Heat-loving quantum oscillations The shape of the Fermi surface in a conductor can be gleaned through quantum oscillations—periodic changes in transport properties as an external magnetic field is varied. Like most quantum properties, the phenomenon can usually be observed only at very low temperatures. Krishna Kumar et al. report quantum oscillations in graphene that do not go away even at the temperature of boiling water. Although “ordinary,” low-temperature quantum oscillations die away, another oscillatory behavior sets in that is extremely robust to heating. These resilient oscillations appear only in samples in which graphene is nearly aligned with its hexagonal boron nitride substrate, indicating that they are caused by the potential of the moiré superlattice that forms in such circumstances. Science, this issue p. 181 Magnetotransport in graphene–hexagonal boron nitride heterostructures exhibits robust oscillations. Cyclotron motion of charge carriers in metals and semiconductors leads to Landau quantization and magneto-oscillatory behavior in their properties. Cryogenic temperatures are usually required to observe these oscillations. We show that graphene superlattices support a different type of quantum oscillation that does not rely on Landau quantization. The oscillations are extremely robust and persist well above room temperature in magnetic fields of only a few tesla. We attribute this phenomenon to repetitive changes in the electronic structure of superlattices such that charge carriers experience effectively no magnetic field at simple fractions of the flux quantum per superlattice unit cell. Our work hints at unexplored physics in Hofstadter butterfly systems at high temperatures.

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石墨烯超晶格中重复布洛赫态引起的高温量子振荡

喜欢热的量子振荡导体中费米表面的形状可以通过量子振荡来收集——随着外部磁场的变化，传输特性的周期性变化。像大多数量子特性一样，这种现象通常只能在非常低的温度下观察到。克里希纳·库马尔等人。报告石墨烯中的量子振荡，即使在沸水的温度下也不会消失。尽管“普通”的低温量子振荡会消失，但另一种振荡行为对加热非常稳健。这些弹性振荡仅出现在石墨烯几乎与其六方氮化硼基板对齐的样品中，表明它们是由在这种情况下形成的莫尔超晶格的电位引起的。科学，这个问题 p。181 石墨烯-六方氮化硼异质结构中的磁传输表现出强大的振荡。金属和半导体中电荷载流子的回旋加速器运动导致其特性中的朗道量子化和磁振荡行为。通常需要低温来观察这些振荡。我们表明石墨烯超晶格支持不依赖于朗道量子化的不同类型的量子振荡。在只有几特斯拉的磁场中，振荡非常稳健，并且在远高于室温的情况下持续存在。我们将这种现象归因于超晶格电子结构的重复变化，使得电荷载流子在每个超晶格晶胞的通量量子的简单分数下实际上没有磁场。