Dynamic stripes and resonance in the superconducting and normal phases ofYBa2Cu3O

Abstract

We describe the relation between spin fluctuations and superconductivity in a highly-ordered sample of YBa2Cu3O6.5 using both polarized and unpolarized neutron inelastic scattering. The spin susceptibility in the superconducting phase exhibits one-dimensional incommensurate modulations at low-energies, consistent with hydrodynamic stripes. With increasing energy the susceptibility curves upward to a commensurate, intense, well-defined and asymmetric resonance at 33 meV with a precipitous high-energy cutoff. In the normal phase, which we show is gapless, the resonance remains surprisingly strong and persists clearly in Q scans and energy scans. Its similar asymmetric spectral form above Tc=59 K suggests that incoherent superconducting pairing fluctuations are present in the normal state. On cooling, the resonance and the stripe modulations grow in well above Tc below a temperature that is comparable to the pseudogap temperature where suppression occurs in local and low-momentum properties. The spectral weight that accrues to the resonance is largely acquired by transfer from suppressed low-energy fluctuations. We find the resonance to be isotropically polarized, consistent with a triplet carrying ∼ 2.6 % of the total spectral weight of the Cu spins in the planes.

Quantum spin excitations through the metal-to-insulator crossover inYBa2Cu3O6+y

“…3(a). While the χ ′′ (Q, ω) at 55 K increases linearly withhω, consistent with the energy dependence of the normal state dynamics susceptibility in other metallic ground state YBCO 7,8,10 Fig. 3(e) gives Q-scans along the [H, H, 2] direction, which is the position expected for the central diffusive mode 15 .…”

“…However, the S(Q, ω) peak intensity for hω = 1 meV is larger at T = 55 K than that at 5 K. To further study the low energy spin fluctuations, we measured the energy dependence of the scattering at the peak Q = (0.5, 0.5, 1.8) and background Q = (0.36, 0.36, 1.8) positions for the acoustic mode 6,7,8,9,10 . The scattering function S(Q, ω) at different temperatures can then be estimated by subtracting the background scattering from the peak position as shown in Fig.…”

“…The magnetic excitation spectra show an "hourglass"-like dispersion with the resonance at the saddle point 9,10,11 . The energies of the mode (E R ) and the spin gap (E gap ) track T c 's as y is varied, and the opening of the spin gap below T c is compensated in part by the spectral weight gain of the resonance 4,5,7,8,9,10 . In the case of optimally doped La 2−x Sr x CuO 4 (LSCO), inelastic neutron scattering measurements reveal that spin excitations also display an hourglass dispersion with a spin gap and incommensurate resonance below T c 4,5,12,13 .…”

“…For YBa 2 Cu 3 O 6+y (YBCO) with y ≥ 0.5, the prominent features in spin fluctuations spectra at the superconducting state include a collective magnetic excitation known as the "resonance" mode, which is sharp in energy and centered at the AF ordering wavevector Q = (1/2, 1/2), and a superconducting spin gap 4,5,6,7,8,9,10,11 . The magnetic excitation spectra show an "hourglass"-like dispersion with the resonance at the saddle point 9,10,11 .…”

Фрустрированный $J_{1}$-$J_{2}$-$J_{3}$ Квантовый Двумерный Антиферромагнетик В Сферически-Симметричном Самосогласованном Подходе

“…Один из наиболее ярких экспериментальных результатов -это скейлинг χ 2D : за-висимость χ 2D от ω и T хорошо (а при малом допировании -практически идеально) описывается эмпирическим скейлинговым законом [1], [36], [43]- [46] Покажем, что в рамках СССП (15) оказывается возможным аналитически иссле-довать скейлинг восприимчивости χ 2D (ω).…”