Switching Material From One State to Another With a Single Flash of Light

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Scientists from the Department of Energy’s SLAC National Accelerator Laboratory and the Massachusetts Institute of Technology have demonstrated a surprisingly simple way of flipping a material from one state into another, and then back again, with single flashes of laser light.

Image Caption: In experiments at SLAC, single pulses of laser light were used to switch tantalum disulfide from one state to another and back again. Clockwise from left: A single light pulse turns the material from its initial, alpha state (red) into a mixture of alpha and beta (blue) states that are separated by domain walls (right). A second light pulse dissolves the domain walls and the material returns to its original state. Switches like this could potentially lead to the development of new types of data storage devices. 

This switching behavior is similar to what happens in magnetic data storage materials and making the switch with laser light could offer a new way to read and write information in next-generation data storage devices, among other unprecedented applications, says Nuh Gedik, the study’s principal investigator at MIT. The team reported their results today in Science Advances.

Frozen Waves of Electrons

In today’s devices, information is stored and retrieved by flipping the spin of electrons with a magnetic field. “But here we flipped a different material property known as charge density waves,” says Alfred Zong, a graduate student in Gedik’s group and one of the study’s lead authors.

Charge density waves are periodic peaks and valleys in the way electrons are distributed in a material. They are motionless, like icy waves on a frozen lake. Scientists want to learn more about these waves because they often coexist with other interesting material properties, such as the ability to conduct electricity without loss at relatively high temperatures, and could potentially be related to those properties.

The new study focused on tantalum disulfide, a material with charge density waves that are all oriented in the same direction in what’s called the alpha state. When the researchers zapped a thin crystal of the material with a very brief laser pulse, some of the waves flipped into a beta state with a different electron orientation, and the alpha and beta regions were separated by domain walls. A second flash of light dissolved the domain walls and returned the material to its pure alpha state.

This transmission electron microscopy image shows a domain wall (marked with yellow circles) between two different states, alpha (red area) and beta (blue area), in a tantalum disulfide crystal. The beta state and domain wall formed after the crystal was hit with a single light pulse. 

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