February 3, 2009 (HP16).  The IOP journal Reports on Progress in Physics announced their selection of 2008 article highlights, which are accessible and downloadable free-of-charge until the end of 2009.  For access, see our Announcement A71.   Below we reproduce abbreviated abstracts of the two articles discussing the high-T_c problem. 

• “From high temperature superconductivity to quantum spin liquid: progress in strong correlation physics”, by Patrick A. Lee,  71, No. 1, 012501 (January 2008). This 19-pages review discusses high temperature superconductors as examples of strongly correlated materials. It also discusses the problem of the quantum spin liquid (a spin system with antiferromagnetic coupling which refuses to order even at zero temperature) as a somewhat simpler version of the high T_c problem. It addresses questions such as: 'What limits T_c if pairing is driven by an electronic energy scale?' 'Why is the high T_c problem hard?' 'Why is there no consensus?' and 'Why is the high T_c problem important?'
• “Two gaps make a high-temperature superconductor?” by S. Hüfner, M. A. Hossain, A. Damascelli and G. A. Sawatzky 71 No. 6, 062501 (June 2008).               One of the keys to the high-temperature superconductivity puzzle is the identification of the energy scales associated with the emergence of a coherent condensate of superconducting electron pairs. These might provide a measure of the pairing strength and of the coherence of the superfluid, and ultimately reveal the nature of the elusive pairing mechanism in the superconducting cuprates. This 9-pages article reviews experimental data which suggests that a superconducting gap and pseudogap coexist over the whole superconducting dome