Inicio 9 Research topics 9 Ultrafast optical control of phase transitions in 2D materials


P2: Fundamental properties of 2D materials
P5: Solid state Quantum devices for information technologies


Dr Allan S. Johnson
Research Group website:


Optical excitation with ultrafast laser pulses has emerged as a powerful new way of controlling 2D and quantum materials, leading to the formation of both novel transient and metastable phases. These can exhibit properties distinct from those in the equilibrium phase diagram, but our understanding of these phases and how to manipulate them is in its infancy. New and more advanced “coherent control” methods based on sequences of pulses have recently emerged as a route to obtain precise control over switching to both transient and metastable phases. In this project we may explore using coherent control to selectively control the reaction pathway inside 2D quantum materials, enabling switching between different states on demand. These experiments will leveraging a range of sources ultrafast sources spanning from the UV to THz that can selectively drive different degrees of freedom, but have not been combined in works to date.

Furthermore, phase change materials play an important role in conventional data storage systems, but while “write” cycles can be typically performed on the femtosecond timescale, erasure back the initial state generally proceeds slowly via thermal relaxation. By leveraging coherent control we aim to controllably direct the material path through phase space enabling rapid, bi-directional switching.

Finally, we have recently pioneered new ultrafast coherent X-ray imaging methods capable of directly measuring electron and structural properties with nanometer resolution at the femtosecond time scale, and the successful candidate will apply our new methodology to study the role of phase co-existence in stabilizing light-induced non-thermal phases. Phase co-existence has been flagged as important in all coherent control experiments thus far, but has not been directly observed.


We are looking for an ambitious and driven candidate interesting in pushing the frontiers of ultrafast control of quantum materials. Typically a PhD in physics, materials science or photonics would be expected, with experience in at least one of ultrafast lasers, time-resolved pump-probe measurements, or coherent X-ray imaging methods. Coding experience developing experimental control software and analysing data are a plus, preferably in python. High knowledge of written and spoken English is required. As experiments at large scale facilities like synchrotrons and XFELs are expected, but also because science is fundamentally collaborative, the candidate must be happy working as part of team while still operating independently and taking ownership of their project.

The candidate will have the chance to undertake experiments around the world and broaden their scientific network, and position themselves at the forefront of this exciting new field.


Stays at the ALBA synchrotron BOREAS beamline and the Max Born Institute for short pulse spectroscopy are envisioned to perform imaging of the nanoscale phase co-existence intrinsic to transitions in quantum materials. Experiments at X-ray free electron lasers in Germany, Switzerland, Korea and Japan are also expected to both image nanoscale phase co-existence and directly measure ultrafast structural changes via diffraction.