RUMOURS of a superconductor that works at room temperature have been circulating for several months. Now South African physicist Johan Prins has finally published his results in a peer-reviewed journal 鈥� a feat that no previous claim of room-temperature superconductivity has ever achieved.
Superconductors transmit current with zero resistance, so no electricity is lost as heat. That creates the promise of ultra-efficient electronic devices and power cables, but the first superconductors to be discovered only worked at temperatures close to absolute zero. The discovery of relatively high-temperature oxide superconductors in the late 1980s raised hopes for materials that might superconduct at room temperature. But the flurry of claims that followed have all since evaporated, leaving most researchers exceedingly sceptical of the idea. The warmest confirmed superconductors only work about 150 degrees below room temperature.
So could Prins, a semiconductor specialist, have finally achieved this elusive goal? The effect he describes, while highly controversial, is certainly intriguing, as it appears in a vacuum just above a surface. All other known superconductors are solids.
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In his experiments, Prins used a layer of synthetic diamond that he had doped with oxygen atoms. By applying a voltage to a gold-plated probe just above the surface of the diamond, he was able to draw electrons out of the diamond into the vacuum, completing a circuit (see Graphic). He says it is this layer of electrons that superconducts.
That wasn鈥檛 Prins鈥檚 original intent. He was actually trying to make a material that emitted electrons when cold, for use in television picture tubes or similar vacuum devices. He wanted to put the electrons into energy states that allowed them to slip easily out of the diamond into the vacuum, but did not let them back in. But when he applied a positive voltage to the probe, the electrons didn鈥檛 behave as expected. Turning up the voltage gradually increased the density of the electron cloud, while the current stayed at practically zero. But when the voltage reached a critical value the current increased sharply, then became steady, while the voltage across the gap dropped to zero.
鈥淲hen I got this effect, I was very upset. I didn鈥檛 want it,鈥� Prins told 快猫短视频. But after analysing the results more carefully, he thinks he knows what is happening. 鈥淭he electrons have to form a superconductor in that region, or the second law of thermodynamics will be failed,鈥� he insists. He believes that at a critical density the electrons in the cloud pair up, as they are known to do in other superconductors. Prins鈥檚 results appear in a special issue of Semiconductor Science and Technology (vol 18, p S131).
The work is so controversial that many superconductor researchers are ducking the issue; one responded 鈥渘o comment鈥� after looking at the paper. 鈥淭here is no experimental proof of superconductivity,鈥� says Sasha Alexandrov of Britain鈥檚 Loughborough University of the result. He argues that it is unlikely electrons would form pairs in a vacuum 鈥� they normally need positively charged atomic nuclei to overcome their mutual repulsion.
But Prins counters that orthodox pair-formation theory fails at temperatures above 33 kelvin. And veteran superconductivity expert Ted Geballe of Stanford University in California says the new results are intriguing. 鈥淭here may be an obvious alternative explanation but I don鈥檛 see any on first look,鈥� he says. 鈥淚 think it鈥檚 worth taking a chance on.鈥�
Even if Prins is right, the discovery won鈥檛 be quite the holy grail that superconductivity researchers are after. The electron layers he鈥檚 working with are between 30 and 120 micrometres thick 鈥� too small for power cables but too large for conventional circuit components. However, the effect might lead to very fast electronic devices larger than conventional chips, or revive the dying field of vacuum electronic devices.
The definitive test for superconductivity is to see whether the material blocks magnetic fields. Now retired from the University of Pretoria and living on a pension, Prins lacks the $100,000 needed for the test, but he has offered to supply samples to anyone with the money and suitable equipment. So far he has had no takers.