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Dr. Rob Kiefl is awarded 2017 Yamazaki Prize

11 September 2017

Dr. Rob Kiefl, Professor in the Department of Physics and Astronomy at the University of British Columbia (UBC), member of the Stewart Blusson Quantum Matter Institute (SBQMI) at UBC and an affiliate Scientist at TRIUMF, has been awarded the 2017 Yamazaki Prize by the International Society for mSR Spectroscopy (ISMS).

The prize is awarded every three years for outstanding and sustained work in µSR (muon spin rotation/relaxation/resonance) science with long-term impact on scientific and/or technical µSR applications. The presentation of the award occurred at the opening session of the International Conference on µSR held on June 26, 2017, in Sapporo, Japan. Prof. T. Yamazaki, for whom the prize is named, is one of Japan’s most distinguished nuclear scientists and pioneered the field of muon spin resonance/rotation/relaxation. It was especially significant that Prof. Yamazaki participated in the award ceremony.

Kiefl received the prize for his development and use of μSR and also beta-detected nuclear magnetic resonance (b-NMR) in the area of condensed matter physics. His contributions to the field have had a significant impact on a wide range of topics, including muonium in semiconductors, exotic superconductors and magnets and most recently developments in b-NMR at TRIUMF for use in studying electronic and magnetic properties of thin films and interfaces.

 We caught up with Dr. Kiefl to ask him a bit about his work:

TRIUMF: You received this award for your career work in µSR spectroscopy and beta-NMR spectroscopy – can you tell us a bit more about your journey to where you are now?

Dr. Robert Kiefl (RK): I think about my career as having three periods.

In the first part, I was focused on studies of muonium, which is the simplest atom composed of two elementary particles- a positive muon and an electron. In semiconductors, the electronic structure of muonium is very different than in vacuum. Its properties are closely connected to those of hydrogen, which is present in all semiconductors. Most of the information we have on isolated hydrogen comes indirectly through studies of muonium since hydrogen itself tends to react quickly with other impurities thus altering the electrical properties of the semiconductor. I worked mostly on developing and applying new methods to study muonium in semiconductors- in particular, high transverse field muon spin rotation and level crossing resonance spectroscopy. That work started when I was a Natural Sciences and Engineering Research Council of Canada (NSERC) postdoc at the University of Zurich and continued when I returned to Vancouver, first as a TRIUMF Research Scientist and later as a faculty member in the Department of Physics and Astronomy at UBC. My research has always been a very collaborative effort. In the case of muonium, my main collaborators were Bruce Patterson (then at the University of Zurich), the late Tom Estle (Rice University), Moreno Celio (then a postdoc in the theory group at TRIUMF), Juerg Schneider (then a postdoc at TRIUMF), Syd Kreitzman (now the Centre for Molecular and Material Science at TRIUMF), Kim Chow (then a UBC Ph.D. student and now at University of Alberta) and Jess Brewer (UBC and a former winner of the Yamazaki prize).

The discovery of high-temperature superconductivity in the late 1980’s caused a dramatic shift in the direction of my research and the path of many others doing mSR. The muon was immediately recognized as a sensitive local probe for exploring the novel properties of this new collective state of matter. We used mSR to probe the intriguing phase diagram of YBa2Cu3Ox, where an antiferromagnet evolves continuously into a high-temperature superconductor as a function of oxygen concentration. Using a novel high transverse field mSR spectrometer (7T), designed mostly by Syd Kreitzman, we were able to study properties of the vortex state in greater detail, along with the internal structure of vortices. Our group also applied mSR to explore other exotic states of condensed matter such as geometrically frustrated magnets and fulleride superconductors. In this period of my research, many collaborations were facilitated by the Canadian Institute for Advanced Research (CIFAR). Some of the important partnerships involved Michel Gingras (first at TRIUMF and then the University of Waterloo), Bruce Gaulin (McMaster University), T. Uemura (Columbia University), Jess Brewer (UBC), Jeff Sonier (Simon Fraser University), and Ian Affleck (UBC). We also benefited greatly from the collaboration with Walter Hardy, Doug Bonn, and Ruixing Liang at UBC, who went on to become world leaders in the growth of YBa2Cu3Ox crystals.

The third period of my career has focused on using radioactive nuclei to probe thin films and interfaces. This change in direction happened in the late 1990’s when Alan Astbury (TRIUMF director at the time) approached me about potential applications for TRIUMF’s Isotope Separator and Accelerator facility (ISAC) in the area of condensed matter physics. Alan's broad vision of science and strong support allowed us to build a first class b-NMR facility. We still enjoy that same support from the current administration at TRIUMF. Many people at TRIUMF played key roles in those early days of the program. Gerald Morris designed the high field spectrometer and emerged as the technical leader of the group. Syd Kreitzman (manager of the CMMS facility at TRIUMF) was responsible for the RF system and related aspects of the data acquisition (DAQ) system. Rene Poutissou, Pierre Amaudruz and later Suzannah Daviel developed the bulk of DAQ system. Phil Levy and later Matt Pearson were responsible for the laser polarizer, which was and still is the most critical component on which the program depends. This requires continual work and new resources as we strive to polarize other elements besides 8Li such as spin ½-31Mg. We also had excellent technical support. Rahim Abasalti remains a critical member of the group who is an expert in UHV technology. Other members of the mSR facility Bassam Hitti and Donald Arseneau also contributed greatly to the cryogenics and DAQ respectively. Andrew MacFarlane, then a new Professor in the Chemistry Department at UBC and Kim Chow at the University of Alberta were important in driving the science program. Zaher Salman, a talented student of Amit Keren at Technion University, joined the group as postdoc early on and was largely responsible for designing and commissioning the low field spectrometer as well as many of the first science results.

As indicated above, many people have had important roles in the TRIUMF b-NMR program. My single most important collaborator has been Andrew MacFarlane (UBC Chemistry) who is responsible for much of our success. Kim Chow was also very important in pushing the science early on. Additionally, external collaborations have always been key to the program. In particular, we have worked with the low energy muon group at Paul Scherrer Institute, especially Zaher Salman and Elvezio Morenzoni. The two methods yield complementary information on thin films and insulators. Low energy muons are ideal for measuring quasi-static magnetic fields, e.g. the magnetic penetration depth in the Meissner state of exotic superconductors or magnetic ordering in thin films. b-NMR provides different information on slow dynamics due to its much longer lifetime. Other collaborations within the SBQMI at UBC and also with the Max Planck Institutes (MPI) have been very important. One example system is in the nickelate films, which will be part the Ph.D. project of Victoria Karner (UBC Chemistry and SBQMI). Postdoc David Cortie (SBQMI) played a very important role in establishing many of these connections. One recent highlight from David’s work was the discovery of near-surface low energy magnetic excitations in the prototypical antiferromagnet Fe2O3.

Polymers films have turned out to be particularly interesting systems to study with b-NMR. These experiments have been driven by Iain McKenzie at TRIUMF in collaboration with Jamie Forrest at Waterloo. The small quadrupole moment of 8Li and resulting quadrupolar relaxation leads to high sensitivity to the molecular dynamics that occur on a wide range of time scales. This also led to a collaboration with Joerg Rottler who is an expert in molecular dynamics within the SBQMI. This is the current Ph.D. project of Derek Fujimoto (SBQMI and UBC Physics and Astronomy).

Similar to mSR, where the muon mimics the behaviour of hydrogen, b-NMR can be used to study the behaviour of other elements, such as Lithium. For example, understanding diffusion of Lithium is of great interest in battery technology. We have collaborations with groups at the MPI and also Jun Sugiyama at Toyota Central Research and Development Labs to measure Lithium diffusion in battery electrode materials and across interfaces. This can be done with b-NMR because fluctuations in the local environment from diffusion cause spin relaxation. Recent results on rutile TiO2, by Ryan McFadden (UBC Chemistry and TRIUMF’s Isotopes for Sciences and Medicine program Ph.D. student) have demonstrated that b-NMR can monitor and distinguish local motion from long-range diffusion. Also, complementary work by Aris Chatzichristos (UBC Physics and IsoSIM Ph.D. student) shows that it is possible to monitor long-range diffusion of 8Li in rutile by looking at the decay of 8Li into 8Be and subsequently into two alpha particles.

We are also part of a new collaboration with PSI, MPI, and ETH in Zurich to study magnetoelectrics with muons and polarized radioactive nuclei. This is a new direction for mSR and b-NMR and will be part of the Ph.D. project of Martin Dehn (SBQMI). We recently made precise measurements of the Mu hyperfine interaction in aerogel and samples of porous silica made at UBC in collaboration with Don Fleming (UBC Chemistry) and Mark MacLachlan (UBC Chemistry and SBQMI), Martin Dehn (UBC Physics and SBQMI PhD student), Glen Marshall (TRIUMF) and Robert Scheuermann at PSI. The idea is to measure the shift in the hyperfine interaction of Mu as it moves on and off the SiO2 surface and thereby extract the binding energy. It is also significant for me since the topic is close to my first mSR paper where we were trying to get muonium into a vacuum-like environment. These results may help in developing an ultraslow muon beam at JPARC. Such a beam will have important applications in both particle and condensed matter physics.

TRIUMF: It sounds like you had quite a few twists and turns throughout your career – would you have done things the same way, looking back?

RK: In science (as in all aspects of life) you can only take one path. No one knows for sure where the other paths would have taken you. However, I am content with where we are now. I anticipate that TRIUMF’s new Advanced Rare Isotope Laboratory (ARIEL) will give us much greater access to the radioactive ion beams, something that currently limits our progress. It is clear that both low-energy muons and radioactive nuclei have an important role in exploring properties of thin films and interfaces field due to the enormous gain in sensitivity compared to conventional NMR.

TRIUMF: The Yamazaki Prize represents the highest recognition in your field, and Dr. Toshimitsu Yamazaki is often thought of as the foremost pioneer in the area of muon spin spectroscopy. How did it feel to have Yamazaki present at the award ceremony?

RK: It was very meaningful. He said some very complementary things about the b-NMR program at TRIUMF and my role in it. Prof. Yamazaki is indeed one of the pioneers in the field of muon spin spectroscopy – anyone who works in µSR would know his name. His research and the work of his grad students have had a profound influence on the mSR spectroscopy, and it was a special honour for me to have him participate in the ceremony.

TRIUMF: What are you most excited about for the future of beta-NMR and muon spin spectroscopy?

RK: Virtually all devices have interfaces which often control how they work. Every material has its own set of structural, electronic and magnetic properties. When you bring two different materials, say A and B, together the interface has its own set of properties which are distinct from either A or B. It is an interesting field for physics research, but it also has broad implications for future devices and applications. I look forward to seeing how b-NMR and mSR will contribute to this emerging field. We are very fortunate to be connected to the Stewart Blusson Quantum Matter Institute at UBC as well as the Max Planck – UBC – the University of Tokyo’s Centre for Quantum Materials. This has an added significance for me since we have a long historical connection with the University of Tokyo in mSR dating back to the beginning of TRIUMF when Yamazaki’s group at the University of Tokyo helped pioneer the field.

Congratulations, Dr. Kiefl!