Alfred Q.R. Baron has been leading development of synchrotron-based hard x-ray techniques for investigation of condensed matter systems for more than 25 years. As a Ph.D. student at Stanford University and post-doc at European Synchrotron Radiation Facility (ESRF), he was instrumental in the development of nuclear resonant scattering (NRS) methods, with specific interest in x-ray coherence and probing neV-scale dynamics, as well as x-ray optics and fast detectors. Moving to SPring-8 in 1998, he accepted responsibility for developing meV-resolved inelastic x-ray scattering (IXS), building Japan’s first x-ray spectrometer for measuring phonons at BL35XU. He then took a position in RIKEN where he was given the opportunity to make the Quantum NanoDynamics beamline, BL43LXU, using, arguably, the most powerful SR source of average x-ray intensity in the world. Dr. Baron now directs the Materials Dynamics Group of the RIKEN SPring-8 Center, and is the Precision Spectroscopy Division Director in the CSRR/JASRI. In addition to teaching the next generation of scientists, running BL43LXU, and performing many investigations of phonons, his interests include many areas of condensed matter physics, with, presently, a focus on understanding mesoscale liquid dynamics, as well as continued development of methods for x-ray experiments, especially IXS.
Atomic motions – phonons in crystals and excitations in disordered materials - are critical for many material properties, including superconductivity, thermoelectricity, elasticity, ferro-electricity, magneto-elastic coupling, nematicity, etc. They are also intimately connected to many phase transitions, and to general features of liquid and glass behavior. Inelastic x-ray scattering (IXS) [1], unique advantages for investigating atomic dynamics compared to neutron scattering, This has made IXS especially valuable for investigating disordered materials and small samples, with successful measurements possible even from ng (nanogram) samples. Present work now extends to a large variety of materials and sample geometries (single crystals, thin films, near critical liquids, samples in diamond anvil cells, etc,) in a range of conditions (2<T<3000K, P>100 GPa, H < 7 T, etc.)
The IXS spectrometer at BL43LXU of the RIKEN SPring-8 Center
We will discuss the present state-of-the art in IXS and focus on extension of the method to higher resolution and to higher pressures. Higher resolution studies are needed to probe the mesoscale region (10-100 nm length scales) that is important for understanding the cross-over from continuum to atomistic dynamics in disordered (liquid and glass) materials. This is a region that is now mostly inaccessible by other methods. Studies at high pressure allow investigation of fundamental geophysical problems such as the composition and evolution of the earth’s core. In these areas, BL43LXU of the RIKEN SPring-8 Center is now uniquely capable and is leading world effort. Specific examples will be drawn from recent work on (a) liquid water that resolves a multi-decade controversy [2] and sets the stage for a comprehensive interpretation of mesoscale liquid dynamics and (b) studies to extreme (>300 GPa) pressure that place constraints of the composition of Earths‘s inner core [3]. These will be presented in the context of the development of specialized instrumentation that has made these very challenging experiments possible [1,4-7]
baron@spring8.or.jp [1] Baron, in Synch. Light Srcs. & FELS, edited by E. Jaeschke, et al, (Springer International Publishing, Cham, n.d.), https://arxiv.org/abs/1504.01098. [2] Ishikawa, Baron, J. Phys. Soc. Japan 90, 83602 (2021) https://doi.org/10.7566/JPSJ.90.083602 [3] Ikuta, Ohtani, Fukui, Sakai, Ishikawa, Baron, To Be Published. [4] Baron, SPring-8 Inf. Newsl. 15, 14 (2010) http://user.spring8.or.jp/sp8info/?p=3138. [5] Baron, Tanaka, Soutome, Takao, Nakamura,Kobayashi, Fujita, Takahashi, Aoyagi, Shimosaki, Seike, Uchiyama, Ishikawa,Chuang, Kimura, Tanaka, Kitamura, Ishikawa, AIP Conf. Proc. 1741, 020033 (2016) http://dx.doi.org/10.1063/1.4952812. [6] Ishikawa, Ellis, Uchiyama, Baron, J. Synch. Rad. 22, 3 (2015) https://doi.org/10.1107/S1600577514021006. [7] Baron, Ishikawa, Fukui, Nakajima, AIP Conf. Proc. 2054, 20002 (2019) https://aip.scitation.org/doi/abs/10.1063/1.5084562