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首页> 外文期刊>Physical Review X >Bipolar Conduction as the Possible Origin of the Electronic Transition in Pentatellurides: Metallic vs Semiconducting Behavior
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Bipolar Conduction as the Possible Origin of the Electronic Transition in Pentatellurides: Metallic vs Semiconducting Behavior

机译：双极传导作为近苯乙烯的电子转型的可能起源：金属VS半导体行为

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The pentatellurides ZrTe 5 and HfTe 5 are layered compounds with one-dimensional transition-metal chains that show a not-yet-understood temperature-dependent transition in transport properties as well as recently discovered properties suggesting topological semimetallic behavior. Here, we report magnetotransport properties for two kinds of ZrTe 5 single crystals grown with the chemical vapor transport (CVT) and the flux method (Flux), respectively. They show distinct transport properties at zero field: The CVT crystal displays a metallic behavior with a pronounced resistance peak and a sudden sign reversal in thermopower at approximately 130?K, consistent with previous observations of the electronic transition; in striking contrast, the Flux crystal exhibits a semiconducting-like behavior at low temperatures and a positive thermopower over the whole temperature range. For both samples, strong effects on the transport properties are observed when the magnetic field is applied along the orthorhombic b and c axes, i.e., perpendicular to the chain direction. Refinements on the single-crystal x-ray diffraction and the measurements of energy dispersive spectroscopy reveal the presence of noticeable Te vacancies in the CVT samples, while the Flux samples are close to the stoichiometry. Analyses on the magnetotransport properties confirm that the carrier densities of the CVT sample are about two orders higher than those of the Flux sample. Our results thus indicate that the widely observed anomalous transport behaviors in pentatellurides actually take place in the Te-deficient samples. For the stoichiometric pentatellurides, our electronic structure calculations show narrow-gap semiconducting behavior, with different transport anisotropies for holes and electrons. For the degenerately doped n -type samples, our transport calculations can result in a resistivity peak and crossover in thermopower from negative to positive at temperatures close to those observed experimentally due to a combination of bipolar effects and different anisotropies of electrons and holes. Our present work resolves the long-standing puzzle regarding the anomalous transport behaviors of pentatellurides, as well as the electronic structure in favor of a semiconducting state.
机译：戊硫脲Zrte 5和HFTE 5是具有一维转变金属链的层状化合物，其显示出在运输特性中的不太理解的温度依赖性转变，以及最近发现的性质，表明拓扑半机行为。在这里，我们报告了用化学蒸汽传输（CVT）生长的两种Zrte 5个单晶的磁传输属性和助焊法（助焊剂）。它们在零场显示不同的传输性能：CVT晶体显示金属行为，具有明显的电阻峰值和恒温器中的突然符号逆转，大约130Ω·k，与先前的电子转换观察一致;在引人注目的对比中，助焊剂晶体在低温下表现出半导体样行为，并在整个温度范围内具有正热电驱动。对于两个样品，当沿正极环B和C轴施加磁场时，观察到对运输性能的强烈影响，即垂直于链条方向。对单晶X射线衍射的改进和能量色散光谱的测量揭示了CVT样品中明显的TE障碍的存在，而助焊剂样品靠近化学计量。 MagnetOcransport属性的分析确认CVT样品的载流子密度大约比助焊剂样品高的两个订单。因此，我们的结果表明，在TE缺陷的样本中，戊脲的广泛观察到的戊脲的异常运输行为。对于化学计量的戊硫化物，我们的电子结构计算显示窄间隙半导体行为，具有不同的孔和电子的传输各向异性。对于掺杂掺杂的N型样品，我们的运输计算可以导致热电机的电阻率峰值和在靠近实验观察到的温度的阳性的电阻率峰值和交叉由于双极效应和电子和孔的不同各向异性的组合而被实验观察到。我们现在的工作解决了关于戊脲的异常运输行为的长期拼图，以及支持半导体状态的电子结构。

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