UCSD was founded in 1960 in the halcyon days of the post Sputnik era. Bernd Matthias, famous for the discovery of the then highest known Tc material Nb3Sn, arrived in La Jolla in the Fall of 1961. Brian, a native of San Diego, joined his group a year later as a graduate student at the time when the Physics, Chemistry and Biology Departments moved up the mesa from their original location at the Scripps Campus on the beach. The BCS theory was then still young and Matthias was a vocal sceptic of it. In spite of this, he and Bardeen were good friends, Bardeen spending parts of each winter in La Jolla enjoying among other things his love of golf. Matthias would typically introduce Bardeen at his annual colloquium in La Jolla by saying: ‘If you don’t know who our speaker is then you shouldn’t be here.’ On one occasion the eminent plasma physicist Marshall Rosenbluth could be heard from the back: ‘We know who the speaker is, who are you?’
Among the recent discoveries that Matthias brought with him from Bell Labs was the systematic way in which rare earth impurities in superconducting La depressed its superconducting Tc, this forming the basis of deGennes’ picture of rare earth element magnetic order. The question was there as to whether this systematic depression would play out the same way in rare earth intermetallic superconducting compounds, and Brian chose to investigate this for his thesis work in superconducting LaAl2. Kondo’s paper on the resistivity minima seen in various metals containing magnetic impurities appeared just at this time, and Sugawara and Euguchi quickly showed that the anomalous depression of Tc for Ce impurities in La seen in Matthias’ data was associated with Ce acting as a Kondo center there. Brian was aware of these developments and immediately noticed that Ce impurities in LaAl2 also showed the Kondo effect. More than this, he found that the Kondo features actually persisted all the way up to the pure compound CeAl2. This early work set a direction that Brian has amplified marvelously in the ensuing half century. Matthias never really had an interest in Kondo physics, claiming that it was just a question of the insolubility of the Kondo atom in the matrix.
Brian developed a parallel interest in the effects of pressure on the Ce Kondo phenomena, dramatically seen in his pressure studies of Ce-doped La. Matthias’ student Dieter Wohlleben was working at this time on his thesis concerning what he called anti-paramagnons in elemental Sc. This was before the era of SHE and Quantum Designs off the shelf magnetometers, and Dieter constructed a Faraday balance magnetometer that operated down to He3 temperatures. Brian and Dieter worked out how to get a pressure clamp that was efficiently compensated to give small magnetic background into the sample space of Dieter’s Faraday balance, a superb experimental achievement. With this, they were able to follow the alpha/gamma transition in elemental Ce and see the loss of local moment that accompanies the alpha phase.
The discovery of the superconducting rare earth Chevrel phases by Fischer in the 1970s, opened a new direction with the study of systems where local moment magnetism coexisted with superconductivity. Brian was centrally involved with mapping this out in the rare earth rhodium borides, where one sees the strong difference between what happens when the local moment order is ferromagnetic versus what happens in the antiferromagnetic case.
Magnetism came full circle in 1979 with Frank Steglich’s discovery of bulk superconductivity in CeCu2Si2 where we have not just co-existence but full incorporation of the magnetic degrees of freedom into those of the conduction electrons. It is interesting that Matthias who always believed there was some deep connection between superconductivity and magnetism could not believe this result even after going over Frank’s data with him. This discovery opened a new era in superconductivity research in which Brian has played a continuing central role. The interesting issues of order parameter and pairing mechanism first came to the fore with these heavy Fermion superconductors, matters that continue to play out in the high Tc materials.
After Matthias died at age 60 in 1980, Brian carried forward in La Jolla the study of superconductivity at the interface with magnetism. The surprise is that this interface still surprises, as he has shown us.