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Dynamically controlling the properties of complex materials with light

Final Report Summary - DCCM (Dynamically controlling the properties of complex materials with light)

The aim of DCCM was to use light to control the electronic and magnetic properties of materials on nanometer length-scales. The project has been very successful and has demonstrated several new techniques and made significant discoveries that will have a lasting impact on the field.

We have shown the mechanisms behind the light induced control of the metal-insulator transition in the phase change material Ge2Sb2Te5. We combined time resolved optical spectroscopy and time resolved electron diffraction to measure changes in the electronic and structural properties of the material (Nature Materials 2015). Our results highlighted a new route to controlling the electronic properties of these materials without changing the atomic structure. This enabled us to design a new ultrafast optical modulator (Advanced Materials 2016). We also investigated the role of strain in order to design more energy efficient materials (Nature Communications 2016) and performed detailed measurements on the electronic and thermal properties of these materials close to the transition threshold (Physical Review B 2016).

We have used X-ray and THz techniques to investigate the role of phase separation in correlated materials. We showed that domains of electronic order can be controlled by the polarization of a THz field (Nature Communications 2015). Interestingly, we could also show that domain orientation was stable to melt-quench cycles, strongly suggesting that strain also plays a strong role in determining the domain structure (Physica Scripta 2016). We have also applied resonant soft X-ray spectroscopy to image phase coexistence in a correlated material for the first time. We exploited X-ray resonances to metal-insulator phase transitions to measure phase coexistence and domain growth as a function of temperature (arXiv:1612.07998) enabling us to examine the microscopic mechanism for domain growth. These results have enabled us to obtain beam time to examine the dynamics of domain growth at the free electron laser, LCLS, in 2018.

We have also made significant progress in understanding how light can control spin dynamics. We have developed a non-linear optical technique to measure spin dynamics. We have used this to show that light can control the antiferromagnetic demagnetization. However, this demagnetization control is indirect. The control comes from the fact that different electronic excited states couple to different structural modes in the crystal, and these modes dictate the demagnetization (Physical Review B 2016). This has important implications for how demagnetization occurs in correlated materials. In addition, our collaboration has performed the world’s first magnetic inelastic X-ray scattering experiment. This enables us to look at spin correlations on nanometer length scales. We found that, while long range spin order could be rapidly and dramatically suppressed, short range spin interactions were robust and were not modified by photoexcitation.

More information on these results can be found at and the PI, Simon Wall, can be contacted at