Researchers report resonant photovoltage features in unbiased monolayer graphene and WSe2/graphene heterostructures. The resonant response had the opposite sign to the nonresonant Drude background—the baseline electrical response outside the resonance—and both responses reversed sign near the charge-neutrality point.
In laboratory measurements, graphene-based Hall-bar devices were exposed to linearly polarized radiation from 45 to 75 GHz while magnetic-field orientation and gate voltage were varied. The work is an arXiv version 1 preprint posted on 26 August 2026; its journal publication status is not reported.
A resonance that changes with frequency
Resonant photovoltage features were observed in both Faraday and Voigt geometries.
The reported resonance frequencies followed a linear relation between radiation frequency and magnetic field. Fits gave a g factor of about 1.99, along with frequency intercepts of roughly minus 5 to minus 7 GHz, zero, and 10.2 GHz. No confidence intervals or formal uncertainty estimates were reported for these values.
Two resonances were commonly observed, while a third weak feature appeared under some conditions. A fourth resonance was clearly detected in a monolayer-graphene dataset taken with the magnetic field in the plane of the material. The occurrence and reproducibility of the additional resonances were not consistently quantified, and reproducibility of the fourth signal across independent devices was not reported.
Widths and device scale
The resonance traces were fitted with Lorentzian functions. Their reported full widths at half maximum, a measure of how broad the signal is, were about 0.05 to 0.6 tesla, corresponding to spin-relaxation times of approximately 18 to 130 picoseconds. No confidence intervals were reported for these extracted times.
The graphene Hall-bar channel was approximately 20 micrometres long. The WSe2/graphene device had mobility up to 1 × 10^4 cm²/V s. The paper also refers to supplemental material for additional magnetotransport information.
A proposed explanation leaves a key question open
The authors' model combines radiation-induced momentum alignment—an organized direction in carrier motion—with skew scattering, in which deflected carriers contribute unevenly to the electrical signal. It treats these as microscopic accounts of both photogalvanic contributions, associates their opposite signs with orthogonal alignments from indirect Drude and direct spin-resonant transitions, and reports that the theory describes the main resonant photocurrent features.
That reported agreement does not resolve why several resonances appear or why some are relatively broad. The paper states that the microscopic origin of the splitting and widths of the multiple electron-spin-resonance features at high Fermi energies remains unresolved.
The result should be read as a device-level observation under the reported laboratory conditions. The supplied analysis does not establish that skew scattering is uniquely supported over other mechanisms, that the multiple resonances have been explained, or that the pattern generalizes across graphene devices and operating conditions.
The authors present the effect as an unbiased photogalvanic probe of electron spin resonance in micron-scale graphene-based devices. Further work will be needed to determine how reproducible the additional resonances are and what produces their splitting and widths.
Paper data and sources
Original title: Electron spin resonance driven photogalvanic effect in graphene-based structures
Authors: C. Bray, I. Yahniuk, L. E. Golub et al.
Journal/Repository: arXiv
Status: Preprint, not yet peer-reviewed
First online: 2026-08-26
DOI: Not available
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