Intrinsic tendency of electronic phase separation into two superconducting states inLa2−xSrx

Abstract

The effect of hydrostatic pressure up to 2 GPa on the superconductiong transitions in La 2−x Sr x CuO 4+δ is investigated. The ambient and high pressure properties of two series of samples with x=0 and x=0.015 and 0< δ <0.1 are characterized and compared by ac-susceptibility measurements. At ambient pressure both sets of samples fit into the same phase diagram as a function of the total hole concentration, n h . For n h < 0.085 there is a single superconducting transition (T c ≈ 30K) with an unusually large pressure coefficient, dT (30) c /dp ≈ 10 K/GP a. At higher hole density (n h > 0.085) a second superconducting transition (T c ≈ 15K) follows the first transition upon cooling and the pressure shift of this transition is negative, dTAt the boundary as the hole density is close to 0.085 the phase separation can be induced by pressure. The results are explained in terms of a strong correlation of the interstitial oxygen with the hole system in the CuO-planes.Pressure, applied at ambient temperature, causes a redistribution of holes.The mobile oxygen dopants follow and enhance T c as well as the tendency to phase 1 separation. If pressure is changed at low temperature (< 100K) the effects on T c and phase separations are greatly diminished because the interstitial oxygen becomes immobile at low T. Our results indicate that the dopant effects are important. Dopants and holes should be treated as a single globally correlated state. When thermodynamic euqilibrium is approached in the oxygen-doped samples, we find that there is an intrinsic tendency of electronic phase separation of doped holes into two distinct superconducting states.

Optimum inhomogeneity of local lattice distortions in La 2 CuO 4+ y

“…The sample shows electronic phase separation into two superconducting phases with two critical temperatures, T c1 ¼ 14 K and T c2 ¼ 27 K (see Fig. S1), in agreement with previous studies (12,47,48). Synchrotron X-ray diffraction (XRD), performed at the European Synchrotron Radiation Facility (ESRF) at Grenoble, shows weak incommensurate diffuse satellites (called Q3 …”

“…For y > 0.055, La 2 CuO 4þy shows more subtle phase separation, characterized by coexistence of two different superconducting phases with different critical temperatures, the first T c1 ¼ 15 AE 1 K and the second T c2 ranging between 27 and 38 K, even while the crystalline lattice shows no splitting of the c-axis. The first critical temperature is sensitive to Oi ordering, and the second critical temperature is similar to that seen for La 2−x Sr x CuO 4 (11,46,47).…”

Two Superconducting Phases and Their Characteristics in Layered BaTi 2 (Sb 1− x Bi x ) 2 O with x = 0.16

“…It is never observed in single-phased superconducting systems of either conventional type II superconductor like MgB 2 [23] or iron-based high-temperature superconductors [18]. Instead, it is quite similar to the behaviour of phase-separated cuprate superconductors, where the diamagnetic susceptibilities of two coexistent superconducting phases tuned by pressure were also found to be correlated [24]. With 8 the electronic phase-separation scenario that areas with different charge densities coexist, our observations can be easily understood.…”

“…With 8 the electronic phase-separation scenario that areas with different charge densities coexist, our observations can be easily understood. When the carrier density in non-superconducting carrier-poor area is increased by external pressure, the carrier-rich area that supports superconductivity can expand dramatically by permeating and spreading into carrier-poor area, as in the case of cuprate superconductors [24][25][26]. Based on our experimental results, marked in light gray in fig.…”

High Pressure Effects on Superconductivity

“…14) and possible p-induced oxygen migration effects have been investigated in La 2 CuO 4+δ and La 1.985 Sr 0.015 CuO 4+δ [109]. Hydrostatic pressure was imposed either at room temperature allowing the redistribution of the interstitial oxygen or below 100 K where oxygen diffusion is kinetically inhibited.…”