University of Electro-Communications

About: University of Electro-Communications is a education organization based out in Tokyo, Japan. It is known for research contribution in the topics: Laser & Robot. The organization has 8041 authors who have published 16950 publications receiving 235832 citations. The organization is also known as: UEC & Denki-Tsūshin Daigaku.

Phase diagram of the two-dimensional extended Hubbard model: Phase transitions between different pairing symmetries when charge and spin fluctuations coexist

Abstract: In order to explore how superconductivity arises when charge fluctuations and spin fluctuations coexist, we have obtained a phase diagram against the off-site repulsion $V$ and band filling $n$ for the extended, repulsive Hubbard model on the square lattice with the fluctuation exchange approximation. We have found the existence of (i) a transition between ${d}_{xy}$ and ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ pairing symmetries, (ii) $f$-pairing in between the ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ and CDW phases for intermediate $0.5lnl1.0$ and large $V$, and (iii) for anisotropic cases the pairing symmetry changing, in agreement with a previously proposed ``generic phase diagram,'' as $d\ensuremath{\rightarrow}f\ensuremath{\rightarrow}s$ when $V$ (hence the charge fluctuations) are increased. All these are consequences of the structure in the charge and spin susceptibilities, which have peaks habitating at common or segregated positions in $k$ space.

Ultrafine grain formation in face centered cubic metals during severe plastic deformation

Abstract: The evolution mechanisms of new high-angle boundaries as well as ultrafine grains at large strains were studied by means of multidirectional forging (MDF) of pure copper at low temperature and aluminum alloy at high temperature, where dynamic recovery operates as a main restoration process. The structural changes can be characterized by the evolution of deformation bands such as microshear or kink bands at moderate strains. Multidirectional forging accelerates the evolution of many mutually crossing microshear or kink bands developed in various directions. The misorientations between (sub)grains increased gradually with increasing cumulative strain, finally leading to the development of a new fine-grained structure. The dynamic grain formation can be resulted from in situ or continuous dynamic recrystallization which is discussed in detail.

Exchange Coupling and Energy-Level Crossing in a Magnetic Chain [Dy2Cu2]n Evaluated by High-Frequency Electron Paramagnetic Resonance

Abstract: A 4f−3d heterometallic polymeric coordination compound [{Dy(hfac)2(CH3OH)}2{Cu(dmg)(Hdmg)}2]n ([Dy2Cu2]n; H2dmg = dimethylglyoxime; Hhfac = 1,1,1,5,5,5-hexafluoropentane-2,4-dione) was synthesized, and the X-ray crystallographic analysis shows that the structure is isomorphous to the known ferrimagnetic [Gd2Cu2]n polymer A centrosymmetric diamond-arrayed ferrimagnetic unit involving the oximate bridge, Dy−O−N−Cu, is repeated to form a discrete chain An onset of the frequency dependence was found in the ac magnetic susceptibility measurements down to 18 K Low-temperature magnetization measurements on [Dy2Cu2]n exhibited magnetic hysteresis with magnetization steps To examine the energy level structure and the exchange coupling between the Dy and Cu ions, high-frequency EPR (HF-EPR) spectra of a polycrystalline sample of [Dy2Cu2]n were recorded at various frequencies (347−5254 GHz) and temperatures We analyzed the spectra by treating the Dy moments as Ising spins and built an exchange-coupling model