Determining the Surface-To-Bulk Progression in the Normal-State Electronic Structure ofSr2RuO4by Angle-Resolved Photoemission and Density Functional Theory

Abstract

We revisit the normal-state electronic structure of Sr(2)RuO(4) by angle-resolved photoemission spectroscopy with improved data quality, as well as ab initio band structure calculations in the local-density approximation with the inclusion of spin-orbit coupling. We find that the current model of a single surface layer (√2×√2)R45° reconstruction does not explain all detected features. The observed depth-dependent signal degradation, together with the close quantitative agreement with the slab calculations based on the surface crystal structure as determined by low-energy electron diffraction, reveal that-at a minimum-the subsurface layer also undergoes a similar although weaker reconstruction. This model accounts for all features-a key step in understanding the electronic structure-and indicates a surface-to-bulk progression of the electronic states driven by structural instabilities. Finally, we find no evidence for other phases stemming from either topological bulk properties or, alternatively, the interplay between spin-orbit coupling and the broken symmetry of the surface.

Thermal Hall conductivity and topological transition in a chiralp-wave superconductor forSr2RuO4

“…At c-axis oriented surfaces of Sr 2 RuO 4 a lattice reconstruction occurs, whereby the RuO 6 octahedra rotate around their c-axis leading to the doubling of the unit * imai@phy.saitama-u.ac.jp cell [13,14]. We have pointed out recently that such a rotation may change the Fermi surface topology of the γ band pushing the Fermi energy through the van Hove points and in this way generate a Lifshitz transition between an electron-and hole-like shape [15].…”

Spin-Orbital Entanglement and the Breakdown of Singlets and Triplets inSr2RuO4Revealed by Spin- and Angle-Resolved Photoemission Spectroscopy

“…A resolution might come from the inclusion of spin-orbit (SO) coupling, which has been conjectured to play a key role in the normal-state electronic structure [13] and may be important when describing superconductivity as well. By mixing the canonical spin eigenstates, the relativistic SO interaction might play a fundamental role beyond simply lifting the degeneracy of competing pairing states [13][14][15][16][17].Thus far, the experimental study of SO coupling's effects on the electronic structure of Sr 2 RuO 4 has been limited to the comparison of band calculations against angle-resolved photoemission spectroscopy (ARPES) [13,[18][19][20][21] -no success has been obtained in observing experimentally either the strength of SO coupling or its implications for the mixing between spin and orbital descriptions. Here we probe this directly by performing spin-resolved ARPES [22], with circularly polarized light: by using the angular momentum inherent in each photon-along with electricdipole selection rules [23]-to generate spin-polarized photoemission from the SO mixed states.…”

“…Thus far, the experimental study of SO coupling's effects on the electronic structure of Sr 2 RuO 4 has been limited to the comparison of band calculations against angle-resolved photoemission spectroscopy (ARPES) [13,[18][19][20][21] -no success has been obtained in observing experimentally either the strength of SO coupling or its implications for the mixing between spin and orbital descriptions. Here we probe this directly by performing spin-resolved ARPES [22], with circularly polarized light: by using the angular momentum inherent in each photon-along with electricdipole selection rules [23]-to generate spin-polarized photoemission from the SO mixed states.…”

“…1(a), 1(b). This choice is dictated by the need to avoid any intensity contamination from the well-known surface reconstruction of Sr 2 RuO 4 [18][19][20], which leads to the detection of folded bands-preventing a clean spin-ARPES study-anywhere in the Brillouin zone except at the Γ point [24]. In addition, as explained below, this choice selects the experimental geometry and initial-state wave functions that are the most straightforward to analyze, facilitating the direct measurement of both the SO interaction strength and the complex nature of the wave function.…”

Thermal Hall conductivity in the spin-triplet superconductor with broken time-reversal symmetry

“…These f -wave pairing states lead to the gapless excitations of quasiparticles. Angle-resolved photoemission spectroscopy (ARPES), de Haas-van Alphen measurement studies [9][10][11][12] and first * imai@phy.saitama-u.ac.jp principles calculations [13,14] indicate that the lowenergy electronic structure of Sr 2 RuO 4 is well described by the Ru 4d t 2g orbitals. The Fermi surface consists of the one-dimensional α and β bands, and the twodimensional γ band.…”