<1> 2000.4.2 ----------------------------------------------
Analytical ground state for the three-band Hubbard model
by C.Waidacher, J.Richter, R.E.hetzel, and K.W.Becker
Physical Review B, Vol.60, No.4, 15 July 1999-II, pp.2255-2261
[Abstract]
For the calculation of charge excitations as those obserbed in, e.g., photoemission spectroscopy or in electron-energy-loss spectroscopy, a correct description of ground-state charge properties is essential. In strong correlated systems like undoped cuprates this is a highly nontrivial problem. In this paper we derive a nonperturbative analytical approximation for the ground state of the three-band Hubbard model on an infinite, half-filled CuO2 plane. By comparison with projector quantum Monte Carlo calculations it is shown that the resulting expressions correctly describe the charge properties of the ground state. Relations to other approaches are discussed. The analytical ground state preserves size consistency and can be generalized for other geometries, while still being both easy to interpret and to evaluate. [S0163-1829(99)01628-8] On the three-band Hubbard model, V.J.Emery, Phys.Rev.Lett.58,2794(1987). On the correct sign for the factors included in the hybridization part of the Hamiltonian, E.Dagotto, Rev.Mod.Phys.66,763(1994), W.Brenig, Phys.Rep.251,153(1995). On the typical set of values for the parameters for explicit calculations, A.K.McMahan, R.M.Martin, and S.Satpathy, Phys.Rev.B38,6650(1988), M.S.Hybertsen, M.Schluter, and N.E.Christiansen, ibid.39,9028(1989), J.B.Grant and A.K.McMahan, ibid.46,8440(1992). [Q] Strong correlations due to Ud are the reason why goundstate properties of Hamiltonian H can be calculated only approximately and/or on finite clusters. On dynamical Green's functions, A.M.Oles and J.Zaanen, Phys.Rev.B39,9175(1989), A.J.Fedro, Yu Zhou, T.C.Leung, B.N.Harmon, and S.K.Sinha,ibid.46,14785(1992), A.Beatrici and A.Gusmao,ibid.51,7508(1995). Numerical simulations, W.H.Stephan,W.von der Linden, and P.Horsch, Phys.Rev.B39,2924(1989), G.Dopf, A.Muramatsu, and W.Hanke,ibid.41,9264(1990), R.T.Scalettar, D.J.Scalapino, R.L.Sugar, and S.R.White,ibid.44,770(1991), G.Dopf, J.Wagner, P.Dietrich, A.Muramatsu, and W.Hanke,Phys.Rev.Lett.68,2082(1992). On a CuO3 corner-sharing chain, C.Waidacher, J.Richter,and K.W.Becker, Europhys.Lett.(to be published). On a relationship to the cumulant formalism, K.W.Becker and P.Fulde, Z.Phys.B72,423(1988), K.W.Becker and W.Brenig,ibid.79,195(1990), P.Fulde, Electron Correlations in Molecules and Solids, 3rd ed.(Springer). On the form of fluctuation operators Fa and the transformation of the ground state, * T.Schork and P.Fulde, J.Chem.Phys.97,9195(1992). On the divergence behavior of a perturbation expansion in lambda, K.W.Becker,W.Brebig,and P.Fulde, Z.Phys.B81,165(1990). On the projector quantum Monte Carlo(PQMC) algorithm, For a review, see W.von der Linden,Phys.Rep.220,53(1992).

<2> 2000.4.14 ----------------------------------------------
Strong coupling superconductivity in heavy fermion systems
L.Glemot, J.P.Brison, J.Flouquet, A.I.Buzdin, D.Jaccard
Physica C317-318(1999)73-81
[Abstract]
One of the primary interests of heavy fermion superconductivity, besides possible unconventional order parameters, is the possibility of a non-phonon-mediated pairing mechanism. It has proved nevertheless very difficult to find an experimental probe of this hypothesis. The upper critical field, H_c2, of UBe_13 has revealed that this compound was in an extreme strong coupling regime, characterized by a strong coupling constant \lambda=15. We present pressure measurements of H_c2 in UBe_13, which probe the pressure dependence of \lambda. The main result is that in this compound, the pairing mechanism is also responsible for a large part of the mass renormalization and cannot arise from electron-phonon interactions. It will be discussed in the framework of the actual interpretations of the heavy masses in heavy fermion sysytems and UBe_13 will be contrasted with the other heavy fermion superconductors. On the ABM superfluid phase, * WF Brinkman, JW Serene, PW Anderson, Phys.Rev.A 10(1974)2386. On the quasi-particle having a record effective mass, HR Ott,Progress in Low Temp.Phys.XI, Elsevier Science Publishers, 1987, p.215. MB Maple et al. , Phys.Rev.Lett.54(1985)477.

<3> 2000.4.24 ----------------------------------------------
電気伝導の理論　-----ランダウアーの公式--------
川畑有郷
日本物理学会誌　Vol.55, No.4, 2000, pp.256-263
[Abstract]
電気伝導は非平衡の現象の中では一番馴染みのあるものであるが，それを扱う理論は完成されているとは言い難い。現在使われている電気伝導の基礎理論には，久保の理論とランダウアーの理論がある。これらの理論は，共に 1957年に発表されながら，ランダウアーの理論がよく使われるようになったのはこの十数年のことである。いわゆるメゾスコピック系の研究が盛んになってからである。応用する対象に制限はあるが単純明快な公式を与えるランダウアーの理論を，複雑ではあるが汎用性のある久保の理論と比べながら解説し，今後どのような発展が必要であるかを考える。
＜文献＞
(1) R.Kubo: J.Phys.Soc.Jpn.12(1957)570.
(2) R.Landauer: IBM J.Res.& Dev.1(1957)223.
(3)川畑有郷：物理学論文選集III「メゾスコピック系」川畑有郷・川村清編（日本物理学会，1994）解説。
(4) S.Tomonaga: Prog.Theor.Phys.5(1950)544.
(5) S.Tarucha, T.Honda, and T.Saku: Solid State Commun.94(1995)413.
(6) 川畑有郷：　新物理学シリーズ31「メゾスコッピック系の物理学」（共立出版，1997）第４章.
(7) T.Izuyama: Prog.Theor.Phys.25(1961)964.
(8) A.Kawabata: Proc.29th Int.WEH Workshop "Interactions and Quantum Transport Properties of Lower Dimensional Systems", Hamburg, 1999, Lecture Notes in Physics, ed. T.Brandes(Springer,2000).
(9) A.Shimizu: 同上

<4> 2000.3.　　----------------------------------------------
清水　明
応用物理　62(1993)881 サブポアソン光の解説

<5> 2000.4.28 ----------------------------------------------
Spectral Properties of the Generalized Spin-Fermion Models
A.L.Kuzemsky
International Journal of Modern Physics B, Vol.13, No.20(1999)2573-2605
[Abstract]
In order to account for competition and interplay of localized and itinerant magnetic behabiour in correlated many body systems with complex spectra the various types of spin-fermion models have been considered in the context of the Irreducible Green's Functions(IGF) approach. Examples are generalized d-f model and Kondo-Heisenberg model. The calculations of the quasiparticle excitation spectra with damping for these models has been performed in the framework of the equation-of-motion method for two-time temperature Green's Functions within a non-perturbative approach. A unified scheme for the construction of Generalised Mean Fields (elastic scattering corrections) and self-energy (inelastic scattering) in terms of the Dyson equation has been generalised in order to include the presence of the two interacting subsystems of localised spins and itinerant electrons. A general procedure is given to obtain the quasiparticle damping in a self-consistent way. This approach gives the complete and compact description of quasiparticles and show the flexibility and richness of the generalised spin-fermion model concept.

<6> 2000.5.14 ----------------------------------------------
The Physical origin of the electron-phonon vertex correction
C.Grimaldi, L.Pietronero, and M.Scattoni
Eur. Phys. J. B 10, pp.247-255(1999)
[Abstract]
In the theory of nonadiabatic superconductivity several features are governed by the electon-phonon vertex correction which has a complex structure both in momentum and frequecy. We derive a physical interpretation of such nonadiabatic effects that permits to link them to specific material properties. We show how the nonadiabatic vertex correction can be decomposed into two terms with different physical origins. In particular, the first term describes the lattice polarization induced by the electrons and it is essentially a single-electon process whereas the second term is governed by the particle-hole excitations due to the exchange part of the phonon-mediated electron-electron interaction. We show that by weakening the influence of the exchange interaction the vertex takes mostly positive values giving rise to an enhanced effective coupling in the scattering with phonons. This weakening of the exchange interaction can be obtained by lowering the density of the electrons, or by considering only long-ranged (small q) electron-phonon couplings.

<7> 2000.5.28 ----------------------------------------------
Self-consistent theory of the electron-phonon interaction in transition metals and their compounds
A.L.Kuzemsky, A.Holas and N.M.Plakida
Physica 122B(1983)168-182
[Abstract]
The renomalized electron and phonon spectra of the Barisic-Labbe-Friedel model of a transition metal are derived. Using the method of double-time thermal Green functions, the self-consistent system of equations including electon-phonon interaction is obtained. For the band and atomic limits of the Hubbard model the explicit solutions for the electron and phonon energies are obtained. The modified Stoner criterion is discussed. The energy gap, appearing between electron bands in the strong correlation limit, persists in the present calculations. The Eliashberg-type equations of superconductivity are obtained.

<8> 2000.6.7 ----------------------------------------------
Modified tight-binding approximation and electon-phonon spectral function for transition metals
A.L.Kuzemsky, A.P.Zhernov
International Journal of Modern Physics B, Vol.4, Nos.7 & 8 (1990) 1395-1407
[Abstract]
The modified tight-binding approximation has been analyzed in detail and is applied to the derivation of an expression for electron-phonon spectral function (EPSF) which enters the strong coupling equations of superconductivity. Numerical calculations of the EPSF and the electron phonon coupling parameter \lambda for five transition metals, V, Nb, Mo, W, Ta have been performed.

<9> 2000.6.20 ----------------------------------------------
Phonons and the Superconducting Transition Temperature
P.B.Allen Edited by G.K.Horton and A.A.Maradudin
Dynamical Properties of Solids Volume 3, Metals, Superconductors, Magnetic Materials, Liquids, North-Hollad Publishing Company, 1980,pp.95-196.

<10> 2000.9.2--------------------------------------------------
V.I.Perel and G.M.Eliashberg
Absorption of Electromagnetic Waves in Plasma
Soviet Physics JETP, Vol.14, No.3, March, 1962, pp.633-637
[Abstract]
The absorption coefficient of electromagnetic waves in a plasma is calculated for e^2/(hbar v)<<1. Application of the temperature diagram technique makes it possible to take systematic account of collective effects and to obtain exact values of the factors in the Coulomb logarithm.

<11> 2000.9.5--------------------------------------------------
J. M. Luttinger
An Exactly Soluble Model of a Many-Fermion System
Journal of Mathematical Physics, Vol.4, No.9, September 1963, pp.1154-1162
[Abstract]
An exactly soluble model of a one-dimensional many-fermion system is discussed. The model has a fairly realistic interaction between pairs of fermions. An exact calculation of the momentum distribution in the ground state is given. It is shown that there is no discontinuity in the momentum distribution in this model at the Fermi surface, but that the momentum distribution has infinite slope there. Comparison with the results of perturbation theory for the same model is also presented, and it is shown that, for this case at least, the perturbation and exact answers behave qualitatively alike. Finally, the response of the system to external fields is also discussed.

<12> 2000.9.6--------------------------------------------------
Marcin Mierzejewski, Janusz Zielinski
Phonon-Induced and Phonon-Free Superconductivity in Correlated Systems: Eliashberg Equations for the Two-Dimensional Hubbard Model
Acta Physica Polonica B, Vol.29(1998),N.12, pp.3907-3924.
[Abstract]
The problem of phonon-induced and phonon-free superconductivity in the two-dimensional Hubbard model has been addressed. We have generalized the Eliashberg equations to account for both on-site and intersite pairing and consider the electron-electron and electron-phonon channels on an equal footing. This approach allows for the discussion of pairing and depairing properties of the local repulsive interaction. We demonstrate the possibility of cooperation between electron-phonon and electron-electron interaction in the stabilization of the d-wave superconductivity, in particular close to the experimental value of optimal doping(\delta -~ 0.15). We have also discussed the problem of phonon-induced superconductivity in the two-dimensional Hubbard model close to the metal-insulator transition. Here, the Coulomb correlations have incorporated within the Hubbard I approximation whereas the superconductivity is treated by the Eliashberg scheme. The results support the view that a d-wave component dominates in the gap function.

<13> 2000.9.7--------------------------------------------------
Marco Zoli
Estimate of the polaron mass in high-Tc superconductors
Physica B265 (1999) pp.150-153
[Abstract]
I study the motion of polarons as a function of temperature in the context of a molecular crystal model in which the discreteness of the lattice is accounted for. The model is based on a non linear Schroedinger equation which can be solved perturbatively if the conditions for the existence of small polarons are assumed. The polaron bandwidth and the site jump hopping probability have been calculated versus temperature and dimensionality. The crossover temperature T_d^* between band-like and hopping motion is reduced in low-dimensional systems due to the enhanced importance of the off-diagonal scattering processes. An Einstein phonon spectrum leads to wrong estimates of the polaron bandwidths. The first and second neighbors intermolecular force constants which parametrize the pair interctions strongly affect the values of the ground state polaron bandwidth and of the hopping probability. We discuss the relevance of the model to high-Tc superconductors in which polaronic features in the transport properties have been pointed out [1]. The estimated effective polaron masses are consistent with Tc values of order -~ 100K. Copyright 1999 Elsevier Science B.V. All rights reserved.

<14> 2000.9.9--------------------------------------------------
P. B. Allen
Phonons and the Superconducting Transition Temperature
Chapter 2, pp.95-196, Dynamical Properties of Solids Vol.3, (1980) Metals, Superconductors, Magnetic Materials, Liquids edited by G. K. Horton and A. A. Maradudin

<15> 2001.-------------------------------------------------