Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session S50: Spectroscopic Evidence for Orbital Transmutation in the Nematic Phase of FeSe.Invited Live
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Sponsoring Units: DCMP Chair: Peter Hirschfeld, University of Florida |
Thursday, March 18, 2021 11:30AM - 12:06PM Live |
S50.00001: Lattice-Shifted Nematic Quantum Critical Point in FeSe1-xSx Invited Speaker: Yann Gallais We report the evolution of nematic fluctuations in FeSe1-xSx single crystals as a function of Sulfur content x across the nematic quantum critical point (QCP) xc=0.17 via Raman scattering. The Raman spectra in the B1g nematic channel consist of two-component, but only the low energy one display clear fingerprints of critical behavior and is attributed to itinerant carriers. Curie-Weiss analysis of the associated nematic susceptibility indicates a substantial effect of nemato-elastic coupling which shifts the location of the nematic QCP. We argue that this lattice-induced shift likely explains the absence of any enhancement of the superconducting transition temperature at the QCP in this system. The presence of two components in the nematic fluctuations spectrum is attributed to the dual aspect of electronic degrees of freedom in Hund's metals, with both itinerant carriers and local moments contributing to the nematic susceptibility. |
Thursday, March 18, 2021 12:06PM - 12:42PM Live |
S50.00002: Understanding the nematic electronic structure of FeSe and its impact on the superconducting state. Invited Speaker: Luke Rhodes Understanding spontaneous electronic nematic ordering in the iron-based superconductors is an important task in the study of unconventional superconductivity. Currently, however, the origin and mechanism of this nematic state, as well as its relationship to superconductivity, are still a subject of debate, both from an experimental and theoretical point of view. In this talk, I will review the peculiar effect of the nematic state on the electronic structure of FeSe. I will focus on recent ARPES measurements [1,2] which report the loss of an electron pocket at the Fermi surface upon entering the nematic state and show how this puzzling Fermi surface transition can provide direct insight into the mechanism of electronic nematicity, by highlighting the importance of the dxy orbital in its origin [3]. |
Thursday, March 18, 2021 12:42PM - 1:18PM Live |
S50.00003: Interplay of nematic order and spin-orbit interaction in iron-based superconductors from ARPES Invited Speaker: Sergey Borisenko I will give an overview of our recent ARPES results on very fine details of the electronic structure of iron-based superconductors (IBS) and their influence on the superconductivity [1-3]. In particular, we have determined the energy scale caused by nematic, spin-orbit, and exchange interactions, as well as the orbital composition of electronic states near the Fermi edge throughout the Brillouin zone in major representatives of three families of IBS. Using the novel ARPES technique based on parallel detection in 3D-momentum space instead of conventional energy-momentum datasets, we obtained new information about the topological properties of IBS. |
Thursday, March 18, 2021 1:18PM - 1:54PM Live |
S50.00004: Electronic Nematicity in FeSe Invited Speaker: Ming Yi Superconductivity emerges in proximity to a nematic phase in most iron-based superconductors. It is therefore important to understand the impact of nematicity on the electronic structure. Orbital assignment and tracking across the nematic phase transition prove to be challenging due to the multiband nature of iron-based superconductors and twinning effects. Here, we report a detailed study of the electronic structure of fully detwinned FeSe across the nematic phase transition using angle-resolved photoemission spectroscopy. We clearly observe a nematicity-driven band reconstruction involving dxz, dyz, and dxy orbitals. The nematic energy scale between dxz and dyz bands reaches a maximum of 50 meV at the Brillouin zone corner. We are also able to track the dxz electron pocket across the nematic transition and explain its absence in the nematic state. Our comprehensive data of the electronic structure provide an accurate basis for theoretical models of the superconducting pairing in FeSe. |
Thursday, March 18, 2021 1:54PM - 2:30PM Live |
S50.00005: Nematicity-induced changes in the Raman response in FeSe Invited Speaker: Girsh Blumberg We use polarization-resolved electronic Raman spectroscopy to study quadrupolar charge dynamics in non-magnetic FeSe1-xSx superconductor. We observe two types of long-wavelength XY symmetry excitations: (i) a low-energy quasi-elastic scattering (QEP) that exhibits critical enhancement upon cooling towards nematic phase transition temperature TS(x), and (ii) a broad electronic continuum with a maximum at 55 meV. We report a surprising discovery of clear pseudo-gap suppression in the low frequency spectra of electronic long-wavelength charge quadrupole excitation below TS(x), with temperature dependence of the gap’s magnitude reminiscent of the nematic order parameter. We relate the pseudo-gap development to significant reconstruction of the bands’ orbital composition near the Fermi pockets. We demonstrate that the intensity of the QEP grows with increasing sulfur concentration x and maximizes at a critical doping xcr ≈ 16% where the nematic transition vanish, while the pseudo-gap size decreases with the suppression of TS(x). We argue that the intense continuum of excitations in the high-temperature phase with tetragonal symmetry arises due to non-Fermi liquid dynamics governed by Pomeranchuk fluctuations and that these fluctuations are suppressed in the symmetry broken orthorhombic low-temperature phase where the Fermi liquid properties recover. |
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