Superconductivity is a property of certain materials manifesting itself by the transport of electrical current without losses. So far, at atmospheric pressure, such materials can only enter the superconducting state when cooled to very low temperatures – the best materials require about -135° Celsius, and many far below that. The temperature where superconductivity sets in is called the material's critical temperature. Superconductors that can operate up to or above the temperature of liquid nitrogen (a cheap cooling agent), at about -195° Celsius, are designated “high-temperature” superconductors – this is in contrast to the earliest superconductors that require the temperature of liquid helium (a rare, expensive cooling agent) of -269° Celsius.
Even with these limitations, superconductors already offer unique advantages for a range of existing and potential applications, from enabling todays magnetic resonance imaging (MRI) machines, to telecommunication relays and generators/motors with very high power-to-weight ratios, e.g. for wind turbines or load-carrying electric vehicles. On the side of fundamental physics, superconductors have been an extremely important area within which physicists have already radically expanded human knowledge of systems of many interacting electrons, which represent the most important frontier of condensed matter physics today. The theories explaining the properties of the first generation of superconductors have been a breakthrough in our understanding of many-electron systems. However, even today, close to four decades after the discovery of high-temperature superconductors, there is no comparable theory available to explain their properties or to predict new ones.
However, without such a theory, there can be no program to deliberately engineer superconductors that work at even higher temperatures, in order to further reduce cooling requirements and thus vastly increase their beneficial use in areas where they would be currently impractical. Another limitation of all existing superconductors is that any wires made out of them loose their superconducting properties when they become too small. This severely impedes the development of integrated high-performance superconducting electronics that has the prospect of enormously increased computing and signal processing speeds compared to todays systems based on conventional semiconductors, while simultaneously greatly reducing power consumption.
This project aims at providing a novel and fundamental theoretical framework that would show how both these goals, being able to deliberately design superconductors with higher critical temperatures, while still functioning at nanoscale sizes, could be achieved. It will do so by leveraging the unparalleled theoretical insight of condensed matter physics into systems of one-dimensional (1D) interacting electrons, compared to higher-dimensional ones (the existing high-temperature superconductors are based on stacks of weakly coupled two-dimensional crystal lattices which are much harder to treat theoretically, one of the main reasons their properties cannot be deliberately engineered). We are developing the basic theory that would allow to reliably predict, and thus purposefully design, the superconducting properties of bulk materials made from such 1D building blocks, and that further hold the prospect of exhibiting high critical temperatures that would be amenable to systematic improvements. Our approach further aims at theory that would allow to engineer superconducting nanowires, a basic building block of highly integrated superconducting electronics.
This framework is further targeted at explaining the basic mechanisms behind a large group of already existing quasi-1D superconductors, which are made up out of systems of weakly coupled 1D electrons, such as the Bechgaard and Fabre salts and chromium pnictide. While these compounds do not show high critical temperatures, their fundamental mechanism for superconductivity is widely assumed to be of the same general type as that of the existing high-temperature superconductors, i.e. based on electron pairing due to repulsive interactions. This mechanism has so far defied a universally accepted theoretical description in any material, which is why this project is targeting our new theory framework to resolve it in the quasi-1D superconductors.
