Pressure dependence of the electronic structure and spin state in Fe1.01Se superconductors probed by x-ray absorption and x-ray emission spectroscopy

Abstract

Pressure dependence of electronic structures and spin states of iron-chalcogenide Fe 1.01 Se superconductors up to ∼66 GPa has been investigated with x-ray emission spectra and x-ray absorption spectra with partial-fluorescence yield. The intensity of the pre-edge peak at energy of ∼7112.7 eV of the Fe K-edge x-ray absorption spectrum of Fe 1.01 Se decreases progressively with pressure up to ∼10 GPa. A new prepeak at energy of ∼7113.7 eV develops for pressure above ∼13 GPa, indicating formation of a new phase. The experimental and the calculated Fe K-edge absorption spectra of Fe 1.01 Se using the FDMNES code agree satisfactorily. The larger compression accompanied by significant distortion around the Fe atoms along the c axis in Fe 1.01 Se upon applying pressure suppresses the Fe 3d-Se 4p and Fe 4p-Se 4d hybridization. The applied pressure suppresses the nearest-neighbor ferromagnetic superexchange interaction and enhances spin fluctuations on the Fe sites in Fe 1.01 Se. A discontinuous variation of the integrated absolute difference values of the Kβ emission line was observed, originating from a phase transition of Fe 1.01 Se for a pressure >12 GPa. Fe 1.01 Se shows a small net magnetic moment of Fe 2+ at ambient pressure, probably arising from strong Fe-Fe spin fluctuations. The satellite line Kβ was reduced in intensity upon applying pressure and became absent for pressure >52 GPa, indicating a continuous reduction of the spin moment of Fe in Fe 1.01 Se superconductors. The experimental results provide insight into the spin state of Fe 1.01 Se superconductors under pressure.

Fractional Quantum Hall Effect in Weyl Semimetals

“…Apart from giving rise to topological response and protected surface states, anomalies can also place strong restrictions on the possible effect of electron-electron interactions. In particular, anomalies prohibit opening a gap without either breaking the protecting symmetry or creating an exotic state with topological order, as was recently discussed extensively in the context of strongly-interacting 2D surface states of 3D symmetryprotected topological orders [20,21] in bosonic [22] and fermionic [23][24][25][26][27][28][29][30] systems. In this Letter, we aim to answer analogous questions in the case of a 3D Weyl semimetal: can one open a gap in a Weyl semimetal without breaking translational or charge conservation symmetries while preserving the chiral and the gravitational anomalies, which lead to the electrical and thermal Hall conductivities of Eqs.…”

Origin of Pressure-induced Superconducting Phase in KxFe2−ySe2 studied by Synchrotron X-ray Diffraction and Spectroscopy

“…The purpose of this work is to reveal both the crystal and electronic structures of K x Fe 2− y As 2 under pressure to clarify the origin of the two superconducting domes. XES technique has made it possible to probe local magnetic moment under pressure by detecting Fe Kβ emission spectra for iron-based superconductor2223242526. We also performed the bulk sensitive x-ray absorption (XAS) measurements with partial fluorescence (PFY) mode at the Fe K absorption edge27.…”

Topological properties of a generalized spin–orbit-coupled Su–Schrieffer–Heeger model

“…There have been several models to realize topological insulators/superconductors in two and three dimensions [1,2]. Also, one-dimensional (1D) systems, for instance, Su-Schrieffer-Heeger (SSH) chain [11] in the presence of sublattice and/or spin degrees of freedom are capable of exhibiting nontrivial phases providing topological insulators [12][13][14][15][16][17][18]. In this framework, several theoretical works have been dedicated to investigating effects of spin-orbit coupling [19], Zeeman magnetic field [20,21], and curvature [22] on topological properties of 1D superlattices by characterizing phase transition points [23].…”