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Interview: Collin Broholm

Johns Hopkins' Colin Broholm recently joined ORNL's Neutron Sciences Directorate as a joint faculty appointment.
OAK RIDGE, Tenn., Nov. 15, 2011 — Collin Broholm, a leader in the international neutron scattering community, recently joined ORNL's Neutron Sciences Directorate as a joint faculty appointment with Johns Hopkins University. He will spend approximately 25 percent of his time working at ORNL.

Broholm is a professor in the Johns Hopkins Department of Physics and Astronomy and Director of the Johns Hopkins-Princeton Institute for Quantum Matter. An experimental physicist in the field of hard condensed matter, he concentrates on anomalous forms of magnetism, superconductivity, and the interplay of the two. For this work he received the 2010 sustained research prize of the Neutron Scattering Society of America.

Broholm has served on numerous committees overseeing instrument development at neutron scattering facilities, including the Spallation Neutron Source and High Flux Isotope Reactor at ORNL, Helmholtz Zentrum in Berlin, and the NIST Center for Neutron Research. He also served on the Basic Energy Sciences Advisory Committee and the Condensed Matter and Materials Research Committee of the National Research Council. How will you be involved with the NScD education program?

At Johns Hopkins, I've taught a course in neutron scattering for years. I am eager to join forces with other institutions involved in neutron scattering to create a course that draws students into using this powerful experimental tool. With SNS coming on line, now is the time to invite another generation into this field. I'm hoping to have both students and post-docs stationed here at times, and we expect to have joint supervision of some students. I'm expecting some of the students will find mentors among ORNL staff. I was pleased to find that Takeshi Egami and Meiyun Chang-Smith of NScD and the Joint Institute of Neutron Sciences are developing various educational initiatives at ORNL, and I look forward to collaborating with them to strengthen ties between ORNL and academia.

With the construction of SNS, and with our understanding of the importance of connecting to the academic environment, we're in a position to build a stronger program. We now have a neutron scattering capability that takes us to the next level, and I'm excited about being a part of the scientific exploitation of that capability, as well as developing the educational program that should surround it. At the University, we have a continuous flow of very bright individuals into our program. In my connection with ORNL, I'll have an opportunity to spend more time on research, but I will retain a strong connection to the academic system and education. That's part of what I bring to ORNL in this joint appointment—a pipeline to a very lively program of graduate and undergraduate education. Do you have particular ideas for working with the Joint Institute for Neutron Sciences? I'm hoping Johns Hopkins students and post docs will be here at Oak Ridge for extended periods of time. JINS will be critical in offering the kind of environment that's inspiring and accommodating to younger people coming here. They want to meet other people from across the country and the world with complementary interests. That's always been an important role of the user facilities—bringing together generations of younger scientists who share an interest in using the infrastructure offered by the facilities but also represent a broad cross section of science. I see JINS as being where a lot of that will take place. Also, I'm looking forward to being involved in pulling in the broader community of scientists who may not be neutron experts or even users but who are consumers of the types of information neutrons can provide. JINS is the place where intense workshops and longer focused research efforts can unfold. What's your primary area of research?

My career has revolved around developing neutron scattering instrumentation and using the technique to probe atomic-scale correlations of electronic systems. Probing and analyzing the collective behavior among systems of interacting particles is key to being able to predict the corresponding emergent properties. This is the central challenge of condensed matter physics. With new tools such as the SNS, we hope to make major inroads on these types of problems. Recently, we've started the Johns Hopkins-Princeton Institute for Quantum Matter. This effort uses advanced spectroscopic techniques to probe strongly correlated materials, combined with materials synthesis, crystal growth, and theory. It's sort of a holistic approach to the physics of strongly correlated systems. Our goal is to make bold progress in understanding strongly correlated systems largely thru the use of neutron scattering. We intend to develop completely new compounds, new chemical substances that display interesting quantum correlated properties. Indeed, the effort has already produced a couple of completely new compounds that we are now in the process of exploring. Why are neutron scattering in general and SNS in particular well suited to studying these systems?

The length and time scales associated with thermal neutron scattering almost perfectly match the length and time scales that are important in our materials. That means neutron scattering is the appropriate and in some cases the only microscope we have on the dynamic world that exists at the atomic scale—the angstrom and picosecond to nanometer and nanosecond realm. The pulsed SNS source allows an increase in the brightness—directly related to the quality and quantity of detailed information we can extract—of one to two orders of magnitude compared with previous instruments. We're excited about putting this power to work on problems that in some cases have lingered for years, such as quantum correlated superconductors and new forms of quasi-particles in magnetic materials. Quasi-particles are collective particles within the solid phase that involve several or many atoms—phonons and magnons, for example. They provide a compact and elegant description of the behavior of materials, and in many cases neutron scattering is uniquely suited to observe and characterize them. Recently, a new class of quasi-particles have been proposed that are not associated with symmetry breaking but rather with violating or straining against a local constraint in a strongly fluctuating state of matter. Evidence for and characterization of such novel quasi-particles can represent significant scientific progress in the field of condensed matter physics. These are challenging experiments, but with the newer, stronger capabilities, I think we're ready to tackle such problems.

Are there particular collaborations you'd like to pursue?

One of the things critical in neutron scattering is a strong connection to new materials synthesis. Such work is taking place in the groups of David Mandrus and Brian Sales at the University of Tennessee and ORNL, and I'm looking forward to discussions and collaborations with them. I'm also very interested in materials theory, particularly computational materials theory, which David Singh is involved in. In addition, at CNMS there's a Nanomaterials Theory Institute that employs leadership-class computing; I want to see how that can be connected to the new neutron scattering capabilities.

I'm also interested in neutron scattering instrument development, and I expect to work with people here on ideas for getting even more detailed results from the instruments. SNS is the brightest pulsed neutron source in the world. The set of instruments built around it are challenged to be the best of their kind. To meet this challenge requires an ongoing process of improving existing instruments as pertinent technologies advance and developing completely new instruments to move the science forward. I'm looking forward to being a part of this process.