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Immersed in external magnetic fields (B), buckled graphene constitutes an ideal tabletop setup, manifesting a confluence of time-reversal symmetry (T) breaking Abelian (B) and T-preserving strain-induced internal axial (b) magnetic fields. In such a system, here we numerically compute two-terminal conductance (G), and four- as well as six-terminal Hall conductivity (σxy) for spinless fermions. On a flat graphene (b=0), the B field produces quantized plateaus at G=±|σxy|=(2n+1)e2/h, where n=0,1,2,⋯. The strain-induced b field lifts the twofold valley degeneracy of higher Landau levels and leads to the formation of additional even-integer plateaus at G=±|σxy|=(2,4,⋯)e2/h, when B>b. While the same sequence of plateaus is observed for G when b>B, the numerical computation of σxy in Hall bar geometries in this regime becomes unstable. A plateau at G=σxy=0 always appears with the onset of a charge-density-wave order, causing a staggered pattern of fermionic density between two sublattices of the honeycomb lattice.
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This content will become publicly available on November 12, 2025
Spin–orbit enabled unconventional Stoner magnetism
The Stoner instability remains a cornerstone for understanding metallic ferromagnets. This instability captures the interplay of Coulomb repulsion, Pauli exclusion, and twofold fermionic spin degeneracy. In materials with spin–orbit coupling, this fermionic spin is generalized to a twofold degenerate pseudospin which is typically believed to have symmetry properties as spin. Here, we identify a distinct symmetry of this pseudospin that forbids it to couple to a Zeeman field. This “spinless” property is required to exist in five nonsymmorphic space groups and has nontrivial implications for superconductivity and magnetism. With Coulomb repulsion, Fermi surfaces composed primarily of this spinless pseudospin property give rise to Stoner instabilities into magnetic states that are qualitatively different than ferromagnets. These spinless-pseudospin ferromagnets break time-reversal symmetry, have a vanishing magnetization, are noncollinear, and exhibit momentum-dependent energy band spin-splittings. In superconductors, for all pairing symmetries and field orientations, this spinless pseudospin extinguishes paramagnetic limiting. We discuss applications to superconducting UCoGe and magnetic NiS_2-xSex
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- Award ID(s):
- 2323857
- PAR ID:
- 10637121
- Publisher / Repository:
- PNAS
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 121
- Issue:
- 46
- ISSN:
- 0027-8424
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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