Reconciliation of local and long-range tilt correlations in underdopedLa2−xBaxCuO4(0≤x

Abstract

A long standing puzzle regarding the disparity of local and long range CuO6 octahedral tilt correlations in the underdoped regime of La2−xBaxCuO4 is addressed by utilizing complementary neutron powder diffraction and inelastic neutron scattering (INS) approaches. Long-range and static CuO6 tilt order with orthogonally inequivalent Cu-O bonds in the CuO2 planes in the low temperature tetragonal (LTT) phase is succeeded on warming through the low-temperature transition by one with orthogonally equivalent bonds in the low temperature orthorhombic (LTO) phase. In contrast, the signatures of LTT-type tilts in the instantaneous local atomic structure persist on heating throughout the LTO crystallographic phase on the nanoscale, although becoming weaker as temperature increases. Analysis of the INS spectra for the x = 1/8 composition reveals the dynamic nature of the LTT-like tilt fluctuations within the LTO phase and their 3D character. The doping dependence of relevant structural parameters indicates that the magnitude of the Cu-O bond anisotropy has a maximum at x = 1/8 doping where bulk superconductivity is most strongly suppressed, suggesting that the structural anisotropy might be influenced by electron-phonon coupling and the particular stability of the stripe-ordered phase at this composition. The bond-length modulation that pins stripe order is found to be remarkably subtle, with no anomalous bond length disorder at low temperature, placing an upper limit on any in-plane Cu-O bondlength anisotropy. The results further reveal that although appreciable octahedral tilts persist through the high-temperature transition and into the high temperature tetragonal (HTT) phase, there is no significant preference between different tilt directions in the HTT regime. This study also exemplifies the importance of a systematic approach using complementary techniques when investigating systems exhibiting a large degree of complexity and subtle structural responses.

Combined single crystal polarized XAFS and XRD at high pressure: probing the interplay between lattice distortions and electronic order at multiple length scales in highTccuprates

“…At ambient pressure the long range LTT symmetry is also captured in the local structure ( Fig. 3(a,b)), in agreement with previous XAFS and PDF work [41,47,48]. The pressure dependence of the (100) diffraction peak also reproduces previous work ( Fig.…”

Staging superstructures in high-TcSr/O codopedLa2−xSrxCuO4+yRay1, Andersen2, Jensen3 et al. 2017Phys. Rev. B5040View full textAdd to dashboardCite

“…A similar gradual transition as seen in the Bmab volume of our samples has also been observed in similar systems on peak positions which were forbidden according to the average or majority structure of the sample [17,29]. In the chemically similar compound La 2−x Ba x CuO 4 octahedral tilt fluctuations can average to look like low-temperature orthorhombic (LTO) structure [30] which may be related to our case. For our range of Sr doping values, both staging and Bmab transition temperatures are below the Bmab transition temperature of the corresponding oxygen-stoichiometric compound [31] (an overview is shown in the Supplemental Material [23]).…”

Charge density wave memory in a cuprate superconductor

“…It is, consequently, highly intriguing that the CDW memory persists well above this transition. Figure 4 shows a sharp cross-over from near-complete to minimal reproduciblity at 240(3) K. This threshold temperature coincides with the LTO phase transition at 236(5) K [34,39], implying that the pinning configuration is effectively determined at this phase transition, where octahedral tilts break the four-fold symmetry of copper-oxide planes. At this LTO transition LTO twin domain boundaries form.…”

“…The speckle modulations on top of the peak envelope arise from coherent interference between different CDW domains. The average size and elongated shape of the speckles on the detector is determined primarily (a) Temperature dependence of normalized CDW peak intensity (blue) and lattice parameters reproduced from[34] (orange). The CDW transition coincides with the LTT structural transition at TLTT.…”