More oscillations in cuprate superconductors

http://www.nature.com/nphys/journal/v7/n3/full/nphys1930.html?WT.ec_id=NPHYS-201103

Since its discovery almost 25 years ago, high-temperature superconductivity has led to a wealth of new theoretical ideas and deepened our understanding of complex condensed-matter systems. At the same time, the study of cuprates has been the driving force for tremendous innovations in the experimental methodology of condensed-matter physics, with methods ranging from photoemission, scanning microscopy, optics and neutron scattering to, in the past few years, quantum oscillations. As reported in Nature Physics¹, measurements by Brad Ramshaw et al. of quantum oscillations in the underdoped high-temperature superconductor YBa₂Cu₃O_6.59 typifies these advances in a number of striking ways. First, the samples studied are the result of two decades of intensive development leading to unique levels of purity that would previously have been unimaginable in such complex oxides. Second, the measurements take place in pulsed magnetic fields that reach both a magnitude of field and a quality of signal-to-noise ratio far beyond what could formerly be achieved. And third, the latest innovation of 'genetic algorithms' allows consistent parameters to be extracted from a large data set of quantum oscillations as a function of field direction and temperature. The authors obtain, among other things, a value of the g-factor of the charge carriers near 2, showing that they are surprisingly like free electrons. This result has profound implications for the nature of the ground state that gives rise to these oscillations.