Electrical Conductivity in Quasicrystals and their Crystal Approximants

1. 高质量样品的主要结果如下：(1)在A1-Pd-Mn二十面体相中，电阻率随温度的降低几乎呈线性增加，在几十开尔文时达到最大值，然后在低mn浓度合金中降低。氦气温度下的比电阻率通常很高，根据合金成分的不同，比电阻率在10^3到10^4 μ OMEGA cm之间。电阻率和磁阻效应的温度依赖性可以用考虑自旋轨道相互作用的弱局域化理论来解释。(2)同样在Al-Pd-Re二十面体相中，电阻率也非常高，且随组成的变化非常敏感。在一些Al_<70>Pd_<20>Re_<10>合金中，氦温度下的电阻率值高达10兆cm，这是有报道过的准晶的最高值。电阻率随温度和磁场的变化，除电阻率最高的样品表现出希望样导电外，均用弱局域化理论解释。(3)在Al-Cu-Ru和Al-Cu-Fe二十面体相中，由于电子-电子相互作用效应，电导率在几十开尔文以下为T^<1/2>，在温度以上，由于弱局域化效应，电导率呈线性变化。霍尔系数的测量表明了载流子密度的温度变化。从目前得到的实验结果可以看出：在高质量准晶体及其高阶近似晶体中，由于费米-表面准布里渊带边界相互作用，在费米能级上总是形成一个较深的赝隙，并且随着赝隙的加深，在费米能级附近的电子具有更强的局域化倾向；这些情况产生了准晶体的电阻率特征行为。

1. Main results obtained for high quality samples are as follows :(1) In A1-Pd-Mn icosahedral phase, electrical resistivity increases almost linearly with deceasing temperature and shows a maximum at few tens of Kelvin and then decreases in low Mn-concentration alloys. The specific resistivity at helium temperature is generally quite high and varies from 10^3 to 10^4 mu OMEGA cm depending on the alloy composition. The temperature dependence of the resistivity, as well as the magnetoresistance effect, can be interpreted by the weak-localization theory that takes into account the spin-orbit interaction.(2) Also in Al-Pd-Re icosahedral phase, the resistivity is extremely high and varies sensitively with the composition. In some Al_<70>Pd_<20>Re_<10> alloys, the resistivity value reaches as high as 1O MEGA cm at helium temperature, which is the highest value ever reported for quasicrystals. Temperature and magnetic field dependences of the resistivity are interpreted by the weak-localization theory except the samples with the highest resistivity which show hoping-like conduction.(3) In Al-Cu-Ru and Al-Cu-Fe icosahedral phases, the electrical conductivity varies as T^<1/2> below a few tens of Kelvin due to the electron-electron interaction effect and as T linear above the temperature due to the weak-localization effect. Hall coefficient measurements have suggested the temperature variation of the carrier density.2. From the experimental results so far obtained, we get the following picture : in both high-quality quasicrystals and their high-order crystal approximants, a deep pseudo-gap is always forms at the Fermi-level due to the Fermi-surface quasi-Brillouin zone boundary interaction, and the electrons near the Fermi-level have a stronger tendency to localize as the pseudo-gap deepens ; these circumstances produce characteristic behavior of electrical resistivity in quasicrystals.