Multigap superconductors in the atomically thin limit

Date: 4 May 2016

Venue: University of Antwerp - Campus Groenenborger - Room U.241 - Groenenborgerlaan 171 - 2020 Antwerpen

Time: 4:00 PM - 5:00 PM

Organization / co-organization: Condensed Matter Theory

Short description: Condensed Matter Theory seminar presented by Jonas Beckaert

All-surface two-dimensional materials are known to harbour properties very different from those of their bulk counterparts. Recent years have seen the rise of atomically thin superconductors, with a caveat that superconductivity is strongly depleted unless enhanced by specific substrates, intercalants, and adatoms. Surprisingly, the role of surface electronic states on superconductivity in such all-surface materials has remained elusive to date. In this seminar, we will present a framework to study the evolution of the superconducting gap spectrum of ultrathin superconductors as a function of the number of atomic layers, going from a monolayer to bulk, fully from first principles.

To this end, we combine density functional (perturbation) theory with anisotropic Eliashberg theory. As an example, we will present our recent results on ultrathin MgB2, in its bulk form the archetypical two-gap superconductor. We will show that new surface states without a bulk equivalent arise, stemming from the free surfaces. Their distinct contribution further enriches multigap superconductivity in MgB2, and displays a non-monotonous evolution with the number of layers. Finally, the compliance of our predictions with recent ARPES measurements will be demonstrated. Our findings bring forward the use of free surfaces as a separate route to tuning multigap superconductivity in atomically thin materials.

Jonas Beckaert, CMT group, UAntwerpen 

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