Regensburg 2025 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 30: Quantum-Critical Phenomena (joint session TT/DY)

DY 30.3: Talk

Thursday, March 20, 2025, 10:00–10:15, H31

Tuning a ferromagnetic quantum phase transition by interface engineering in artificial heterostructures — Robin Heumann¹, Robert Gruhl¹, Ludwig Scheuchenpflug¹, Leonard Schüler², Vasily Moshnyaga², and •Philipp Gegenwart¹ — ¹Lehrstuhl für Experimentalphysik VI, Universität Augsburg — ²Erstes Physikalisches Institut, Georg-August-Universität-Göttingen

The substitution series Sr_{1 − x}Ca_xRuO₃ between the itinerant ferromagnet SrRuO₃ (SRO) and the non-Fermi liquid paramagnetic metal CaRuO₃ (CRO) constitutes a broadly smeared quantum phase transition (QPT) between x=0.7 and 1. To avoid the impact of structural disorder we explore the possibility of tuning ferromagnetism by confining SRO to thin layers placed in between those of CRO. Ordered epitaxial [SRO_n/CRO_m]_K superlattices, with n ranging from 8 down to the monolayer limit, keeping m/n=2 and 3 with K=32/n, were grown on SrTiO₃ (100) substrates, characterized and investigated by electrical transport and Hall effect measurements. We observe stable ferromagnetism from SRO layers for n≥ 3 and fragile low-temperature ferromagnetism due to the SRO/CRO interfaces. The latter survives down to the monolayer limit n=1, explaining the difficulty to cross a ferromagnetic QPT in Sr_{1 − x}Ca_xRuO₃. We also find that the effective interface density K/(n+m) is a new suitable control parameter and construct the T_C vs K/(n+m) phase diagram.

Keywords: quantum phase transition; ruthenates; heterostructures; interface engineering; non-Fermi liquid