From daily news and career tips to monthly insights on AI, sustainability, software, and more—pick what matters and get it in your inbox.
Discover the engineering revolution transforming modern defense with Strength, Stealth, Speed: The Very Fast Future of Advanced Defense
Access expert insights, exclusive content, and a deeper dive into engineering and innovation all with fewer ads or a completely ad-free experience.
All Rights Reserved, IE Media, Inc.
Follow Us On
Future of Defense
Access expert insights, exclusive content, and a deeper dive into engineering and innovation all with fewer ads or a completely ad-free experience.
All Rights Reserved, IE Media, Inc.
Finding the semiconductor material’s Higgs mode allowed researchers to tune their band gaps, making them better suited for solar cell applications.
Scientists at the Argonne National Laboratory (ANL) in the US found an elusive type of vibration, called the Higgs mode, in a semiconductor material for the first time. The collective movement of atoms resulted in a change in the symmetry of the crystal, which can be tuned to optimize the material’s properties.
If you recall science taught at school, you will remember that in gases molecules are loosely packed and are in motion, whereas in solids, molecules are densely packed and rigid, which gives them a defined shape. Yet, even within solids, atoms are in a constant motion. Much of this is vibrational motion, which is random and uncoordinated.
Scientists know that certain inputs can turn this random motion into coordinated, in-sync movement. Collectively, these vibrations make a sound, referred to as phonons. By tuning phonons, scientists have also found a way to influence the structure and behavior of materials.
Researchers at ANL were using light to change the phonon activity in a semiconductor material called metal halide perovskites. These materials are crucial as we look to build the next generation of solar cells, advanced sensors and quantum technologies.
During one of their experiments, where the scientists exposed a two-dimensional perovskite crystal to ultrafast laser pulses, they noticed a complex and elusive type of vibration that modulated the symmetry of the crystal itself. This is called Higgs mode.
Throughout history, researchers have found mathematical analogs of Higgs mode in various materials. The Higgs boson in particle physics, or that in superconductivity, which allows electricity to flow through a material with no resistance.
The Higgs mode is an oscillation in a system to a degree where it shows some symmetry or order. It typically emerges when a system undergoes a phase transition due to a phenomenon known as spontaneous symmetry breaking.
On this occasion, ANL researchers observed Higgs mode for the first time in a semiconductor material.
The researchers were working with butylammonium lead iodide, a metal halide perovskite which is used to make single-layer semiconducting crystals. Finding its Higgs mode allowed researchers to tune their band gaps, making them better suited for solar cell applications.
Band gaps of a semiconductor material determine which light frequencies it can absorb to make electricity in a solar cell and which ones they scatter. In their experiments, when the researchers exposed the semiconductor to ultrafast laser pulses, small groups of atoms in it began to oscillate.
The interactions between the electrons of these oscillating atoms changed their angles too. Interestingly, this also changed the bandgap of the material.
“We found that the bandgap increased and decreased periodically and rapidly,” said Richard Schaller, a scientist at ANL who was involved in the work. “Essentially, the color of the sample oscillated as it rocked through different crystal symmetries — turning redder and then bluer, over and over.”
The researchers also found that this Higgs mode steered the crystal toward a phase that cannot be achieved by heating it. This demonstrates that light-based excitation of material is different from heat-based excitation, thereby offering a new way to explore material phases and properties.
“If we can use light to control structural and electronic changes in materials on ultrafast time scales they might find use as optical switches in modern microelectronics and quantum technologies,” added Ayushi Shukla, postdoctoral researcher at ANL in a press release.
“Also, stabilizing novel, high-symmetry phases with low band gaps could open exciting opportunities for photovoltaic applications.”
The research findings were published in Nature Materials.
Ameya is a science writer based in Hyderabad, India. A Molecular Biologist at heart, he traded the micropipette to write about science during the pandemic and does not want to go back. He likes to write about genetics, microbes, technology, and public policy.
Premium
Follow
