Jens Biegert & Maciej Lewenstein

Institut de Ciències Fotòniques (ICFO)

Superconductors are materials that exhibit the ability to conduct electricity without any resistance. This phenomenon is observed in materials when they are cooled below the so-called superconductor transition temperature, often at very low temperatures (a few degrees above the absolute 0). Among these materials, there are the so-called high-temperature superconductors, which behave as superconductors at temperatures above 77K (the boiling point of liquid nitrogen). These materials are showing to be essential in the development of new electronic and information processing devices as well as optical quantum computers and even for improving the efficiency of electrical transmission lines.

However, high-temperature superconductivity has been seen to be closely linked to the control of their microscopic dynamics. So far, the detection of the different microscopic quantum phases in these complex materials has resulted quite challenging. Not only are the physical processes of these dynamic states still incomplete due to their wide array of quantum states, but the current methods used to explore their dynamics at microscopic scales are lagging sensitivity. Therefore, new tools to better understand the dynamic evolution of these types of superconductors are needed.

Now, an international team of researchers, led by ICREA Professors Jens Biegert and Maciej Lewenstein, propose a new methodology based on the use of High Harmonic spectroscopy (HHS) to investigate the transitions between the different phases of YBCO, a copper oxide cuprate material which is a well-known high-temperature superconductor. This study represents a major scientific breakthrough since it is the first time that highly non-linear and non-perturbative diagnostics/detection methodology is used to understand the behavior of strongly correlated materials.

In view of the experimental results obtained, the researchers have also gone beyond and present a new theoretical model to identify the connection between the measured optical spectra and the transition between the different quantum states of the YBCO: strange metal, pseudogap, and superconductor.