Spin dynamics in the high-T system YBa2Cu306+x: the heavily doped regime (original) (raw)

Spin dynamics in the high-Tc system YBa2Cu3O6+x

Physica B: Condensed Matter, 1992

We report on inelastic neutron scattering experiments carried out on single crystals of the YBaZCu,O,+, system. The spin dynamics has been systematically investigated in five typical regimes: the pure and doped AF states (x = 0.15, 0.37), the weakly doped (X = 0.45, 0.51, 0.53) and the heavily doped (X = 0.69, 0.92) metallic states which all exhibit a superconducting ground state. The hole doping strongly affects the AF order, dynamical AF correlations remain in the metallic state which, surprisingly, involves only in-plane spin components. An energy gap has been found in the spin excitation spectrum of any superconducting samples, however, it becomes weaker close to the I-M transition. A quite unusual T dependence of the spin excitation spectra was found.

High-energy spin excitations inYBa2Cu3O6.5

Physical Review B

Inelastic neutron scattering has been used to obtain a comprehensive description of the absolute dynamical spin susceptibility χ ′′ (q, ω) of the underdoped superconducting cuprate YBa 2 Cu 3 O 6.5 (T c = 52K) over a wide range of energies and temperatures (2 meV ≤hω ≤ 120 meV and 5K ≤ T ≤ 200K). Spin excitations of two distinct symmetries (even and odd under exchange of two adjacent CuO 2 layers) are observed which exhibit two different gaplike features (rather than a single "spin pseudogap"). The excitations show dispersive behavior at high energies.

Spin fluctuations in the metallic and superconducting states in the high-Tc system YBa2Cu3O6+x

Physica B: Condensed Matter, 1993

The spin dynamics in single-crystals of YBaaCu306+ x has been successfully investigated by inelastic neutron scattering experiments, as a function of temperature in the metallic state over the whole doping range from the weakly doped (x = 0.45, 0.51) to the heavily doped (x = 0.69, 0.92) and the overdoped (x = 1) regimes. Dynamical AF correlations remain in the metallic state but the in-plane correlation length becomes very short (~/a ~-0.8) as the doping increases. However, the AF coupling between the two CuO 2 layers is not affected, except in the overdoped regime. At low temperatures, the spin excitation spectrum exhibits an energy gap in any superconducting sample. Its value, EG/kT c ~-3.5, becomes much weaker close to the I-M transition, Moreover, a pseudo-gap persists above T c in the heavily doped regime. The results are compared with the magnetic excitation spectra found for the typical heavy fermion materials Cefu 6 and CeRu2Si 2.

Low-energy spin fluctuations in YBa2Cu3O6.1 and ErBa2Cu3O6+x A Cu (1) T1 NQR study

Physica C: Superconductivity, 1994

63Cu( 1 ) NQR signals and their relaxation have been measured in YBa2Cu306.1 and ErBa2CuaO6+x at temperatures between 10 K and 300 K. In YBa2Cu306.1 a peak is observed in the spin-lattice relaxation, T/-~, around 140 K. An explanation in terms of doped-hole motion is presented and alternative O (4)-O (5) diffusion mechanisms are critically discussed. In ErBa2Cu306+x the low-temperature T i-1 is dominated by magnetic fluctuations of Er; quantitative agreement is found when the correct ground state and magnetic dynamic properties of the rare earth are taken into account.

Incommensurate spin dynamics of high-Tc superconductor YBa2Cu3O7−δ

Journal of Physics and Chemistry of Solids, 1999

High energy inelastic neutron scattering measurements were performed in order to elucidate the wave vector and energy dependence of the spin dynamics in YBa 2 Cu 3 O 6.7 (T c 68 K) and YBa 2 Cu 3 O 7 (T c 93 K) by using pulsed neutron techniques. The incommensurability of spin dynamics was clearly observed for the under-doped compound. The peaks appear at (1/2d ,1/2,0) and (1/2,1/2^d ,0) around the antiferromagnetic zone center of (1/2,1/2,0). The incommensurability d is 0.11^0.01 (r.l.u.) for the lower energy region, and the incommensurate peaks seem to merge at about 39 meV. ᭧

Spin dynamics in the metallic state of the high-Tc superconducting system YBa2Cu3O6 + x

Physica B: Condensed Matter, 1995

The spin dynamics in single crystals of YBa2Cu306+ x has been successfully investigated, by inelastic neutron scattering (INS) experiments, as a function of temperature in the metallic state over the whole doping range from the weakly doped (x = 0.45, 0.51) to the heavily doped (x = 0.69, 0.83, 0.92) and the overdoped (x = 0.97, 1) regimes. Dynamical AF-correlations persist in all the metallic state. ActuallY, the imaginary part of the magnetic susceptibility X" consists of two contributions which have different doping and temperature dependence s. At low temperature, X" exhibits an energy gap in any superconducting samples which becomes much weaker close to the insulating-metallic transition. To emphasize the characteristic features of the spin dynamics in YBCO, INS results obtained by other groups are compared with our experiments. Several theoretical approaches, which intend to describe the energy line shape of the dynamical magnetic susceptibility; are also discussed.

Spin susceptibility in underdoped YBa2Cu3O6+x

Physical Review B - PHYS REV B, 2000

We report a comprehensive polarized and unpolarized neutron scattering study of the evolution of the dynamical spin susceptibility with temperature and doping in three underdoped single crystals of the YBa2Cu3O6+x high temperature superconductor: YBa2Cu3O6.5 (Tc=52 K), YBa2Cu3O6.7 (Tc=67 K), and YBa2Cu3O6.85 (Tc=87 K). The spin susceptibility is determined in absolute units at excitation energies between 1 and 140 meV and temperatures between 1.5 and 300 K. Polarization analysis is used extensively at low energies. Transitional matrix elements, including those between spin states, in a bilayer system such as YBa2Cu3O6+x can be generally classified into even and odd, according to the sign change under a symmetry operation that exchanges the layers, and both even and odd excitations are detected in YBa2Cu3O6.5 and YBa2Cu3O6.7. While the even spin excitations show a true gap which depends on doping, the odd spectrum is characterized by a weakly doping-dependent pseudogap. Both even and...

Neutron-scattering study of the dynamical spin susceptibility in YBa2Cu3O6.6

Physical review. B, Condensed matter, 1992

We report a detailed neutron-scattering study of the dynamical spin susceptibility in a single crystal of YBa&Cu306+, with x = 0.6 and T, = 53 K. The measurements cover the energy range from 5 to 50 meV, and temperatures from 10 to 100 K. It is shown that antiferromagnetic correlations between nearest-neighbor Cu02 layers are quite strong. As a result, only in-phase bilayer spin fluctuations are observed at low energies, with the out-of-phase fluctuations making a weak appearance at 40 meV. Within the two-dimensional (2D) Brillouin zone corresponding to a single layer, the imaginary part of the dynamical susceptibility g" (Q, e) exhibits a broad peak about the point corresponding to antiferromagnetic order Q&F with a width that is mildly energy dependent. At 10 K, g" (QAF, tu) has a rather sharp peak near 27 meV; integrating y" over the 2D magnetic Brillouin zone makes the peak in energy much broader. (We have verified that the falloff at high energies also occurs in a previously studied crystal with z = 0.5, T, = 50 K.) Although the amplitude at 5 meV and 10 K is near zero, considerable spectral weight is observed at energies well below the weak-coupling limit for 2E, where 6 is the superconducting gap. The temperature dependence of the 2D Q-integrated g" is well described by a simple function containing a temperature-independent energy gap of 9 meV. A study of the Q dependence of g" at her = 15 meV indicates that the signal falls off rather abruptly on moving away from QAF (compared to a simple Gaussian distribution). Measurements along two di6erent directions in the 2D zone suggest that the width of the distribution about QAF is anisotropic. These results are discussed in the context of current theoretical models.

Spin dynamics in the normal and superconducting states of YBa2Cu3O6+x

Physica C: Superconductivity, 1994

The spin dynamics of CuO2-1ayers in the high-Tc superconducting system YBa2Cu306÷ x has been extensively investigated by inelastic neutron scattering on single crystals. In this paper we will review the most important results recently obtained on the evolution of magnetic excitation spectra in the weakly, heavily and overdoped regimes, from both sides of T c.

Neutron scattering study of YBa2Cu3O6+x single crystals

Physica B: Condensed Matter, 1990

Inelastic neutron scattering studies of YBa,Cu,O,,, single crystals are reported. In the pure AF phase (x = 0.15, T, = 410 K) the ZD-character of the spin wave spectrum and the exchange parameters have been established. A small amount of p holes in CuO, planes (x = 0.37, T, = 180 K, nh = 1.8%) strongly modifies the spin dynamics at low q: strong damping of in-plane spin excitations and renormalization of the spin wave velocity. In the superconducting state (X = 0.45, T, = 34.8 K) we have found dynamical magnetic correlations and an anomalous decrease of the intensity at low energy in the vicinity of T.