superconducting materials
Uploaded by pavan on Jul 01, 2014
SUPERCONDUCIVITY- DISAPPERANCE OF RESISTIVITY
In the case of conductors resistance arises due to the thermal vibrations present in the material, these vibrations increases with the increase of temperature.as the temperature of the material decreases resistance also decreases linearly. But there are certain strange materials where the resistance of material abruptly goes down to zero as the temperature is decremented. Because as the temperature decreases thermal vibrations starts to decease and thereby resistance of a material drops down to null value. The temperature at which the resistance drops suddenly to zero is termed as critical temperature and material is said to exist in a state called superconducting state and the phenomenon is called superconductivity. This concept was put forward by a scientist kamerlingh ones while doing experiment on mercury, he could observe the drastic change of resistance at 4.2 K proving the phenomena of superconductivity. The pheonomenon of superconductivity is observed only at low temperature, hence it is also known as low temperature physics. The property of superconductor can be best understood as follows.
Consider a core of positive ions present inside a material, let us assume an electron having larger energy is approaching towards the +ve ion core of the material, as it is in the vicinity of +ve ion they undergo distortion with the thermal vibrations present in them due to which the energy of the electron will decrease. Consider another electron having higher energy from the other end is interacting with positive ion core, after sometime the energy of the second electron will try to decrease, thereby the thermal vibrations present in this ion core alone will be acting as a mediator to bound thes two electrons in pair, because a certain repulsive force will exist always between two electrons if there is no mediator between them, hence this interaction is called as electron-lattice-electron interaction. The bound energy of this electrons is very low of the order of 0.024 ev, on application of thermal energy we can easily break this pair of electrons and transform the material to conducting phase. These pair of electrons are called as cooper...