"Probing the Superconducting State of Sr₂RuO₄ with Strains: New Perspectives on an Old Puzzle"

Presented by Dr. Giordano Mattoni, Program Specific Assistant Professor, from Kyoto University in Japan

Sr₂RuO₄ has fascinated physicists for over 30 years as a leading candidate for unconventional superconductivity, a state of matter where electrons pair up in unusual ways not explained by conventional theories. Despite intense study, the exact nature of its superconducting state remains elusive. At the heart of the debate lies the symmetry of the order parameter, which describes how electrons pair in the superconducting phase. Recent experiments applying uniaxial strain have added new insights but also deepened the mystery. In particular, the smooth variation of the superconducting transition temperature (Tc) under certain strain directions suggests a simple, one-component order parameter. On the other hand, ultrasound measurements detecting sudden changes in the elastic moduli of Sr₂RuO₄ point toward a more complex, two-component scenario.

In this talk, I will first give an overview of Sr₂RuO₄ and the long-standing puzzle surrounding its superconductivity. I will then introduce our recent experimental developments involving both uniaxial and shear strains in Sr₂RuO₄ crystals and measuring changes in Tc using sensitive magnetic techniques. Our findings offer a fresh angle on the problem and help test the competing theories of the superconducting state. This approach highlights the broader potential of strain as a powerful and versatile tool for tuning and controlling the electronic properties of quantum materials.