Nobel Prize in Physics: Scientific work from Berlin contributes to the evidence of theoretical predictions

Prof. Dr. Michael Steiner

Pioneering new areas of physics through measurement of quantum effects

Nobel Prize in Physics demonstrates close interweave of predictions and experimental evidence from large-scale scientific facilities. Researcher in Berlin recalls exciting experiments in an important new subject area

 The Helmholtz-Zentrum Berlin (HZB) and the Institut Laue-Langevin (ILL) for neutron science and technology located in Grenoble, France are pleased about this year’s Nobel Prize in Physics that will be presented together with other Nobel Prizes in Stockholm on December 10th. “The decision of the Nobel Committee for Physics recognises the crucial advances in one of the most exciting subject areas of solid-state physics achieved through theoretical work done by David J. Thouless, Duncan M. Haldane and J. Michael Kosterlitz”, says Prof. Anke Kaysser-Pyzalla, Scientific Director of HZB. “We warmly congratulate them on this honour. At the same time, we are proud that HZB as well has made contributions to the exploration of exotic quantum properties during its long tradition of scientific work that in the end led to the experimental evidence for the theoretical predictions made by Haldane.”

Researchers in Berlin had worked on caesium-nickel chloride (CsNiCl3) crystals as part of its long and successful collaboration with ILL from 1985 to 1995. Prof. emer. Dr. Michael Steiner, head of the HZB from 1998 to 2009 (the former Hahn Meitner Institute / HMI) had studied the spin dynamics of a crystal of this type as an HMI scientist at ILL. The goal was to detect a novel quantum phase in this system predicted by Haldane in his 1983 publication. Steiner’s experiments were designed to detect directly the isotropic spin excitation above an energy gap predicted by Haldene. The experiments required instruments that were only at ILL in such quality at the time. An energy gap was finally found, but further experiments in collaboration with Steiner’s then doctoral student Mechthild Enderle and the Japanes physicist Kazuhisa Kakurai were only able to experimentally prove in 1990 that the new phase predicted by Haldane in one-dimensional antiferromagnets of CsNiCl3 actually exists.

The Nobel Committee for Physics quotes this work in explaining the scientific background to the Nobel Prize and emphasises that the work contributed importantly to understanding the Haldane phase in antiferromagnetic-coupled spin chains. They showed that a macroscopic quantum state forms in these kinds of spin chains where the spins located within the interior of the chain constitute a novel complex dynamic structure.

The research work of the Nobel laureates at that time provided the theoretical concepts for today’s current research in the field of topological phases and phase transitions. Potential applications are already in evidence today, such as research on topological insulators. These are substances that conduct current in a very stable manner at their surface, but act as insulators within their interior. They play an important role in the development of materials for energy-efficient information technology.

At HZB today, Professor Oliver Rader and his Department of Green Spintronics are actively researching this subject. In addition, Rader coordinates the German Research Foundation (DFG) Priority Programme in topological insulators. In addition, Professor Bella Lake and her Department of Quantum Phenomena in New Materials are working on the detection and explanation of new quantum phases, a focus of interest in solid-state physics today.

Michael Steiner recalls the beginnings of this development, when multi-particle physics made a real comeback at the end of the 1980s. The new concepts developed for theoretically describing quantum effects, such as the phase postulated by Haldane, was all the talk and the search was on for ways to prove their existences. When the new high-efficiency instruments for neutron scattering became available at ILL, the necessary experimental means were finally at hand to study quantum ground states for magnetic models in detail.

“Antiferromagnetism cannot be fully explained without quantum effects”, says Steiner. “We are able to pioneer new areas of physics by being able to study these kinds of quantum effects through use of our large-scale facilities like neutron and synchrotron sources. I’m pleased that this fundamental theoretical work leading to new discoveries is being recognised through the Nobel Prize.”