Density of states and spectral function of a superconductor out of a quantum-critical metal
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arXiv
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| Auteurs principaux: | , |
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| Format: | Preprint |
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2023
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| _version_ | 1866917574867943424 |
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| author | Zhang, Shang-Shun Chubukov, Andrey V. |
| author_facet | Zhang, Shang-Shun Chubukov, Andrey V. |
| contents | We analyze the validity of a quasiparticle description of a superconducting state at 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, should restore a coherent quasiparticle behavior. We argue that this does not necessarily hold as in some cases the fermionic self-energy remains singular slightly above the gap edge. This singularity gives rise to markedly non-BCS behavior of the density of states and to broadening and eventual vanishing of the quasiparticle peak in the spectral function. We analyze the set of quantum-critical models with an effective dynamical 4-fermion interaction, mediated by a gapless boson at a QCP, $V(Ω) \propto 1/Ω^γ$. 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 data. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2301_13679 |
| institution | arXiv |
| publishDate | 2023 |
| record_format | arxiv |
| spellingShingle | Density of states and spectral function of a superconductor out of a quantum-critical metal Zhang, Shang-Shun Chubukov, Andrey V. Superconductivity Strongly Correlated Electrons We analyze the validity of a quasiparticle description of a superconducting state at 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, should restore a coherent quasiparticle behavior. We argue that this does not necessarily hold as in some cases the fermionic self-energy remains singular slightly above the gap edge. This singularity gives rise to markedly non-BCS behavior of the density of states and to broadening and eventual vanishing of the quasiparticle peak in the spectral function. We analyze the set of quantum-critical models with an effective dynamical 4-fermion interaction, mediated by a gapless boson at a QCP, $V(Ω) \propto 1/Ω^γ$. 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 data. |
| title | Density of states and spectral function of a superconductor out of a quantum-critical metal |
| topic | Superconductivity Strongly Correlated Electrons |
| url | https://arxiv.org/abs/2301.13679 |