Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 0909.3904

Angular Dependence of X-ray Absorption Spectrum for Field-aligned Fe-based Superconductors

B. C. Chang·Y. B. You·T. J. Shiu·M. F. Tai·H. C. Ku·Y. Y. Hsu·L. Y. Jang·J. F. Lee·Z. Wei·K. Q. Ruan·X. G. Li
View original source ↗Read source document ↗Export metadata ↓

Abstract

Anisotropic Fe K-edge and As K-edge X-ray absorption near edge spectrum (XANES) measurements on superconducting (T_c = 52 K) (Sm_{0.95}La_{0.05})FeAs(O_{0.85}F_{0.15}) field-aligned microcrystalline powder are presented. The angular dependence of Fe pre-edge peak (dipole transition of Fe-1s electrons to Fe-3d/As-4p hybrid bands) relative to the tetragonal ab-plane of aligned powder indicates larger density of state (DOS) along the c-axis, and is consistent with the LDA band structure calculation. The anisotropic Fe K-edge spectra exhibit a chemical shift to lower energy compared to FeO which are closely related to the itinerant character of Fe^{2+}-3d^6 orbitals. The anisotropic As K-edge spectra are more or less the mirror images of Fe K-edge due to the symmetrical Fe-As hybridiztion in the FeAs layer. Angular dependence of As main peak (dipole transition of As-1s electrons to higher energy hybrid bands) was observed suggesting character of As-4d e_g orbitals.

Explore related subjects

cond-mat.supr-con

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

B. C. Chang, Y. B. You, T. J. Shiu, M. F. Tai, H. C. Ku, Y. Y. Hsu, L. Y. Jang, J. F. Lee, Z. Wei, K. Q. Ruan, X. G. Li. 2009-09-22. Angular Dependence of X-ray Absorption Spectrum for Field-aligned Fe-based Superconductors. https://doi.org/10.1103/physrevb.80.165108

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Theoretical Prediction of Optimal $T_c$ and Fermi Pockets in Nickelate Superconductors

High-pressure bilayer $La_{3-x}Sm_{x}Ni_{2}O_{7-δ}$ (LSNO) reaches a record $T_c=96 K$, triggering wide discussion on the $T_c$ ceiling of nickelate superconductors. We show monoclinic and tetragonal LSNO share the same octahedral quantum-well motif governing $T_c$ with $YBa_{2}Cu_{3}O_{7-δ}$ (YBCO). Using the Planckian quantum-well scaling $T_c = Λ/ξ^{2}$ ($ξ$: lattice-modulated quantum-well depth), we obtain $T_c=93.4 K$ and $97.1 K$ for monoclinic and tetragonal LSNO, matching experimental values $92 K$ and $96 K$. Despite distinct stoichiometry and global symmetry ($P2_1/m$ for LSNO, $Pmmm$ for orthorhombic YBCO), both systems have nearly identical $ξ$ ($3.6629$ angstrom vs. $3.6720$ angstrom) and consistent $T_c$ responses. Further calculations yield a universal $T_c$ limit $\sim100 K$ for rare-earth nickelates, irrespective of stacking sequences. We examine four nickelate multilayer stacking variants: 2222 (pure bilayer), 1212 (alternating single-bilayer), 2323 (bilayer-trilayer), and 1313 (single-trilayer). Mirror symmetry breaking of coupled twin quantum wells, unique to bilayer nickelates, dictates $γ$ Fermi pocket formation and ambient-pressure superconductivity. We further prove Fermi surfaces constitute a hologram of quantum-well electrons, establishing intrinsic links between quantum-well symmetry breaking, Fermi pocket structural evolution, and superconducting properties.

cond-mat.supr-con↗
arXiv2026

Enhanced superconductivity in palladium hydrides by non-perturbative electron-phonon effects

Palladium hydrides exhibit the largest isotope-effect anomaly in superconductivity: replacing hydrogen with heavier isotopes increases the superconducting critical temperature. Although this behavior is commonly attributed to strong anharmonic hydrogen vibrations, \textit{ab initio} treatments have so far incorporated anharmonic effects only through phonon renormalization, neglecting non-linear contributions to the electron-phonon interaction vertices. While such approaches reproduce the anomalous isotope trend, they severely underestimate the critical temperatures. Here, we show that non-linear electron-phonon coupling is essential in palladium hydrides. A straightforward inclusion of higher-order perturbative terms leads to a qualitative breakdown: the critical temperature is overestimated and the isotope anomaly is lost. We therefore adopt a non-perturbative framework based on an explicit evaluation of the ion-mediated electron-electron interaction, enabling anharmonic effects to be treated consistently in both the phonon spectra and the interaction vertices. Applied to PdH and PdD, it restores the anomalous isotope effect and brings calculated critical temperatures into significantly improved agreement with experiments.

cond-mat.supr-con↗
arXiv2026

Optical manifestations of loop currents in Haldane's model and in time-reversal-breaking superconductors

We present a theoretical study of optical manifestations of loop currents in Haldane's model and in time-reversal-breaking superconductors. For Haldane's model, we calculate the expectation value of loop currents in terms of model parameters and relate it with the integrated optical spectral weight for the frequency-dependent ac Hall conductivity. Thus, experimental measurements of the latter can provide information about the presence and magnitude of steady loop currents in the system. Then we elaborate on loop currents in a chiral superconductor on the honeycomb lattice, studied earlier by Brydon et al. (2019). We demonstrate that a sharp optical absorption peak in the ac Hall conductivity originates from excitations between the lower and upper Dirac bands, activated by the time-reversal-breaking superconductivity. The frequency of the peak is twice the energy difference between the Fermi level and the Dirac point. The optical spectral weight of the peak is directly related to the magnitude of loop currents induced in the unit cells by the chiral superconducting pairing, in similarity to Haldane's model.

cond-mat.supr-con↗