Inhomogeneous Electronic Structure Probed by Spin-Echo Experiments in the Electron Doped High-TcSuperconductorPr1.85

F. Zámborszky

¹

,

Guoqing Wu

²

,

Jun Shinagawa

³

et al.

Abstract

63 Cu nuclear magnetic resonance (NMR) spin-echo decay rate (T −1 2 ) measurements are reported for the normal and superconducting states of a single crystal of Pr1.85Ce0.15CuO4−y (PCCO) in a magnetic field B0 = 9 T over the temperature range 2 K< T <200 K. The spin-echo decay rate is temperature-dependent for T < 55 K, and has a substantial dependence on the radio frequency (rf) pulse parameters below T ≈ 25 K. This dependence indicates that T −1 2 is strongly effected by a local magnetic field distribution that can be modified by the rf pulses, including ones that are not at the nuclear Larmor frequency. The low-temperature results are consistent with the formation of a static inhomogeneous electronic structure that couples to the rf fields of the pulses.

Progress and perspectives on electron-doped cuprates

“…They interpret these peculiar transport features as evidence for stripe formation in the underdoped n-type cuprates. In Pr 1.85 Ce 0.15 CuO 4 Zamborszky et al (2004) found signatures in the NMR spin-echo decay rate (1/T 2 ) for static inhomogeneous electronic structure. Similarly, Bakharev et al (2004) found via Cu NMR evidence for an inhomogeneous "blob-phase" (bubble) in reoxygenated superconducting Nd 1.85 Sr 0.15 CuO 4 .…”

“…This is in contrast to the hole-doped system where in the Néel state (x < 0.02) the internal field was constant (Borsa et al, 1995;Harshman et al, 1988), which has been taken as evidence for phase separation (Chou et al, 1993;Matsuda et al, 2002). Extensive NMR measurements have also been done by Bakharev et al (2004); Williams et al (2005); Zamborszky et al (2004) that have given important information about inhomogeneity in these systems. These measurements are discussed in more detail in Sec.…”

Neutron Scattering Studies of Antiferromagnetic Correlations in Cuprates

“…They found evidence for several distinct local environments, and argued that doped regions reached the percolation limit at x ≈ 0.14, at the phase boundary for superconductivity. Recent NMR studies have also found evidence of electronic inhomogeneity [255,256].…”

Effect of disorder on the pairing properties of electron-doped high-Tcsuperconductors

“…17 On the other hand, it is expected that the increase of doping density may lead to the increase of disorders due to the potential fluctuations created by the dopants. Consistent with this statement, very recent spin-echo probe in Pr 1.85 Ce 0.15 CuO 4−y carried out by Zamborszky et al 18 and neutron scattering studies on Pr 0.88 LaCe 0.12 CuO 4−␦ by Dai et al 19 indicate that the electron-doped cuprates are, indeed, inhomogeneous though the origin of this inhomogeneous electronic configuration is undetermined at present. In a d x 2 −y 2-wave superconductor, the disorder can result in the localization of the quasiparticle excitations and may induce component of another symmetry pairing under some conditions.…”