PRESSURE CONTROL OF ORGANIC CONDUCTOR-DISCOVERY OF NEW TYPE OF NARROW GAP SEMICONDUCTORS

许多有机导体表现出与温度无关的导电性。通常，它们被认为是脏金属，其导电性受杂质散射的支配。这项研究的主要结果之一是发现了具有不受温度影响的导电性的纯有机导体。在这些导体中，载流子密度和迁移率随温度变化很大。然而，我们看到的是不受温度影响的传导，因为密度和迁移率的变化抵消了。到目前为止，我们还不知道在有机导体和无机导体中还有其他材料具有如此奇特的性质。根据低温下的密度变化，我们发现它们是具有极窄能隙的半导体。α-(BEDT-TTF)_2I_3、α-(BEDT-TSeF)_2I_3、O-(BEDT-TTF)_2I_3和α-(BEDT-STF)_2I_3等有机导体在高压下都属于这一类材料。这些材料的另一个特征行为是在低温磁场下观察到的。载流子的性质随电场的增大而变化。改变有三个步骤。在低场极限下，载流子的质量约为0.02m，其中m为自由电子质量。在中间场中，载流子质量上升到接近m的值。在10T等高场中，载流子质量看起来要重得多。

Many organic conductors exhibit temperature-independent conductivity. Usually, they are considered to be dirty metals of which the electrical conduction is governed by impurity scattering. One of the main results of this investigation is the finding of pure organic conductors which shows temperature independent conductivity. In those conductors, both carrier density and mobility vary strongly with temperature. Nevertheless, we see temperature independent conduction because the effect of the change in the density and mobility just cancel out. Up to now, we know no other materials with such curious character both among organic and inorganic conductors. According to the density change at low temperatures, we found that they are semiconductors with extremely narrow energy gap.Organic conductors such as α-(BEDT-TTF)_2I_3, α-(BEDT-TSeF)_2I_3, O-(BEDT-TTF)_2I_3 and α-(BEDT-STF)_2I_3 belongs to this category of materials in case they are placed under high pressures.Another characteristic behavior of those materials is observed at low temperature under magnetic field. The property of carriers varies with increasing field. There are three steps of change. At low field limit, carriers have the mass of about 0.02m. where m is the free electron mass. In the intermediate field, the mass rises to a value close to m. In the high fields such as 10T, carrier mass looks to be much heavier.