Abstract
At high magnetic fields, monolayer graphene hosts competing phases distinguished by their breaking of the approximate SU(4) isospin symmetry. Recent experiments have observed an even denominator fractional quantum Hall state thought to be associated with a transition in the underlying isospin order from a spin-singlet charge density wave at low magnetic fields to an antiferromagnet at high magnetic fields, implying that a similar transition must occur at charge neutrality. However, this transition does not generate contrast in typical electrical transport or thermodynamic measurements and no direct evidence for it has been reported, despite theoretical interest arising from its potentially unconventional nature. Here, we measure the transmission of ferromagnetic magnons through the two-dimensional bulk of clean monolayer graphene. Using spin polarized fractional quantum Hall states as a benchmark, we find that magnon transmission is controlled by the detailed properties of the low-momentum spin waves in the intervening Hall fluid, which is highly density dependent. Remarkably, as the system is driven into the antiferromagnetic regime, robust magnon transmission is restored across a wide range of filling factors consistent with Pauli blocking of fractional quantum Hall spin-wave excitations and their replacement by conventional ferromagnetic magnons confined to the minority graphene sublattice. Finally, using devices in which spin waves are launched directly into the insulating charge-neutral bulk, we directly detect the hidden phase transition between bulk insulating charge density wave and a canted antiferromagnetic phase at charge neutrality, completing the experimental map of broken-symmetry phases in monolayer graphene.
| Original language | English |
|---|---|
| Article number | 021060 |
| Journal | Physical Review X |
| Volume | 12 |
| Issue number | 2 |
| DOIs | |
| State | Published - Jun 2022 |
Bibliographical note
Funding Information:A. F. Y. and H. Z. acknowledge discussions with I. Sodemann. A. H. M., C. H., and N. W. acknowledge support from the ARO under Grant No. W911NF-16-1-0472 and from the Welch Foundation under Grant No. F1473. Z. P. acknowledges support by the Leverhulme Trust Research Leadership Grant No. RL-2019-015. M. P. Z. acknowledges support from the ARO through the MURI program (Grant No. W911NF-17-1-0323). Experimental work by H. Z. and A. F. Y. was supported by the National Science Foundation under DMR-1654186. A portion of this work was performed at the National High Magnetic Field Laboratory, which is supported by the National Science Foundation Cooperative Agreement No. DMR-1644779 and the state of Florida. K. W. and T. T. acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan, Grant No. JPMXP0112101001, JSPS KAKENHI Grant No. JP20H00354, and the CREST(JPMJCR15F3), JST.
Publisher Copyright:
© 2022 authors. Published by the American Physical Society.
ASJC Scopus subject areas
- Physics and Astronomy (all)