Polshyn, HryhoriyISTA ; Zhu, J.; Kumar, M. A.; Zhang, Y.; Yang, F.; Tschirhart, C. L.; Serlin, M.; Watanabe, K.; Taniguchi, T.; MacDonald, A. H.; Young, A. F.
Magnetism typically arises from the joint effect of Fermi statistics and repulsive Coulomb interactions, which favours ground states with non-zero electron spin. As a result, controlling spin magnetism with electric fields—a longstanding technological goal in spintronics and multiferroics1,2—can be achieved only indirectly. Here we experimentally demonstrate direct electric-field control of magnetic states in an orbital Chern insulator3,4,5,6, a magnetic system in which non-trivial band topology favours long-range order of orbital angular momentum but the spins are thought to remain disordered7,8,9,10,11,12,13,14. We use van der Waals heterostructures consisting of a graphene monolayer rotationally faulted with respect to a Bernal-stacked bilayer to realize narrow and topologically non-trivial valley-projected moiré minibands15,16,17. At fillings of one and three electrons per moiré unit cell within these bands, we observe quantized anomalous Hall effects18 with transverse resistance approximately equal to h/2e2 (where h is Planck’s constant and e is the charge on the electron), which is indicative of spontaneous polarization of the system into a single-valley-projected band with a Chern number equal to two. At a filling of three electrons per moiré unit cell, we find that the sign of the quantum anomalous Hall effect can be reversed via field-effect control of the chemical potential; moreover, this transition is hysteretic, which we use to demonstrate non-volatile electric-field-induced reversal of the magnetic state. A theoretical analysis19 indicates that the effect arises from the topological edge states, which drive a change in sign of the magnetization and thus a reversal in the favoured magnetic state. Voltage control of magnetic states can be used to electrically pattern non-volatile magnetic-domain structures hosting chiral edge states, with applications ranging from reconfigurable microwave circuit elements to ultralow-power magnetic memories.
We acknowledge discussions with J. Checkelsky, S. Chen, C. Dean, M. Yankowitz, D. Reilly, I. Sodemann and M. Zaletel. Work at UCSB was primarily supported by the ARO under MURI W911NF-16-1-0361. Measurements of twisted bilayer graphene (Extended Data Fig. 8) and measurements at elevated temperatures (Extended Data Fig. 3) were supported by a SEED grant and made use of shared facilities of the UCSB MRSEC (NSF DMR 1720256), a member of the Materials Research Facilities Network (www.mrfn.org). A.F.Y. acknowledges the support of the David and Lucille Packard Foundation under award 2016-65145. A.H.M. and J.Z. were supported by the National Science Foundation through the Center for Dynamics and Control of Materials, an NSF MRSEC under Cooperative Agreement number DMR-1720595, and by the Welch Foundation under grant TBF1473. C.L.T. acknowledges support from the Hertz Foundation and from the National Science Foundation Graduate Research Fellowship Program under grant 1650114. K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan, Grant Number JPMXP0112101001, JSPS KAKENHI grant numbers JP20H00354 and the CREST(JPMJCR15F3), JST.
Polshyn H, Zhu J, Kumar MA, et al. Electrical switching of magnetic order in an orbital Chern insulator. Nature. 2020;588(7836):66-70. doi:10.1038/s41586-020-2963-8
Polshyn, H., Zhu, J., Kumar, M. A., Zhang, Y., Yang, F., Tschirhart, C. L., … Young, A. F. (2020). Electrical switching of magnetic order in an orbital Chern insulator. Nature. Springer Nature. https://doi.org/10.1038/s41586-020-2963-8
Polshyn, Hryhoriy, J. Zhu, M. A. Kumar, Y. Zhang, F. Yang, C. L. Tschirhart, M. Serlin, et al. “Electrical Switching of Magnetic Order in an Orbital Chern Insulator.” Nature. Springer Nature, 2020. https://doi.org/10.1038/s41586-020-2963-8.
H. Polshyn et al., “Electrical switching of magnetic order in an orbital Chern insulator,” Nature, vol. 588, no. 7836. Springer Nature, pp. 66–70, 2020.
Polshyn H, Zhu J, Kumar MA, Zhang Y, Yang F, Tschirhart CL, Serlin M, Watanabe K, Taniguchi T, MacDonald AH, Young AF. 2020. Electrical switching of magnetic order in an orbital Chern insulator. Nature. 588(7836), 66–70.
Polshyn, Hryhoriy, et al. “Electrical Switching of Magnetic Order in an Orbital Chern Insulator.” Nature, vol. 588, no. 7836, Springer Nature, 2020, pp. 66–70, doi:10.1038/s41586-020-2963-8.