Ultrasonic studies of structural phase transitions and superconductivity in La2−xBaxCuO4−δ and La2−xSrxCuO4−δ

NMR study on the local structure in La-based high-Tccuprates

“…Thus determined transition temperature precisely agrees with the macroscopic structural phase transition, that is, the onset of the orthorhombicity observed by X-ray diffraction as seen in Fig. A1 [6,15]. The transition temperature T d2 can also be determined from the ultrasonic velocity as a slight hardening point.…”

“…Therefore, we can further conclude that this incoherent LTT structure stabilizes only SDW but not CDW. This odd order must set the T c anomaly at x=0.12 very weak in the rare earth free-LSCO [5,6]. Consequently, the disappearance of signal below 30 K is considered to be due to the wipe out effect of the SDW.…”

“…Such an anomalous behaviour was first reported by Fukase et al in the midst of 80's as the anomalous reduction in elastic constant from T* which is much higher than T d1 . [6] The determination of T d1 by the elastic measurements is shown in Appendix [15,17].…”

“…The superconducting transition temperature is determined as the onset of a diamagnetic signal under an applied field of 20 Oe. The structural phase transition temperature from HTT to LTO in the sample with x=0.12 and 0.15 is determined to be 240 and 180 K respectively from the temperature dependence of the ultrasonic sound velocity as described in Appendix [6,15]. Cu-NMR "angle-swept spectra" were obtained by plotting the spin-echo amplitude against the sample rotation angle, with keeping magnetic field and resonance frequency to be constant [17,18].…”

Magnetic order inLa1.9Sr0.1CuO4

“…The LTT phase was also indicated by electron diffraction and ultrasonic measurements. 10,11,13 There have been several reports of magnetic ordering in La 2−x Sr x CuO 4 (x around 0.11) at low temperatures. 4,[6][7][8][9][10] .…”