Abstract (WS-D, poster)

PS-D1 DMFT+FLEX approach for the phase diagram for d-wave superconductors
Kitatani, Motoharu
Department of physics, University of Tokyo, Japan
Participation: from 11/24 to 12/5

We propose to combine the dynamical mean field theory (DMFT) with the fluctuation exchange approximation (FLEX) to investigate strongly correlated systems and especially to obtain a phase diagram for d-wave superconductors. The DMFT+FLEX method, which can also be viewed as a proposal for a new Luttinger-Ward functional, describes the momentum-dependent effective pairing interaction, so that the method describes anisotropic pairing superconductors along with the local correlation effect that is important in Mott physics. We have applied the formalism to the two-dimensional repulsive Hubbard model to obtain superconducting transition temperature. The result does indeed exhibit a Tc-dome structure, while the ordinary FLEX does not. We have traced back the origin of the dome to the local vertex correction from DMFT that gives a filling dependent effect on the FLEX self-energy.

PS-D2 Total orbital angular momentum of 2D chiral superfluids
Nie, Wenxing
Institute for Advanced Study, Tsinghua University, China
Participation: from 11/17 to 11/28

For \(p_x+ip_y\) paired superfluid, the total orbital angular momentum is naively expected to be \(N/2\), where \(N\) is the number of fermions. On the other hand, one might also think that the pairing gap formation only affects the states near the Fermi surface, and as a consequence that the magnitude of total orbital angular momentum is significantly suppressed from $N/2$. The apparent contradiction between the two viewpoints is called "intrinsic angular momentum paradox" [1].
We investigate the validity of Ishikawa-Mermin-Muzikar formula [2] first and find tits breakdown near the boundary of the system. Since the angular momentum is not well defined in uniform or infinite systems, we need consider finite system with boundary. Therefore, we study the total angular momentum of 2D chiral superfluids confined in rotational symmetric potential, in the framework of Bogoliubov-de-Gennes theory. We find the total angular momentum for \(p_x+ip_y\) superfluid is \(N/2\). But the total angular momentum for higher order chiral superfluids (eg, \(d+id^{\prime}\) and \(f+if^{\prime}\)) is greatly suppressed. The differences will be elucidated in terms of the current distribution and the structure of edge states [3].
[1] A. J. Leggett, Quantum Liquids : Bose Condensation and Cooper Pairing in Condensed-Matter Systems (Oxford Graduate Texts).
[2] M. Ishikawa, Prog. Theor. Phys. 57, 1836 (1977), N. D. Mermin and P. Muzikar, Phys. Rev. B 21, 980 (1980)
[3] W.-X. Nie, Y. Tada, M. Oshikawa, in preparation.

PS-D3 Symmetry protected topological phase in magnetization plateau
Takayoshi, Shintaro
National Institute for Materials Science, Japan
Participation: from 11/24 to 12/5

Symmetry protected topological (SPT) phase is a gapped state with short range entanglement, which is protected by imposing some symmetry into a system. A typical example of the SPT phase is a Haldane (AKLT) state, which is protected by time-reversal, link-inversion, and Z\(_2{\times}\)Z\(_2\) symmetries. We discuss a symmetry protection of spin systems in magnetization plateau by using Berry phase term in field theories. We can also show that plateau states are protected by link-inversion symmetry through a matrix product representation.

PS-D4 DMFT study of the local correlation effects in quasi-periodic system
Takemori, Nayuta
Tokyo Institute of Technology, Japan
Participation: from 11/25 to 11/28

We study a 2D half-filled Hubbard model on a Penrose lattice by means of real-space dynamical mean-field theory. Calculating the double occupancy and renormalization factor at each site, we discuss how low-temperature properties are affected by local correlations on the quasi-periodic structure. We show that the Mott transition occurs in the Penrose lattice system. Furthermore we find that a spatially-dependent renormalization characteristic of the quasi-periodic lattice emerges due to the strong local correlations.