Watching energy flow in solids with ultrafast electron bursts

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The way individual atoms and molecules move in materials has important consequences on properties such as electrical conductivity, heat capacity and acoustics.  Even in solids, atoms are always moving back and forth about some average position, and this motion occurs through specific wave-like modes called phonons. Phonons form elementary excitations in the material and can therefore carry energy in the form of heat.  As temperature increases, so do the number of phonons and vice-versa.  The group of Dr. Bradley Siwick has recently performed a measurement which shows how energy populates and flows between specific phonon modes as a material returns to equilibrium after having been excited by laser pulse.  They capture the evolution of the material by taking pictures with electrons, not light, at intervals of 10-13 s. Very few techniques exist which are able to distinguish between individual phonon modes, yet alone at their natural time-scales.  Siwick and his team guarantee that this technique represents a massive leap forward for researchers looking to unravel the connections between phonons and exotic phenomena such as superconductivity and charge density wave systems.

This research was published in Phys. Rev. B and highlighted in the Americal Physical Society magazine Viewpoint.

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