The electron–hole plasma in charge-neutral graphene is predicted to realize a quantum critical system in which electrical transport features a universal hydrodynamic description, even at room temperature1,2. This quantum critical ‘Dirac fluid’ is expected to have a shear viscosity close to a minimum bound3,4, with an interparticle scattering rate saturating1 at the Planckian time, the shortest possible timescale for particles to relax. Although electrical transport measurements at finite carrier density are consistent with hydrodynamic electron flow in graphene5–8, a clear demonstration of viscous flow at the charge-neutrality point remains elusive. Here we directly image viscous Dirac fluid flow in graphene at room temperature by measuring the associated stray magnetic field. Nanoscale magnetic imaging is performed using quantum spin magnetometers realized with nitrogen vacancy centres in diamond. Scanning single-spin and wide-field magnetometry reveal a parabolic Poiseuille profile for electron flow in a high-mobility graphene channel near the charge-neutrality point, establishing the viscous transport of the Dirac fluid. This measurement is in contrast to the conventional uniform flow profile imaged in a metallic conductor and also in a low-mobility graphene channel. Via combined imaging and transport measurements, we obtain viscosity and scattering rates, and observe that these quantities are comparable to the universal values expected at quantum criticality. This finding establishes a nearly ideal electron fluid in charge-neutral, high-mobility graphene at room temperature4. Our results will enable the study of hydrodynamic transport in quantum critical fluids relevant to strongly correlated electrons in high-temperature superconductors9. This work also highlights the capability of quantum spin magnetometers to probe correlated electronic phenomena at the nanoscale. Viscous Dirac fluid flow in room-temperature graphene is imaged using quantum diamond magnetometry, revealing a parabolic Poiseuille profile for electron flow in a high-mobility graphene channel near the charge-neutrality point.

中文翻译：

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石墨烯中狄拉克流体的粘性流动成像

预计电荷中性石墨烯中的电子 - 空穴等离子体将实现量子临界系统，其中电传输具有普遍的流体动力学描述，即使在室温下也是如此1,2。预计这种量子临界“狄拉克流体”的剪切粘度接近最小界限 3,4，粒子间散射率在普朗克时间饱和 1，这是粒子松弛的最短时间尺度。尽管在有限载流子密度下的电传输测量与石墨烯 5-8 中的流体动力学电子流一致，但在电荷中性点处粘性流的清晰证明仍然难以捉摸。在这里，我们通过测量相关的杂散磁场，直接对室温下石墨烯中的粘性狄拉克流体流动进行成像。纳米级磁成像是使用量子自旋磁力计进行的，该磁力计在金刚石中实现了氮空位中心。扫描单自旋和宽场磁力测量揭示了电荷中性点附近高迁移率石墨烯通道中电子流的抛物线泊肃叶分布，建立了狄拉克流体的粘性传输。这种测量与在金属导体和低迁移率石墨烯通道中成像的传统均匀流动剖面形成对比。通过组合成像和传输测量，我们获得了粘度和散射率，并观察到这些量与量子临界状态下预期的普遍值相当。这一发现在室温下在电荷中性、高迁移率的石墨烯中建立了一种近乎理想的电子流体。我们的结果将使研究与高温超导体中强相关电子相关的量子临界流体中的流体动力学传输成为可能。这项工作还突出了量子自旋磁力计在纳米尺度上探测相关电子现象的能力。使用量子金刚石磁力计对室温石墨烯中的粘性狄拉克流体流动进行成像，揭示了电荷中性点附近高迁移率石墨烯通道中电子流的抛物线泊肃叶分布。