Disentangling spin polarization from driven circular ionic motion in EuTiO₃

@misc{allington2026disentangling,
  title = {{Disentangling spin polarization from driven circular ionic motion in EuTiO$_3$}},
  author = {Clifford J. Allington and Matthew J. Lutz and Enoch and Ho and Fabian Graf and Martina Basini and Hiroki Ueda and Michael Grimes and Alexander B. Elliott and Megan F. Biggs and Ravi Finn and Shih-Wen Huang and Merideth A. Henstridge and Matthias C. Hoffmann and Takahiro Sato and Roberto Alonso-Mori and Diling Zhu and Quynh L. Nguyen and Vincent Esposito and Jeffrey T. Babicz Jr. and Elizabeth Skoropata and Biaolong Liu and Eugenio Paris and Arnau Romaguera Camps and Elia Razzoli and Roman Mankowsky and Flavio Capotondi and Nicolas Jaouen and Daniele Pergolesi and Milan Radovic and Matteo Savoini and Steven L. Johnson and Jeremy A. Johnson and Urs Staub},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2609.28214},
  eprint = {2609.28214},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.28214},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - Disentangling spin polarization from driven circular ionic motion in EuTiO_3
AU  - Clifford J. Allington
AU  - Matthew J. Lutz
AU  - Enoch
AU  - Ho
AU  - Fabian Graf
AU  - Martina Basini
AU  - Hiroki Ueda
AU  - Michael Grimes
AU  - Alexander B. Elliott
AU  - Megan F. Biggs
AU  - Ravi Finn
AU  - Shih-Wen Huang
AU  - Merideth A. Henstridge
AU  - Matthias C. Hoffmann
AU  - Takahiro Sato
AU  - Roberto Alonso-Mori
AU  - Diling Zhu
AU  - Quynh L. Nguyen
AU  - Vincent Esposito
AU  - Jeffrey T. Babicz Jr.
AU  - Elizabeth Skoropata
AU  - Biaolong Liu
AU  - Eugenio Paris
AU  - Arnau Romaguera Camps
AU  - Elia Razzoli
AU  - Roman Mankowsky
AU  - Flavio Capotondi
AU  - Nicolas Jaouen
AU  - Daniele Pergolesi
AU  - Milan Radovic
AU  - Matteo Savoini
AU  - Steven L. Johnson
AU  - Jeremy A. Johnson
AU  - Urs Staub
PY  - 2026
DA  - 2026/10/23
PB  - arXiv
DO  - 10.48550/arxiv.2609.28214
UR  - https://arxiv.org/abs/2609.28214
AB  - Coherently driven circular ionic motion has been reported to produce large helicity-dependent optical responses attributed to transient magnetization. However, the microscopic nature and magnitude of this phenomenon, sometimes referred to as dynamical multiferroicity, remain strongly debated. Here, we directly study the connection between ionic circulation induced by a high-field circular terahertz (THz) drive and its effect on the spin system of EuTiO_3 using X-rays. This material exhibits an optical response consistent with the putative magnetic signal observed in related non-magnetic materials. Furthermore, the presence of Eu^2+ ions enables the use of X-ray magnetic circular dichroism (XMCD) to test for the creation of transient spin polarization. Simultaneously, ultrafast X-ray diffraction (XRD) measures the circular ionic motion from which we determine the mechanical angular momentum. We find a classical ionic contribution of 3×10^−8 μ_B from XRD and upper limits of 0.03 μ_B and 0.11 μ_B from the sensitivity of XMCD at the europium M_5 and L_2 edges, probing the 4f and 5d shells of Eu^2+, respectively. These observations show that large-amplitude circular ionic motion in this system is not accompanied by a detectable spin polarization despite the clear signature in the optical data, with the XMCD upper bounds and classical contribution differing by many orders of magnitude.
ER  -