Thermal treatment effect of the oxidized La2CuO4+δ: The access of continuous and discontinuous Tc

Scale-free structural organization of oxygen interstitials in La2CuO4+y

“…In the optimum doping range, 0.1 < y < 0.12, a single T c = 40 K superconducting phase appears but many experiments [11][12][13][14][15]23,24 indicate a complex magnetic, electronic and structural phase separation. Annealing the sample at 370 K, where i-O does not escape from the sample, followed by quenching below 200 K, yields a mixed state, displaying two critical temperatures 11,12 , 32< T c1 < 36 K and T c2 =16 K; we therefore call this state the T c =16+32 K phase.…”

“…In the optimum doping range, 0.1 < y < 0.12, a single T c = 40 K superconducting phase appears but many experiments [11][12][13][14][15]23,24 indicate a complex magnetic, electronic and structural phase separation. Annealing the sample at 370 K, where i-O does not escape from the sample, followed by quenching below 200 K, yields a mixed state, displaying two critical temperatures 11,12 , 32< T c1 < 36 K and T c2 =16 K; we therefore call this state the T c =16+32 K phase. The mixed state has been thought to originate from the coexistence of regions with the same average doping level but with two different orderings of the dopants, with some unknown i-O selforganization; also, no information is available on the relation between this unknown superstructure and the high-temperature superconducting phase.…”

Anomalous dispersion of longitudinal optical phonons in oxygen-doped La2−xSrxCuO4+δ

“…Quenched Sr 2+ doping creates a superconductor where T c varies continuously with doping, forming the so-called superconducting dome for 0.05 x 0.25. Meanwhile the mobile O dopants only seem to allow for certain superconducting phases to emerge (T c ≈ 15, 30, 40 K) due to oxygen content [22], pressure [23], or thermal treatment [24].…”

The flux dynamics behavior of the two competing high temperature superconducting phases in underdoped LaCuO4.06

“…Since a similar phase separation is not observed in the cation--doped La 2--x Sr x CuO 4 , its origin has been associated to the high mobility of the oxygen interstitials (O--i). In the metallic phase at higher doping levels (i.e., for 0.055<δ<0.12) only one crystalline structure (Fmmm) is detected, but the superconducting transition exhibits two well--defined steps at 15 K and around 30 K pointing out the occurrence of an electronic phase separation in two distinct superconducting phases [38,39]. Using scanning micro X--ray diffraction [40] it has been shown that in the metallic phase there is a phase separation between puddles of striped ordered O--i embedded in a host space of disordered O--i [40].…”