In sufficiently clean metals, it is possible for electrons to collectively flow as a viscous fluid at finite temperature. These viscous effects have been predicted to give a notable magnetoresistance, but whether the magnetoresistance is positive or negative has been debated. We argue that regardless of the strength of inhomogeneity, bulk magnetoresistance is always positive in the hydrodynamic regime. We also compute transport in weakly inhomogeneous metals across the ballistic-to-hydrodynamic crossover, where we also find positive magnetoresistance. The nonmonotonic temperature dependence of resistivity in this regime (a bulk Gurzhi effect) rapidly disappears upon turning on any finite magnetic field, suggesting that magnetotransport is a simple test for viscous effects in bulk transport, including at the onset of the hydrodynamic regime.

中文翻译：

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电子流体中粘性磁阻的征兆

在足够干净的金属中，电子有可能在有限的温度下集体作为粘性流体流动。预计这些粘性效应会产生显着的磁阻，但是人们一直在争论磁阻是正还是负。我们认为，不管非均质性的强度如何，在流体力学条件下，体磁电阻始终为正。我们还计算了穿过弹道-流体动力学交叉点的弱非均质金属中的输运，在那里我们也发现了正磁阻。在任何有限的磁场中打开后，这种状态下电阻率的非单调温度依赖性（整体古尔芝效应）都会迅速消失，这表明磁传输是对整体传输中粘性效应（包括在流体动力学阶段开始）的简单测试。