Insulator or a metal? When a metal is cooled to low temperatures and placed in an external magnetic field, its resistivity may oscillate as the magnitude of the field is varied. Seeing these so-called quantum oscillations in an insulating material would be very unusual. Xiang et al. report such findings in the insulator ytterbium dodecaboride (YbB12) (see the Perspective by Ong). In addition to oscillations in resistivity, the authors observed oscillations in the magnetic torque. The results present a challenge to theories that aim to explain the insulating state of YbB12. Science, this issue p. 65; see also p. 32 In the insulator YbB12, both resistivity and magnetic torque show quantum oscillations, albeit with different effective masses. In metals, orbital motions of conduction electrons on the Fermi surface are quantized in magnetic fields, which is manifested by quantum oscillations in electrical resistivity. This Landau quantization is generally absent in insulators. Here, we report a notable exception in an insulator—ytterbium dodecaboride (YbB12). The resistivity of YbB12, which is of a much larger magnitude than the resistivity in metals, exhibits distinct quantum oscillations. These unconventional oscillations arise from the insulating bulk, even though the temperature dependence of the oscillation amplitude follows the conventional Fermi liquid theory of metals with a large effective mass. Quantum oscillations in the magnetic torque are also observed, albeit with a lighter effective mass.

中文翻译：

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绝缘体电阻率的量子振荡

绝缘体还是金属？当金属冷却到低温并置于外部磁场中时，其电阻率可能会随着磁场强度的变化而振荡。在绝缘材料中看到这些所谓的量子振荡是非常不寻常的。向等人。在绝缘体十二硼化镱 (YbB12) 中报告了这样的发现（见 Ong 的观点）。除了电阻率的振荡外，作者还观察到磁扭矩的振荡。结果对旨在解释 YbB12 绝缘状态的理论提出了挑战。科学，这个问题 p。65; 另见第。32 在绝缘体 YbB12 中，电阻率和磁扭矩均显示量子振荡，尽管有效质量不同。在金属中，费米表面上传导电子的轨道运动在磁场中被量化，这表现为电阻率的量子振荡。这种朗道量化在绝缘体中通常不存在。在这里，我们报告了绝缘体中的一个显着例外——十二硼化镱 (YbB12)。YbB12 的电阻率比金属电阻率大得多，表现出明显的量子振荡。这些非常规振荡来自绝缘体，即使振荡幅度的温度依赖性遵循具有大有效质量的金属的传统费米液体理论。还观察到磁扭矩中的量子振荡，尽管有效质量更轻。我们报告了绝缘体中的一个显着例外——十二硼化镱 (YbB12)。YbB12 的电阻率比金属电阻率大得多，表现出明显的量子振荡。这些非常规振荡来自绝缘体，即使振荡幅度的温度依赖性遵循具有大有效质量的金属的传统费米液体理论。还观察到磁扭矩中的量子振荡，尽管有效质量更轻。我们报告了绝缘体中的一个显着例外——十二硼化镱 (YbB12)。YbB12 的电阻率比金属电阻率大得多，表现出明显的量子振荡。这些非常规振荡来自绝缘体，即使振荡幅度的温度依赖性遵循具有大有效质量的金属的传统费米液体理论。还观察到磁扭矩中的量子振荡，尽管有效质量更轻。即使振荡幅度的温度依赖性遵循具有大有效质量的金属的传统费米液体理论。还观察到磁扭矩中的量子振荡，尽管有效质量更轻。即使振荡幅度的温度依赖性遵循具有大有效质量的金属的传统费米液体理论。还观察到磁扭矩中的量子振荡，尽管有效质量更轻。