Composition Dependence of the In-Plane Cu-O Bond-stretching LO Phonon Mode in YBa₂Cu₃O₆₊ₓ

An inelastic pulsed neutron scattering study was performed on the dependence of the dispersion and spectral intensity of the in-plane Cu-O bond-stretching LO phonon mode on doped charge density. The measurements were made in the time-of-flight mode with the multiangle position sensitive spectrometer of the ISIS facility on single crystals of YBa2Cu3O6+x (x=0.15, 0.35, 0.6, 0.7, and 0.95). The focus of the study is the in-plane Cu-O bond-stretching LO phonon mode, which is known for strong electron-phonon coupling and unusual dependence on composition and temperature. It is shown that the dispersions for the samples with x=0.35, 0.6, and 0.7 are similar to the superposition of those for x=0.15 and 0.95 samples, and cannot be explained in terms of the structural anisotropy. It is suggested that the results are consistent with the model of nanoscale electronic phase separation, with the fraction of the phases being dependent on the doped charge density

Composition dependence of the in-plane Cu-O bond-stretching LO phonon mode in YBa2Cu3O6+x.

An inelastic pulsed neutron scattering study was performed on the dependence of the dispersion and spectral intensity of the in-plane Cu-O bond-stretching LO phonon mode on doped charge density. The measurements were made in the time-of-flight mode with the multiangle position sensitive spectrometer of the ISIS facility on single crystals of YBa2Cu3O6+x (x=0.15, 0.35, 0.6, 0.7, and 0.95). The focus of the study is the in-plane Cu-O bond-stretching LO phonon mode, which is known for strong electron-phonon coupling and unusual dependence on composition and temperature. It is shown that the dispersions for the samples with x=0.35, 0.6, and 0.7 are similar to the superposition of those for x=0.15 and 0.95 samples, and cannot be explained in terms of the structural anisotropy. It is suggested that the results are consistent with the model of nanoscale electronic phase separation, with the fraction of the phases being dependent on the doped charge density. © 2008, American Physical Societ

Obliquity-driven mountain permafrost-related fluvial magnetic susceptibility cycles in the Quaternary mid-latitude long-term (2.5 Ma) fluvial Maros Fan in the Pannonian Basin

Magnetic susceptibility (SUS) of the Quaternary long-term mid-latitude Maros fluvial fan (Pannonian Basin) was recorded to understand the stratigraphic features of source proximal fluvial depositional settings. Three fully cored 500 m deep boreholes were sampled with 0.5 m intervals; low field and frequency dependent magnetic susceptibility were measured, and complementary hysteresis and SEM-EDAX investigations were performed on selected samples. Logged SUS data were also used to log correlations established by a comparison of wireline log and laboratory measurements. The time-series analyses of the SUS records reveal the apparent occurrence of the ~41 ka frequency together with the customary ~100 ka cycles. Towards the source-distal sections the intensity of the ~41 ka cycles decreases, while that of the ~100 ka cycles remains strong. Stratigraphic and spectral similarities were observed between fluvial fan and loess SUS records ; however, based on complementary magnetic data, the magnetic phase of the Maros Fan sections is related to the detrital magnetite that originates from the catchment during early postglacial permafrost degradations. The amplification of the ~41 ka cycles revealed can be attributed to the very high SUS values in source proximal settings and to the special stratigraphic feature of the distributive fluvial settings. This comprises the increased avulsion frequency on the fluvial fans in ‘glacial recession periods’, in concert with the ‘early postglacial’ occurrence of the permafrost-related magnetite originated from the catchment. As a local phenomenon, this is significant since it records the obliquity-driven variations of permafrost development in a catchment. However, fluvial and alluvial fans are widespread depositional landforms within the Eurasian Mountains and were possibly the same during the Quaternary deglaciations. Thus, obliquity-driven SUS variations of source-proximal fan deposits attached or adjacent to regions of loess deposition should also be considered when scanning for potential source material of aeolian deposits

Fluvial magnetic susceptibility as a proxy for long-term variations of mountain permafrost development in the Alp-Carpathian region

Low field magnetic susceptibility (MS) records of 13 reference boreholes representing the whole Quaternary fluvial succession of the Great Hungarian Plain were correlated to develop regional stratigraphy. Data from 12 of the boreholes were published between 2016 and 2020, the Tiszainoka borehole is newly reported in this paper. Eleven magnetic susceptibility cycles, capped by the most emergent master MS peaks (MP) and bordered by susceptibility termination surfaces, have been correlated. Supported by the already evaluated palaeomagnetic reversals and instability events, MPs have been correlated to the cold stages of the marine isotope stage (MIS) records. MPs represent MIS 104, 100, 98, 82, 60, 52, 34(-36) and 26 of increased heavy oxygen isotope value, constituting the significant Early Pleistocene glaciations, and MIS 18, 16, 12, 8, 6 and 2 mostly representing the substantial Middle and Upper Pleistocene European glaciation events. The interpretation of early postglacial fluvial MS maxima, that emphasise the escape of weathering-sensitive magnetic minerals from the catchment area triggered by the thawing of mountain permafrost, is confirmed by the correlation of MPs to the changes of the global ice volume. As a result, fluvial MS records can be considered as a proxy for mountain permafrost development in the catchment areas. Regional correlations confirmed that the Körös and Jászság Basins and the Makó Trough are sites of almost continuous fluvial records of the past 2600 ka. Thus, the Pannonian Quaternary fluvial succession is sufficiently complete to provide satisfactory record of mountain permafrost development of the Alp-Carpathian region the latter being a globally relevant European representative of mid-latitude mountain regions. The similarity of the Pannonian fluvial MS succession as a permafrost proxy to the marine ice-rafted detritus (IRD) and Chinese loess/palaeosol MS records promises the possibility of comparative investigations of globally relevant proxy records and mid-latitude mountain permafrost development