Quantum magnetic excitations from stripes in copper oxide superconductors

Abstract

In the copper oxide parent compounds of the high-transition-temperature superconductors the valence electrons are localized--one per copper site--by strong intra-atomic Coulomb repulsion. A symptom of this localization is antiferromagnetism, where the spins of localized electrons alternate between up and down. Superconductivity appears when mobile 'holes' are doped into this insulating state, and it coexists with antiferromagnetic fluctuations. In one approach to describing the coexistence, the holes are believed to self-organize into 'stripes' that alternate with antiferromagnetic (insulating) regions within copper oxide planes, which would necessitate an unconventional mechanism of superconductivity. There is an apparent problem with this picture, however: measurements of magnetic excitations in superconducting YBa2Cu3O6+x near optimum doping are incompatible with the naive expectations for a material with stripes. Here we report neutron scattering measurements on stripe-ordered La1.875Ba0.125CuO4. We show that the measured excitations are, surprisingly, quite similar to those in YBa2Cu3O6+x (refs 9, 10) (that is, the predicted spectrum of magnetic excitations is wrong). We find instead that the observed spectrum can be understood within a stripe model by taking account of quantum excitations. Our results support the concept that stripe correlations are essential to high-transition-temperature superconductivity.

Energy gaps in the failed high-Tc superconductor La1.875Ba0.125CuO4

“…Recently, although some experiments in the superconducting state indicate a distinction between the superconducting gap and pseudogap 10-14 , others in the normal state, either by extrapolation from high-temperature data 15 The first high-T c superconductor discovered, La 2−x Ba x CuO 4 (LBCO), holds a unique position in the field because of an anomalously strong bulk T c suppression near x = 1/8. Right around this 'magic' doping level, scattering experiments by neutrons 18,19 and X-rays 20 find a static spin and charge (stripe) order. By itself, this observation raises a series of intriguing questions: whether the stripe order is a competing order that suppresses the superconductivity in LBCO-1/8; if the answer is positive, which aspect, the pairing strength or the phase coherence, is involved in the T c suppression and how this mechanism applies to other dopings or families.…”

Magnetic Excitation in Lightly-Doped Bi2.4Sr1.6CuO6+y

“…since IC peaks exist along [1,1] direction measured by triple axis spectrometer, and not existence along [1,1] direction. In the low-energy region below 4 meV, a pair of IC peaks along the latter direction was confirmed by triple-axis spectrometer, while a single broad peak corresponding to the tails of intensity of IC peaks is observed along the former direction [4].…”

“…Clear enhancement of magnetic intensity can be seen around the AF zone center of (0.5, 0.5) and its intensity distribution from the (0.5, 0.5) looks isotropic. In order to characterize the isotropy of the intensity distribution, we further sliced the data along [1,1] and [1,1] directions through (0.5, 0.5), At each energy, the isotropic commensurate peak centered at (0.5, 0.5) was observed. Solid lines are results of least-square fitting by assuming single Gaussian function with a background of which intensity is proportional to Q 2 (∝ h 2 + k 2 ).…”

“…Neutron scattering experiments on La 2−x Sr x CuO 4 (LSCO) clarified the doping evolution of spin excitation changing from the spin-wave excitation in the non-doped parent system to an hourglass-shaped one in the superconducting (SC) system [1]. Since the hourglass excitation can be seen in the SC phase of other family YBa 2 Cu 3 O 6+y (YBCO) and Bi 2 Sr 2 CaCu 2 O 8+y (Bi2212) [2,3], the existence of such a characteristic excitation is recognized to be universal in the hole-doped cuprate oxide.…”

Neutron Scattering Study of Spin Fluctuations in La2−xSrxCuO4 by Four-Dimensional Mapping of Neutron Cross-Sections Using the 4SEASONS Chopper Spectrometer

“…Using this technique, the spin fluctuations in the hole concentration range of superconductivity were demonstrated to show a characteristic "hour-glass" dispersion, where the magnetic signal disperses inward up to approximately 50 meV (= E cross ) and disperses outward above E cross [5,6]. Interestingly, two maxima have been reported in the dynamical magnetic susceptibility spectra of superconducting LSCO: at approximately 15 and 50 meV [7].…”