CM seminar : Light-Matter Interaction in Charge Density Waves

Abstract: When electrons in a solid are excited with light, they can alter the free energy landscape and access regions that are beyond reach in thermal equilibrium. This accessibility becomes of importance in the presence of phase competition, when one state of matter is favored over another by only a small energy scale that, in principle, is surmountable with light. In this talk, I will discuss a few of our recent ultrafast electron diffraction results on charge density wave (CDW) materials showing that, under far-from-equilibrium conditions, we observe strong evidence for topological defects. These defects are crucial in explaining how the amplitude of the CDW recovers well before long-range phase coherence. I will also show that in certain CDW materials, these defects can be manipulated with light to form metastable structures. Lastly, I will show that light can be used to unleash a CDW that is not present in equilibrium.



Bio: Anshul did his undergraduate studies at UCLA before moving onto get his PhD from the Univeristy of Illinois. There, he developed a new experimental method to probe condensed matter systems which now goes by the name of momentum-resolved electron energy loss spectroscopy or M-EELS. Using this method, he showed that the charge density wave transition in 1T-TiSe2 is driven by exciton condensation. He then pursued postdoctoral research studies at MIT using ultrafast electron diffraction studies on various charge density wave systems. He returned to UCLA where he is now an assistant professor of physics.