
07/25/2025
In a groundbreaking achievement, researchers at Penn State have done what once seemed impossible: they’ve strongly violated Kirchhoff’s Law of Thermal Radiation, a bedrock principle of physics since 1860. This historic breakthrough could revolutionise how we harness and control heat, opening the door to advanced technologies in solar energy, thermal sensing, and heat regulation.
Kirchhoff’s Law states that, under identical conditions, a material must emit the same amount of thermal radiation it absorbs. For over a century and a half, this law has been a core part of thermodynamics, shaping everything from infrared sensors to space telescopes. But now, using a specially engineered metamaterial, the Penn State team has shattered that symmetry.
Their creation is a two-micrometer-thick film made of five precisely layered semiconductors, engineered to behave in extraordinary ways. When subjected to a strong magnetic field, this material displayed nonreciprocal thermal behavior, it emitted significantly more heat in one direction than it absorbed. The team achieved a contrast of 0.43 across a broad 10-micron wavelength range, doubling any previously recorded efforts.
To make this possible, they developed a custom magnetic thermal emission spectrophotometer, an instrument capable of measuring subtle differences in directional heat flow. The level of precision and control demonstrated here is unprecedented and marks a radical shift in our understanding of thermal dynamics.
What’s more, the metamaterial can be transferred onto different surfaces, meaning it has real-world potential. Devices equipped with this technology could manipulate heat just like electrical diodes control current. This paves the way for ultra-efficient energy harvesting, next-generation infrared sensors, and thermal systems that operate at levels once thought thermodynamically unreachable.
This isn’t just a clever lab trick. It’s a fundamental rethinking of the rules that govern how heat behaves, rules that now, thanks to modern materials and magnetic fields, are being rewritten in real time.
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