Superconductivity, antiferromagnetism, and neutron scattering

Abstract

High-temperature superconductivity in both the copper-oxide and the iron-pnictide/chalcogenide systems occurs in close proximity to antiferromagnetically ordered states. Neutron scattering has been an essential technique for characterizing the spin correlations in the antiferromagnetic phases and for demonstrating how the spin fluctuations persist in the superconductors. While the nature of the spin correlations in the superconductors remains controversial, the neutron scattering measurements of magnetic excitations over broad ranges of energy and momentum transfer provide important constraints on the theoretical options. We present an overview of the neutron scattering work on high-temperature superconductors and discuss some of the outstanding issues.

Antiferromagnetic order and spin dynamics in iron-based superconductors

“…In copper oxide superconductors, superconductivity can only be induced by electron and hole doping into the nearly perfect CuO 2 plane, and impurity substitution at the Cu sites by other elements dramatically suppresses superconductivity (Armitage et al, 2010;Fujita et al, 2012;Kastner et al, 1998;Kivelson et al, 2003;Tranquada et al, 2014). The situation is much different for iron pnictides.…”

“…For copper oxides, superconductivity can be induced by charge carrier doping (electrons or holes) into the CuO 2 , resulting complicated phase diagrams with many incipient states competing with superconductivity (Armitage et al, 2010;Fujita et al, 2012;Kastner et al, 1998;Kivelson et al, 2003;Tranquada et al, 2014). The undoped copper oxides such as La 2 CuO 4 (Vaknin et al, 1987) and YBa 2 Cu 3 O 6+x (Tranquada et al, 1988) are simple antiferromagnets with the neighboring spins oppositely aligned.…”

“…The undoped copper oxides such as La 2 CuO 4 (Vaknin et al, 1987) and YBa 2 Cu 3 O 6+x (Tranquada et al, 1988) are simple antiferromagnets with the neighboring spins oppositely aligned. When holes are doped into the parent compounds, the static AF order is gradually suppressed, but spin excitations (or short-range spin fluctuations) survive across the entire superconducting dome and couple with superconductivity via a collective magnetic excitation termed neutron spin resonance (Eschrig, 2006;Fujita et al, 2012;Tranquada et al, 2014). However, inelastic neutron scattering experiments designed to study the doping evolution of spin excitations were only carried out on the La 2−x Sr x CuO 4 family of cuprates across the entire phase diagram from the undoped parent compounds to heavily overdoped non-superconducting samples (Lipscombe et al, 2007;Wakimoto et al, 2007).…”

Electron doping evolution of the neutron spin resonance inNaFe1−xCoxAs

“…Regardless of the dramatic differences in the ground states of their parent compounds and the microscopic origins of magnetism in different families of unconventional superconductors, inelastic neutron scattering experiments have revealed that superconductivity induces a collective magnetic excitation, termed neutron spin resonance, near the antiferromagnetic (AF) ordering wave vector of their parent compounds [4][5][6][7][8] . Experimentally, the resonance occurs at an energy E r and enhances dramatically below T c like the superconducting order parameter.…”

Neutron scattering studies of spin-phonon hybridization and superconducting spin gaps in the high-temperature superconductorLa2−x(Sr,Ba)xCuOWagman1, Carlo2, Gaudet3 et al. 2016Phys. Rev. B13921View full textAdd to dashboardCite

“…This notation implies a pseudotetragonal unit cell that is both convenient and appropriate given the relatively small orthorhombicity present in these materials [16][17][18][19] . The quasi-2D spin excitations are also known to be highly dispersive and to extend to energies ∼ 200 -300 meV depending on the precise level of doping [20][21][22][23] . Recent time-of-flight neutron scattering on lightly doped, x = 0.035, non-superconducting LBCO has revealed very interesting resonant enhancement of the magnetic spectral weight as a function of energy, that is co-incident with the low energy crossings of the highly dispersive spin excitations with weakly dispersive optic phonons 19 .…”