November 15, 2019

Looks Like We Have a New Material State

Stephen Wilson, a professor of materials at UC Santa Barbara’s College of Engineering, specializes in the “long before” area of material studies. That means he works to develop materials without a specific application, hopefully creating new materials that demonstrate sought-after new states on their own. In that effort, he and his colleagues have developed what is known as a “quantum spin liquid state.”

It’s important to understand that the quantum state exists on the atomic and sub-atomic level. Physics on this level can operate in unexpected ways.

On the quantum level, electrons deep within a material operate differently on both individual and collective levels from the electrons in another material. The difference is in each electron’s “spin,” or its intrinsic magnetic moment—the ability to produce a magnetic field—and ability to communicate with the magnetic moments of other electrons.

There are many recognized types of spin, and scientists suspect they’ll find more.

“There are certain, more classical moments that let you know to a very high degree of certainty that the spin is pointing in a particular direction,” Wilson says in a press release. “In those, the quantum effects are small. But there are certain moments where the quantum effects are large, and you can’t precisely orient the spin, so there is uncertainty, which we call ‘quantum fluctuation.'”

“In conventional materials, the magnetic moments talk to one another and want to orient relative to one another to form some pattern of order,” Wilson says. In classical materials, or the materials that are common and visible to the human eye, this pattern isn’t always consistent. It can be broken apart by thermal fluctuations, “just heat from the environment,” he says. “If the material is warm enough, it is nonmagnetic, meaning the moments are all sort of jumbled relative to one another.”

But on the quantum level, magnetic moments can fluctuate. A quantum fluctuation is a temporary change in the amount of energy in a point in space.

As scientist Matt Strassler explains via metaphor, “normal intuition would lead us to expect that anything like a marble sitting in anything like a bowl would sit quietly at the bottom. But a quantum mechanical particle in a trap of some sort will have a position and motion that are constantly fluctuating. These fluctuations have energy; the motion-energy of a quantum particle in a trap is never zero.”

The new state could have value, Wilson explains, because “quantum fluctuations become more relevant as a material cools, while thermal fluctuations increase as it heats up, so you want to find a magnet that doesn’t order until you can get it cool enough such that the quantum fluctuations preclude it from ever ordering.”

It’s unclear what the new material could precisely accomplish, but its odd characteristics are drawing Wilson’s attention. When studying the physics of matter, types of matter are ranked from order to disorder. Matter is usually most ordered at its lower temperatures, like ice.

But this new material, NaYbO2 (sodium ytterbium oxide), remains disordered at the lowest measurable temperature: .005 degrees Centigrade above absolute zero. Wilson’s team is curious to explore what that means. So are we.

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