Magnetic-Field-Induced Enhancement of the Vortex Pinning in the Overdoped Regime of La_2-xSr_xCuO₄: Relation to the Microscopic Phase Separation

Abstract

In order to investigate the inhomogeneity of the superconducting (SC) state in the overdoped high-T c cuprates, we have measured the magnetic susceptibility, χ, of La 2−x Sr x CuO 4 (LSCO) single crystals in the overdoped regime in magnetic fields parallel to the c-axis up to 7 T on warming after zero-field cooling. It has been found for x = 0.198 and 0.219 that the temperature dependence of χ in 1 T shows a plateau, that is, χ is almost independent of temperature in a moderate temperature-range in the SC state. Moreover, a so-called second peak in the magnetization curve has markedly appeared in these crystals. These results indicate an anomalous enhancement of the vortex pinning and strongly suggest the occurrence of a microscopic phase separation into SC and normal-state regions in the overdoped high-T c cuprates.

Hole trapping by Ni, Kondo effect, and electronic phase diagram in nonsuperconducting Ni-substitutedLa2−xSrxCu1−Suzuki1, Adachi2, Tanabe3 et al. 2010Phys. Rev. B23190View full textAdd to dashboardCite

“…Accordingly, it is much convinced that the quantum phase transition in LSCO occurs not at a single point of p in the ground state but in an extended region of p, that is, the change of the ground state upon hole doping is crossover-like due to the phase separation. Since the T -linear behavior of ρ has been observed in various high-T c cuprates [16][17][18] and the occurrence of the phase separation has been proposed in various overdoped cuprates, [33][34][35][36][37][38][39][40][41][42][43][44] the present results together with former ones [19,20] strongly suggest that HTSC emerges around the quantum critical region affected by the phase separation.…”

“…It has been suggested from the magnetization, [33][34][35][36][37][38] specific heat [39][40][41] and µSR [42][43][44] measurements that a microscopic phase separation into SC and normalstate regions takes place in a sample of the overdoped high-T c cuprates. Based on these results, it is possible in Ni-substituted LSCNO that a phase-separated state consisting of the magnetically ordered region observed in the underdoped regime and the metallic region observed in the overdoped regime is realized in a sample around the boundary between the magnetically ordered and metallic phases in the phase diagram.…”

Distinct Fe-induced magnetic states in the underdoped and overdoped regimes of La2−xSrxCu<

“…Finally, we briefly discuss Fe-substitution effects on the nano-scale phase separation into SC and normal metallic regions in the overdoped regime of LSCO, which has been suggested from µSR, [53] magnetic-susceptibility [54,55] and specifit-heat measurements. [56,57] In the phaseseprated overdoped regime, it seems that the magnetic correlation due to Cu spins still remains in the SC region and that the normal-state region is rather metallic.…”

Electronic Homogeneity in the Overdoped Regime of the Electron-Doped High-TcSuperconductors

“…The T c 's of crystals with x = 0.13, 0.15 and 0.17 are 20.5 K, 12.2 K and 5.1 K, respectively. It is found that, compared with M of overdoped LSCO with x = 0.198 [3], the hysteresis is quite small and no second magnetization peak is observed in PLCCO. These results suggest that the vortex pinning is relatively weak in PLCCO, implying a rather homogeneous electronic state in contrast to the inhomogeneous one in overdoped LSCO.…”

“…The low-temperature specific heat measurements have revealed the existence of a finite value of the Sommerfeld constant in the SC ground state [2]. In addition, from the magnetization-hysteresis-loop measurements, a so-called second magnetization peak has been observed in the overdoped regime, indicating the enhancement of the vortex pinning [3]. These results suggest that the electronic state in overdoped LSCO is so inhomogeneous as to be composed of normal and SC states.…”