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Ballistic Electron Transport Characteristics in Ultrahigh-Purity Metal Single Crystals

超高纯金属单晶的弹道电子输运特性

基本信息

批准号：
10640350
负责人：
HASHIMOTO Eiji
金额：
$ 2.18万
依托单位：
Hiroshima University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 1999
项目状态：
已结题

项目摘要

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.

为了了解量子极限下电导率的性质，在4.2K下对RRR（≡R D2300K D2/R D24.2K D2）大于150000的超高纯度铝单晶的电子导电性进行了测量。在这种材料中，导电电子的平均自由程在低温下达到约5mm。主要研究结果总结如下。(1)负弯曲电阻的取向依赖性（负弯曲电阻是电子的弹道传导效应）在主表面为（001）的十字形试样中观察到。当电子从<110>移动到<100>时，这种效应减弱，显示出与费米表面结构的强相关性。在<100>方向上，第二区费米面最接近区域边界。(2)体积残余电阻率的各向异性公认的知识告诉我们，像铝这样的立方金属不应该有电阻率的各向异性。然而，在超高纯度区域，我们发现ρ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ。这种各向异性行为与(1)中描述的弹道电子输运特性的取向依赖性一致。沿[001]的ρ γ γ值约为沿[110]的2倍。(3)电子平均自由程增大时的非线性I- V特性。欧姆定律，j =σ·E，在非均匀电场作用下，对试样的任何部分都不成立。这意味着电子分布对平衡的偏离不能再被看作是一阶无穷小：即使外加电场很小，电子分布函数也不总是保持其立方对称。这证实了上述ρ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ γ。