Nearly Singular Magnetic Fluctuations in the Normal State of a High- T c Cuprate Superconductor

Abstract
Polarized and unpolarized neutron scattering was used to measure the wave vector– and frequency-dependent magnetic fluctuations in the normal state (from the superconducting transition temperature, T c = 35 kelvin, up to 350 kelvin) of single crystals of La 1.86 Sr 0.14 CuO 4 . The peaks that dominate the fluctuations have amplitudes that decrease as T −2 and widths that increase in proportion to the thermal energy, k B T (where k B is Boltzmann's constant), and energy transfer added in quadrature. The nearly singular fluctuations are consistent with a nearby quantum critical point.