Abstract
A family of titanium oxypnictide materials () becomes superconducting when a charge and/or spin-density wave is suppressed. With hole doping, isovalent doping and pressure, a whole range of tuning parameters is available. We investigate how charge doping controls the superconducting transition temperature . To this end, we use experimental crystal structure data to determine the electronic structure and Fermi surface evolution along the doping path. We show that a naive approach to calculating via the density of states at the Fermi level and the McMillan formula systematically fails to yield the observed variation. On the other hand, spin-fluctuation theory pairing calculations allow us to consistently explain the increase with doping. All alkali-doped materials () are described by a sign-changing -wave order parameter. Susceptibilities also reveal that the physics of the materials is controlled by a single Ti orbital.
5 More- Received 24 August 2021
- Revised 14 October 2021
- Accepted 19 November 2021
DOI:https://doi.org/10.1103/PhysRevB.104.184519
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