadratic coupling energy decreases by more than an order of magnitude in films with dCu=1.0 nm and increases in films with dCu=2.1 nm. The fourth-order magnetic anisotropy is shown to be related to the existence of biquadratic exchange energy. 相似文献
6.
B. Bonnier 《Physics letters. [Part B]》1978,78(1):107-109
The infinite coupling limit of the ground state energy of the anharmonic oscillator is numerically derived using only the first few orders of the perturbative expansion. When applied to the analysis of the Gell-Man-Low β function in the Φ44 model, this method suggests the absence of zeroes for positive coupling. 相似文献
7.
The coupling between the zone center phonons and continua has been observed and interpreted from the changes in the line shape of the TO Raman spectra and the existence of a side band on the low energy side of the LO phonon in mixed GaxIn1?xP. 相似文献
8.
A.D. GromkoY.-D. Chuang A.V. Fedorov Y. AiuraY. Yamaguchi K. OkaY. Ando D.S. Dessau 《Journal of Physics and Chemistry of Solids》2002,63(12):2299-2304
Using angle-resolved photoemission spectroscopy we have performed a detailed study of bilayer splitting in Bi2Sr2CaCu2O8+δ as a function of doping level and temperature. In heavily overdoped samples where the splitting is the clearest, we extract an intracell coupling t⊥∼55 meV. As a function of photon energy the intensity ratio of the bonding and antibonding bands varies, allowing us to detect the bilayer splitting effect in the optimal and underdoped regimes. Surprisingly, with reduced doping the intracell coupling is not measurably reduced. Upon cooling to the superconducting state, a gap Δ opens in both bands yet the magnitude of the splitting remains unchanged. 相似文献
9.
T. Sinha Rituparna Kanungo C. Samanta Sudip Ghosh P. Basu H. Rebel 《Zeitschrift für Physik A Hadrons and Nuclei》1976,355(4):397-400
Alpha-particle scattering from the resonant (3 1 + ) and non-resonant continuum states of 6Li is studied at incident energy 10 MeV/A. The α + d breakup continuum part within the excitation energy E ex = 1.475–2.475 MeV is discretized in two energy bins. Unlike the results at higher incident energies, here the coupled-channel calculations show significant breakup continuum coupling effects on the elastic and inelastic scattering. It is shown that even when the continuum-continuum coupling effects are strong, the experimental data of the ground state and the resonant as well as discretized non-resonant continuum states impose stringent constraint on the coupling strengths of the non-resonant continuum states. 相似文献
10.
Katsuyoshi Takanod Kazuhiro Ikeuchi Hiromi Oike 《Journal of Physics and Chemistry of Solids》2004,65(12):1985-1992
The information of the Fe and Tb magnetic moments in [Fe(12 nm)/Tb(15 nm)]25 multilayer was got separately with X-ray magnetic circular dichroism (XMCD) measurements at various temperature. The Tb magnetic moments become to twist with increasing the applied magnetic field, as follows. (1) When the applied field H is less than the coercive force HC, Fe and Tb magnetic moments align anti-parallel, Fe moments being parallel to the magnetic field. This would be due to the ordinary exchange coupling between Fe and Tb magnetic moments. (2) H>HC, a twisted magnetic structure appears when the sample temperature is low, particularly lower than 150 K. This magnetic phase could come from the competition among the exchange coupling, the Zeeman energy and the anisotropic energy. 相似文献
11.
M. Taniguchi S. Suga S. Shin K. Inoue M. Seki H. Kanzaki H. Nakashima Y. Shiraki 《Solid State Communications》1982,44(7):1079-1082
Core-exciton spectra of AlxGa1?xAs have been measured in the photon-energy region from 19 to 27 eV by use of synchrotron radiation. The core-excitons associated with the Ga 3d core-hole and the conduction electron around the lowest L6 and X6 symmetry points are found to be coupled with each other through intervalley electron-hole interactions. Quantitative analyses have elucidated that intervalley Coulomb term is playing a dominant role for this coupling. Another higher energy doublet structure is interpreted as due to the transition from the Ga 3d core-levels to the rather flat region in the second lowest conduction band around the L6 and L4, 5 symmetry points. 相似文献
12.
T. Sinha Rituparna Kanungo C. Samanta Sudip Ghosh P. Basu H. Rebel 《Zeitschrift für Physik A Hadrons and Nuclei》1996,355(1):397-400
Alpha- particle scattering from the resonant (3 1 + ) and non-resonant continuum states of6Li is studied at incident energy 10 MeV/A. Theα+d breakup continuum part within the excitation energyE ex=1.475–2.475 MeV is discretized in two energy bins. Unlike the results at higher incident energies, here the coupled-channel calculations show significant breakup continuum coupling effects on the elastic and inelastic scattering. It is shown that even when the continuum-continuum coupling effects are strong, the experimental data of the ground state and the resonant as well as discretized non-resonant continuum states impose stringent constraint on the coupling strengths of the non-resonant continuum states. 相似文献
13.
P. Horsch 《Solid State Communications》1976,18(1):27-30
Using the Weger-Labbé-Friedel model the electron-phonon coupling in Nb3Sn for scattering between orthogonal families of Nb-chains is calculated. It is shown that interchain coupling may cause the softening of the shear modulus C44 with decreasing temperature. This mechanism gives rise to a softening over the whole Brillouin zone of all those acoustical phonons the long wavelength behaviour of which depends on C44. A Fermi energy of 17 meV is necessary to fit the experimental data. 相似文献
14.
Despite the intensive efforts for determining the mechanism that causes high-temperature superconductivity in copper oxide materials, no consensus on the pairing mechanism has been reached. Recent advances in high resolution angle-resolved photoemission spectroscopies have suggested that a sizeable electron-phonon coupling exists as the principal cause for kinks in the dispersion relations (energy versus wave vector) of the electronic states. Here, we report on a systematic study about the influence of the electron-phonon coupling parameter “λ” in the electronic quasiparticle dispersions of a wide family of CuO composites. In particular, the influence of the doping level in the cuprate families, La2−xSrxCuO4, Bi2Sr2CaCu2O8+x and Y Ba2Cu3O6+x over the dressing of the charge carriers, i.e., on the enhancement of the effective mass and the strength of the coupling mode for the nodal direction of the Fermi surface has been analyzed. Universal effects as the nodal kinks at low energies are theoretically reproduced, emphasizing the necessary distinction between the general electron mass-enhancement parameter λ∗ and the conventional electron-phonon coupling parameter λ. Our analysis shows a remarkable agreement between theory and experiment for different samples and at different doping levels. In fact, in LSCO family, the coupling constant λ calculated consistently with the nodal kink dispersions, reproduces the observed critical temperatures Tc, the gap ratio 2Δ0/kBTc, and other parameters which have been studied from a wide set of natural and empirical equations which have been used along the last decades. It will be concluded that the strong renormalisation of the band structure can be explained in terms of the phonon coupling mode, and must therefore be included in any microscopic theory of superconductivity, even for those materials in which the contribution to the pair formation can be less dominant. Nevertheless, in more anisotropic structures, simulations reducing the Coulomb effects to encourage the phonon mechanism reveal as seems unavoidable to consider additional coupling modes that justify the higher critical temperatures observed in BSCCO and YBCO samples. 相似文献
15.
We present the first investigation of the stress-induced coupling between X1c and X3c conduction band minima in zincblende type semiconductors. The high uniaxial stress values achieved in this work (X= 19 kbar) enable us to observe a nonlinear behavior of the X1c minima due to the stress-induced X1c-X3c coupling. This coupling is described by a single deformation potential 6E36 = 13 eV. 相似文献
16.
S. Nagel 《Journal of Physics and Chemistry of Solids》1985,46(8):905-919
The MSXα cluster technique has been used to study the electronic structure of hematite α-Fe2O3, where iron is formally in a 3d56S state. The calculated energy levels are compared with X-ray emission and photoelectron spectra. The wave functions have been used to compute the charge distribution, as well as hyperfine parameters such as quadrupole coupling constant, isomer shift and magnetic hyperfine field. The results indicate a considerable influence of chemical bonding on these parameters due to charge transfer and covalency. From the calculated field gradient and the measured quadrupole coupling constant a nuclear quadrupole moment for 57mTe of about 0.11b is deduced. This value is smaller than the most recent estimates of 0.15b based on the ionic model but not as small as the value of 0.082b obtained from first principles calculations on iron dihalides. 相似文献
17.
Yu. N. Ovchinnikov A. M. Dyugaev 《Journal of Experimental and Theoretical Physics》2000,90(1):144-152
It is shown that there are two energy scales in the Kondo problem: T k and T 0, one of which (T k) is exponentially small in the coupling constant g. The second scale T 0is proportional to the squared coupling constant. Perturbation theory is valid only in the region T? T 0. The point T 0 is apparently the crossover from weak to strong coupling. The first indications of the breakdown of the hypothesis of only one energy scale in the Kondo problem appear in fourth order of perturbation theory. 相似文献
18.
Perturbation series (PS) in powers of the coupling constant g for the D-dimensional anharmonic oscillator with power anharmonicity gr2N is considered. The high order PS coefficients ?k for the ground state energy are calculated explicitly with the help of recurrence relations among intergers. The rate of approach ?k to their asymptotics as a function of space dimension D is discussed. 相似文献
19.
Based on the dilute gas approximation (DGA) with repulsive and dipole interactions we discuss the N dependence of the vacuum energy density, 〈αSFμνaFμνa〉 and of the topological charge correlation function at the crossover point of the instanton driven β function with the strong coupling one. 相似文献
20.
In connection with the experiment on oxygen isotope effect of Bi2Sr2CaCu2O8 with the angle-resolved photoemission spectroscopy (ARPES), we theoretically study the isotope-induced band shift in ARPES by the Hartree-Fork and quantum Monte Carlo methods. We find that this band shift can be clarified based on a quadratically coupled electron-phonon (e-ph) model. The large ratio of band shift versus phonon energy change is connected with the softening effect of phonon, and the positive-negative sign change is due to the momentum dependence of the e-ph coupling. 相似文献