Diamonds are not the stable heat conductor they were thought to be

In a collaborative effort between universities, national research institutions, and industry, the University of Warwick’s facilities and expertise played a crucial role in discovering ‘hot spots’ around atomic defects (imperfections of a material’s microscopic structure) in diamonds, thereby challenging assumptions about the material known to be the world’s best natural heat conductor. 

Researchers discovered that when light hits certain molecular-scale defects inside a diamond, it can create ultra-small ‘hot spots’ that momentarily distort the surrounding crystal, causing heat to be trapped for a few trillionths of a second, rather than allowing it to spread out. These distortions last just long enough to affect the behaviour of these defects. 

The defect sheds energy by producing high-energy phonons, which are vibrations that tend to remain local rather than spreading through the material

Professor James Lloyd-Hughes of the Department of Physics at the University of Warwick explained: “Finding a hot ground state for a molecular-scale defect in diamond was extremely surprising for us. Diamond is the best thermal conductor, so one would expect energy transport to prevent any such effect. However, at the nanoscale, some phonons… hang around near a defect, creating a miniature hot environment that pushes on the defect itself.” 

The researchers went on to explain why diamond doesn’t dissipate this energy immediately: the defect sheds energy by producing high-energy phonons, which are vibrations that tend to remain local rather than spreading through the material. Because these phonons propagate slowly and scatter rapidly, they briefly trap heat in a small region around the defect before breaking down into faster vibrations, carrying the heat away. 

Diamond-based quantum sensors can measure magnetic fields, temperature, and other physical properties with extraordinary accuracy

Dr Jiahui Zhao from the University of Warwick’s Department of Physics noted the significance, as even brief environmental changes, she explained, can influence a diamond’s stability, accuracy, and performance in quantum technologies. These findings are especially important for mechanisms that rely on extreme precision. 

Diamond-based quantum sensors, for example, can measure magnetic fields, temperature, and other physical properties with extraordinary accuracy. Although recent research shows that quantum sensors are already outperforming classical devices in laboratories – and are even starting to be applied commercially – their performance relies on maintaining exceptionally stable conditions. 

Localised heating inside diamonds could introduce subtle noise or instability, potentially limiting the accuracy of these sensors. The same issue applies to future quantum computers, where even miniscule environmental disturbances can disrupt the fragile quantum states.  

By revealing how heat behaves around defects, the Warwick study provides crucial insight for the future of quantum technology. Understanding and managing these hot spots could help improve the reliability of diamond-based components and help meet the demanding requirements of next-generation quantum technologies.