Remembering Alan Luther

Nordita has learned with sadness of the passing of Nordita emeritus professor Alan Luther.

Alan Luther was a leading theoretical physicist whose contributions to condensed matter physics, particularly the theory of strongly correlated and one-dimensional systems, had a lasting impact on the field. After receiving his PhD from the University of Maryland in 1967 and holding positions at the Technical University of Munich, Brookhaven National Laboratory and Harvard University, he joined Nordita as a professor in 1976.

In 2001, he received the Oliver E. Buckley Prize of the American Physical Society for his pioneering work with Victor J. Emery on one-dimensional Fermi systems.

During more than three decades at Nordita, Alan played an important role in shaping the institute's research environment. We invited colleagues who knew him to share their memories. The reflections below speak to both his scientific contributions and his efforts to build connections between researchers across institutions and national borders.

Alexander Balatsky:

Alan Luther was a defining face of Nordita, and he will long be remembered as such — inseparable from what we now call quantum materials. His work on low-dimensional systems became required reading for generations of students, embodying the deep connection between basic science and real-world challenges that sat at the very core of Nordita's mission. His passing marks the close of an important and impactful era in Nordita's history.

Beyond the science, Alan was the visionary who forged Nordita's exchanges with the Landau Institute in the 1970s and 1980s, at a moment of rapid and uncertain change in the Soviet Union. Those exchanges have transcended physics — I remember scientists returning to the Landau Institute from Nordita visits full of ideas and energy. The discovery of high-temperature superconductivity in oxides fed the energy and made the interactions rare and alive. Alan and Nordita demonstrated how to build an environment where scientific interactions could reach across the East-West divide and bring people together as human beings. In helping to tear down those walls, Alan left a mark far greater than any single result. For some of us, he and those memories are the reason we came to Nordita when the opportunity arose.

Paolo Di Vecchia:

Here I want to mention two important contributions of Alan Luther while he was at Nordita. The first one is a scientific one. He wrote two important papers with I. Peschel (Phys. Rev. B9, 2911 (1974)) and with V. Emery (Phys. Rev. Lett. 33, 598 (1974)) where they study one- dimensional electron gases obtaining results that essentially show the equivalence of two two-dimensional theories as the sine-Gordon one and the Thirring model. Actually, the two previous papers were written when Alan was still at Harvard. When he came to Nordita he continued to work in this direction publishing another paper on the same line (Phys. Rev. 14, 2153 (1976)). Then he tried to extend the bosonisation rules to three dimensions (Phys. Rep.49, 261 (1979) and to four dimensions in a paper with Schotte (Nucl. Phys. B 242, 407 (1984)). In the particle physics community the previous results in two dimensions are known to be obtained by S. Coleman who was also working at Harvard. He published his work on Phys. Rev. 11, 2088 (1975) and in the notes added in proof he writes

"Schroer has also pointed out that many of the results obtained here are in close correspondence with the results of one-dimensional electron gasses by Luther and collaborators. Luther and I are in total agreement with Schroer on this point; we are also united in our embarrassment that we were incapable of reaching this conclusion unprompted. (Our offices are on the same corridor.)"

The other one has been very important for both scientific and political aspects. Together with his friend Khalatnikov working at the Landau Institute in Moscow, Alan organised a few meetings that took place in Moscow and in Copenhagen. Scientists from Nordita collected a number of prominent physicists working in the west and took them mostly to Moscow but also in other places, while Khalatnikov brought a big group of Russian physicists mostly to Copenhagen, but also in other Scandinavian towns. These meetings usually went on for two weeks and were extremely important not only from a scientific, but also from a political point of view in a period in which the two communities were separated and no interaction was allowed because of the Cold War. In my opinion this is a very good example on how important is to keep scientific and human contacts in periods of international turbulences.

Finally I want to mention that Alan, through his contacts with Khalatnikov, was able to bring Sasha Polyakov to Copenhagen for three months in 1976. This was very fruitful scientifically and at the end of his stay in Copenhagen Nordita organised a conference that was attended by many people. I enclose a picture of this conference where you can see Alan participating.