University of Minnesota
School of Physics & Astronomy

Physics and Astronomy Calendar

Monday, January 13th 2020
2:30 pm:
Speaker: Igor Marković, University of St. Andrews, UK
Subject: Electronically driven spin reorientation transition of the correlated polar metal Ca3Ru2O7
Note the date and time of the seminar.

We use angular-resolved photoemission spectroscopy (ARPES) and ab initio calculations to study the low-energy electronic band structure of a bilayer ruthenate system, Ca3Ru2O7, across a wide temperature range. Ca3Ru2O7 is a polar metal which undergoes two magnetic transitions [1]: a Néel ordering at 56 K and a spin-reorientation at 48 K. At low temperatures we find it to be a compensated semimetal, in general agreement with previous ARPES [2] and de Haas-van Alphen [3] experiments. Our measurements across the 48 K transition, however, reveal dramatic changes in the low-energy electronic structure, with a destruction of a large hole-like Fermi surface upon cooling, accompanied by a sudden onset of quasiparticle coherence. We demonstrate how the Fermi surface is gapped away by a "hidden" Rashba-type spin-orbit coupling, enabled by the bulk structural distortions and unlocked when the spin reorients perpendicular to the local symmetry-breaking potential at the Ru sites. We argue that the electronic energy gain associated with the band hybridisation is actually the key driver for the phase transition, reflecting a delicate interplay between spin-orbit coupling and strong electronic correlations in this system, and pointing to a new form of magnetocrysalline anisotropy driven by Fermi surface transitions.

[1] Cao, et al., Phys. Rev. Lett. 78 (1997) 1751
[2] Baumberger et al., Phys. Rev. Lett. 96 (2006) 107601
[3] Kikugawa et al., J. Phys. Soc. Jpn. 79 (2010) 024704

Faculty Host: Martin Greven

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