Ye Yuhao, Wang Jinhua, Nie Pan, Zuo Huakun, Li Xiaokang, Behnia Kamran, Zhu Zengwei, Fauqué Benoît
Wuhan National High Magnetic Field Center and School of Physics, Huazhong University of Science and Technology, Wuhan, 430074, China.
Laboratoire de Physique et d'Etude des Matériaux (CNRS) ESPCI Paris, PSL Research University, 75005, Paris, France.
Nat Commun. 2024 Nov 12;15(1):9794. doi: 10.1038/s41467-024-54021-7.
In graphite, a moderate magnetic field confines electrons and holes into their lowest Landau levels. In the extreme quantum limit, two insulating states with a dome-like field dependence of the their critical temperatures are induced by the magnetic field. Here, we study the evolution of the first dome (below 60 T) under hydrostatic pressure up to 1.7 GPa. With increasing pressure, the field-temperature phase boundary shifts towards higher magnetic fields, yet the maximum critical temperature remains unchanged. According to our fermiology data, pressure amplifies the density and the in-plane effective cyclotron mass of hole-like and electron-like carriers. Thanks to this information, we verify the persistent relevance of the BCS relation between the critical temperature and the density of states in the weak-coupling boundary of the dome. In contrast, the strong-coupling summit of the dome does not show any detectable change with pressure. We argue that this is because the out-of-plane BCS coherence length approaches the interplane distance that shows little change with pressure. Thus, the BCS-BEC crossover is tunable by magnetic field and pressure, but with a locked summit.
在石墨中，适度的磁场会将电子和空穴限制在它们的最低朗道能级。在极端量子极限下，磁场会诱导出两种绝缘态，其临界温度呈现出类似穹顶状的磁场依赖性。在此，我们研究了在高达1.7吉帕的静水压力下第一个穹顶（低于60特斯拉）的演化情况。随着压力增加，场-温度相边界向更高磁场方向移动，但最大临界温度保持不变。根据我们的费米学数据，压力会增大类空穴和类电子载流子的密度以及面内有效回旋质量。基于这些信息，我们验证了在穹顶的弱耦合边界中，临界温度与态密度之间的BCS关系始终具有相关性。相比之下，穹顶的强耦合顶点在压力作用下未显示出任何可检测到的变化。我们认为这是因为面外BCS相干长度接近面间距，而面间距随压力变化很小。因此，BCS - BEC交叉可以通过磁场和压力进行调节，但顶点是锁定的。
