A transport study reports a current-activated resistance feature in twisted graphene, together with differential-resistance peaks that shift as an in-plane magnetic field changes. The paper presents the pattern as a possible ferro-Josephson response, a proposed link between spin-domain-wall precession and an extra voltage signal in the device.
The principal device was a twisted monolayer-trilayer graphene stack with a 1.29° twist angle. Measurements focused on filling factor 3, where an anomalous Hall response indicated that valley degeneracy was broken, meaning the valley states were no longer equivalent.
Researchers used four-terminal lock-in transport in a dilution refrigerator. The nominal base temperature was 10 mK, the AC current was kept below 1.5 nA, and the modulation used for differential-resistance measurements, which track the response to a small current change, ranged from 10 to 80 pA.
A peak that appears only under the right conditions
At zero in-plane field, the longitudinal resistance developed a peak whose width and shape depended strongly on AC bias and disappeared below 0.4 nA. The zero-field phenomenon was reported only in the region where valley degeneracy was broken and the anomalous Hall effect appeared.
The activation test found that the higher-resistance state required nonzero current to turn on. Its activation current could approach zero at zero in-plane field and grew approximately linearly as the field increased.
The field shifts the electrical resonances
Differential-resistance spectra provided a second field-dependent signature. At zero in-plane field, multiple peaks approached zero bias. As the in-plane field increased, the first peak shifted to higher bias and eventually disappeared.
Where the resonance dispersed cleanly, its slope was a few nanoamps per millitesla. In the phenomenological model, that scale corresponded to about 200 precessing moments in the wall. The paper describes the field relation as approximate, and the slopes varied between data sets and between in-plane field directions.
History changes the response
The differential-resistance spectra were roughly isotropic within the plane, meaning they changed little with the direction of the in-plane field. Much larger out-of-plane magnetic fields barely affected them.
In-plane magnetoresistance depended on sample history, and the relevant features were not observed in every scan. In one preparation sequence, the out-of-plane field was ramped past approximately -130 mT and returned toward zero; magnetoresistance was absent until it immediately reappeared when the field crossed zero.
The central magnetoresistance remained robust at 700 mK even though the thermal energy exceeded the quoted Zeeman energy scale, in the tens of nanoelectronvolts, by several orders of magnitude.
The explanation rests on a model
These observations are the basis of the paper's phenomenological interpretation. The model gives the wall an orientation-dependent energy in an in-plane field, predicts a critical current that increases linearly with the absolute in-plane field, and predicts a square-root onset of voltage that produces a differential-resistance peak.
The paper's proposed voltage relation associates an additional voltage drop with spin-texture precession and with how quickly the wall's spin orientation changes. In ordinary terms, the model treats the changing spin orientation as part of the measured electrical response.
That interpretation remains model-based. The work is an arXiv preprint, version 2, dated 2 Sep 2026. The authors state that source data are available, while other supporting data can be obtained from the corresponding author upon request.
Paper data and sources
Original title: Signatures of a ferro-Josephson effect in twisted graphene
Authors: Ruiheng Su, Zhenxiang Gao, Christopher Coleman et al.
Journal/Repository: arXiv
Status: Preprint, not yet peer-reviewed
First online: 2026-08-26
DOI: Not available
Original paper · Full text