标题： 拓扑相变诱导的极端磁阻在TaSb$_{2}$ 显示英文标题

标题： Topological phase transition induced extreme magnetoresistance in TaSb$_{2}$

摘要： 我们在单晶TaSb$_{2}$在1.5 K和15 T的中等条件下报告了172万百分比的极大正磁阻。磁阻（MR$\propto\,B^{1.96}$）的二次增长在15 T时仍未饱和，这是这种半金属中电子和空穴袋之间几乎完美的补偿，$<0.1\%$的不匹配的表现。补偿机制通过温度依赖的MR、霍尔和热电系数（Nernst和Seebeck）得到确认，揭示了在约20 K和60 K分别发生的两个明显的费米面重构过程，\textit{即}未自发对称性破缺的Lifshitz转变。利用磁阻和磁化率的量子振荡，并得到密度泛函理论计算的支持，我们确定了TaSb$_{2}$的主要空穴费米面沿$F-L$线形成独特的肩部结构。该肩部口袋的平坦带顶仅比费米能级高几meV，在肩部口袋消失时导致20 K时观察到的拓扑相变。温度进一步升高使费米能级上升到主要空穴口袋的带顶，导致60 K时空穴口袋完全消失的第二次Lifshitz转变。 显示英文摘要

摘要： We report extremely large positive magnetoresistance of 1.72 million percent in single crystal TaSb$_{2}$ at moderate conditions of 1.5 K and 15 T. The quadratic growth of magnetoresistance (MR $\propto\,B^{1.96}$) is not saturating up to 15 T, a manifestation of nearly perfect compensation with $<0.1\%$ mismatch between electron and hole pockets in this semimetal. The compensation mechanism is confirmed by temperature-dependent MR, Hall and thermoelectric coefficients of Nernst and Seebeck, revealing two pronounced Fermi surface reconstruction processes without spontaneous symmetry breaking, \textit{i.e.} Lifshitz transitions, at around 20 K and 60 K, respectively. Using quantum oscillations of magnetoresistance and magnetic susceptibility, supported by density-functional theory calculations, we determined that the main hole Fermi surface of TaSb$_{2}$ forms a unique shoulder structure along the $F-L$ line. The flat band top of this shoulder pocket is just a few meV above the Fermi level, leading to the observed topological phase transition at 20 K when the shoulder pocket disappears. Further increase in temperature pushes the Fermi level to the band top of the main hole pocket, induced the second Lifshitz transition at 60 K when hole pocket vanishes completely.