By Camilla Shumaker
Photos by Whit Pruitt

Two Honors College students have tackled – and solved – an important question about matter that sheds new light on the quantum world. Guided by mentor Salvador Barraza-Lopez, associate professor of physics, students Tyler Bishop and Erin Farmer have uncovered new information about tin oxide and have published their research in Physical Review Letters.

“It’s a problem that needs to be solved, and no one has solved it yet,” said Farmer about the project. “That’s an amazing way to spend your time.”

While researchers have created forms of tin oxide with two layers, single layers of the material have yet to be obtained, so the students performed complicated calculations and used computer simulations to study how the material would behave in monolayer form.

“In physics we distinguish between hard condensed matter, from which things like transistor radios and phones come about, and soft condensed matter, which relates to emulsions such as shampoos and lotions, polymers and cells,” said Salvador Barraza-Lopez. “The thing that is exciting about this work is that it marries ideas from hard and soft condensed matter. It’s a completely unexplored area and actually quite interesting.”

Many common materials exhibit new properties in two-dimensional, or monolayer, form, and the study of these materials can lead to insights into the tiny particles that make up matter, as well as the quantum rules that govern them. Tin oxide is made up of atoms arranged in rectangular shapes, like bricks in a wall. In most materials with a structure like this, the “bricks” are oriented either vertically or horizontally, with different sections, or domains, of the material exhibiting different orientations. In order for the units to shift from a vertical to a horizontal orientation, energy must be added to the system. The amount of energy required for this is specific to the material, and researchers refer to it as “J.” This energy requirement forms a “barrier” which holds the units in place. According to the researcher’s calculations, however, the value of J for a single layer of tin oxide is so low that the particles can “tunnel” through this barrier and exist in both a vertical and a horizontal configuration at once. This is called quantum paraelastic behavior.

Farmer contributed to the research by calculating the transition temperature of the material, which is the temperature at which the energy of the system equals J, allowing the material to shift from a rectangular shape to a square shape, from which it can shift into a differently oriented rectangle.

After Farmer performed this calculation, Bishop used computer simulations to study the behavior of the material. He was able to confirm Farmer’s prediction of the transition temperature, but analyzing all the data from the simulations was a long process—months of staring at sequences of numbers. This task might have been too tedious for many students, but Bishop was able to keep focused by concentrating on the meaning behind the data.

“One thing that’s difficult is that when you’re just staring at all the numbers, you get lost and you forget what’s happening,” he explained. “So you have to constantly keep in mind, what am I actually doing rather than what am I typing in; what does the structure look like; what are the atoms doing? I take one number at a time and imagine where it is.”

“I think that’s what makes a physicist and a scientist in general,” Barraza-Lopez added. “That ability of going ahead of the number, to see where it should be. Tyler is able to sustain focus for a long time because he’s actually producing his own understanding of the numbers.”