TY - JOUR
T1 - Role of nematicity in controlling spin fluctuations and superconducting Tc in bulk FeSe
AU - Acharya, Swagata
AU - Pashov, Dimitar
AU - Van Schilfgaarde, Mark
N1 - Funding Information:
We thank Qisi Wang and Jun Zhao for sharing with us the raw data for spin susceptibilities. This work was supported by the Simons Collaboration on the Many-Electron Problem. S.A. was supported (in later stages of this work) by the ERC Synergy Grant, Project No. 854843 FASTCORR (Ultrafast Dynamics of Correlated Electrons in Solids). M.v.S. and D.P. were supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award No. FWP ERW7906. We acknowledge PRACE for awarding us access to SuperMUC at the GCS at LRZ, Germany; Irene-Rome hosted by TGCC, France; the STFC Scientific Computing Department's SCARF cluster; and the Cambridge Tier-2 system operated by the University of Cambridge Research Computing Service funded by EPSRC Tier-2 Capital Grant No. EP/P020259/1. This work was also partly carried out on the Dutch National e-Infrastructure with the support of the SURF Cooperative.
Publisher Copyright:
© 2022 American Physical Society.
PY - 2022/4/1
Y1 - 2022/4/1
N2 - FeSe undergoes a transition from a tetragonal to a slightly orthorhombic phase at 90 K and becomes a superconductor below 8 K. The orthorhombic phase is sometimes called a nematic phase because quantum oscillation, neutron, and other measurements detect a significant asymmetry in x and y. How nematicity affects superconductivity has recently become a matter of intense speculation. Here, we employ an advanced ab initio Green's function description of superconductivity and show that bulk tetragonal FeSe would, in principle, superconduct with almost the same critical temperature Tc as the nematic phase. The mechanism driving the observed nematicity is not yet understood. Since the present theory underestimates it, we simulate the full nematic asymmetry by artificially enhancing the orthorhombic distortion. For benchmarking, we compare theoretical spin susceptibilities against experimentally observed data over all energies and relevant momenta. When the orthorhombic distortion is adjusted to correlate with observed nematicity in spin susceptibility, the enhanced nematicity causes spectral weight redistribution in the Fe-3dxz and Fe-dyz orbitals, but it leads to at most a 10-15% increment in Tc. This is because the dxy orbital always remains the most strongly correlated and provides most of the source of the superconducting glue. Nematicity suppresses the density of states at the Fermi level; nevertheless, Tc increases, in contradiction to both BCS theory and the theory of Bose-Einstein condensation. We show how the increase is connected to the structure of the particle-particle vertex. Our results suggest that while nematicity may be an intrinsic property of bulk FeSe, it is not the primary force driving the superconducting pairing.
AB - FeSe undergoes a transition from a tetragonal to a slightly orthorhombic phase at 90 K and becomes a superconductor below 8 K. The orthorhombic phase is sometimes called a nematic phase because quantum oscillation, neutron, and other measurements detect a significant asymmetry in x and y. How nematicity affects superconductivity has recently become a matter of intense speculation. Here, we employ an advanced ab initio Green's function description of superconductivity and show that bulk tetragonal FeSe would, in principle, superconduct with almost the same critical temperature Tc as the nematic phase. The mechanism driving the observed nematicity is not yet understood. Since the present theory underestimates it, we simulate the full nematic asymmetry by artificially enhancing the orthorhombic distortion. For benchmarking, we compare theoretical spin susceptibilities against experimentally observed data over all energies and relevant momenta. When the orthorhombic distortion is adjusted to correlate with observed nematicity in spin susceptibility, the enhanced nematicity causes spectral weight redistribution in the Fe-3dxz and Fe-dyz orbitals, but it leads to at most a 10-15% increment in Tc. This is because the dxy orbital always remains the most strongly correlated and provides most of the source of the superconducting glue. Nematicity suppresses the density of states at the Fermi level; nevertheless, Tc increases, in contradiction to both BCS theory and the theory of Bose-Einstein condensation. We show how the increase is connected to the structure of the particle-particle vertex. Our results suggest that while nematicity may be an intrinsic property of bulk FeSe, it is not the primary force driving the superconducting pairing.
UR - http://www.scopus.com/inward/record.url?scp=85129443464&partnerID=8YFLogxK
U2 - 10.1103/PhysRevB.105.144507
DO - 10.1103/PhysRevB.105.144507
M3 - Article
AN - SCOPUS:85129443464
SN - 2469-9950
VL - 105
JO - Physical Review B
JF - Physical Review B
IS - 14
M1 - 144507
ER -