A. Tsukada

Lattice instability in high temperature superconducting cuprates probed by x-ray absorption spectroscopy

In contrast to conventionl superconductivity where phonons lead to the formation of Cooper pairs, in high-tempratures superconductivity (HTSC), the role of electron-phonon coupling has long been neglected. The in-plane Cu-O bonds in HTSC cuprates show unconventionalbroadening at low temperature as carier are doped. Here we focus on high-quality polarized x-ray absorption spectroscopy (XAS)data for a model HTSC system, (La,Sr)2CuO4 (LSCO). Thin film signal crystal samples were prepared by state-of-the-arts MBE, precisely controlling compositions. High quality data was obtained by use of a segmented x-ray detector. the inplane CuO radial distribution function (RDF)in LSCO (x = 0.15)shows broadening as temprature is lowered, which shows a sharp drop at the critical temprature which is followed by a gradual increase (disorder). Comparing the data with resistivity, we find a remarkeble coinsidence between the sharpening and the onset supercondectivity. Since the sharpening of RDF is interpreated as correleted motion of oxyzen atoms (phase coherence due to supercondectivity), the result demonstrate that the super conducting state directly relates to the unconventionl oxyzen displacements in a bond stretching mode. The result will be discussed in relation to the local models of distortion of the diffrent nature (metallic vs. insulating) that is strongly influnced by strain.

Doping of Ce in T-La2CuO4 : Rigorous test for electron-hole symmetry for high-Tc superconductivity

We report that Ce doping was achieved in La2CuO4 with the K2NiF4 (T) structure for the first time by molecular beam epitaxy. A synthesis temperature of as low as ~ 630C and an appropriate substrate choice, i.e., (001)LaSrGaO4 (a ~ 3.843 A), enebled us to incorporate Ce into K2NiF4 lattice and to obtain Ce-doped T-La2-xCexCuO4 up to x ~ 0.06. The doping of Ce makes T-La2CuO4 more insulating, which is in sharp contrast to Sr (or Ba) doping in T-La2CuO4, which make the compound metallic and superconducting. The observed smooth increase in resistivity from the hole-doped side (T-La2-xSrxCuO4) to the electron-doped side (T-La2-xCexCuO4) indicates that the electron-hole symmetry is broken in the T-phase materials.

Anomalously sharp superconducting transitions in overdoped La 2 − x Sr x CuO 4 films

We present measurements of

Charge transfer gap for T'-RE2CuO4 and T-La2CuO4 as estimated from Madelung potential calculations

ab

Grain boundary weak link in a-b plane in MgB2 film

-plane resistivity

XAS study of superconducting thin film single crystals without doping

{ensuremath{rho}}_{text{ab}}(T)

Superconducting weak bonds at grain boundaries in MgB2

and superfluid density (

Local structure of superconducting (La,Sr){sub 2}CuO{sub 4} under strain: Microscopic mechanism of strain-induced T{sub c} variation

{n}_{text{s}}ensuremath{propto}{ensuremath{lambda}}^{ensuremath{-}2}

MBE growth and properties of T'-La2CuO4 thin films

,

Lattice Instability in High-Temperature Superconducting Cuprates: Polarons Probed by EXAFS

ensuremath{lambda}=text{magnetic}