"Physics of high T_c superconductivity: the role of spin and charge excitations (spinons and holons)"
Sung-Ho Salk

Aug 08, 2002

講演題目：　Physics of high T_c superconductivity: the role of spin and charge excitations (spinons and holons)
講　師　：　Sung-Ho Salk
　　　　　(韓国ポハン大学・教授)
日　時　：　平成14年08月08日 (木) 14:00-
場　所　：　北海道大学大学院理学研究科物理学専攻　大学院講義室 理学部2号館（2－11号室）

要　旨　：
　　High T_c superconductivity is one of the most challenging subjects incondensed matter physics for both fundamentals and　applications. In the area of its basics one of the most　searched subjects is the mechanism of　superconductivity for doped cuprates, which still remains to be resolved. First, multifaceted aspects of experimental observations will be briefly reviewed. They are the ARPES, STM, muSR, NMR, NQR, INS, optical concuctivity measurements and specific heat measurements. Based on these observations we then make a judicious review of various proposed theories by paying attention to the charge and spin degrees of freedom. These theories include the original RVB theory, slave-boson theories of U(1) and SU(2), SO(5), DDW, CDW and numerical simulations. We then introduce our theory of slave-boson theory which differs from the earlier ones developed by other researchers especially in　the treatment of Heisenbeg term. By paying a rigorous　 attention to the spin and charge degrees of freedom we explain the physics of why this new theory predicts well in agreement with numerous observations, including the muSR measurements of superfluid weight vs. T_c and specific heat measurements. Time permitting we will also discuss the vortex binding-unbinding transition at low temperatures in the underdoped region.


世話人　 小田　研
moda@sci.hokudai.ac.jp
北海道大学大学院理学研究科

"Hadronic and Quark/Gluon Degrees of Freedom in Hadron Interactions"
Prof. Earle L. Lomon

Nov 16, 1999

講演題目：　Hadronic and Quark/Gluon Degrees of Freedom in Hadron Interactions
講　師　：　Prof. Earle L. Lomon
　　　　　(Department of Physics, Massachusetts Institute of Technology, U.S.A.)
日　時　：　平成11年11月16日 (火) 16:00-17:00
場　所　：　北海道大学理学部２号館大学院講義室（2-2-11）

要　旨　：
The success of Quantum Chromodynamics (QCD) in its perturbative,high momentum transfer regime, leads to the expectation that it is thegeneral theory for the strong interaction of hadrons. But the direct, lattice QCD, calculations of non-perturbative multi-hadron reactions are not now feasible. I will describe a model for QCD which incorporates its critical features of asymptotic freedom with quark and gluon degrees of freedom at short range, and confinement to hadron degrees of freedom at long range. In this hybrid model the inner and outer regions are connected by a boundary condition determined by R-Matrix theory, enabling the description of the transition from confinement to asymptotic freedom. A consequence is the prediction of exotic multi-quark state resonances, whose position and width are mainly determined by perturbative QCD with gluon exchange, but are coupled to the continuum and molecular resonances by the long range hadron exchange forces. Observable consequences in the baryon-baryon (S=0,－1 and－2), and meson-baryon (S=1) sectors will be described and compared with available data. Ways to improve the accuracy and realism of the model will be described.

世話人　 原田稔
（mharada@res.otaru-uc.ac.jp）
小樽商科大学一般教育

"Probing the Energy Gap of High Temperature Superconductors with Tunneling Spectroscopy: Evidence for Exotic Pairing"
Prof. John Zasadzinski

Oct 21, 1999

講演題目：　Probing the Energy Gap of High Temperature Superconductors with Tunneling Spectroscopy: Evidence for Exotic Pairing
講　師　：　Prof. John Zasadzinski
　　　　　(Illinois Institute of Technology and Argonne National Laboratory)
日　時　：　平成11年10月21日 (木) 16:30-17:00
場　所　：　北海道大学理学部２号館大学院講義室（2-2-11）

要　旨　：
TTunneling spectroscopy is presented for a variety of high temperature　superconducting cuprates. The data for electron doped compounds such as　Nd-Ce-Cu-O which have a relatively low Tc = 22K are consistent with an　s-wave energy gap and ordinary phonon mediated pairing. However, the　tunneling data for hole-doped cuprates such as Bi-Sr-Ca-Cu-O (Bi2212) with　an optimal Tc = 95 K are more consistent with a d-wave energy gap. The　doping dependence of the energy gap parameter in Bi2212 is anomalous,　increasing to very large values in the underdoped regime even as Tc　decreases. This gap parameter follows the trend of the antiferromagnetic　exchange energy, J, which indicates that the pairing is of magnetic origin.　 The high bias tunneling spectra reveal a dip feature that is often quite　pronounced and may be related to the resonance peak in the magnetic　excitations probed by neutron scattering. Also, the high bias features　include a secondary peak which might be an indication of a competing　pseudogap of magnetic origin.

小田研　（北海道大学大学院理学研究科）
（moda@sci.hokudai.ac.jp）

"Dissipative Quantum Brain Dynamics"
Prof. Giuseppe Vitiello

Jun 02, 1999

講演題目：　Dissipative Quantum Brain Dynamics
講　師　：　Prof. Giuseppe Vitiello
　　　　　(Dipartimento di Fisica, Universita' di Salerno, Italy)
日　時　：　平成11年6月2日 (水) 16:30-17:30
場　所　：　北海道大学理学部２号館大学院講義室（2-2-11）

要　旨　：
The quantum model of brain has been extended to dissipative dynamics in order to solve the problem of memory capacity. This gave rise to an interesting framework to study consciousness related mechanisms. The brain is modeled as an open system interacting with the environment and the information storage is represented through the dynamical generation of collective modes under external stimuli. We find different life-times for modes of different momentum. This suggests interesting features related with memory persistence time. Also stimulated by the increasing interest in quantum features of neural net dynamics, either in connection with information processing in biological systems, or in relation with a computational strategy based on the system quantum evolution　(quantum computation), we study the classical limit of the dissipative quantum brain dynamics in order to exhibit a link with neural net dynamics.

世話人　 石川健三
（ishikawa@particle.sci.hokudai.ac.jp）
北海道大学大学院理学研究科

"NMR in Mesoscopic Magnetic　Molecular Rings and Clusters"
Prof　F. Borsa

Feb 12, 1999

講演題目：　NMR in Mesoscopic Magnetic　Molecular Rings and Clusters
講　師　：　Prof　F. Borsa
　　　　　(Pavia University (Italy) and Iowa State University)
日　時　：　平成11年2月12日 (金) 11:00-
場　所　：　北海道大学理学部２号館大学院講義室（2-2-11）

要　旨　：
Molecular magnets are mesoscopic magnetic systems which can be synthesized in bulk quantities by chemical techniques and can be prepared in crystalline form whereby each molecule is an independent magnetic entity with negligible intermolecular magnetic interactions. After reviewing briefly some recent NMR studies [1,2,3] of the spin dynamics in different types of magnetic rings and clusters I will focus the attention on low temperature proton NMR and mSR results in the antiferromagnetic (AFM) molecule [Fe10(OCH3)20(C2H2O2Cl)10] (in short Fe10) and the ferrimagnetic cluster [Mn12O12(CH3COO A)16(H2O)42CH3-COOH4H2O] (in short Mn12). The Fe10 is an antiferromagnetically coupled ring with nearest neighbor exchange coupling　constant J/kB =13.8 K and a total S=0 non magnetic ground state. The 1H nuclear relaxation data as a function of applied magnetic field (performed in part at the Grenoble high field facility) show　spectacular cross relaxation effects at the critical field for which the energy levels of the singlet ground state and the first few magnetic excited states become almost degenerate (level crossing) [5]. Mn12 is a molecular magnet with a high spin ground state and a large crystal field easy axis anisotropy. At low temperatures one can observe quantum tunneling effects in the relaxation of the magnetization of the molecule. I will present proton and muon relaxation data versus temperature and applied magnetic field. The data can be explained in terms of thermal fluctuations of the direction of the Mn12 magnetization in its S=10 ground state [4]. Spin-echo 1H NMR experiments in conditions off equilibrium demonstrate the possibility of monitoring the very slow relaxation of the　Mn12 magnetization at T << 3K from the time dependence of of the amplitude of echo signal [5].
1) A. Lascialfari, D. Gatteschi, F. Borsa, A. Cornia, Phys. Rev. B 55, 14341 (1997).
2) A. Lascialfari , Z.H.Jang , F.Borsa, D.Gatteschi and A.Cornia, Journal of Applied Physics 83, 6946 (1998).
3) A. Lascialfari, D. Gatteschi, F. Borsa, A. Shastri, Z. H. Jang, P. Carretta, Phys. Rev. B 57, 514 (1998).
4) A.Lascialfari, Z.H.Jang, F.Borsa, P.Carretta and D.Gatteschi, Phys. Rev. Letters 3773 (1998).
5) Z.H.Jang, A.Lascialfari, F. Borsa, A.Cornia, D.Gatteschi, M.H.Julien, (Unpublished).

世話人　 熊谷健一
（kumagai@phys.sci.hokudai.ac.jp）
北海道大学・大学院理学研究科・物理学専攻