A universal phase diagram for the new superconductors

Subir Sachdev, Harvard University, DMR 0757145

The last 3 decades have seen the discovery of many new super-conductors (SC), very different from traditional low temperature (T) SC. These new SC can have much higher critical temperatures (Tc), and all display antiferromagnetism (AF). Important experimental discoveries in the past two years (including Fermi pockets observed by quantum oscillations, and AF by neutron scattering and muon spin resonance) support a unified theory based upon the quantum phase transition of the onset of AF in a metal. The theory leads to a phase diagram as a function of T, applied magnetic field (H), and electron density (x) or pressure (p). AF and SC compete with each other in some regions of the phase diagram.

Predictions of

theory

Observations in three

families of new

superconductors

Underlying our theory of the new superconductors is the theory of quantum phase transitions. The P.I. had written a well-reviewed and popular book on this subject (pictured). The just released second edition is significantly expanded and contains an in-depth treatment of introductory material, suitable for adoption in a course for graduate students. Lectures on these topics were presented at the Les Houches school, the Mahabaleshwar Winter School, and the Windsor School on condensed matter physics.

There is now widespread interest in the string theory community on the problem of quantum criticality in condensed matter, spurred in part by a series of papers by the P. I.. Lectures were presented to combined audiences of string and condensed matter theorists at Groningen, Milos, Boulder, Bangalore, and Los Alamos. The Boulder meeting was a TASI school, co-organized by the P.I.

PDFs of all these lectures are available on the web

A universal phase diagram for the new superconductors

Subir Sachdev, Harvard University, DMR 0757145

A well-attended public lecture on “The quantum phases of

matter” was presented in Boulder, Colorado. Similar

lectures were given in Groningen and Bangalore, and

more are planned in the coming months. An article is being prepared for Scientific American, based on these

lectures.