TITLE: Photoinduced phase transitions: twenty years of VO2
AUTHOR: Allan Johnson (IMDEA Nanociencia).
WHEN: March, 5th - 12PM
WHERE: Salón de Actos, ICMM-CSIC
ABSTRACT: Quantum materials can exhibit dramatic properties like superconductivity or colossal magnetoresistance which arise from their strongly correlated internal degrees of freedom. Understanding these emergent properties is extremely challenging as a perturbation to one degree of freedom will naturally propagate to all others, making isolating cause and effect difficult. One route to decouple these degrees of freedom is via ultrafast photoexcitation, which can outrun these couplings in the time domain. This is especially true with ultrafast phase transitions, where the key degrees of freedom come to the forefront. However, understanding these light-induced phase transitions comes with it's own complications as the pathway through phase space the material takes may be very different from in equilibrium. In this talk I will revisit one of the most studied photoinduced phase transitions, the insulator to metal transition of vanadium dioxide. Originally this transition was taken as the archetypal example of the smooth coherent transition light could introduce in complex materials, but recent work has challenged this picture and I will show instead that VO2 shows an ultrafast electronic and structural disordering transition. Nevertheless we find new non-thermal control pathways are possible in this material, and discuss the outlook for other photoinduced phase transitions.
