Magnetoresistance and valley degree of freedom in bulk bismuth
Magnetoresistance and valley degree of freedom in bulk bismuth
复制标题
块状铋的磁阻和谷自由度
DOI：
10.1088/1361-648x/aaced7
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发表时间：
2018-01
期刊：
影响因子：
--
通讯作者：
Yuki Fuseya
中科院分区：
文献类型：
--
作者：
Zengwei Zhu;Benoit Fauque;Kamran Behnia;Yuki Fuseya
在本文中，我们首先回顾了基于半经典理论的多谷系统的磁电阻的基本方面。然后，我们将回顾在一个原型的多谷系统，其中的电导率是由不同的谷的贡献之和的磁阻的实验证据和理论理解。块体铋具有三个谷，具有极各向异性的有效质量。因此，每个谷中的导磁率对磁场的取向极其敏感。因此，旋转磁场起到谷值阀的作用，调节每个谷值对总电导率的贡献。除了这种简单的半经典效应，在高场极限下，由于复杂的朗道谱，还出现了其他现象。在量子极限附近，磁场的方向显著影响着各谷区载流子的分布，即磁场诱导了谷区极化。此外，实验发现，远远超过量子极限，一两个山谷变得完全空无一物。这是凝聚态物理学中唯一一个费米海在没有金属-绝缘体转变的情况下被磁场完全干燥的情况。铋在量子极限附近有两个长期存在的问题：空穴的大的各向异性塞曼分裂，以及量子振荡中的额外峰，这些峰不能归属于任何已知的朗道能级。这些问题的解决，考虑到带间效应由于自旋轨道耦合前者，和贡献的孪生晶体为后者。到目前为止，整个光谱都可以用单粒子理论来解释。最后，我们将讨论在这个系统中的输运和谷对称性破缺的热力学特征。这个术语指的是在高磁场和低温下观察到的三重对称性的自发损失。它的理论认识仍然缺失。我们将讨论可能的解释。
In this paper, we first review fundamental aspects of magnetoresistance in multi-valley systems based on the semiclassical theory. Then we will review experimental evidence and theoretical understanding of magnetoresistance in an archetypal multi-valley system, where the electric conductivity is set by the sum of the contributions of different valleys. Bulk bismuth has three valleys with an extremely anisotropic effective mass. As a consequence the magnetoconductivity in each valley is extremely sensitive to the orientation of the magnetic field. Therefore, a rotating magnetic field plays the role of a valley valve tuning the contribution of each valley to the total conductivity. In addition to this simple semiclassical effect, other phenomena arise in the high-field limit as a consequence of an intricate Landau spectrum. In the vicinity of the quantum limit, the orientation of magnetic field significantly affects the distribution of carriers in each valley, namely, the valley polarization is induced by the magnetic field. Moreover, experiment has found that well beyond the quantum limit, one or two valleys become totally empty. This is the only case in condensed matter physics where a Fermi sea is completely dried up by a magnetic field without a metal–insulator transition. There have been two long-standing problems on bismuth near the quantum limit: the large anisotropic Zeeman splitting of holes, and the extra peaks in quantum oscillations, which cannot be assigned to any known Landau levels. These problems are solved by taking into account the interband effect due to the spin–orbit couplings for the former, and the contributions from the twinned crystal for the latter. Up to here, the whole spectrum can be interpreted within the one-particle theory. Finally, we will discuss transport and thermodynamic signatures of breaking of the valley symmetry in this system. By this term, we refer to the observed spontaneous loss of threefold symmetry at high magnetic field and low temperature. Its theoretical understanding is still missing. We will discuss possible explanations.
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