University of Warwick scientists discover "hot spots" around atomic defects in diamonds - challenging assumptions about the world's best heat conductor.
Diamond, famous in material science for being the best natural heat conductor on Earth - but new research reveals that, at the atomic scale, it can briefly trap heat in unexpected ways. The findings could influence how scientists design diamond-based quantum technologies, including ultra-precise sensors and future quantum computers.
In a study published in Physical Review Letters, researchers from University of Warwick and collaborators showed that when certain molecular-scale defects in diamond are excited with light, they create tiny, short-lived "hot spots" that momentarily distort the surrounding crystal. These distortions last only a few trillionths of a second but are long enough to affect the behaviour of quantum-relevant defects.
"Finding a hot ground state for a molecular-scale defect in diamond was extremely surprising for us", explained Professor James Lloyd-Hughes, Department of Physics, University of Warwick. "Diamond is the best thermal conductor, so one would expect energy transport to prevent any such effect. However, at the nanoscale some phonons - packets of vibrational energy - hang around near defect, creating a miniature hot environment that pushes on the defect itself."
The team studied a specific atomic defect in diamond where a nitrogen atom sits in place of a carbon atom and bonds to hydrogen - known as the Ns:H-C0 defect. When the researchers excited the defect's C-H bond with ultrafast infrared laser pulses, they expected the heat to dissipate immediately into the diamond lattice.
Instead, advanced spectroscopy revealed a curious effect: the defect briefly entered what scientists call a 'hot ground state' - meaning the surrounding crystal was still hot, and the defect was altered. The presence of built-up vibrational energy nearby shifted the defect's infrared signature to a higher energy, taking a few picoseconds to peak and then decay.
Dr. Junn Keat, PDRA, Department of Physics, University of Oxford and former PhD student at Warwick said: "For this study we used multidimensional coherent spectroscopy (2DIR) to study the defect, which allows us to separate the response of the defect produced by light with different energies.
"This is the first time we've applied this technique to the study of diamond defects, and the direct observation of hot ground state formation was beyond our expectations. We are very pleased with the results of this novel approach and are excited to see what else we can study with this technique."
The team also explained why diamond fails to remove this energy instantly. The defect releases its energy by generating particular phonons with large energy - the kinds of vibrations that do not travel far. These phonons move slowly and scatter quickly, creating a tiny bubble of heat around the defect before they eventually decay into faster-moving, heat-carrying vibrations.
Dr. Jiahui Zhao, Department of Physics, University of Warwick added: "Momentary local heating matters because defects are tiny, sensitive quantum systems, and even fleeting changes in their environment can affect their stability, precision, and usefulness in quantum technologies."
Defects like the nitrogen-vacancy (NV) and silicon-vacancy (SiV) centres in diamond serve as sensitive sensors and building blocks for quantum information processing. Their performance depends on keeping their spin states stable-and these spin states are strongly influenced by vibrations in the surrounding lattice.
The new findings indicate that optical techniques used to control defects may unintentionally generate small, short-lived pockets of heat. These local temperature spikes can subtly disturb the spin states, potentially affecting coherence times and the overall performance of diamond-based quantum devices.
