Thickness matters in graphene stacks If you stack graphene monolayers on top of each other, the number of layers will affect the properties of the material. Intuitively, one would expect that as the stack becomes thicker, the results will converge as the sample starts to resemble graphite. Nam et al. measured the conductance of graphene multilayers of increasing thickness. Studying samples up to seven layers thick, they found that in all of them, electronic correlations caused a phase transition at a nonzero critical temperature. However, the critical temperature, as well as the nature of the low-temperature state, depended strongly on the number of layers. This unexpectedly persistent dependence showed no signs of slowing down and will motivate further theoretical and experimental work. Science, this issue p. 324 Stacks of graphene up to seven layers thick show a strong dependence of the critical temperature on the number of layers. Suspended Bernal-stacked graphene multilayers up to an unexpectedly large thickness exhibit a broken-symmetry ground state whose origin remains to be understood. We show that a finite-temperature second-order phase transition occurs in multilayers whose critical temperature (Tc) increases from 12 kelvins (K) in bilayers to 100 K in heptalayers. A comparison of the data with a phenomenological model inspired by a mean-field approach suggests that the transition is associated with the appearance of a self-consistent valley- and spin-dependent staggered potential that changes sign from one layer to the next, appearing at Tc and increasing upon cooling. The systematic evolution with thickness of several measured quantities imposes constraints on any microscopic theory aiming to analyze the nature of electronic correlations in this system.

中文翻译：

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石墨烯多层膜中的一系列有限温度电子相变

石墨烯堆叠中的厚度很重要 如果将石墨烯单层堆叠在一起，层数将影响材料的特性。直觉上，人们会认为随着堆栈变厚，结果会随着样品开始类似于石墨而收敛。南等人。测量了厚度增加的石墨烯多层的电导率。他们研究了多达七层厚的样品，发现在所有这些样品中，电子相关性导致了非零临界温度下的相变。然而，临界温度以及低温状态的性质在很大程度上取决于层数。这种出乎意料的持续依赖没有显示出放缓的迹象，并将推动进一步的理论和实验工作。科学，这个问题 p。324 高达七层厚的石墨烯堆栈显示出临界温度对层数的强烈依赖性。悬浮的伯纳尔堆叠石墨烯多层膜达到出人意料的大厚度表现出对称性破坏的基态，其起源仍有待了解。我们表明，有限温度二阶相变发生在多层膜中，其临界温度 (Tc) 从双层中的 12 开尔文 (K) 增加到七层中的 100 K。将数据与受平均场方法启发的现象学模型进行比较表明，转变与自洽的谷和自旋相关交错电位的出现有关，该电位从一层到下一层改变符号，出现在Tc 并随冷却增加。