Berlin 2024 – scientific programme

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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur

KFM 18: SrTiO₃: A Versatile Material from Bulk Quantum Paraelectric to 2D Superconductor: Poster (joint session TT/KFM/MA/O)

KFM 18.8: Poster

Wednesday, March 20, 2024, 15:00–18:00, Poster E

Experimental signatures of gate tunable superconductivity in Al/STO heterostructures — •Jaydean Schmidt, Matthias Kronseder, Nicola Paradiso, and Christoph Strunk — Department of Exp. and Appl. Physics, University of Regensburg (Germany)

We demonstrate the effect of strong electric fields on aluminum (Al) thin films epitaxially grown on strontium titanite (STO) substrates. As a quantum paraelectric, STO has a large dielectric constant (ε ≈ 7000), causing strong charge accumulation at the interface. STO based heterostructures have gained significant attention in the context of interface superconductivity [1]. The growth of certain metals onto STO induces the formation of oxygen vacancies in STO, acting as double electron donors in the highly conductive interface layer.

By applying an external electric field, we obtain a hole density of the combined Al/STO system n ≈ 2 - 7 × 10²⁰/ m². These values are similar to Al films (≈ 10²¹/ m²) but much higher than the values measured for LAO/STO interface 2DEGs (≈ 10¹⁸/ m²), indicating a charge flow dominated by Al charge carriers. Furthermore, both T_c(n) and B_c(T,n) are gate tunable, up to 15% and 50%, respectively. We found that T_c ≈ 0.92 - 1.06   K is much lower compared to isolated thin Al films (≈ 1.4   K) yet higher than in STO. The system thus behaves like a bilayer of two superconductors with different gap that forms one proximity coupled system. It is surprising that the hybrid film remains gate tunable, despite the high carrier density of Al.

[1] N. Reyen et. al, Science, 317, 1196 (2007)