共查询到20条相似文献,搜索用时 15 毫秒
1.
T. McAvoy J. Zhang C. Waldfried D.N. McIlroy P.A. Dowben O. Zeybek T. Bertrams S.D. Barrett 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(4):747-755
The experimental band structure of Mo(112) and the effects by temperature and adsorbate are presented. A surface resonance,
identified as crossing the Fermi level at about 1/3 from to of surface Brillouin zone, was observed to be very sensitive to both contamination and temperature. We find evidence of adsorbate
and temperature induced reconstruction of the Mo(112) surface. Examination of low-energy electron diffraction (LEED) and scanning
tunneling microscopy (STM) data provides evidence for an adsorbate induced reconstruction of the Mo(112) surface with periodicities
consistent with the Fermi level crossing of the surface resonance. The reconstruction is found to occur at coverages as low
as 0.03 Langmuirs of oxygen or carbon. The reconstruction and/or adsorbate affects the density of states and bands near the
Fermi level of a
1 symmetry.
Received 3 March 1999 and Received in final form 1 October 1999 相似文献
2.
We show how Fermi liquid theory results can be systematically recovered using a renormalization group (RG) approach. Considering
a two-dimensional system with a circular Fermi surface, we derive RG equations at one-loop order for the two-particle vertex
function in the limit of small momentum () and energy () transfer and obtain the equation which determines the collective modes of a Fermi liquid. The density-density response function
is also calculated. The Landau function (or, equivalently, the Landau parameters F
l
s
and F
l
a
) is determined by the fixed point value of the -limit of the two-particle vertex function (). We show how the results obtained at one-loop order can be extended to all orders in a loop expansion. Calculating the quasi-particle
life-time and renormalization factor at two-loop order, we reproduce the results obtained from two-dimensional bosonization
or Ward Identities. We discuss the zero-temperature limit of the RG equations and the difference between the Field Theory
and the Kadanoff-Wilson formulations of the RG. We point out the importance of n-body () interactions in the latter.
Received: 27 June 1997 / Received in final form: 17 December 1997 / Accepted: 26 January 1998 相似文献
3.
P. Schwaller T. Greber P. Aebi J.M. Singer H. Berger L. Forró J. Osterwalder 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(2):215-225
Full k
-maps of the electronic structure near the Fermi level of differently doped cuprates measured with angle-scanned photoelectron
spectroscopy are presented. The valence band maximum of the antiferromagnetic insulator Sr2CuO2Cl2, which is taken as a representative of an undoped cuprate, and the Fermi surfaces of overdoped, optimally doped and underdoped
Bi2Sr2CaCu2O8+δ high-temperature superconductors are mapped in the normal state. The results confirm the existence of large Luttinger Fermi
surfaces at high doping with a Fermi surface volume proportional to (1+x), where x is the hole concentration. At very low doping, however, we find that this assumption based on Luttinger's theorem is not
fulfilled. This implies a change in the topology of the Fermi surface. Furthermore the intensity of the shadow bands observed on the Fermi surface of Bi2Sr2CaCu2O8+δ as a function of the doping is discussed.
Received 12 October 1999 and Received in final form 12 April 2000 相似文献
4.
J. Alnis M. Auzinsh 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(1):91-97
The paper presents a discussion on the problem of alignment-orientation conversion in an excited state of molecules. It is
shown that a rather strong alignment-orientation conversion effect in the excited molecular state can be caused by a joint
action of an external magnetic field and hyperfine interaction. The orientation thus created is transverse, i.e. perpendicular to the direction of the external magnetic field. The magnitude of this effect is analyzed as dependent on molecular
parameters.
Received 15 July 1999 and Received in final form 17 November 1999 相似文献
5.
M. Stebelski M. Lisowski E. Zipper 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(2):215-222
Quantum coherence of electrons interacting via the magnetostatic coupling and confined to a mesoscopic cylinder is discussed. The electromagnetic response of a system is
studied. It is shown that the electromagnetic kernel has finite low frequency limit what implies infinite conductivity. It
means that part of the electrons is in a coherent state and the system can be in general described by a two-fluid model. The
coherent behavior is determined by the interplay between finite size effects and the correlations coming from the magnetostatic
interactions (the interaction is considered in the mean field approximation). The related persistent currents depend on the
geometry of the Fermi surface. If the Fermi surface has some flat portions the self-sustaining currents can be obtained. The
relation of the quantum coherent state in mesoscopic cylinders to other coherent phenomena is discussed.
Received: 9 July 1997 / Revised: 19 September 1997 / Accepted: 4 November 1997 相似文献
6.
G. Seibold F. Becca F. Bucci C. Castellani C. Di Castro M. Grilli 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(1):87-97
The concept of frustrated phase separation is applied to investigate its consequences for the electronic structure of the
high T
c
cuprates. The resulting incommensurate charge density wave (CDW) scattering is most effective in creating local gaps in k-space when the scattering vector connects states with equal energy. Starting from an open Fermi surface we find that the
resulting CDW is oriented along the (10)- and (or) (01)-direction which allows for a purely one-dimensional or a two-dimensional
“eggbox type” charge modulation. In both cases the van Hove singularities are substantially enhanced, and the spectral weight
of Fermi surface states near the M-points, tends to be suppressed. Remarkably, a leading edge gap arises near these points, which, in the eggbox case, leaves
finite arcs of the Fermi surface gapless. We discuss our results with repect to possible consequences for photoemission experiments.
Received 14 June 1999 相似文献
7.
T. Saikawa A. Ferraz 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(1):65-74
A precursor effect on the Fermi surface in the two-dimensional Hubbard model at finite temperatures near the antiferromagnetic
instability is studied using three different itinerant approaches: the second order perturbation theory, the paramagnon theory
(PT), and the two-particle self-consistent (TPSC) approach. In general, at finite temperature, the Fermi surface of the interacting
electron systems is not sharply defined due to the broadening effects of the self-energy. In order to take account of those
effects we consider the single-particle spectral function A(, 0) at the Fermi level, to describe the counterpart of the Fermi surface at T = 0. We find that the Fermi surface is destroyed close to the pseudogap regime due to the spin-fluctuation effects in both
PT and TPSC approaches. Moreover, the top of the effective valence band is located around = (π/2,π/2) in agreement with earlier investigations on the single-hole motion in the antiferromagnetic background. A crossover
behavior from the Fermi-liquid regime to the pseudogap regime is observed in the electron concentration dependence of the
spectral function and the self-energy.
Received 8 September 2000 and Received in final form 20 December 2000 相似文献
8.
R. Citro M. Marinaro 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(2):235-242
The spin magnetic susceptibility of the p-d model is calculated by means of a perturbation theory in the hybridization term V through a generalized cumulant expansion (GCE). The analysis is approached from the paramagnetic metallic phase. The results
qualitatively reproduce some unusual magnetic properties in the normal state of the hole-doped cuprates, supporting the scenario
of a Van Hove singularity near the Fermi level.
Received 15 October 1998 and Received in final form 24 March 1999 相似文献
9.
We study the director field around a spherical particle immersed in a uniformly aligned nematic liquid crystal and assume
that the molecules prefer a homeotropic orientation at the surface of the particle. Three structures are possible: a dipole,
a Saturn-ring, and a surface-ring configuration, which we investigate by numerically minimizing the Frank free energy supplemented
by a magnetic-field and a surface term. In the dipole configuration, which is the absolutely stable structure for micron-size
particles and sufficiently strong surface anchoring, a twist transition is found and analyzed. We show that a transition from
the dipole to the Saturn ring configuration is induced by either decreasing the particle size or by applying a magnetic field.
The effect of metastability and the occurrence of hysteresis in connection with a magnetic field are discussed. The surface-ring
configuration appears when the surface-anchoring strength W is reduced. It is also favored by a large saddle-splay constant K24. A comparison with recent experiments [#!itapdb:Poulin1997!#,#!itapdb:Poulin1998!#] gives a lower bound for W, i.e., for the interface of water and pentylcyanobiphenyl (5CB) in the presence of the surfactant sodium dodecyl sulfate.
Received 2 November 1998 相似文献
10.
M. Amoruso I. Meccoli A. Minguzzi M.P. Tosi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(3):441-447
We evaluate the small-amplitude excitations of a spin-polarized vapour of Fermi atoms confined inside a harmonic trap. The
dispersion law is obtained for the vapour in the collisional regime inside a spherical trap of frequency , with n the number of radial nodes and the orbital angular momentum. The low-energy excitations are also treated in the case of an axially symmetric harmonic confinement.
The collisionless regime is discussed with main reference to a Landau-Boltzmann equation for the Wigner distribution function:
this equation is solved within a variational approach allowing an account of non-linearities. A comparative discussion of
the eigenmodes of oscillation for confined Fermi and Bose vapours is presented in an Appendix.
Received 23 February 1999 and Received in final form 21 April 1999 相似文献
11.
M. Huth M. Jourdan H. Adrian 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(4):695-699
The node structure of the superconducting order parameter of the heavy-fermion system is analyzed within the weak-coupling theory. A pairing interaction induced by the exchange of antiferromagnetic spin excitations
is assumed as suggested by recent inelastic neutron scattering experiments and tunneling spectroscopy. The multi-sheeted Fermi
surface is taken into account. Based on a model susceptibility for the simple antiferromagnetic structure of , line nodes result at the rim of the magnetic Brillouin zone.
Received 29 July 1999 相似文献
12.
E.M. de Sousa Luz A.F. Siqueira U.M.S. Costa M.L. Lyra 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):115-118
The recent improvements on the technology for developing high-quality thin magnetic films has renewed the interest in the
study of surface effects in both static and dynamic magnetic responses. In this work, we use a Monte-Carlo algorithm with
Metropolis dynamics together with a spreading of damage technique to study the interplay between the effects of finite thickness
and surface ordering field in thin ferromagnetic Ising (S=1/2) films. We calculate, near the bulk critical temperature and several values of the surface field, the dependence on the
film thickness of the average magnetization M and Hamming distance D. We employ a finite size scaling analysis to show that both obey an effective one-parameter scaling but exhibit distinct
characteristic surface fields. At their corresponding characteristic surface fields both M and D become roughly thickness independent and we estimate the critical exponent characterizing the behavior of the typical scaling
lengths.
Received 29 March 1999 and Received in final form 21 April 1999 相似文献
13.
The effect of a surface electric field produced by ionic adsorption on the molecular orientation of a nematic liquid crystal
sample is analyzed. The eigenvalue problem for a semi-infinite medium is analytically solved both for strong and weak anchoring
situations. The threshold instabilities are numerically determined and it is shown that the homeotropic pattern can be destabilized
also in the situation of strong anchoring. The dependence of the threshold field on the anchoring strength and on the surface
polarization is determined by taking into account also the coupling of the quadrupolar component of the flexoelectric coefficient
with the field gradient.
Received 4 November 1999 and Received in final form 4 April 2000 相似文献
14.
Zu Wei Yan Xi Xia Liang 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(3):531-538
A variational theory is proposed to study the surface states of electrons in a semi-infinite ternary mixed crystal, by taking
the effect of electron-surface optical (SO) phonon interaction into account. The energy and the wave function of the electronic
surface-states are calculated. The numerical results of the energies of the surface states of the polarons and the self-trapping
energies are obtained as functions of the composition x and surface potential V0 for several ternary mixed crystal materials. The results show that the electron-phonon interaction lowers the surface-state
levels with the energies from several to scores of meV. It is also found that the self-trapping energy of the surface polaron
has a minimum at some middle value of the composition x. It is indicated that the electron-phonon coupling effect can not be neglected.
Received 4 January 1999 and Received in final form 7 January 2000 相似文献
15.
E.Ya. Sherman C. Ambrosch-Draxl 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(2):251-259
We consider in detail Raman scattering by vibration of the apical oxygen ions in the RBa2Cu3O7 superconducting cuprates. The scattering intensity is very sensitive to the ratio of diagonal and off-diagonal matrix elements
of electron-phonon coupling, bandstructure, and carrier concentration. Our results show a large quantitative difference between
the results of frozen-phonon and perturbational approach to the Raman process. The discrepancy becomes especially large when
interband transitions to the states near the Fermi level are close to resonance with the incident light. The calculation of
phonon-induced ion charge fluctuations shows an analogous discrepancy. The reason for these effects is the possibility of
carrier redistribution between different parts of the Fermi surface arising in the frozen-phonon approximation. Our results
show that Raman scattering in superconducting superlattices is very sensitive to the properties of the states near the Fermi
level. For this reason experiments performed on the superlattices can help to resolve the discrepancy.
Received 8 December 1999 相似文献
16.
The freezing transition of a network model for tensionless membranes confined to two dimensions is investigated by Monte Carlo
simulations and scaling arguments. In this model, a freezing transition is induced by reducing the tether length. Translational
and bond-orientational order parameters and elastic constants are determined as a function of the tether length. A finite-size
scaling analysis is used to show that the crystal melts via successive dislocation and disclination unbinding transitions, in qualitative agreement with the predictions of the Kosterlitz-Thouless-Halperin-Nelson-Young
theory. The hexatic phase is found to be stable over only a very small interval of tether lengths.
Received 4 June 1999 and Revised in final form 1 September 1999 相似文献
17.
J. Altmann W. Brenig A.P. Kampf 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(3):429-433
We have investigated the evolution of the electronic properties of the t-t'-U Hubbard model with hole doping and temperature. Due to the shape of the Fermi surface, scattering from short wavelength spin
fluctuations leads to strongly anisotropic quasi-particle scattering rates at low temperatures near half-filling. As a consequence,
significant variations with momenta near the Fermi surface emerge for the spectral functions and the corresponding ARPES signals.
At low doping the inverse lifetime of quasiparticles on the Fermi surface is of order varying linearly in temperature from energies of order t down to a very low energy scale set by the spin fluctuation frequency while at intermediate doping a sub-linear T-dependence is observed. This behavior is possibly relevant for the interpretation of photoemission spectra in cuprate superconductors
at different hole doping levels.
Received 31 July 2000 相似文献
18.
19.
Electric field light scattering results on aqueous solutions of linear, flexible NaPSS at minimal ionic strength are reported.
Samples of molecular weights between 356 kg/mol and 2870 kg/mol were investigated. With increasing field strength the intensity
as a function of wavenumber develops a pronounced oscillating behaviour. Besides the well-known first peak a second maximum
is observed at the position at which a weak maximum for some samples already occurs at zero field. The overall intensity strongly
depends on the frequency of the electric field. The electro-optical effect shows a maximum at 300 kHz. Increasing the particle
concentration gives a large increase of the peak maximum, normalized to concentration. If plotted versus scattering angle the relative intensity increase is maximum for samples of medium molecular weight. The results strongly
indicate a stretching and alignment of the chains, thus leading to or enlarging the short range order of the chains.
Received 9 April 1999 and Received in final form 18 August 1999 相似文献
20.
M. Gangl H. Ritsch 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,8(1):29-40
We develop quantum models for the combined external and internal motion of atoms in a strongly coupled driven cavity mode
including the transverse degrees of freedom. Using a simplified Gaussian mode function we determine the parameter regimes
and prospects of 3D cooling and confinement of one or two atoms in the cavity field. Analysing the field dynamics for slow
atoms traversing the cavity, we show that the spectrum of the transmitted and spontaneously scattered light contains ample
information on the motional dynamics of the atom and can be nicely used to investigate the cooling properties of the system.
Including several atoms in the dynamics we show how motional correlations build up by the common interaction with the cavity
field. This can be looked upon as collisions at far distance and can be monitored via the transmitted field dynamics.
Received 5 March 1999 and Received in final form 4 May 1999 相似文献