Anomalous magneto-optical response at $\mathrm{RuO_2 / WSe_2}$ van der Waals interface

• URL: http://arxiv.org/abs/2606.20262v1
• Date: Thu, 18 Jun 2026 14:11:11 GMT
• Title: Anomalous magneto-optical response at $\mathrm{RuO_2 / WSe_2}$ van der Waals interface
• Abstract summary: Rut dioxide ($mathrmRuO$) has been proposed as an altermagnetic candidate, although its magnetic ground state remains controversial.<n>Here, we probe weak interfacial magnetic states at the surface of (001)-oriented $mathrmRuO$ films using the magnetic proximity effect (MPE)<n>Results suggest that the valley states are governed predominantly by interfacial exchange fields associated with weak surface magnetic states in $mathrmRuO$, which do not produce a conventional linear Zeeman response within the applied magnetic field range.
• Score: 1.041244287595653
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: Ruthenium dioxide ($\mathrm{RuO_2}$) has been proposed as an altermagnetic candidate, although its magnetic ground state remains controversial. Here, we probe weak interfacial magnetic states at the surface of (001)-oriented $\mathrm{RuO_2}$ films using the magnetic proximity effect (MPE) in a van der Waals heterostructure consisting of monolayer tungsten diselenide ($\mathrm{WSe_2}$) atop $\mathrm{RuO_2}$. Temperature-dependent magneto-optical spectroscopy reveals an anomalous excitonic energy shift and a deviation from conventional Varshni behavior below 55 K that are absent in an encapsulated $\mathrm{WSe_2}$ control sample. The anomalous shift reverses sign upon field cooling with opposite magnetic field polarity, indicating a magnetic origin. Polarization-resolved measurements further show a nearly field-independent and fluctuating valley splitting in $\mathrm{WSe_2 / RuO_2}$ in strong contrast to the conventional linear Zeeman splitting observed in the control bare $\mathrm{WSe_2}$ sample. These results suggest that the valley states are governed predominantly by interfacial exchange fields associated with weak surface magnetic states in $\mathrm{RuO_2}$, which do not produce a conventional linear Zeeman response within the applied magnetic field range. Importantly, this approach enables direct optical probing of emergent surface magnetism without introducing an additional ferromagnetic layer, positioning MPE-based optical probing as a tool for investigating weak surface magnetism and offering new possibilities for studying magnetic materials with controversial magnetic states.

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