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arXiv 1802.01544cond-mat.str-el
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Dirac-Weyl半金属Na $_3$ Bi和GdPtBi中手征反常磁电阻的实验研究

Experimental tests of the chiral anomaly magnetoresistance in the Dirac-Weyl semimetals Na$_3$Bi and GdPtBi

Sihang Liang, Jingjing Lin, Satya Kushwaha, Jie Xing, Ni Ni, R. J. Cava, N. P. Ong

摘要:

在狄拉克/外尔半金属中,当电场平行于磁场$\bf B$施加时,手征异常表现为外尔节点的最低(手征)朗道能级之间的电荷泵送产生的“轴向”电流。手征异常的证据是从纵向磁电阻(LMR)在Na $_3$ Bi和GdPtBi。然而,电流喷射效应(电流密度$\bf J$的聚焦)引起了对LMR实验的普遍关注。在这里,我们实现了一个石蕊测试,允许在钠$_3$铋和GdPtBi的本征LMR从纯电流喷射效应(纯铋),以明确区分。电流喷射沿样品的中间脊(脊)增强了$J$,同时在边缘处减小了它。我们通过比较脊部的局部电压降(表示为电阻$R_{spine}$)和边缘的局部电压降($R_{edge}$)来测量失真。在Bi中,$R_{spine}$随$B$急剧增加,但$R_{edge}$降低(喷射效应占主导地位)。然而,在Na $_3$ Bi和GdPtBi中,$R_{spine}$和$R_{edge}$均降低(喷射效应是次显性的)。数值模拟可以完全消除喷射畸变。我们发现,本征纵向电阻率$ρ_{xx}(B)$在钠$_3$铋减少了10.9倍之间$B$ = 0和10 T。第二个石蕊测试获得的平面角磁阻的参数图。这些结果大大加强了手征异常诱导LMR的内在本质的证据。我们简要地讨论了如何挤压测试可以扩展到测试ZrTe $_5$。

英文摘要:

In the Dirac/Weyl semimetal, the chiral anomaly appears as an "axial" current arising from charge-pumping between the lowest (chiral) Landau levels of the Weyl nodes, when an electric field is applied parallel to a magnetic field $\bf B$. Evidence for the chiral anomaly was obtained from the longitudinal magnetoresistance (LMR) in Na$_3$Bi and GdPtBi. However, current jetting effects (focussing of the current density $\bf J$) have raised general concerns about LMR experiments. Here we implement a litmus test that allows the intrinsic LMR in Na$_3$Bi and GdPtBi to be sharply distinguished from pure current jetting effects (in pure Bi). Current jetting enhances $J$ along the mid-ridge (spine) of the sample while decreasing it at the edge. We measure the distortion by comparing the local voltage drop at the spine (expressed as the resistance $R_{spine}$) with that at the edge ($R_{edge}$). In Bi, $R_{spine}$ sharply increases with $B$ but $R_{edge}$ decreases (jetting effects are dominant). However, in Na$_3$Bi and GdPtBi, both $R_{spine}$ and $R_{edge}$ decrease (jetting effects are subdominant). A numerical simulation allows the jetting distortions to be removed entirely. We find that the intrinsic longitudinal resistivity $ρ_{xx}(B)$ in Na$_3$Bi decreases by a factor of 10.9 between $B$ = 0 and 10 T. A second litmus test is obtained from the parametric plot of the planar angular magnetoresistance. These results strenghthen considerably the evidence for the intrinsic nature of the chiral-anomaly induced LMR. We briefly discuss how the squeeze test may be extended to test ZrTe$_5$.

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