"Frustration" plus a pulse of laser light resulted in a stable "supercrystal" created by a team of researchers led by Penn State and Argonne National Laboratory, together with University of California, Berkeley, and two other national laboratories.
This is one of the first examples of a new state of matter with long-term stability transfigured by the energy from a sub-pico-second laser pulse. The team's goal, supported by the Department of Energy, is to discover interesting states of matter with unusual properties that do not exist in equilibrium in nature.
"We are looking for hidden states of matter by taking the matter out of its comfortable state, which we call the ground state," says the Penn State team leader Venkatraman Gopalan, professor of materials science. "We do this by exciting the electrons into a higher state using a photon, and then watching as the material falls back to its normal state. The idea is that in the excited state, or in a state it passes through for the blink of an eye on the way to the ground state, we will find properties that we would desire to have, such as new forms of polar, magnetic and electronic states."
Finding these states is done by a pump-probe technique when a laser fires a photon at the sample for 100 femtoseconds at a wavelength of 400 nanometers -- blue light. The pump light excites the electrons into a higher energy state and is quickly followed by a probe light, which is a gentler pulse of light that reads the state of the material. The challenge for the team was to find a way to maintain the intermediate state of matter, because the state may exist for only some tiny fraction of a second and then disappear. However, the researchers discovered that, at room temperature, the supercrystal is stuck in that state essentially forever.
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