In 1986, Bednorz and Müller discovered a family of materials based on copper (cuprates) that are high critical temperature superconductors (HTc). Only a few months later, they were jointly awarded the Nobel Prize in physics—the shortest time between the discovery and the prize award for any scientific Nobel Prize. Superconductors are so exciting because they lose their electrical resistance and can carry electricity without losses. With zero resistance cables, we could build more effective motors, wind generators or computers. Superconductors would reduce effectively the strain on the grid, decreasing risks associated with power supply failure at consumption peaks. We would help reducing our dependence from fossil fuels. Eliminating resistance of electrical conductors would be transformational to our society as a whole.
But superconductors still require being cooled and are expensive to utilize. Unfortunately, today, we don't have superconductivity at room temperature. And we nearly work in the dark when we search for materials with higher superconducting critical temperature—because it’s so difficult to understand why superconductivity occurs. Determining the origin of the HTc superconductivity is one of the major problems in condensed matter physics.
The iron pnictide materials are known since relatively recently and these have stirred again the community of condensed matter physicists. We are slowly seeing that these materials might hold the key to the long-sought solution of the puzzle. They are high Tc superconductors, but they are metals, not insulators as the cuprates, and their electronic properties are highly tunable showing a high degree of correlation with lattice, magnetism and among electrons themselves. These correlations might hold the key to unlock the mystery of HTc superconductivity.
The purpose of the ERC StG project “Using extreme magnetic field microscopy to visualize correlated electron materials (PNICTEYES)” is to contribute to solve the puzzle of HTc superconductivity by directly visualizing these correlations.
To achieve this objective, we use scanning tunneling microscopes (STM) at extreme magnetic fields, designed and built by me and the people who work with me. These microscopes provide neat images of electronic correlations because they are operated close to zero temperature and at very high magnetic fields, directly probing the electronic ground state. In my group, we operate solenoids capable of providing magnetic fields up to 22T, i.e. approximately 5000 times the Earth’s magnetic field. My group is now hosting the most intense magnetic field available outside international high magnetic field facilities, as the European Magnetic Field Laboratory (EMFL) or the National High Magnetic Field Laboratory at the US (MagLab). I have led the construction of a new microscope for this magnet and I am also building further microscopes. For example, within a recently awarded ERC PoC, I will considerably reduce the size of the microscope so that it fits in many new environments. With this effort, I also hope to help building up the capacities of large facilities.
The results obtained in this project have helped us to better understand how the competition between magnetism and superconductivity favors the emergence of superconductivity at high temperatures. We have seen that the magnetic order shapes the interaction between electrons producing anisotropic superconducting properties. We have also learned that quantum fluctuations change the properties of the superconductor under magnetic field, producing new spatial distribution of the paired electrons that can be related with emergence of HTc superconductivity.
