Large magnetic field-induced spectral weight enhancement of high-energy spin excitations in La1.88Sr0.12CuO4La_{1.88}Sr_{0.12}CuO_{4}

We report electronic Raman scattering experiments on a superconducting ${\rm La_{1.88}Sr_{0.12}CuO_{4}}$ single crystal in a magnetic field. At low temperatures, the spectral weight of the high-energy two-magnon peak increases linearly with field and is amplified by a factor of more than two at 14 T. The effect disappears at elevated temperatures and is not present in undoped ${\rm La_{2}CuO_{4}}$. This observation is discussed in terms of an electronically inhomogeneous state in which the field enhances the volume fraction of a phase with local antiferromagnetic order at the expense of the superconducting phase.Comment: to appear in PR

Quantum spin correlations through the superconducting-normal phase transition in electron-doped superconducting Pr0.88LaCe0.12CuO4-d

The quantum spin fluctuations of the S = 1/2 Cu ions are important in determining the physical properties of the high-transition temperature (high-Tc) copper oxide superconductors, but their possible role in the electron pairing for superconductivity remains an open question. The principal feature of the spin fluctuations in optimally doped high-Tc superconductors is a well defined magnetic resonance whose energy (Er) tracks Tc (as the composition is varied) and whose intensity develops like an order parameter in the superconducting state. We show that the suppression of superconductivity and its associated condensation energy by a magnetic field in the electron-doped high-Tc superconductor, Pr0.88LaCe0.12CuO4-d (Tc = 24 K), is accompanied by the complete suppression of the resonance and the concomitant emergence of static antiferromagnetic (AF) order. Our results demonstrate that the resonance is intimately related to the superconducting condensation energy, and thus suggest that it plays a role in the electron pairing and superconductivity.Comment: PDF Format: 35 pages, 4 main text figures, 6 supplemental figures; Accepted for publication in PNA

Raman study of electronic excitations in MgB2 with application of high magnetic field

We present the first results of Raman scattering with application of magnetic field on magnesium diboride (MgB2). In this work, we have investigated the magnetic field dependence of the 72 meV (E-2g mode) and the pair-breaking peak around 100 cm(-1) which corresponds to sigma-band gap. Intensity enhancement of Raman features around 800 cm(-1) accompanied with broadening in the line shape of E-2g mode has been observed in some polycrystalline samples at 0 GPa. Results are compared with previous Raman study under hydrostatic pressure. (c) 2006 Elsevier B.V. All rights reserved

Isotope effect on the optical phonons of YBa₂Cu₄O₈ studied by far-infrared ellipsometry and Raman scattering

The phonon spectra of YBa₂Cu₄O₈ polycrystalline samples with different isotope substitution for Ba, Cu, and O have been studied using far-infrared ellipsometry and Raman scattering. The observed isotope shifts of Raman- and infrared-active phonons provide insight into their relative Ba, Cu, and O normal mode content. This allows us to examine mode eigenvectors obtained from lattice dynamical calculations using ab initio electronic structures based on the full potential linear muffin-tin-orbital within the local density approximation. Our Raman results demonstrate that the 104 cm⁻¹ A