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Tadafumi Ohsaku

Publications and source records attributed to Tadafumi Ohsaku.

25 records · Page 2Linked to original sources
arXiv2003

Chiral Symmetry and Collective Excitations in p-wave, d-wave and f-wave Superconductors

We discuss the origin of charge density wave (CDW) and spin density wave (SDW) in p-wave, d-wave and f-wave superconductors. To describe the low-energy quasiparticle excitation of p-wave case, we introduce a two- (one for time and one for space) dimensional massless Dirac model. After the non-Abelian bosonization is performed, the charge and spin density waves emerge from the model. By using this scheme, we try to explain the characteristic aspect of phase diagrams of various compounds, oxides and organic superconductors. The purpose of this paper is to make an argument that the dimensionality of the nodal excitation in superconductors plays an important role in the determination of the structure of the phase diagram.

cond-mat.supr-con↗
arXiv2002

BCS and Generalized BCS Superconductivity in Relativistic Quantum Field Theory. II. Numerical Calculations

We solve numerically various types of the gap equations developed in the relativistic BCS and generalized BCS framework, presented in part I of this paper. We apply the method for, not only the usual solid metal but also other physical systems, by using homogeneous fermion gas approximation. We examine the relativistic effects on the thermal properties and the Meissner effect of the BCS and generalized BCS superconductivity of various cases.

cond-mat.supr-con↗
arXiv2001

Theory of Quantum Electrodynamical Self-consistent Fields

To obtain the basis for combining various many-body techniques to QED in a consistent manner, we investigate the theory of quantum electrodynamical self-consistent fields. The reserch interest was born mainly of the electronic structure theory, thus we consider of atomic and moleculer systems as our main subjects. But the formalism is more fundamental. First, we derive the quantum electrodynamical Hartree-Fock theory by using the Green's function method. Then we construct a relativistic Hamiltonian written by creation-annihilation operators for electron and positron in a general form, and check that it reproduces the Hartree-Fock theory. We use this Hamiltonian to derive the time-dependent Hartree-Fock theory and random phase approximation, in the operator formalism. The relativistic Slater determinant of the Thouless parametrization is also used. Finally we discuss the applications and futher possible developments.

physics.atom-ph↗
arXiv2001

Quantum Electrodynamical Density-matrix Functional Theory and Group-theoretical Consideration of its Solution

For studying the group theoretical classification of the solutions of the density functional theory in relativistic framework, we propose quantum electrodynamical density-matrix functional theory (QED-DMFT). QED-DMFT gives the energy as a functional of a local one-body $4\times4$ matrix $Q(x)\equiv -<ψ(x)\barψ(x)>$, where $ψ$ and $\barψ$ are 4-component Dirac field and its Dirac conjugate, respectively. We examine some characters of QED-DMFT. After these preparations, by using Q(x), we classify the solutions of QED-DMFT under O(3) rotation, time reversal and spatial inversion. The behavior of Q(x) under nonrelativistic and ultrarelativistic limits are also presented. Finally, we give plans for several extensions and applications of QED-DMFT.

physics.chem-ph↗
arXiv2001

QED-SCF, MCSCF and Coupled-cluster Methods in Quantum Chemistry

We investigate the method to combine the techniques of quantum chemisty with QED. In our theory, we treat the N-electron system and the Dirac sea on an equal footing; we regard both of them as the dynamical degrees of freedom of a many-body system. After the introduction of our QED-SCF method, the QED-SCF solutions are classified into several classes on the basis of group-theoretical operations such as time reversal, parity and O(3) rotational symmetry. The natural orbitals of general QED-SCF solutions are determined by diagonalizing the first order density matrix. Thus, we obtain the possibility to treat the system under strong QED effect by the methods of quantum chemistry, such as QED-MCSCF and QED-coupled-cluster approaches.

physics.chem-ph↗
arXiv2001

BCS and generalized BCS superconductivity in relativistic quantum field theory. I. formulation

We investigate the BCS and generalized BCS theories in the relativistic quantum field theory. We select the gauge freedom as U(1), and introduce a BCS-type effective attractive interaction. After introducing the Gor'kov formalism and performing the group theoretical consideration of the mean fields, we solve the relativistic Gor'kov equation and obtain the Green's functions in analytical forms. We obtain various types of gap equations.

cond-mat.supr-con↗