14 DAY TRIAL // Superconductivity occurs when a certain material that has been cooled at extremely low temperatures, a few Kelvins for example, experiences a transformation which enables it to conduct electrical currents without opposing electrical resistance. Against general belief, not all materials can become superconductors; for example, silver, gold and some ferromagnetic materials do not present this property when subjected to temperatures close to absolute zero.
There are two separate types of superconducting materials, behaving in different ways, traditional low-temperature superconductors and high-temperature superconductors. Low temperature superconductors have been discovered in the early 20th century, they are mostly common and present superconducting properties at temperatures close to absolute zero, while high-temperature superconductors are mostly ceramic based material. Don't let the name fool you though, because they become superconductors at temperatures of about 90 Kelvin.
High temperature superconductors have been discovered in 1986, during an experiment involving a cuprate-perovskite ceramic material. However, there have been more than twenty years since their discovery, and the mechanism that triggers this behavior has mostly remained a mystery. Much in the same way as the low-temperature superconductors, during exposure to low temperature, the high-temperature supercondutors seem to form electron bonds, but the nature of these strange bonds is somehow elusive.
Assistant professor at Boston College, Vidya Madhavan believes that the quantum momentum of the electrons could be responsible for the strange force. During an experiment designed to compare the quantum momentums of electrons and the vibrational energies released during the binding of the electrons, she found significant similarities, fact that makes the electrons' spin the most likely candidate for the elusive force.
Superconductivity takes place when low temperatures bond electrons together, which at normal temperatures are virtually un-joinable. The experiment involved cooling the probed material with liquid helium, and applying a scanning tunneling microscopy technique, in order to determine the approximate behavior of the electrons through the material.
High-temperature superconducting materials are classified in two categories. Most of them are 'hole doped' materials, which means that the free electrons from the material have been removed, leaving behind a positive electric charge, also known as a hole. The second type is represented by the high-temperature superconducting materials that have electrons excess, called electron doped materials. Common sense tells us that the two should behave in similar ways, as both present superconducting properties at relatively high temperatures.
However, scientists found that the hole doped materials seemed to present an electron bonding force in the form of photon particles, which could probably originate in the electrons quantum momentum, thus confirming the theory that the bonding force between electrons in superconducting materials is determined by their spin. However, the spin alone cannot be held entirely responsible for the whole force exerted by the electrons. Thus, the scientists need to make further experiments in order to find the full explanation of the superconductivity phenomena.