Energy Focus: Observation of highest ever superconductivity transition temperature confirms conventional theory
- PDF / 209,200 Bytes
- 1 Pages / 585 x 783 pts Page_size
- 49 Downloads / 204 Views
S
uperconducting materials appear to provide a path to an extremely high effi ciency electrical grid, more sensitive scientifi c instrumentation, and improved medical imaging devices. To achieve their full potential, however, a material that can superconduct at room temperatures is required. All current superconducting materials require very low temperatures. In an article published online by Nature in August (DOI: 10.1038/nature14964), A.P. Drozdov and M.I. Eremets of Max Planck Institute (MPI), with collaborators from MPI and Johannes Gutenberg University, have provided convincing evidence for conventional superconductivity in H2S at a record high temperature of 203 K (–70°C) at a pressure of 145 GPa. “This work reports compelling evidence for superconductivity at temperatures higher than 200 K, which is very exciting indeed and raises the prospects for still higher Tc superconducting materials,” says Amit Goyal, Director of RENEW at the University at Buffalo
a
b
and Emeritus Corporate Fellow at Oak Ridge National Laboratory. The previous record-holding materials for high Tc, the temperature at which a material begins to demonstrate superconductivity, belonged to the cuprates and iron arsenides. One such material, a mercury cuprate, has a Tc of 164 K. However, the mechanism that leads to superconductivity in these materials is not well understood, so it has not been clear where to look for further progress. The Bardeen–Cooper–Schrieffer or BCS theory for conventional superconductors, on the other hand, is a wellunderstood theory. Superconductivity in these materials has previously been capped at a Tc of 39 K in MgB2. Materials with a high density of hydrogen are expected to exhibit the necessary features to achieve superconductivity according to BCS theory. “Because the H-based compounds become superconducting due to conventional BCS electron–phonon superconductivity, their Tc has been calculated and predicted by theorists for many years, notably Neil Ashcroft. A high Tc on the order of 80 K was predicted but the experimental value of 203 K blows this away and confirms the conjecture of the value of the high phonon
frequencies in metallic H,” says David C. Larbalestier of the National High Magnetic Field Laboratory at Florida State University. Though temperatures of 203 K can be achieved with refrigeration, H 2S showed its highest T c at pressures of at least 145 GPa, 1.43 million atmospheres, where it likely formed H3S. “Since this was achieved only at very high pressures, its direct impact to applications is small. This work emphasizes that materials with very high T c based on the BCS mechanism are possible to find if a favorable combination of high-frequency phonons, strong electron–phonon coupling, and a high density of states are all met,” Goyal says. Though the material presented in the Nature article is not suited for practical use, its behavior, when subjected to a strong magnetic fi eld, or when hydrogen is replaced with the deuterium isotope, corroborates theoretical predictions. “The ‘normality’ of
Data Loading...
