Greenaway M T, Kumaravadivel P, Wengraf J, Ponomarenko L A, Berdyugin A I, Li J, Edgar J H, Kumar R Krishna, Geim A K, Eaves L
Department of Physics, Loughborough University, Loughborough, LE11 3TU, UK.
School of Physics and Astronomy, University of Nottingham, Nottingham, NG7 2RD, UK.
Nat Commun. 2021 Nov 4;12(1):6392. doi: 10.1038/s41467-021-26663-4.
Oscillatory magnetoresistance measurements on graphene have revealed a wealth of novel physics. These phenomena are typically studied at low currents. At high currents, electrons are driven far from equilibrium with the atomic lattice vibrations so that their kinetic energy can exceed the thermal energy of the phonons. Here, we report three non-equilibrium phenomena in monolayer graphene at high currents: (i) a "Doppler-like" shift and splitting of the frequencies of the transverse acoustic (TA) phonons emitted when the electrons undergo inter-Landau level (LL) transitions; (ii) an intra-LL Mach effect with the emission of TA phonons when the electrons approach supersonic speed, and (iii) the onset of elastic inter-LL transitions at a critical carrier drift velocity, analogous to the superfluid Landau velocity. All three quantum phenomena can be unified in a single resonance equation. They offer avenues for research on out-of-equilibrium phenomena in other two-dimensional fermion systems.
对石墨烯进行的振荡磁阻测量揭示了大量新奇的物理现象。这些现象通常在低电流下进行研究。在高电流下，电子会被驱动至远离与晶格振动的平衡状态，以至于它们的动能可能超过声子的热能。在此，我们报告了单层石墨烯在高电流下的三种非平衡现象：（i）当电子经历朗道能级间（LL）跃迁时发射的横向声学（TA）声子频率出现“类多普勒”频移和分裂；（ii）当电子接近超音速速度时，出现伴有TA声子发射的朗道能级内马赫效应；以及（iii）在临界载流子漂移速度下发生弹性朗道能级间跃迁，类似于超流态的朗道速度。这三种量子现象可以统一在一个单一的共振方程中。它们为研究其他二维费米子系统中的非平衡现象提供了途径。
