Superconductivity

The two volumes Superconductivity and Novel Superconductors” edited by K. H. Bennemann and J. B. Ketterson are comprised of 24 chapters which cover very different actual topics in superconductivity. As compared to the previous books on “Physics of Superconductors” edited by the same duo in 2003, the new versions have been complemented by five chapters which cover Neutron scattering and the magnetic response of superconductors and related compounds (S. M. Hayden), Concepts in high temperature superconductivity (E. W. Carlson et al.), Coexistence of singlet superconductivity and magnetic order in bulk magnetic superconductors and SF heterostructures (M. L. Kulic, A. I. Buzdin), Impurity nanostructures and quantum interference in superconductors (D. K. Morr), Principles of Josephson-junction-based quantum computations (S. E. Shafranjuk, J. B. Ketterson).

 

Especially interesting is here the lastly mentioned article which gives a very comprehensive survey on how to develop strategies for designing elementary logic operations using Josephson quantum bit devices. Similarly useful is the article by M. L. Kulic and A. I. Buzdin where the possibility of coexistence of magnetic order and superconductivity is explored. This question is very topical currently since the simultaneous occurrence of both orders would open new fields in applications as, e.g., new kinds of coupled quantum bit devices. Even though the authors conclude that ferromagnetism and superconductivity practically never coexist, spiral magnetism might be realized. Another option for coexistence is the fabrication of superlattices of superconductors and ferromagnets which can induce spatial oscillations in the superconducting amplitude. Even though the article by S. M. Hayden gives a nice survey on the experimental technique of neutron scattering in superconductors, which is an important tool in characterizing superconductivity, it misses to include comments on the lattice response to superconductivity which can well be explored by this technique. I find both articles by E. W. Carlson et al. and by D. K. Morr less instructive. The former develops a scenario of the stripe phase in a highly correlated electron liquid. This approach is restricted to the side of the phase diagram which lies close to the border of the antiferromagnetic regime. The physics at optimum doping, i.e., far away from this region, are only speculatively addressed even though this is the regime which is of uppermost interest. The latter article by D. K. Morr concentrates on the role which impurities play in superconductors. There mainly surface effects are dealt with and especially cases relevant for a d_x²_−y² superconducting order parameter discussed. This topic is most relevant in understanding recent STM data. What is missing here, however, is a link to the preceding chapter by L. P. Gor'kov who also considers the effects on superconductivity induced by impurities. It would have been beneficial to the article if analogies and differences between both work had been highlighted.

 

Regarding all other chapters of the books little updating has been done in most of the articles, many of them being not even changed at all as compared to the 2003 edition. An exception in this respect is the article on Electron-phonon superconductivity by F. Marsiglio and J. P. Carbotte where new results for MgB₂ are included and discussed in detail.

 

Both books together certainly cover broad and interesting aspects of superconductivity with focus on high-temperature superconductivity and are well suited for scientists working in the field as well as graduate students. It is, however, a pity, that the updated version mostly ignores experiments obtained in the last five years. Also, lattice effects, isotope studies, polaron and bipolaron signatures, the pairing symmetry of cuprates (which has been shown to be more complex than simple d_x²_−y²) are missing. In order to provide a real overview on the physics of superconductors and especially cuprate superconductors, these topics need to be included. I hope that the next edition of these books also accounts for the above topics.