A research group led by Yuki Sato, a graduate student of the Graduate School of Science, Kyoto University, analyzes the peculiar metallic state that appears in the process of a cuprate superconductor becoming a superconducting state.As a result, it was discovered that electrons are arranged by collective self-organization to create a certain liquid crystal state.This achievement is a result of joint research with the University of Tokyo, Kyushu Sangyo University, Korea Institute of Science and Technology, and Max Planck Institute in Germany.
Superconductivity is a phenomenon in which electrical resistance becomes completely zero when certain substances are cooled to extremely low temperatures.In copper oxide, substances showing superconductivity at temperatures higher than -240 ° C have been discovered one after another.In this cuprate superconductor, a peculiar metallic state appears in which some electrons in a specific direction disappear at a temperature higher than that causing superconductivity.No definitive conclusion has been reached regarding this state (pseudo-gap state), which is one of the most important issues in modern physics.
In this research, we used a method (high-sensitivity magnetic torque measurement) that enables precise measurement with thousands of times higher sensitivity than before, and simulated a pure single crystal of a typical cuprate superconductor (YBa2Cu3Oy). The magnetic properties in the gap state were investigated.As a result, in the pseudo-gap state, the magnetic properties of matter differ depending on the direction (0 ° direction and 90 ° direction), and the electron population spontaneously arranges to create a new type of ordered state with spatial asymmetry. It became clear that the change was rapid (phase transition phenomenon).Such an electronic state is called an electron nematic phase.
This is the first time that it has been clarified that the change to the pseudogap state is a phase transition to the electron nematic phase, which is an important guideline for elucidating the high-temperature superconducting phenomenon.In the future, it is expected that the relationship between the electron nematic phase and the mechanism of high-temperature superconductivity will be controversial.
Paper information:[Nature Physics] Thermodynamic evidence for a nematic phase transition at the onset of the pseudogap in YBa2Cu3Oy
