Heating freezes electrons in twisted bilayer graphene

Lian, Biao

doi:10.1038/d41586-021-00843-0

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07 April 2021

Heating freezes electrons in twisted bilayer graphene

Electrons usually move more freely at higher temperatures. But they have now been observed to ‘freeze’ as the temperature rises, in a system consisting of two stacked, but slightly misaligned, graphene sheets.

Biao Lian ⁰

Biao Lian
1. Biao Lian is in the Department of Physics, Princeton University, Princeton, New Jersey 08544, USA.
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Particles in a substance randomly jiggle about more vigorously at higher temperatures, causing solids to melt into liquids above a critical temperature. In thermodynamics, higher temperatures favour the formation of states that have larger amounts of entropy, a measure of disorder. The liquid state of a substance typically has a larger entropy than has the solid state, because the movement of atoms is more disordered. However, an exception occurs for helium-3, which freezes into a solid as the temperature rises¹. This behaviour is known as the Pomeranchuk effect, and occurs because solid ³He has a larger entropy than does the liquid form — a phenomenon associated with the fluctuation of the spin (angular momentum) of ³He atoms. Writing in Nature, Saito et al.² and Rozen et al.³ now describe a similar effect in a graphene system, in which electrons are found to ‘freeze’ as the temperature increases.

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Nature 592, 191-193 (2021)

doi: https://doi.org/10.1038/d41586-021-00843-0

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