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| Natura: | Preprint |
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2026
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| Accesso online: | https://arxiv.org/abs/2605.16625 |
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| _version_ | 1866913134316355584 |
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| author | Sous, John |
| author_facet | Sous, John |
| contents | Phonon-mediated superconductivity is conventionally thought to be capped at a transition temperature $T_{\mathrm{c}}$ no larger than roughly one-tenth of the phonon frequency $Ω$, a bound rooted in the breakdown of Migdal-Eliashberg theory at intermediate coupling and in the heaviness of bipolarons formed in standard models with phonons that couple to the electron density. In this review I describe a route to phonon-mediated high-$T_{\mathrm{c}}$ superconductivity that bypasses this bound. The key ingredient is a class of electron-phonon couplings in which lattice distortions modulate the electron hopping and therefore its kinetic energy rather than its potential energy, known as the Peierls model (also known as Su-Schrieffer-Heeger model). In these models phonon exchange generates an interaction that binds two electrons into a small but unusually light bipolaron. Using sign-problem-free quantum Monte Carlo simulations of a bond-Peierls model on the square and cubic lattices, my collaborators and I have shown that a dilute liquid of such bipolarons forms an $s$-wave superconductor with a $T_{\mathrm{c}}/Ω$ that significantly exceeds the conventional bound, that this conclusion is robust against screened Coulomb repulsion, and that $T_{\mathrm{c}}/Ω$ -- despite being reduced -- remains above bound in presence of strong long-range Coulomb repulsion. A semi-classical instanton analysis explains why, at strong coupling, bipolarons in models with phonon-modulated hopping are lighter than their density-coupled (Holstein) counterparts. I close with a discussion of materials in which this physics may be operative, in particular the iron-based pnictide superconductors, and of design principles that follow from it. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2605_16625 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Bipolaronic High-Temperature Superconductivity from Phonon-Modulated Hopping: A Perspective Sous, John Superconductivity Strongly Correlated Electrons Phonon-mediated superconductivity is conventionally thought to be capped at a transition temperature $T_{\mathrm{c}}$ no larger than roughly one-tenth of the phonon frequency $Ω$, a bound rooted in the breakdown of Migdal-Eliashberg theory at intermediate coupling and in the heaviness of bipolarons formed in standard models with phonons that couple to the electron density. In this review I describe a route to phonon-mediated high-$T_{\mathrm{c}}$ superconductivity that bypasses this bound. The key ingredient is a class of electron-phonon couplings in which lattice distortions modulate the electron hopping and therefore its kinetic energy rather than its potential energy, known as the Peierls model (also known as Su-Schrieffer-Heeger model). In these models phonon exchange generates an interaction that binds two electrons into a small but unusually light bipolaron. Using sign-problem-free quantum Monte Carlo simulations of a bond-Peierls model on the square and cubic lattices, my collaborators and I have shown that a dilute liquid of such bipolarons forms an $s$-wave superconductor with a $T_{\mathrm{c}}/Ω$ that significantly exceeds the conventional bound, that this conclusion is robust against screened Coulomb repulsion, and that $T_{\mathrm{c}}/Ω$ -- despite being reduced -- remains above bound in presence of strong long-range Coulomb repulsion. A semi-classical instanton analysis explains why, at strong coupling, bipolarons in models with phonon-modulated hopping are lighter than their density-coupled (Holstein) counterparts. I close with a discussion of materials in which this physics may be operative, in particular the iron-based pnictide superconductors, and of design principles that follow from it. |
| title | Bipolaronic High-Temperature Superconductivity from Phonon-Modulated Hopping: A Perspective |
| topic | Superconductivity Strongly Correlated Electrons |
| url | https://arxiv.org/abs/2605.16625 |