A superconductor is a material that has zero resistivity, depending on the condition the material is subjected to. In particular temperature and pressure. Below certain temperatures-the critical temperature-certain materials gain the property of superconductivity. Low temperature superconductors (LTS) exist below the boiling point of liquid nitrogen, which means that they can only be utilised within those conditions which is not extremely practical. LTS’s are used in MRI (magnetic resonance imaging) and NMR (nuclear magnetic resonance). High temperature superconductors have a critical temperature above the boiling point of liquid nitrogen, which is more practical. However, known HTS’s are brittle ceramics which are not ductile whatsoever and are extremely expensive to make. Therefore, the uses for an HTS has been theorised as of yet they are not viable to use in machines such as MRI scanners. It has been further theorised that Hydrogen under a pressure of around 2.6 million atmospheres changes structure so that it forms a superconductor. This superconductor could exist at room temperature much like carbon retains its form as a diamond. If such pressures could be achieved the possibilities of superconductors would be immense such as the availability to transfer electricity on a national grid system with no energy loss. However, what causes a previously normal conductor, to become a superconductor under conditions, such as a low temperature?
An electric current is a flow of electrons through a medium. In a normal conductor the electrons bump into other electrons and atoms which provides a resistance to the flow. In a superconductor however if the temperature is low enough electrons can be seen to flow without any resistance. Several theories have been put forward to explain this phenomenon. Superconductivity’s first best theory was suggested by Ginzburg and Landau in 1950. They theorised that there is a special field that surrounds the superconductor, this field gives mass to massless photons. This field was not proposed to be a new fundamental field but instead a collective motion of atoms, electrons and electromagnetic fields. This theory did not actually specify on what the field actually was, this was achieved by Bardeen, Cooper, and Schrieffer(BCS) all American physicists. They came up with the ‘BCS theory of superconductivity in 1957. The theory consisted of the idea of ‘Cooper pairs’, pairs of particles that team up at low temperatures, and make up Ginzburg and Landau’s field. Electrons in a cooper pair are bosons, despite a single electron being a fermion. This is due to the spin in the combined particle being a whole number which is a characteristic of a boson. Bosons are force carrying fields that can pile up as they do not take up space (like matter fields which cannot pile up for that reason). The pairs act together to combat the resistant interaction that one electron faces with an equal and opposite force on the other one. This resulted in paired electrons flowing through the superconductor unhampered.
When electrons collide in a normal conductor their electric field gently vibrates which emits low-energy photons, this emission of photons causes the electrons to lose energy and their velocity also reduces, diluting current. As photons have mass in both theories that means that the photons have to have a certain minimum energy as E=Mc2. Below the critical temperature electrons don’t have enough energy to make these photons and therefore no energy is lost and can move without resistance
An electric current is a flow of electrons through a medium. In a normal conductor the electrons bump into other electrons and atoms which provides a resistance to the flow. In a superconductor however if the temperature is low enough electrons can be seen to flow without any resistance. Several theories have been put forward to explain this phenomenon. Superconductivity’s first best theory was suggested by Ginzburg and Landau in 1950. They theorised that there is a special field that surrounds the superconductor, this field gives mass to massless photons. This field was not proposed to be a new fundamental field but instead a collective motion of atoms, electrons and electromagnetic fields. This theory did not actually specify on what the field actually was, this was achieved by Bardeen, Cooper, and Schrieffer(BCS) all American physicists. They came up with the ‘BCS theory of superconductivity in 1957. The theory consisted of the idea of ‘Cooper pairs’, pairs of particles that team up at low temperatures, and make up Ginzburg and Landau’s field. Electrons in a cooper pair are bosons, despite a single electron being a fermion. This is due to the spin in the combined particle being a whole number which is a characteristic of a boson. Bosons are force carrying fields that can pile up as they do not take up space (like matter fields which cannot pile up for that reason). The pairs act together to combat the resistant interaction that one electron faces with an equal and opposite force on the other one. This resulted in paired electrons flowing through the superconductor unhampered.
When electrons collide in a normal conductor their electric field gently vibrates which emits low-energy photons, this emission of photons causes the electrons to lose energy and their velocity also reduces, diluting current. As photons have mass in both theories that means that the photons have to have a certain minimum energy as E=Mc2. Below the critical temperature electrons don’t have enough energy to make these photons and therefore no energy is lost and can move without resistance