Phone : +1 860 486 0444
- Current research and funding
- Charge inhomogeneity in correlated electron systems
- Tuning Strain with Negative Thermal Expansion Materials
- Selected Publications:
Prof. Wells is a full professor in the Physics Department at the University of Connecticut and a member of the Institute of Materials Science at the University of Connecticut. He has served as a visiting scientist at Brookhaven National Laboratory, USA and the Paul Scherrer Institute, Switzerland. He has been named a Cottrell Scholar of the the Research Foundation, a Sloan Fellow, and a CAREER award winner from the American National Science Foundation.
Current research and funding
Charge inhomogeneity in correlated electron systems
Materials with strongly correlated electrons differ from traditional materials in that the conduction electrons are localized, in the sense of the Heisenberg Uncertainty Principle. That means that it is meaningful to ask “where are the electrons?”. This appears to be a particularly interesting question in cases where dopant ions are mobile, allowing for doped charges to rearrange with minimal Coulomb repulsion. We have found that the ordering of doped charges is common, and in many cases leads to electronic phase separation to different effective charge densities. Studying these effects is difficult and needs advanced techniques.
Our group synthesizes transition metal oxide compounds with extreme oxygen cocentrations and studies them using resonant x-ray scattering, a technique that combines the electronic information from x-ray absorption spectroscopy with the structural information from scattering or diffraction. We are regular users of the REIXS beamline at the Canadian Light Source, one of the best beamlines worldwide for this type of study, and we also use synchrotrons throughout the USA. We also use muon spin rotation to look at spatial distribution of the different electronic phases that result. These studies are primarily conducted at the Paul Scherrer Institute in Switzerland.
This work is funded by Basic Energy Sciences at the United States Department of Energy.
Tuning Strain with Negative Thermal Expansion Materials
Films grown can be grown on substrate crystals such that the film lattice constant matches that of the underlying crystal, known as coherent growth. In some cases, substantial strain can be induced in the film and the properties tuned accordingly. However, this approach only works for very thin films, often so thin such that they are not suitable for many experiements or for applications. An alternative route is to grow thick films on substrates with a large difference in thermal expansion. Perhaps the largest difference that can be achieved are with materials showing negative thermal expansion, i.e. they grow larger upon cooling. We are evaluating the use of such materials as substrates for strongly correlated electron materails that are expected to have strong tunabiliity using strain. This project involves synthesizing new materials and characterization of their properties at synchrotrons and neutron facilities.
- Z. H. Zhu, F. J. Rueckert, J. I. Budnick, W. A. Hines, Ch. Niedermayer, L. Keller, H. Luetkens, B. Dabrowski, S. Kolesnik, and B. O. Wells “Distinct Magnetic Phases in Structurally Uniform SrCoO3-y” Phys. Rev. B 93, 224412 (2016)
- L. Udby, J. Larsen, N. B. Christensen, M. Boehm, Ch. Niedermayer, H. E. Mohottala, T. B. S. Jensen, R. Toft-Petersen, F. C. Chou, N. H. Andersen, K. Lefmann, B. O. Wells “Measurement of unique magnetic and superconducting phases in superoxygenated high-Tc cuprates” Phys. Rev. Lett. 111, 227001 (2013)
- F. J. Rueckert, Y. F. Nie, C. Abughayada, S. A. Sabok-Sayr, H. E. Mohottala, J. I. Budnick, W. A. Hines, B. Dabrowski, and B. O. Wells “Suppression of magnetic phase separation in epitaxial SrCoOX films” Appl. Phys. Lett. 102, 152402 (2013)
- C. K. Xie, Y. F. Nie, B. O. Wells, J. I. Budnick, W. A. Hines, and B. Dabrowski “Magnetic phase separation in SrCoOx (2.5 ≤ x ≤ 3)” Appl. Phys. Lett. 99, 052503 (2011)