摘要:

AbstractX‐ray photoemission spectra, resistivity and susceptibility of CeNi2Sb2and CeCu2Sb2were measured and are discussed. The results indicate that these alloys are Kondo systems. For comparison of the valence band properties, the spectra of the isostructural alloys of RT2X2‐type with R = La, Gd, T = Cu, Ni and X = Sn, Sb were investigated,

ISSN:0003-3804    

DOI:10.1002/andp.19945060602

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe problem of interacting electrons moving under the influence of a strong magnetic field in two dimensions on a finite disk is reconsidered. First, the results of exact diagonalizations for up toN= 9 electrons for Coulomb as well as for a short‐range interaction are used in the search for a peculiar ground state corresponding to filling factor 1/3. Not for the Coulomb, but only for the short‐range interaction, can the 1/3‐state be safely identified amongst the spectra of various filling factors close to 1/3. Second, the propositions of the concept of quasiparticles, as used in the hierarchical theory, are examined in view of the exact results for the disk geometry. Whereas the theory for the quasiholes is in complete accordance with the spectra, for the quasielectrons, finite size corrections make an analysis difficult. For the quasielectron energy, an extrapolation toN→ ∞ is given and compared with the corresponding extrapolations of three different proposals for trial wave functions. While the limiting value for the best trial wave function is very close to the limit of the exact results, the behavior of the finite size corrections of the exact energies and of the trial wave functions, respectively, is qualitatively rather

ISSN:0003-3804    

DOI:10.1002/andp.19945060603

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractWe calculate Fermi‐surface properties of the Cuprate superconductors within the three band Hubbard model (also called the Emery model) using a cluster expansion for the proper selfenergy. The Fermi‐surface topology is in agreement with angular‐resolved photoemission data for dopings ∼ 20%. We discuss possible violations of the Luttinger sum‐rule for smaller dopings and the role of van‐Hove singularities in the density of states of the Zhang‐Rice singlets. We calculate the shift in the chemical potential upon doping and find quantitative agreement with recen

ISSN:0003-3804    

DOI:10.1002/andp.19945060604

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractWe study the magnetic response of mesoscopic quantum dots in the ballistic regime where the mean free pathleis larger that the sizeLof the sample, yet smaller thanL(KFL)d−1. In this regime, disorder plays an important role. Employing a semiclassical picture we calculate the contribution of long tranjectories which are strongly affected by static disorder and which differ sharply from those of clean systems. In the case of a magnetic field, they give rise to a large linear paramagnetic susceptibility (which is disorder independent), whose magnitude is in agreement with recent experimental results. In the case of a Aharonov‐Bohm flux, the susceptibility is disorder dependent and is proportional to the mean free path as in the diffusive regime. We also discuss the corresponding non‐linear susceptibil

ISSN:0003-3804    

DOI:10.1002/andp.19945060605

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractFor systems above the marginal dimensiond*, where mean field theory starts to become valid, such as Ising models ind= 5 for whichd* = 4, hyperscaling is invalid and hence it was suggested that finite size scaling is not ruled by the correlation length ξ (∝ |t|−1/2in Landau theory,tbeing the distance from the critical point) but by a “thermodynamic length”l(∝ |t|−2/d). Early simulation work by Binder et al. using nearest neighbor hypercubicL5lattices withL⩽ 7 yielded some evidence for this prediction, but the renormalized coupling constantgL= −3 + 〈M4〉/〈M2〉2atTcwasgL≈ −1.0 instead of the prediction of Brézin and Zinn‐Justin,gL(Tc) = −3 + Γ4(1/4)/(8 π2) ≈ −0.812. In the present work, we try to shed light on this controversy obtaining much more precise Monte Carlo data using multihistogram techniques and lattices as large asL= 17 (i.e., 1419857 Ising spins). While our value ofTcagrees nicely with recent high temperature series work (KBTc/J≈ 8.7774 ± 0.0035), the coupling atTc{gL(Tc) ≈ −0.958 ± 0.050} confirms the work for small lattices and disagrees with the analytical prediction. Hence the data are better consistent with a shift of the effective critical temperatureTc(L) ‐Tc(∝) ∝L−d/2 rather than withL−(d−2)according to the analytical theory. If the latter behavior is cor

ISSN:0003-3804    

DOI:10.1002/andp.19945060606

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractWe solve several low temperature problems of an infinite range metallic spin glass model. A compensation problem ofT0 divergencies is solved for the free energy which helped to extract the quantum critical behaviour of the spin glass order parameters as a function of δJ =J–Jc(T= 0). The critical valueJc(T= 0) = 3/16pF−1of the frustrated spin couplingJ, which separates spin glass from nonmagnetic (spin liquid) phase, is determined exactly in the static saddle point solution for a semielliptic metallic band model in terms of the density of states at the Fermi level. In addition to the replica‐overlap order parameter 〈Qab〉,a≠b, the diagonal 〈Qaa〉 is confirmed as order parameter by the result 〈Qaa〉SP∼ (δJ)β, β = 1, and its susceptibility χaaaa∼(‐δJ)−γwith γ = 1/2 atT= 0. The value for γ agrees with the one for the transverse field Ising spin glass. The low γ decay of 〈Qaa〉, ∼Tis obtained exactly in the whole quantum di

ISSN:0003-3804    

DOI:10.1002/andp.19945060607

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

ISSN:0003-3804    

DOI:10.1002/andp.19945060601

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY