Evidence for decay of spin waves above the pseudogap of underdopedYBa2Cu3O6.35

Abstract

The magnetic spectrum at high energies in heavily underdoped YBa 2 Cu 3 O 6.35 ͑T c =18 K͒ has been determined throughout the Brillouin zone. At low energy, the scattering forms a cone of spin excitations emanating from the antiferromagnetic ͑0.5,0.5͒ wave vector with an acoustic velocity similar to that of insulating cuprates. At high-energy transfers, below the maximum energy of 270 meV at ͑0.5,0͒, we observe zone-boundary dispersion much larger and spectral weight loss more extensive than in insulating antiferromagnets. Moreover, we report phenomena not found in insulators, an overall lowering of the zone-boundary energies and a large damping of ϳ100 meV of the spin excitations at high energies. The energy above which the damping occurs coincides approximately with the gap determined from transport measurements. We propose that as the energy is raised, the spin excitations encounter an extra channel of decay into particle-hole pairs of a continuum that we associate with the pseudogap.

Two-dimensional incommensurate and three-dimensional commensurate magnetic order and fluctuations in La2−xBaxCuO

“…Inelastic neutron scattering studies are consistent with an "hour glass" dispersion, wherein low energy spin excitations disperse out of IC wavevectors and merge or nearly-merge at the C wavevector to form a resonant spin excitation [23][24][25][26][27][28][29][30] . At higher energies, the excitations disperse out from the C wavevector, before turning over near the Brillouin zone boundaries 23,31,32 .…”

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

“…3(f) 14 suggests that our sample might be close to the magnetic quantum critical point resulting from the spin-glass phase. We also note that the low energy scale around 2.0 meV in our sample is in the superconducting state, different from those in the lowerdoping YBCO 15,16,33 .…”

“…Although such behavior is remarkably similar to those of optimally doped YBCO and thus suggests a common microscopic origin 4,5 , the situation in the underdoped YBCO and LSCO differs quite dramatically. For deeply underdoped YBa 2 Cu 3 O 6.353 (T c = 18 K), the spin excitations spectra become gapless and resonance-less; however, they are dominated by commensurate spin excitations and a central diffusive mode associated with a spin-glass phase 14,15,16 . On the other hand, spin excitations in the underdoped La 1.875 Ba 0.125 CuO 4 are also gapless and resonance-less but display an hourglass dispersion with incommensurate scattering extending to zero energy 5,17,18 .…”

Weak spin interactions in Mott insulating La2O2Fe2OSe2McCabe1, Stock2, Rodriguez3 et al. 2014Phys. Rev. BSelf Cite4527630View full textAdd to dashboardCite

“…Analogous to the cuprates, the spin exchange constants and spin-wave dispersions in these parent compounds are large, extending up to energy transfers of ∼100 meV, reflecting strong Fe-Fe coupling [19][20][21][22][23][24]. Electronic structure calculations for La 2 O 2 Fe 2 OSe 2 suggest similar exchange constants to the pnictides but with considerable electronic band narrowing [14].…”

“…This is remarkably small when compared with Mott insulating La 2 CuO 4 and YBa 2 Cu 3 O 6+x (with a bandwidth of over 300 meV) and with the parent phases of the pnictides (the top of the band in BaFe 2 As 2 is ∼100 meV and ∼150 meV in CaFe 2 As 2 ) or the chalcogenide Fe 1+x Te (where excitations extend up to ∼150-200 meV) [19][20][21]23,24]. The small bandwidth observed for La 2 O 2 Fe 2 OSe 2 implies that magnetic exchange interactions are about an order of magnitude smaller than in the cuprates and pnictides.…”