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Figure 1: The resistivity of magic-angle graphene—under certain conditions—increases linearly with temperature. This “strange metal” behavior implies that the transport of electrons within the material is defined by a short scattering time that scales as the Planck constant divided by the temperature. Figure 1: The resistivity of magic-angle graphene—under certain conditions—increases linearly with temperature. This “strange metal” behavior implies that the transport of electrons within the material is defined by a short scattering time that scales as the Planck constant divided by the temperature.
Graphic: APS/Alan Stonebraker

Viewpoint: Graphene Reveals Its Strange Side

Experiments on magic-angle graphene reveal a “strange metal” phase and transport behavior consistent with so-called Planckian dissipation.

Subir Sachdev, Department of Physics, Harvard University
February 18, 2020 | Physics 13, 20

Magic-angle graphene captured the attention of condensed-matter physicists in 2018 when it was discovered that this material—made of two sheets of graphene with slightly misaligned lattice orientations (Fig. 1)—is a superconductor. Moreover, observations showed that the phase diagram of magic-angle graphene is similar to that of copper oxide high-temperature superconductors, with an insulating region next to a dome-shaped superconducting region (see Trend: Bilayer Graphene’s Wicked, Twisted Road). Now, Pablo Jarillo-Herrero from the Massachusetts Institute of Technology, Cambridge, and his colleagues report that magic-angle graphene has another remarkable feature of the cuprate phase diagram: a “strange metal” phase in which the resistivity scales linearly with temperature down to very low temperatures [1]. This temperature dependence is unlike that of most metals and has proved difficult to explain with traditional models of electron conduction. The one clue that theorists have is that the strange metal phase is associated with a low-temperature transport behavior called Planckian dissipation [23]. The same association is found by Jarillo-Herrero and colleagues in magic-angle graphene, providing further evidence that strange metals are united by a fundamentally new form of transport that theorists are busy trying to characterize.

Read also: Strange Metal in Magic-Angle Graphene with near Planckian Dissipation [Phys. Rev. Lett. 124, 076801 (2020), 2.18.2020]

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