It is known that more heated bodies carry electric current worse, than cooled. The reason for that – the so-called thermal resistance of metals.
What is the thermal resistance
Thermal resistance is the resistance of the conductor (site of a chain) caused by the thermal movement of carriers of a charge. Here it is necessary to understand the electrons and ions which are contained in substance as charges. From the name it is clear that it is about the electric phenomenon of resistance.
Thermoresistance essence
The physical essence of thermoresistance consists in dependence of mobility of electrons on temperature of substance (conductor). Let's understand from where such regularity.
The conductivity in metals is provided with free electrons which under the influence of electric field get the directed movement along lines of electric field. Thus, it is reasonable to ask a question: what can obstruct the traffic of electrons? Metal contains an ionic crystal lattice which, certainly, slows down transfer of charges from one end of the conductor on another. Here it is necessary to notice that ions of a crystal lattice are in oscillating motion, therefore, they occupy the space limited not to their amount, but scope of amplitude of their fluctuations. Now it is necessary to think of what means increase in temperature of metal. The fact is that fluctuations of ions of a crystal lattice and also the thermal movement of free electrons just are also essence of temperature. Thus, increasing temperature, we increase amplitude of fluctuations of ions of a crystal lattice, so, we create a bigger obstacle to the directed movement of electrons. Thereof resistance of the conductor increases. On the other hand, at increase in temperature of the conductor also the thermal movement of electrons increases. It means that their movement becomes more and more chaotic, than directed. The more metal temperature, the freedom degrees which direction does not coincide with the direction of electric field prove more. It causes also bigger number of collisions of free electrons with ions of a crystal lattice. Thus, thermoresistance of the conductor is caused not only by the thermal movement of free electrons, but also thermal oscillating motion of ions of a crystal lattice which becomes more and more noticeable at metal temperature increase. From everything told it is possible to draw a conclusion that the best conductors are "cold". For this reason superconductors which resistance equals to zero contain at extremely low temperatures estimated by Calvin's units.