Ballistic Electron Transport Characteristics in Ultrahigh-Purity Metal Single Crystals

To understand the nature of the electronic conductivity in the quantum limit， measurements have been made at 4.2 K on the electronic conduction in single crystals of ultrahigh-purity aluminum with RRR （ ≡ R-D2300 K ― D2/R-D24. 2 K ― D2） of more than 150000。在这种材料中，一个导体电子在低温度下到达约5毫米的平均自由路径。主要结果按以下内容汇总。（1）负弯曲阻力的定向依赖性，一种电子的平衡性行为的影响，被观察到与（001）主表面的交叉形状的特性。这种效果被削弱了，因为一个电子射击转换<110><100>是从费米表面的结构中显示了一个强有力的相关性。在这个<100>方向上，第二区域费米表面离区域边界最近。（2） Anisotropy of the Bulk Residual Resistivity D2b D2Accepted wisdom tells us that there should be no anisotropy of resistivity in a cubic metal like aluminum。However， in the region of ultrahigh purities， we identified anisotropy of Odd2b D2：Odd2b D2 increases in the order of the [110]、[111] and [001] current directions。这一同向异性行为是一致的，描述为ballistic electron transport characteristics（1）。D2 value along [001] is about twice as large as that along [110]。（3） Nonlinear I-V CharacteristicsWhen the electron mean free path is enlarged。Ohm's Law， j =σ·E，并不局限于该物种在一个非均匀的电场下的作用。这意味着，从电子分布的equilibrium中的偏移可以被视为一个初始顺序无限的：电子分布函数并不总是保留其立方体对称性，即使应用的电子领域也很小。此confirms the anisotropy of D2b D2above。

To understand the nature of the electrical conductivity in the quantum limit, measurements have been made at 4.2 K on the electronic conduction in single crystals of ultrahigh-purity aluminum with RRR ( ≡ RィイD2300KィエD2/RィイD24.2KィエD2) of more than 150000. In this material, the mean free path of a conduction electron reaches about 5 mm at low temperatures. Main results are summarized as follows.(1) Orientation Dependence of Negative Bend resistanceNegative bend resistance, an effect of the ballistic conduction of electrons, was observed in cross-shaped specimens with the (001) main surface. This effect is weakened as an electron-shot shifts from <110> to <100> , showing a strong correlation with the structure of the Fermi surface. In the <100> direction, the second-zone Fermi surface is nearest to the zone boundary.(2) Anisotropy of the Bulk Residual Resistivity ρィイD2bィエD2Accepted wisdom tells us that there should be no anisotropy of resistivity in a cubic metal like aluminum. However, in the region of ultrahigh purities, we identified anisotropy of ρィイD2bィエD2: ρィイD2bィエD2 increases in the order of the [110], [111] and [001] current directions. This anisotropic behavior is consistent with the orientation dependence of the ballistic electron transport characteristics described in (1). The ρィイD2bィエD2 value along [001] is about twice as large as that along [110].(3) Nonlinear I- V CharacteristicsWhen the electron mean free path is enlarged. Ohm's law, j =σ・E, does not hold for any portion of the specimen under the action of a nonuniform electric field. This means that the deviation from equilibrium of the electron distribution can nolonger be regarded as being a first order infinitesimal : the electron distribution function does not always remain its cubic symmetry even though the applied electric field is small. This confirms the anisotropy of ρィイD2bィエD2 above.