Searching for Non-Bulk Superconductors: Estimating Substrate T<sub>c</sub> Enhancement Via Electron-Phonon Coupling in 2D thin films
ORAL
Abstract
The demonstrated enhancement of the Tc in an iron selenide (FeSe) overlayer due to interactions with its SrTiO3 substrate opened up a whole new area of material combinations to explore in the decades old search for room temperature superconductivity.
The superconducting critical temperature (Tc) of FeSe increases from 8 K, when in its bulk phase, to 70 K when grown as a monolayer on a SrTiO3 substrate1. The increase of Tc in FeSe has been attributed to coupling with phonon modes in the SrTiO3 substrate as well as the modification of its band structure due to topological surface states. If we assume it is due to phonon coupling, Eliashberg theory gives us an opportunity to calculate the strength of electron-phonon coupling computationally, and so try and predict new material interfaces with similarly enhanced Tc. However, calculating the coupling strength using full Eliashberg theory is unfeasible for large systems like interfaces where many-atom slab calculations of the electronic structure are necessary.
Using a computationally inexpensive frozen phonon approach we have developed a technique which can be used to screen interfaces for enhanced superconducting Tc that results from electrons in thin films of superconducting material coupling with substrate phonons. We have applied this method to mono- and bi- layers of Ti and TiN on MgO substrates and demonstrated strong coupling in the thin overlayers due to specific phonons in the subsrate.
1. Hsu, F. C. et al. Superconductivity in the PbO-type structure α-FeSe. Proc. Natl Acad. Sci. USA 105, 14262–14264 (2008)
The superconducting critical temperature (Tc) of FeSe increases from 8 K, when in its bulk phase, to 70 K when grown as a monolayer on a SrTiO3 substrate1. The increase of Tc in FeSe has been attributed to coupling with phonon modes in the SrTiO3 substrate as well as the modification of its band structure due to topological surface states. If we assume it is due to phonon coupling, Eliashberg theory gives us an opportunity to calculate the strength of electron-phonon coupling computationally, and so try and predict new material interfaces with similarly enhanced Tc. However, calculating the coupling strength using full Eliashberg theory is unfeasible for large systems like interfaces where many-atom slab calculations of the electronic structure are necessary.
Using a computationally inexpensive frozen phonon approach we have developed a technique which can be used to screen interfaces for enhanced superconducting Tc that results from electrons in thin films of superconducting material coupling with substrate phonons. We have applied this method to mono- and bi- layers of Ti and TiN on MgO substrates and demonstrated strong coupling in the thin overlayers due to specific phonons in the subsrate.
1. Hsu, F. C. et al. Superconductivity in the PbO-type structure α-FeSe. Proc. Natl Acad. Sci. USA 105, 14262–14264 (2008)
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Presenters
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Oliver A Dicks
University of British Columbia
Authors
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Oliver A Dicks
University of British Columbia