Exploring strong correlations in the calcium ruthenates with spectroscopic techniques
Bibliographic record
Abstract
The rich multiband physics of the calcium ruthenates gives rise to a complex free-energy landscape shaped by the strong interplay among spin-orbit coupling effects, electronic interactions, lattice distortions, and spin correlations. This competition produces a variety of emergent quantum phenomena with promise for future applications. For instance, beyond its Mott-insulating ground state, the single-layer Ca₂RuO₄ hosts an unconventional current-induced non-equilibrium metallic state, while an incommensurate cycloidal magnetic phase arises in the bilayer Ca₃Ru₂O₇ system. By simultaneously employing transport measurements with angle-resolved photoemission spectroscopy (ARPES), this work reveals how the electronic band structure evolves across the current-induced insulator-to-metal transition in Ca₂RuO₄. A reduction of the insulating band gap and a modification of the Ru bands are observed in the current-induced phase. Historically, transport-ARPES has been confined to the study of materials with clearly defined features in energy; by using core level spectra as the energy reference, not only can transport-ARPES be extended to any ARPES suitable material. Meanwhile, Raman measurements in an external magnetic field reveal an unusually large field-induced energy shift of a phonon mode in Ca₃Ru₂O₇, pointing to exceptionally strong spin–phonon coupling in a regime where the Dzyaloshinskii–Moriya interaction plays the dominant role. While even larger couplings have been observed in some 5d compounds such as the osmates, this is the largest reported value among the ruthenates, underscoring the delicate interplay between the different degrees of freedom in the system, making these materials highly tunable by small perturbations. For instance, applying < 1% compressive strain can shift the insulator-to-metal transition by more than 70K. This thesis therefore integrates external electromagnetic fields with advanced spectroscopic probes in order to study regions of the ruthenate free-energy landscape not previously explored by conventional techniques. A complex landscape is uncovered, illustrating how these materials can be finely tuned with current, field, doping, or strain, offering new insights into the underlying physics of 4d systems and opening opportunities for their incorporation into future quantum devices. Additionally, with the developments in transport-ARPES, this thesis builds upon our ever growing capability to look at strongly correlated electron systems in operando.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".