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Areas of Current Research
Areas of Current Research
Materials Physics– Condensed matter materials, usually oxides and sulfides, are chosen for study based on their promise to exhibit unusual quantum states of matter. These materials include insulators, magnets, conductors, and superconductors. They tend to be low-dimensional, in the sense that they contain sheets or chains that are primarily responsible for their unusual properties. For example, one compound under study has one-dimensional chains that conduct electricity very well, but it is a poor electrical conductor in the other two crystallographic directions (see: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.112.186602 ). Another compound has magnetic atoms that are strongly coupled along one crystallographic direction, and weakly coupled in the other direction (see: https://journals.aps.org/prb/abstract/10.1103/PhysRevB.96.024433 ).
Why is this research important? - Condensed matter systems provide an environment where quantum effects are always present. When electrons are constrained to low-dimensions, they interact much more strongly than they would in three dimensions. This can lead to unusual effects. For example, Luttinger liquids form in one-dimensional systems, which causes a fraction of the electrons to pair up and form spin equal to 1 particles called bosons. This is similar to what occurs in a superconductor, but it is associated with the geometric constraint. Strong interactions like this may be the underlying mechanism of high-temperature superconductivity, which occurs in compounds with two-dimensional layers.
Research Approach– Interesting materials are identified, and we attempt to grow single crystals using three different methods: optical float zone, vapor transport, and flux growth. The crystals are characterized with analytical techniques, such as x-ray diffraction to determine their quality. Measurements of numerous physical properties are carried out in our laboratory, and through collaborations. The data are analyzed, and the samples and measurements are improved upon as needed until the best quality data are obtained. The results are then compared to current theories in condensed matter physics. The general approach is illustrated in the flowchart shown in Fig. 1.
The Physics of Ice – We are interested in investigating the basic physical properties of H2O ice. Recently we published our data on the thermal expansion of single-crystal H2O and D2O ice, which has a relative resolution that is at least 10,000 times higher than any past measurements. (see: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.121.185505 ) The data reveal a phase transition near 100 K that was never before observed; it is associated with rotations of the H2O molecules that kick in above that temperature. Our next goal is to measure the compressibility of H2O and D2O ice with very high resolution.
Why is this research important? - Hydrogen-bonded solids abound in biology and chemistry and are important for the pharmaceutical and plastics industries. Ice is arguably the world's best-known hydrogen-bonded solid. However, ice turns out to be extremely complicated and poorly understoood, partly because the complex nature of the hydrogen bond. High-quality measurements of the fundamental physical properties of ice is an important way to improve our theoretical understanding of ice, and the physics surrounding hydrogen-bonding and its influence on the physical properties of condensed-matter systems.
New Measurement Techniques - Our laboratory also develops new measurement techniques. An example of this work is the thermal expansion technique used in our laboratory. (see: https://aip.scitation.org/doi/full/10.1063/1.2884193 )
The Research Laboratory
The Research Laboratory
Optical image furnace – This device has dual elliptical cavities that focus high intensity light to reach temperatures of up to 2300 ˚C for the growth of large single crystals, about the size of your finger. They can be cut, shaped, and oriented using Laue x-ray diffraction so that measurements can be made along known crystallographic directions. The picture to the right shows and interior view of the furnace.
Numerous furnaces are available (above left) for growing samples in a variety of environments, with temperature reaching up to 1700 ˚C. They can be used for annealing samples, synthesizing polycrystalling samples, and for the growth of single crystals. A glass blowing bench (above right) with a propane-oxygen torch is used for sealing samples in fused-quartz tubes under vacuum for controlled reactions. A Laue x-ray diffraction unit in our laboratory is used for characterizing and orienting single crystals. A powder diffraction unit, available in MSU's ICAL facility (see: http://www.physics.montana.edu/ical/ ), is used for determining crystal structures and searching for secondary phases.
A Quantum Design Physical Properties Measurement System with a 9 tesla magnet is the workhorse for most of our measurements. It can measure specific heat and electrical resistivity between 0.35 K and 400 K, magnetic susceptibility between 1.9 K and 1000 K, and a number of other physical properties. It can also serve as a temperature-control platform for additional experiments. For example, we place pressure cells into the chamber to measure the influence of high pressure (up to 18,000 atmospheres) on the electrical resistivity. This device uses liquid helium; the gas is captured and liquified with a ATL-160 helium liquefaction system, also from Quantum Design.
Fused silica thermal expansion cell next to a US nickel to show the scale. The wedge is used to adjust the capacitor gap prior to beginning to measure.
Our thermal expansion measurement system was developed by undergraduate and graduate students under the direction of Dr. Neumeier. The heart of this device is a thermal expansion cell made entirely from fused quartz, which has an extremely small thermal expansion coefficient. The cell is pictured to the left and described here: https://aip.scitation.org/doi/full/10.1063/1.2884193 . With this simple device, length changes of 0.1 angstrom can be detected by measuring the change is the spacing between two capacitor plates that are controlled by the sample's length. The sample is visible as the black parallelepiped between the wedge and the upper part of the cell. This device allows us to investigate how electronic phase transitions, such as when a material enters the superconducting state, influence the crystal structure of solids. It also allows us to study structural transitions with unsurpassed relative resolution.
What is the role of young researchers in this work? - First and foremost, work in a research laboratory trains young scientists. The training cannot be obtained in any other manner. Our student researchers become adept at many experimental and analytical techniques and develop strong communication skills. These skills transfer well into future careers in science or elsewhere. More specifically, young scientists learn to grow samples and operate laboratory equipment in order to carry out experiments. Sometimes they even construct their own equipment in order to reach the goals of their research. They are guided in this process by the research team, but quickly become responsible for their own independent research projects, which benefit from collaboration with the team. Finally, young researchers are provided with the opportunity to discover new aspects of our physical world, and to tell others about their discoveries. They report the results of their work at conferences and in publications; their results provide the inspiration for future research at MSU and elsewhere.
About Professor Neumeier: John Neumeier was raised on the New Jersey shore. In 1984 he completed his undergraduate work at Stockton State College in Pomona, NJ. Six years later he received his Ph.D. in Physics from UC San Diego for research on high-temperature superconductivity under the direction of Prof. M. B. Maple. Following postdoctoral work at the University of Munich (LMU) and Los Alamos National Laboratory, he received a faculty appointment at Florida Atlantic University. In 2002 he joined the faculty in the Physics Department at Montana State University. He has coauthored over 170 research articles on magnetism, superconductivity, thermodynamic properties of matter, and measurement technologies. He has a particular interest in studying underappreciated issues in science. His research has attracted funding from the National Science Foundation, the Department of Energy, the Office of Naval Research, and NATO. He was elected a fellow of the American Physical Society in 2013. While at MSU, he has guided research projects of numerous students and hosted visiting scholars from Asia, Brazil, and Europe. He teaches introductory and advanced courses in physics. For the academic year 2019-2020 he is on sabbatical in Lorena, Brazil. For more information about his publications, click on this link: Google Scholar - Neumeier.
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