Metallic Phase in Lightly DopedLa2−xSrxC

Abstract

In the low doping range of x from 0.01 to 0.06 in La2−xSrxCuO4, a narrow electron paramagnetic resonance (EPR) line has been investigated. This line is distinct from the known broad line, both due to probing Mn 2+ ions. The narrow line is ascribed to metallic regions in the material, and its intensity increases exponentially upon cooling below ∼ 150 K. The activation energy deduced ∆ = 460(50) K is nearly the same as that found in the doped superconducting regime by Raman and neutron scattering. The intensity of the narrow EPR line follows the same temperature dependence as the resistivity anisotropy in lightly doped La2−xSrxCuO4 single crystals.

Spin Texture and Spin Dynamics in Superconducting Cuprates Near the Phase Transition Revealed by the Electron Paramagnetic Resonance

“…[24]) that the local charge carrier concentration in CuO 2 planes can be influenced by isotope mass change of the in-plane oxygen ions due to the microscopic electronic phase separation into metallic and dielectric regions in the CuO 2 plane. The results of the EPR study of such a phase separation in lightly doped La 2−x Sr x CuO 4 showed that the starting point for the creation of metallic regions is a formation of a bipolaron by two three-spin-polarons (3SP) via exchange by phonons [25,26]. EPR experiments demonstrated that by cooling, bipolarons condense into metallic clusters or stripes similar to the process described in the previous Section.…”

“…The broad line disappears at y = 0.4 which can be related to the delocalization of the electronic holes in the stripes. The CuO 2 planes experience the electronic phase separation into metal and dielectric regions which were detected earlier by the EPR study [25]. The phase transition of underdoped cuprates into the superconducting state is accompanied by a strong planar isotope effect on the critical temperature T c what can indicate an important role of electron-phonon interactions in a formation of bipolarons and the metal regions in the CuO 2 planes.…”

Electron Paramagnetic Resonance in Superconducting Cuprates

“…Such a behavior was actually observed in these experiments. The microscopic electronic phase separation into metallic and dielectric regions in the CuO 2 planes was observed previously by the EPR method in lightly doped La 2Àx Sr x CuO 4 also in a metallic state [34]. It was proposed then that the starting point for the creation of metallic regions is a formation of a bipolaron by two three-spin-polarons with an assistance of phonons [35].…”

Inhomogeneous Electronic Distribution in High-Tc Cuprates

“…[6][7][8][9][10][11][12] The stripe order has also been observed by x-ray scattering. [12][13][14][15][16][17] Furthermore, an electron paramagnetic resonance study showed that micro-scopic electronic phase separation occurs in La 2−x Sr x Cu 0.98 Mn 0.02 O 4 with 0.01 ≤ x ≤ 0.06, 18 and a Cu nuclear magnetic resonance (NMR) study suggested that a large charge droplet ('blob') is formed in the electron-doped Nd 1.85 Ce 0.15 CuO 4−δ . 19 Much theoretical works has also been performed to study the behavior of the doped carriers in HTSC.…”