TY - JOUR
T1 - Density of States and Spectral Function of a Superconductor out of a Quantum-Critical Metal
AU - Zhang, Shang Shun
AU - Chubukov, Andrey V.
N1 - Publisher Copyright:
© 2023 American Physical Society.
PY - 2023/8/25
Y1 - 2023/8/25
N2 - We analyze the validity of a quasiparticle description of a superconducting state above a metallic quantum-critical point (QCP). A normal state at a QCP is a non-Fermi liquid with no coherent quasiparticles. A superconducting order gaps out low-energy excitations, except for a sliver of states for non-s-wave gap symmetry, and at a first glance, restores coherent quasiparticle behavior. We argue that this does not necessarily hold as the fermionic self-energy may remain singular above the gap edge. This singularity gives rise to markedly non-BCS behavior of the density of states and to the appearance of a nondispersing mode at the gap edge in the spectral function. We analyze the set of quantum-critical models with an effective dynamical four-fermion interaction V(ω)∝1/ωγ, where ω is a frequency of a boson, which mediates the interaction. We show that coherent quasiparticle behavior in a superconducting state holds for γ<1/2, but breaks down for larger γ. We discuss signatures of quasiparticle breakdown and compare our results with the photoemission data for Bi2201 and Bi2212.
AB - We analyze the validity of a quasiparticle description of a superconducting state above a metallic quantum-critical point (QCP). A normal state at a QCP is a non-Fermi liquid with no coherent quasiparticles. A superconducting order gaps out low-energy excitations, except for a sliver of states for non-s-wave gap symmetry, and at a first glance, restores coherent quasiparticle behavior. We argue that this does not necessarily hold as the fermionic self-energy may remain singular above the gap edge. This singularity gives rise to markedly non-BCS behavior of the density of states and to the appearance of a nondispersing mode at the gap edge in the spectral function. We analyze the set of quantum-critical models with an effective dynamical four-fermion interaction V(ω)∝1/ωγ, where ω is a frequency of a boson, which mediates the interaction. We show that coherent quasiparticle behavior in a superconducting state holds for γ<1/2, but breaks down for larger γ. We discuss signatures of quasiparticle breakdown and compare our results with the photoemission data for Bi2201 and Bi2212.
UR - http://www.scopus.com/inward/record.url?scp=85169291623&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85169291623&partnerID=8YFLogxK
U2 - 10.1103/PhysRevLett.131.086502
DO - 10.1103/PhysRevLett.131.086502
M3 - Article
C2 - 37683155
AN - SCOPUS:85169291623
SN - 0031-9007
VL - 131
JO - Physical review letters
JF - Physical review letters
IS - 8
M1 - 086502
ER -