共查询到20条相似文献,搜索用时 31 毫秒
1.
Lars Kyllingstad 《Nuclear Physics A》2009,820(1-4):167c
We study the thermodynamics of massless 4-theory using screened perturbation theory, which is a way to systematically reorganise the perturbative series. The free energy and pressure are calculated through four loops in a double expansion in powers of g2 and m/T, where m is a thermal mass of order gT. The result is truncated at order g7. We find that the convergence properties are significantly improved compared to the weak-coupling expansion. 相似文献
2.
R. Mélin K. Biljaković J.C. Lasjaunias P. Monceau 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):417-430
We show that the dynamics of disordered charge density waves (CDWs) and spin density waves (SDWs) is a collective phenomenon.
The very low temperature specific heat relaxation experiments are characterized by: (i) “interrupted” ageing (meaning that
there is a maximal relaxation time); and (ii) a broad power-law spectrum of relaxation times which is the signature of a collective
phenomenon. We propose a random energy model that can reproduce these two observations and from which it is possible to obtain
an estimate of the glass cross-over temperature (typically T
g≃ 100-200 mK). The broad relaxation time spectrum can also be obtained from the solutions of two microscopic models involving
randomly distributed solitons. The collective behavior is similar to domain growth dynamics in the presence of disorder and
can be described by the dynamical renormalization group that was proposed recently for the one dimensional random field Ising
model [D.S. Fisher, P. Le Doussal, C. Monthus, Phys. Rev. Lett. 80, 3539 (1998)]. The typical relaxation time scales like ∼τexp(T
g/T). The glass cross-over temperature Tg related to correlations among solitons is equal to the average energy barrier and scales like T
g∼ 2xξΔ. x is the concentration of defects, ξ the correlation length of the CDW or SDW and Δ the charge or spin gap.
Received 12 December 2001 相似文献
3.
E. Braaten A. Nieto 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(1):143-159
Quantum corrections to the properties of a homogeneous interacting Bose gas at zero temperature can be calculated as a low-density
expansion in powers of , where is the number density and a is the S-wave scattering length. We calculate the ground state energy density to second order in . The coefficient of the correction has a logarithmic term that was calculated in 1959. We present the first calculation of the constant under the
logarithm. The constant depends not only on a, but also on an extra parameter that describes the low energy scattering of the bosons. In the case of alkali atoms, we argue that the second order quantum correction is dominated by
the logarithmic term, where the argument of the logarithm is ,and is the length scale set by the van der Waals potential.
Received 2 February 1999 相似文献
4.
We have examined the issue of the kinetic energy of particles in the ground state of an ideal boson gas. By assuming that the particles, on dropping into the ground state, retain the kinetic energy they possess at the Bose-Einstein temperature TB, we obtain new expressions for the pressure and internal energy of the gas below TB, that are free of the difficulties associated with the corresponding expressions in current theory. Furthermore, these new equations yield a value for the maximum density temperature in liquid 4He that is very close to the measured value. 相似文献
5.
The effect of the physically correct boundary conditions and the nonvanishing ground state energy on Bose-Einstein condensation of quantum particles confined to a cubic volumeV=L
3 is evaluated. The transition point is shifted towards higher temperatures by the confinement, the specific heat below the onset of condensation is no longer proportional toT
3/2, and the pressure does depend on the volume. Precise expressions for the modification of the ground state population and for the shift of the condensation temperature are derived, together with an expansion of the internal energy and of the specific heat. Numerical computations confirm the accuracy of our analytical approximations.Dedicated to Herbert Wagner, whose work on quantum Fermi liquids proved to be also very stimulating for quantum Bose liquids. 相似文献
6.
D.A. Knyazev 《Solid State Communications》2007,144(12):518-520
In this paper, we report studies of the electron-electron interaction effects in 2D electron systems. The interaction manifests in renormalization of the effective spin susceptibility, effective mass, g∗-factor, conductivity etc. By applying in-plane magnetic field, we tuned the effective interaction between the electrons and compared with theory the temperature dependence of the conductivity. We find a good agreement with interaction corrections calculated within the Fermi liquid theory. To address the question on the origin of the metal-insulator transition (MIT) in 2D, we explored transport and magnetotransport properties in the vicinity of the MIT and compared our data with solutions of two equations of the renormalization group (RG) theory, which describes temperature evolutions of the resistivity and interaction parameters for 2D electron system. We found a good agreement between the ρ(T,B∥) data and the RG-theory in a wide range of the in-plane fields. These results support the Fermi liquid type origin of the metallic state and the interpretation of the observed 2D MIT as the true quantum phase transition. 相似文献
7.
T. Beier H. Häffner N. Hermanspahn S. Djekic H.-J. Kluge W. Quint S. Stahl T. Valenzuela J. Verdú G. Werth 《The European Physical Journal A - Hadrons and Nuclei》2002,15(1-2):41-44
We describe a double-Penning-trap experiment suitable for testing QED in strong fields by determining the electronic g-factor of a single hydrogen-like ion in its ground state. Our measurements on 12C5 + reach a relative accuracy of 2×10-9, where the largest uncertainty results from the mass of the electron. Together with equally precise theoretical predictions
therefore, it is possible to evaluate a new value for the electron's mass. The possibilities to obtain other fundamental constants
and nuclear parameters are lined out.
Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002
RID="a"
ID="a"e-mail: t.beier@gsi.de 相似文献
8.
A.V. Papoyan M. Auzinsh K. Bergmann 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(1):63-71
We report results of a theoretical and experimental study of the ground state nonlinear Hanle effect under strong laser excitation.
It is shown that besides the well-known zero-magnetic field suppression of absorption on F
g = F→F
e = F - 1 transitions caused by population trapping, an optical pumping induced enhanced absorption occurs on F
g = F→F
e = F + 1 transitions for small B-fields. The latter effect becomes more pronounced for high F values. The experiment with atomic vapor of Cs (D2 line, F
g = 4) confirms an increase of the spectrally unresolved fluorescence yield at zero magnetic field and 600 mW/cm2 laser intensity by 9% or 42%, when excitation occurs with linearly or circularly polarized light, respectively. The results
of the experiment agree with numerical simulation studies using equations of motion for a density matrix.
Received 24 November 2001 / Received in final form 25 March 2002 Published online 24 September 2002 相似文献
9.
R. Zitzler Th. Pruschke R. Bulla 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(4):473-481
We discuss the ground state magnetic phase diagram of the Hubbard model off half filling within the dynamical mean-field theory.
The effective single-impurity Anderson model is solved by Wilson's numerical renormalization group calculations, adapted to
symmetry broken phases. We find a phase separated, antiferromagnetic state up to a critical doping for small and intermediate
values of U, but could not stabilize a Néel state for large U and finite doping. At very large U, the phase diagram exhibits an island with a ferromagnetic ground state. Spectral properties in the ordered phases are discussed.
Received 9 January 2002 Published online 25 June 2002 相似文献
10.
Souha Kammoun Hajer Souissi Ramzi Maalej Mohamed Dammak Mohamed Kamoun 《Journal of luminescence》2009,129(5):411-415
The experimental studies have provided evidence of the occurrence of transitions from the 3T1g(3F) ground state to the crystal-field levels 3T2g(3F), 3T1g(3P) and 3A2g(3F) for the V3+ centres in Al2O3 crystal; and from the 3A2g(3F) ground state to the crystal-field levels 3T2g(3F), 3T1g(3F) and 3T1g(3P) for the Ni2+ centres in LiNbO3 crystal (levels are assigned to irreps of the Oh point symmetry group). Using the experimental spectroscopic data, theoretical calculations of the crystal-field levels of V3+:Al2O3 and Ni2+:LiNbO3 are carried out based on the Racah theory. The observed crystalline-field splittings of the V3+ and Ni2+ terms were accounted for using a C3 symmetry Hamiltonian. The spin-orbit interaction was taken into account in this work. The Racah, crystal-field and spin-orbit parameters, which fit experimental and theoretical energy levels, have been reliably obtained. A good agreement between the theoretical and experimental results for the energy levels of V3+:Al2O3 and Ni2+:LiNbO3 has been obtained. 相似文献
11.
Properties of ground state and anomalous quantum fluctuations in one-dimensional polaron-soliton systems—the effects of electron-two-phonon interaction and non-adiabatic quantum correlations
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Based on the Holstein model Hamiltonian of one-dimensional molecular crystals, by making use of the expansion approach of the correlated squeezed-coherent states of phonon instead of the two-phonon coherent state expansion scheme, the properties of the ground state and the anomalous quantum fluctuations are investigated in a strongly coupled electron-phonon system with special consideration of the electron-two-phonon interaction. The effective renormalization (αi) of the displacement of the squeezed phonons with the effect of the squeezed-coherent states of phonon and both the electron-displaced phonon and the polaron-squeezed phonon correlations have been combined to obtain the anomalous quantum fluctuations for the corrections of the coherent state. Due to these non-adiabatic correlations, the effective displacement parameter αi is larger than the ordinary parameter α (0) i . In comparison with the electron-one-phonon interaction (g) corrected as αig, we have found the electron-two-phonon interaction (g1) corrected as αi2 g1 is enhanced significantly. For this reason, the ground state energy (E(2) 0 ) contributed by the electron-two-phonon interaction is more negative than the single-phonon case (E(1) 0 ) and the soliton solution is more stable. At the same time, the effects of the electron-two-phonon interaction greatly increase the polaron energy and the quantum fluctuations. Furthermore, in a deeper level, we have considered the effect of the polaron-squeezed phonon correlation (f-correlation). Since this correlation parameter f > 1, this effect will strengthen the electron-one and two-phonon interactions by fαig and f2αi2 g1, respectively. The final results show that the ground state energy and the polaron energy will appear more negative further and the quantum fluctuations will gain further improvement. 相似文献
12.
基于一维分子晶体系统的 Holstein 模型,采用压缩-相干态展开方法,计及电子-声子间量子关联和重整化平移修正,分析和研究电子-双声子相互作用对极化子-孤子系统基态性质和量子涨落的影响.推导了一维极化子-孤子系统的封闭形式非线性方程.应用非线性项展开方法,给出非线性方程的解析解和相关基态特性结果.研究表明,仅当电子-双声子耦合强度 g1<0时非线性方程才有孤波解,此时声子量子涨落效应随着压缩的增加,极化子-孤子系统基态能量变得更负,孤子局域减少,孤子态更加稳定;另一方面,电子密度涨落〈Δ2n〉和声子坐标-动量的不确定量〈Δ2p〉〈Δ2q〉比无声子压缩效应的大,极化子结合能变得更负.特别是,当g1<0时,双声子效应的量子涨落〈Δ2n〉与〈Δ2p〉〈Δ2q〉的值比单声子情况有明显增加.
关键词:
压缩-相干态展开
极化子-孤子态与量子涨落
电子-双声子相互作用
非线性薛定谔方程 相似文献
13.
14.
The analytical potential energy functions have been calculated for the ground state X1Σ+g and four excited electronic states a1Πg, A3Σ+u, B′3Σ?u and B3Πg of N2 molecule using the algebraic and energy-consistent methods (AM-ECM). Based on our previously published full AM vibrational energies and spectroscopic constants, the low-lying force constants fn, the expansion coefficients an and the variational parameters λ in the AM–ECM potentials are determined for these states. The computed AM–ECM potential energy curve of each state is in excellent agreement with the experimental data and better than other analytical potentials. 相似文献
15.
We demonstrate that TiOCl is a good model inorganic system to investigate spin-Peierls state. Our 35Cl and 47,49Ti NMR data show that a pseudo spin-gap behavior below T*=135 K precedes successive phase transitions at Tc=94 K and into a singlet spin-Peierls ground state with a large energy gap Eg/kB=430 K. 相似文献
16.
Andreas Bock 《Annalen der Physik》1999,8(6):441-486
Using Raman spectroscopy and transport measurements we investigate thin epitaxial films of Y1—x(Pr, Ca)xBa2Cu3O6+y. We explore the electronic Raman responses in A1g, B1g, and B2g symmetry obtained after subtraction of phononic excitations, and especially, the 2Δ peaks that form out of the electronic background below Tc. We find that the energy of the B1g 2Δ peak, which is a measure of the gap value, increases monotonically with decreasing doping until the peak becomes unresolvable. In contrast, the peak in A1g symmetry follows Tc being still resolvable in the Pr-doped films. The B2g response is weak and a 2Δ peak is only detected at the highest doping level. As a consequence of strong electron-phonon coupling, the B1g phonon at ∼340 cm—1 exhibits a pronounced Fano-type line shape. We use a phenomenological model to describe the line shape that takes into account real and imaginary part of the electronic response. It allows us to obtain the self-energy corrections and the mass-enhancement factor λ as a measure of the coupling. In the normal state we find λ = 0.015 around optimal doping and decreasing values with decreasing doping. The electron-phonon coupling increases strongly below Tc in overdoped samples in which the B1g 2Δ peaks appear in the vicinity of the phonon. Self-energy effects observed in the superconducting state can only partly be assigned to the redistributing electronic response. Anomalies with respect to frequency, linewidth, and intensity remain. They appear at increasing temperatures with decreasing doping and we provide evidence that they are connected to the presence of the pseudogap. We supplement our study by a comparison with single crystal data and investigate the influence of site-substitutional disorder on the electronic response and the electron-phonon interaction. 相似文献
17.
The leptodermous expansion of the total ground state energy of a nucleus into volume, surface, curvature and gauss curvature
contributions has been studied starting from a semi-classical energy density formalism of extended Thomas Fermi type. A numerical
procedure was used to obtain the surface energy and curvature energy contributions from surface moments of energy density
profilesH(r) for a sequence of nuclei withN=Z and neglecting the coulomb interaction for the three Skyrme forces. A transition to the liquid drop model type expansion
in increasing powers ofA
−1/3 is then made, taking into account the dependence of the central density and the surface structure on the mass of the nucleus.
It is found that there is no inconsistency between the curvature contribution to the total energy in the leptodermous expansion
and theA
−1/3 term contribution in the liquid drop model expansion. It has been shown that the earlier apparent anomaly between the above
two methods arises due to the use of semi-infinite approximation and the mass dependence of the central density and the surface
structure of finite nuclei. 相似文献
18.
19.
C. Honerkamp 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(1):81-91
We compare the one-loop renormalization group flow to strong coupling of the electronic interactions in the two-dimensional
t-t'-Hubbard model with t' = - 0.3t for band fillings smaller and larger than half-filling. Using a numerical N-patch scheme ( N = 32, ..., 96) we show that in the electron-doped case with decreasing electron density there is a rapid transition from
a d
x2 - y2-wave superconducting regime with small characteristic energy scale to an approximate nesting regime with strong antiferromagnetic
tendencies and higher energy scales. This contrasts with the hole-doped side discussed recently which exhibits a broad parameter
region where the renormalization group flow suggests a truncation of the Fermi surface at the saddle points. We compare the
quasiparticle scattering rates obtained from the renormalization group calculation which further emphasize the differences
between the two cases.
Received 19 December 2000 and Received in final form 28 February 2001 相似文献
20.
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