Postquench gap dynamics of two-band superconductors

Journal Article · 23 October 2019 · Physical Review B

DOI: https://doi.org/10.1103/PhysRevB.100.144513 · OSTI ID:1579928

Cui, Tianbai  ^[1]; Schütt, Michael ^[2]; Orth, Peter P.  ^[3]; Fernandes, Rafael M. ^[1]

---

1. Univ. of Minnesota, Minneapolis, MN (United States)
2. Paul Scherrer Inst. (PSI), Villigen (Switzerland)
3. Iowa State Univ., Ames, IA (United States); Ames Lab., Ames, IA (United States)

Recent experimental progress in the fields of cold quantum gases and ultrafast optical spectroscopy of quantum materials allows us to controllably induce and probe nonadiabatic dynamics of superconductors and superfluids. The time evolution of the gap function before relaxation with the lattice is determined by the superposition of coherently evolving individual Cooper pairs within the manifold of the Bardeen-Cooper-Schrieffer (BCS) wave function. While dynamics following an abrupt quench of the pairing interaction strength in the single-band BCS model has been exactly solved due to the integrability of the model, the dynamics of postquench multiband superconductors remain under scrutiny. Here, we develop a generalization of the Volkov-Kogan Laplace-space perturbative method that allows us to determine the nonadiabatic gap dynamics of two-band fully gapped superconductors for a wide range of quench amplitudes. Our approach expands the long-time dynamics around the steady-state asymptotic value of the gap, which is self-consistently determined, rather than around the equilibrium value of the gap. We explicitly demonstrate that this method recovers the exact solution of the long-time gap dynamics in the single-band case and perfectly agrees with a numerical solution of the two-band model. We discover that dephasing of Cooper pairs from different bands leads to faster collisionless relaxation of the gap oscillation with a power law of t^–3/2 instead of the well-known t^–1/2 behavior found in the single-band case. Moreover, the gap oscillations display beating patterns arising from the existence of two different asymptotic gap values. Our results have important implications to a variety of two-band superconductors driven out of equilibrium, such as iron-based superconductors, MgB₂, and SrTiO₃.

• Research Organization: Ames Laboratory (AMES), Ames, IA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
• Grant/Contract Number: AC02-07CH11358; SC0012336
• OSTI ID: 1579928
• Report Number(s): IS-J--10110
• Journal Information: Physical Review B, Journal Name: Physical Review B Journal Issue: 14 Vol. 100; ISSN 2469-9950; ISSN PRBMDO
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English