Seminar - Simon Wall: "Phase transitions in quantum materials"
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Simon Wall, ICFO Barcelona
Phase transitions in quantum materials
Quantum materials exhibit some of the most fascinating properties found in solids, such as high temperature superconductivity, insulator-metal phase transitions and colossal magnetoresistance. Despite extensive research, the origins of these properties remain poorly understood. In this talk, I will examine the case of vanadium dioxide (VO2), one of the first, and most studied “quantum” materials, which shows an insulator-metal phase transition close to room temperature.
In this talk I will discuss the results of two new techniques we have developed which enable us to gain deeper insights into quantum materials, and specifically discuss their application to VO2. I will discuss how resonant soft X-ray holography can be used to measure nanoscale phase separation in inhomogeneous films, and enables the direct observation of domain growth. I will then go on to hard X-ray probes that enable the measurement of non-equilibrium phase transitions on the atomic scale. By using time-resolved diffuse X-ray scattering, we show that disorder is a key component in the structural transition, even though the structural transition occurs within a few hundred femtoseconds.