Tender X-Ray RIXS at PETRA-III: A new way to investigate 4d TMs and 5f electron systems

by Dr Hlynur Gretarsson (PETRA III, DESY, Hamburg)

Monday 4 Nov 2024, 14:30 → 15:30 Europe/Berlin

PH HS 3 (Physics Department)

Collective excitations of spins (e.g. magnons) have traditionally been measured using inelastic neutron scattering (INS) - a technique that offers superb energy resolution (<1meV) and sample environment (e.g. low temperature <1K and high-magnetic field). However, in the last 15 years we have witnessed the technique of resonant inelastic x-ray scattering (RIXS) [1] emerge as an alternative/complementary to those INS measurements thanks to the 2010 discovery of a magnon in the high-T_c cuprate La_2-xSr_xCuO₄ [2].

 RIXS can be divided into three camps based on the resonance x-ray energy being used; soft, tender and hard x-ray RIXS. Broadly speaking these three energy ranges correspond to the L₃-edges of the 3d, 4d, and 5d transition metals (TMs). At PETRA-III we picked the tender range, which in 2016 was non-existing for the field of RIXS [3]. This has allowed us to look at spin and charge dynamics in 4d TMs [4], among them the fascinating ruthenates, as well in Uranium based materials [5].

 In this talk I will present our RIXS work on various ruthenates including the Ruddlesden-Popper series Ca_n+1Ru_nO_3n+1 with n=1 and 2 (single [4] and bi-layer [6]). Understanding quantum magnetism in these d⁴ perovskites is a challenging task due the presence of SOC in a combination with large structural distortions. In Ca₂RuO₄ we have attempted to tune the distortion using epitaxially grown films as well as looking at the distortion’s role in the existing metal-insulator transition, while in Ca₃Ru₂O₇ we have observed dramatic changes with miniscule doping. I will then contrast this work with a cubic Ru d⁴-system RuO_2, a material that was an early candidate for altermagnetism [7].

[1] Luuk J. P. Ament et al., Rev. Mod. Phys. 83, 705 (2011) https://doi.org/10.1103/RevModPhys.83.705
[2] L. Braicovichet al., Phys. Rev. Lett. 104, 077002 (2010) https://doi.org/10.1103/PhysRevLett.104.077002
[3] H. Gretarsson et al., J. Synchrotron Rad. 27, 538-544 (2020) https://doi.org/10.1107/S1600577519017119
[4] H. Gretarsson et al., Phys. Rev. B 100, 045123 (2019) https://doi.org/10.1103/PhysRevB.100.045123
[5] A. Marino et al., Phys. Rev. B 108, 045142 (2023) https://doi.org/10.1103/PhysRevB.108.045142
[6] J. Bertinshaw et al., Phys. Rev. B 103, 085108 (2021) https://doi.org/10.1103/PhysRevB.103.085108
[7] L. Šmejkal et al., Phys. Rev. X 12, 040501 (2022) https://doi.org/10.1103/PhysRevX.12.040501