It is possible to make a material emit more radiation than it absorbs, violating the laws of physics in a way that could make energy-harvesting devices more efficient
By Karmela Padavic-Callaghan
1 July 2025
By breaking a law of physics, researchers can improve energy-harvesting devices like solar cells
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Researchers have broken a centuries-old law of physics, putting us on a path towards making better energy-harvesting devices, such as solar cells.
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Linxiao Zhu at the Pennsylvania State University has wanted to break Kirchoff’s law of thermal radiation for almost a decade. Dating back to the 1800s, this law dictates that objects emit as much thermal radiation – or heat – as they absorb. It is related to the most fundamental laws of physics that govern heat and energy: the laws of thermodynamics. These put a constraint on any device that absorbs light, and until recently, researchers thought those constraints were non-negotiable.
“In a usual textbook, you will read that Kirchoff’s law of thermal radiation is unconditionally true, and it’s required by the second law of thermodynamics. But in fact, it’s not,” says Zhu.
We have seen one previous violation of this law, but only for a narrow range of wavelengths, or colours, of radiation. Zhu and his colleagues have now broken it more dramatically than ever before.
To do so they needed two things: a carefully structured material and a magnetic field. This is because both structure and magnetism affect what happens to particles that make up radiation – like the photons that make up light – and the energy they carry once they hit a material.