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UID:69d90caef00a9
DTSTART:20220131T090000Z
SEQUENCE:0
TRANSP:OPAQUE
DTEND:20220131T120000Z
LOCATION:Online (Teams) and ICFO Auditorium
SUMMARY:ICFO | DANIEL PÉREZ SALINAS
CLASS:PUBLIC
DESCRIPTION:In the recent decades\, there has been a surge of interest in t
 he wide array of emergent phenomena found in strongly correlated materials
 . Understanding the inner workings of this type of systems is a major chal
 lenge due to the complex way in which multiple degrees of freedom\, such a
 s electronic\, structural and spin\, interact with each other and themselv
 es in non-trivial fashion. One of the most striking outcomes of these subt
 le interactions in correlated materials is the richness of their phase dia
 grams\, which include exotic states that still elude a complete physical d
 escription. It is in the transition from one phase to another where the in
 sights into the complex microscopic mechanisms may be most readily found\,
  and so the study of phase transitions has become a staple in correlated m
 aterials science.The experimental techniques used to track phase transitio
 ns are steadily becoming more precise and\, with the improvements\, previo
 usly overlooked aspects of a phase transition become more apparent\, such 
 as inhomogeneity or disorder\, which add another layer of complexity that 
 may clash with our current understanding. This is particularly important i
 n the relatively young field of ultrafast studies of correlated materials\
 , which tackles these systems in a largely uncharted territory: non-equili
 brium situations. In this thesis\, we develop novel experimental technique
 s which push towards an assessment of disorder and/or inhomogeneity in non
 -equilibrium phase transitions\, while still being able to accurately trac
 k the dynamics of the degrees of freedom involved. We then apply these tec
 hniques in two systems of current interest: La0.5Sr1.5MnO4\, a prototypica
 l layered manganite\, and VO2\, one of the most emblematic correlated mate
 rials.For La0.5Sr1.5MnO4\, we introduce an all-optical tabletop pump-probe
  setup that is able to track the ultrafast melting of charge- and orbital-
 order parameter with high accuracy. We show how\, in contrast with previou
 s descriptions\, the transition is incoherent and fits with the paradigm o
 f an order-disorder process. A key factor in these dynamics\, which is som
 etimes overlooked\, is spatial phase separation into the depth of the mate
 rial. With our setup\, the role of initial inhomogeneity and its evolution
  can be readily tested.For VO2\, we employ facility-scale X-ray sources to
  directly image phase inhomogeneity in the metal-to-insulator transition w
 ith coherent X-ray diffraction techniques. We show quantitative imaging of
  phase separation and domain growth statically\, which in our experimental
  setups should be able to distinguish intermediate phases appart from the 
 usual monoclinic insulator and rutile metal. We find no evidence of previo
 usly claimed intermediate phases such as monoclinic metal VO2. Finally\, w
 e show the first non-scanning spatially-resolved observation of the ultraf
 ast phase transition in VO2 with nanometer resolution\, where we identify 
 a global\, prompt change in the domain pattern in the femtosecond scale.
DTSTAMP:20260410T144358Z
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