Neutron scattering studies of spin-phonon hybridization and superconducting spin gaps in the high-temperature superconductorLa2−x(Sr,Ba)xCuO

Abstract

We present time-of-flight neutron-scattering measurements on single crystals of La2−xBaxCuO4 (LBCO) with 0 ≤x≤ 0.095 and La2−xSrxCuO4 (LSCO) with x = 0.08 and 0.11. This range of dopings spans much of the phase diagram relevant to high temperature cuprate superconductivity, ranging from insulating, three dimensional (3D) commensurate long range antiferromagnetic order, for x ≤ 0.02, to two dimensional (2D) incommensurate antiferromagnetism co-existing with superconductivity for x ≥ 0.05. Previous work on lightly doped LBCO with x = 0.035 showed a clear resonant enhancement of the inelastic scattering coincident with the low energy crossings of the highly dispersive spin excitations and quasi-2D optic phonons. The present work extends these measurements across the phase diagram and shows this enhancement to be a common feature to this family of layered quantum magnets. Furthermore we show that the low temperature, low energy magnetic spectral weight is substantially larger for samples with non-superconducting ground states relative to any of the samples with superconducting ground states. Spin gaps, suppression of low energy magnetic spectral weight as a function of decreasing temperature, are observed in both superconducting LBCO and LSCO samples, consistent with previous observations for superconducting LSCO.

Gapless spin excitations in superconducting La2−xCa1+xCu2O6 with Schneeloch1, Zhong2, Stone3 et al. 2019Phys. Rev. BSelf Cite5130View full textAdd to dashboardCite

“…There is also an enhancement of χ (ω) at ∼ 20 meV in the SC55 sample compared to the NSC sample. This feature appears to be similar to the one identified previously in lightly-doped La 2−x Ba x CuO 4 by Wagman et al [43], observed in other La-214 samples [19,22], and attributed to spin-phonon hybridization [65]. The apparent absence of such a feature in the NSC sample suggests that the coupling between spin-excitations and phonons requires a sufficient level of hole doping.…”

Spin excitations coupled with lattice and charge dynamics in La$_{2-x}$Sr$_{x}$CuO$_4$

“…They argued that the intensity enhancement was associated with a modification of the exchange coupling constant J using a vibration mode of Cu-O-Cu bond. A similar peak-structure was also reported for the UD region of LBCO and LSCO 21 . Motivated studies presented above, the purpose of this study is to gain insight into the relationship between intensity enhancement and superconductivity relating to spin excitations and clarifying the necessary conditions for intensity enhancement.…”

Reinvestigation of crystal symmetry and fluctuations in La$_2$CuO$_4$

“…Our measurements also capture the antiferromagnetic spin waves. We check for a possible interaction between the spin waves and a low-energy optical mode of the type seen in Ba-and Sr-doped LCO [45,46], but find no evidence for such an interaction in the commensurate antiferromagnet, consistent with another recent neutron study [47].…”

“…In studies of antiferromagnetic spin fluctuations in La 2−x Ba x CuO 4 and La 2−x Sr x CuO 4 , Wagman et al [45,46] have identified evidence for spin-phonon coupling at energies in the range of 15-20 meV. We have observed a similar effect in our own samples of La 2−x Ba x CuO 4 [63] and La 2−x Sr x CuO 4 [64], and even in superconducting La 2−x Ca 1+x Cu 2 O 6 [65].…”