I had quite a bit of interest in high-Tc superconductivity. It was the first giant bubble I experienced before moving to silly-con valley in the dot-com era. Despite pouring of immense amount of money, the theory of high-Tc superconductivity remained unknown.
A new paper claims to have made progress in that respect and is worth reading.
The identity of the fundamental broken symmetry (if any) in the cuprate pseudogap state is unresolved. In fact, two apparently distinct forms of electronic symmetry breaking, one of intra-unit-cell rotational symmetry (Q=0 nematic) and the other of lattice translational symmetry (Q?0 density wave), are reported extensively. However, indications of linkage between these two phenomena suggest the prospect of a unified fundamental description, with one intriguing possibility being an intra-unit-cell nematic density wave. Here we carry out site-specific measurements within each CuO2 unit-cell, segregating the results into three separate electronic structure images containing only the Cu sites (Cu(r)) and only the x/y-axis O sites (Ox(r) and Oy(r)). Phase resolved Fourier analysis reveals directly that the incommensurate modulations in the Ox(r) and Oy(r) sublattice images consistently exhibit a relative phase of ?. We confirm this discovery on two highly distinct cuprate compounds, ruling out tunnel matrix-element and materials specific systematics. These observations demonstrate by direct sublattice phase-resolved visualization that the cuprate density wave consists essentially of spatial modulations of the intra-unit-cell nematicity; this state can equally well be described as an intra-unit-cell density wave with a d-symmetry form factor.
Wired magazine sheds some light on the discovery. We recommend you to skip the first seven and last seven paragraphs and stick to the middle of the report -
The microbes in this case are ripples of electrons inside the superconductors that are called charge density waves. The fine-grained structure of the waves, reported in two new papers by independent groups of researchers, suggests that they may be driven by the same force as superconductivity. Davis and his colleagues directly visualized the waves in a study posted online in April, corroborating indirect evidence reported in February by a team led by Riccardo Comin, a postdoctoral fellow at the University of Toronto.
Its a beautiful paper, said Dirk Morr, a professor of physics at the University of Illinois, Chicago, speaking of the work of Davis and his colleagues. One can really trust this result and build our theories from it.
Subir Sachdev, a professor of physics at Harvard University who helped devise Davis study, correctly predicted the form of the charge density waves in a paper last year, which detailed a possible mechanism behind both the waves and high-temperature superconductivity. Though further tests are needed, Sachdevs theory is garnering support from many experts, who say it succinctly captures key features of the materials.
Taken together, the various findings are at last starting to build a comprehensive picture of the physics behind high-temperature superconductivity. This is the first time I feel like were making real progress, said Andrea Damascelli, a professor of physics at the University of British Columbia who led two recent studies on charge density waves. A lot of different observations which have been made over decades did not make sense with each other, and now they do.