Ground state of magic-angle graphene at charge neutrality
In plain words
With no electrons added, some magic-angle devices are insulators and others conduct weakly, and the state of an ideal, unstrained sample is unknown.
Precise statement
In magic-angle twisted bilayer graphene at $\nu = 0$, transport finds either a semimetal or an insulator depending on device, hBN alignment and heterostrain. Determine the ground state of the unaligned, low-strain system: a Kramers intervalley-coherent insulator, a valley- or spin-polarized insulator, or a nematic semimetal, the candidates of Hartree-Fock and strong-coupling theory for different strain. An answer identifies the order parameter and whether a charge gap exists at heterostrain below $0.05\%$.
What would settle it
STM imaging of intervalley order and tunnelling gap at $\nu = 0$, with transport on the same devices, for samples with measured heterostrain below 0.05% and no hBN alignment.
Status in the literature
Unverified note
Samples differ and no strain-controlled identification exists as of 2026, to this survey's knowledge.