An intriguing new aspect of the problem of high temperature superconductivity has been discovered by UoB Physics researchers. High temperature superconductors have the potential to revolutionise electrical power usage across society. However, despite more than 30 years of intense study, we still do not fully understand why these materials superconduct. A key issue is the nature of the normal-metal state, where the superconductivity is suppressed. In particular, it is believed that the anomalous normal state of high temperature superconductors – often labelled ‘strange metal’ – and conventional metals lies at the root of the problem as to why superconductivity occurs.
Using very high magnetic fields in Bristol and the European Magnetic Field Laboratory (EMFL) facilities in Dresden, Toulouse and Nijmegen, a UoB Physics research team led by Tony Carrington and including Carsten Putzke and Nigel Hussey has shed new light on how the strange metal state which hosts high temperature superconductivity emerges out of a more conventional metallic state as the electron density is tuned using dopant atoms. The results, described in a paper published in Nature Physics, show that in superconducting samples of Tl2Ba2CuO6 and Bi2Sr2CuO6 the Hall number in the high field, zero temperature limit is much lower than would be expected from the electron density suggesting that the electrons have a dual quantum nature – being both coherent and incoherent in the same material. Curiously, this reduction in Hall number also seems to correlate with the rise in the linear-in-temperature coefficient of the temperature dependent resistivity. The latter fact has been suggested to arise from scattering at the maximum rate allowed by quantum mechanics – the so called Planckian dissipation limit. Understanding exactly how decoherence affects the transport properties and superconductivity could prove to be a crucial part of the high-Tc cuprate puzzle.