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We investigate superconductivity in a two-band system with an electron- and hole-like band, where one of the bands is away from the Fermi level (or incipient). We argue that the incipient band contributes significantly to spin-fluctuation pairing in the strong coupling limit where the system is close to a magnetic instability, and can lead to a large Tc. In this case, Tc is limited by a competition between the frequency range of the coupling (set by an isolated paramagnon) and the coupling strength itself, such that a dome-like Tc dependence on the incipient band position is obtained. The coupling of electrons to phonons is found to further enhance Tc. The results are discussed in the context of experiments on monolayers and intercalates of FeSe.
The importance of electron-hole interband interactions is widely acknowledged for iron-pnictide superconductors with high transition temperatures (Tc). However, high-Tc superconductivity without hole carriers has been suggested in FeSe single-layer f
Large pulsed magnetic fields up to 60 Tesla are used to suppress the contribution of superconducting fluctuations (SCF) to the ab-plane conductivity above Tc in a series of YBa2Cu3O(6+x). These experiments allow us to determine the field Hc(T) and th
Superconductivity is significantly enhanced in monolayer FeSe grown on SrTiO3, but not for multilayer films, in which large strength of nematicity develops. However, the link between the high-transition temperature superconductivity in monolayer and
In contrast to bulk FeSe, which exhibits nematic order and low temperature superconductivity, atomic layers of FeSe reverse the situation, having high temperature superconductivity appearing alongside a suppression of nematic order. To investigate th
Large pulsed magnetic fields up to 60 Tesla are used to suppress the contribution of superconducting fluctuations (SCF) to the ab-plane conductivity above Tc in a series of YBa2Cu3O6+x single crystals. The fluctuation conductivity is found to vanish