Condensed Matter & Surface Physics Research

Condensed matter and surface physics represents the single largest area of world-wide physics research. These subjects encompass a diverse range of theoretical and experimental sub-fields such as correlated systems, magnetism, nanomaterials, and systems with surfaces and interfaces. The condensed matter and surface science group has eight faculty members participating in numerous projects involving experimental and/or theoretical aspects. This group interacts with students, colleagues in other departments, members of the interdisciplinary Laboratory for Surface Studies, and researchers at various national user facilities.

Laboratory for Surface Science

The Laboratory for Surface Studies (LSS) is an interdisciplinary research center at UWM comprised of faculty and students from chemistry, physics, and engineering, united by the desire to understand the structural, chemical, electronic, and magnetic properties of materials at the nanoscale. Started in the mid-1960s and designated a University of Wisconsin Center of Excellence, LSS remains a leading and vibrant part of the UWM research environment. The experimental and theoretical research activities today span a broad range of topics, from traditional problems in surface science, to current areas of interest such as biophysics, nanotechnology, tribiology, catalysis, and materials science at the atomic scale.

Faculty Research

Two half-Vortices coupled to dislocations in a PDW superconductor

Daniel Agterberg is a theorist working in the area of superconductivity and strongly correlated electronic materials, focusing on topics such as the nature of high-temperature superconductors and the consequences of topological structures on electronic wave functions. His research is driven by close communications with experimentalists to identify relevant problems that lie at the forefront of materials science, and combines analytical many-body/symmetry-based techniques with numerical calculations. He has recently collaborated with Scientists at Cornell University, the Swiss Federal Institute of Technology (ETH-Zurich), Stanford University, and the University of Tokyo.

HRTEM of Fe3O4(111)/MgO(111) polar surface

Marija Gajdardziska-Josifovska’s group uses atomic resolution transmission electron microscopy, diffraction, and spectroscopy methods to understand how the combination of ionicity and limited dimensionality leads to new physical properties and useful applications. Her funded research program aims to elucidate the stabilization mechanisms for polar oxide surfaces and interfaces by studying their atomic and electronic structures. The focus is on polar oxide systems with applications in energy, environment, and novel forms of electronics. Her group also works with a wide range of nanostructures, with recent funded work on hybrid nanosensors, based on tin oxide nanoparticles supported on carbon nanotubes or graphene sheets, and complex oxide nanoparticles with promising multiferroic properties. In the area of biophysics she collaborates with colleagues from the life sciences to develop targeted magnetic nanotechnology therapies for stroke and cancer, and to study naturally occurring magnetic nanocrystalline biominerals created by the iron storage proteins in plants and bacteria. She has contributed to technique developments in nanodiffraction, electron holography, reflection electron microscopy, and dynamical in-situ transmission electron microscopy. Her research has been supported by grants from the National Science Foundation, the Department of Energy, and the Research Corporation.

For more information: Gajdardziska-Josifovska’s Research Website

 

Floating zone crystal growth chamber

Prasenjit Guptasarma is interested in the materials science of systems with strongly correlated electrons. His work seeks to elucidate the fundamental physics of unusual electronic and magnetic properties of materials, such as those near a critical phase transition, or bordering an unconventional quantum physical ground state. Current activities in his group include studies in the areas of novel superconductivity and magnetism, ferroelectricity, and multiferroics. Guptasarma’s research lab hosts equipment for floating-zone growth of high-purity bulk single crystals, growth of nanostructures using high-pressure and solution-based techniques, and measurement of properties such as magnetic, transport, dielectric, specific heat, and ultrasound velocity, at extreme temperatures (350mK – 800K) and in magnetic fields (up to 9 Tesla). In addition, his group performs experiments at synchrotron light sources, neutron sources, and high magnetic field facilities in North America and abroad.

For more information: Guptasarma’s Research Website

 

IR Spectra of Micrasterius Algae

Carol Hirschmugl studies the surface physics of adsorbates on epitaxial and bulk oxide systems, focusing on environmentally and technologically relevant problems. Her investigative approaches include far and mid-infrared absorption spectroscopy and picoampere low energy electron diffraction to study low energy dynamics and structure at aqueous-oxide interfaces. In addition, Hirschmugl is developing a rapid chemical imaging technique using infrared imaging microscope coupled to an synchrotron source, which will be used to examine real-time biochemical changes in vivo.

Atomic-scale imaging of ridges on epitaxial graphene on 6H-SiC(0001)

Lian Li conducts research to unveil structure and property relationships of condensed matter at the atomic scale. His current focus is on diluted magnetic semiconductors (DMS). The research addresses two fundamental questions in condensed matter physics: 1) how are local magnetic moments created in semiconductors (e.g., graphene and GaN), and 2) how do these moments interact with each other to attain long-range ferromagnetic ordering. The studies involve material growth using molecular beam epitaxy (MBE), atomic-scale characterization using spin-polarized scanning tunneling microscopy (SP-STM) and spectroscopy, synchrotron-based x-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD), and first-principles calculations.

For more information: Li’s Research Website

 

TeGe(001)-(1×1) bridge-site structure with missing Te row

Paul Lyman conducts research focused on growth of novel thin films and determination of surface reconstructions. One principal effort (in collaboration with Prof. Dilano Saldin) involves developing and applying phase retrieval methods to help solve surface structures directly from x-ray diffraction data. Materials of interest include oxides and wide-bandgap semiconductors, especially the structure of polar oxides. In addition to standard UHV preparation methods, his group is interested in air-stable oxide reconstructions, and growth of thin epitaxial films using atomic layer deposition (ALD). The fine control afforded by the ALD technique allows the construction of novel multilayered materials, such as (Mg,Zn)O alloys.

For more information: Lyman’s Research Website

 

Ultrasonic properties of URu_2Si_2

Bimal Sarma’s interest in condensed matter is the study of materials in extreme environments — at extremely low temperatures and extremely high magnetic fields. Sarma, whose work has spanned a wide arena of experimental physics from neutron diffraction to low-temperature techniques, has been concerned with the use of sound waves to investigate phase transitions and the actual phases themselves in magnetic systems and superconducting/superfluid systems. Sarma’s landmark study of heavy-fermion superconductors showed the existence of a metallic superconductor whose microscopic behavior does not conform to the standard BCS model of electron-pairing and led to the remarkable discovery of multiple superconducting phases in UPt3. Sarma’s current studies involve high-Tc and heavy-fermion superconductivity and the phases of materials in some of the highest magnetic fields.

For more information: Sarma’s Research Website

 

Calculated spectral weight for interfacial graphene on 6H-SiC(0001) and for epitaxial graphene

Michael Weinert’s research is focused on understanding the electronic, magnetic, and structural properties of complex materials at the atomic level, primarily through the use of first-principles electronic structure calculations. Much of his research is done in close collaboration with experimentalists, both at UWM and elsewhere. Research topics include the effects of external electric fields on the electronic and magnetic properties of surfaces, interfaces, and nanostructures; phase stability of alloys and the role of defects; the electronic structure of oxides and related systems; magnetic semiconductors; the interpretation of various electron spectroscopies (e.g., STM, APECS, photoemission); and the development of new computational approaches and high-performance (parallel) computing applied to materials physics.

For more information: Weinert’s Research Website