Twisted and nematic
Electrons in quantum materials can break rotational symmetry even when the underlying crystal lattice does not. This phenomenon, called nematicity, has been observed in many unconventional superconductors. Cao et al. found that magic-angle twisted bilayer graphene, in which superconductivity was recently discovered, also exhibits nematicity. The breaking of rotational symmetry was observed through transport measurements, which exhibited characteristic anisotropy.
Science, this issue p. 264
Strongly interacting electrons in solid-state systems often display multiple broken symmetries in the ground state. The interplay between different order parameters can give rise to a rich phase diagram. We report on the identification of intertwined phases with broken rotational symmetry in magic-angle twisted bilayer graphene (TBG). Using transverse resistance measurements, we find a strongly anisotropic phase located in a “wedge” above the underdoped region of the superconducting dome. Upon its crossing with the superconducting dome, a reduction of the critical temperature is observed. Furthermore, the superconducting state exhibits an anisotropic response to a direction-dependent in-plane magnetic field, revealing nematic ordering across the entire superconducting dome. These results indicate that nematic fluctuations might play an important role in the low-temperature phases of magic-angle TBG.
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