The Advanced Photon Source
a U.S. Department of Energy Office of Science User Facility

Nanoscale Control of Order Parameters Explored by Time-Resolved X-ray Probes

Type Of Event
Presentation
Sponsoring Division
XSD
Location
446/Conf. Rm.
Building Number
446
Room Number
Conf. Rm.
Speaker
Vladimir Stoica
Host
Xiaoyi Zhang
Start Date
09-20-2019
Start Time
10:00 a.m.
Description

Abstract:

Formation and stability of complex materials such as nanoscale heterostructures involve the competition and cooperation of multiple allowable states with very distinct properties, which can be the key for tuning functionalities of these materials. To understand this problem, one needs to not only have means to characterize these phases, but also suitable techniques to control these states of matter. Here, I will show several examples to illustrate my recent work in this area. In the first part, I will focus on emergent phases in PbTiO3/SrTiO3 superlattices, which can be manipulated with dimensionality and strain and controlled with ultrafast light pulses. One example is the creation of a persistent polar supercrystal by sub-picosecond laser pulses, which was revealed by X-ray probes of the lattice. The supercrystal consist of 3D ordering of polar vortices, it is stable at room temperature and can be erased by heating. In contrast, a similar superlattice grown with a different state of in-plane strain shows the presence of polar skyrmions, which can be erased by ultrafast laser excitation. In the second part, I will focus on the investigation of phase transitions between the insulating and metallic phases triggered with laser excitation. By using resonant scattering and spectroscopies, we can follow the separation of fundamental processes occurring in a regime of strong coupling between order parameters. Results for NdNiO3 and La0.7Ca0.3MnO3 will be compared to understand the role of lattice, electronic, and magnetic order on the phase transition. Finally, I will present some thoughts on new concepts from ultrafast laser techniques that can be used in conjunction with time-resolved X-ray probes to advance the capabilities at the APS in both the near term and post upgrade.

 

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