Condensed matter physics encompasses a variety of research topics that pertain to the properties of solids and liquids. Condensed matter physics is a critical field in which fundamental insights into basic science enable progress in technology. Some of the most remarkable and surprising manifestations of quantum behavior are seen in condensed matter systems - features like superconductivity, superfluidity, the integer and fractional Hall effects, and quantum tunneling. Understanding such properties has led to a myriad of technological applications in areas such as semiconductors, magnetic storage and spin electronics (spintronics), permanent magnets, solid-state laser materials, optical devices, and superconductors. Our department has many active and interconnected research programs in areas such as high temperature superconductors, magnetism, surface physics, transport in complex oxides, laser materials and devices, and the phase behavior and properties of alloys. Our research has led to a wide variety of collaborations with other institutions around the world, some of which are described below. Of special note is our department's close connection with Brookhaven National Laboratory on Long Island in New York. At least five faculty members regularly pursue experiments/collaborations at the Laboratory and our two most recent hires were made through an agreement that provides for special bridge positions in conjunction with Brookhaven. Following is a description of research programs in condensed matter physics arranged by research group.
Research into high temperature superconductivity remains a cornerstone of solid state physics. In a series of compounds that are built around networks of copper and oxygen planes, superconductivity has been observed at temperatures up to 170 K. This contrasts with traditional materials in which the highest temperature at which superconductivity was known to occur was 23 K. Not only is superconductivity at such elevated temperatures a remarkable phenomenon in itself, but also a whole range of properties of these materials tests the limits of our current understanding of solids. Research into these materials touches almost every area of condensed matter physics, including many-body systems, magnetism, low-dimensional physics, metal-insulator transitions, and defect properties. In addition, the remarkable properties of superconductors holds promise for a revolution in electronics technology in the twenty-first century. Work at the University of Connecticut includes a new and growing synthesis effort as well as experiments in nuclear magnetic resonance, muon-spin rotation, x-ray absorption spectroscopy, x-ray diffraction, photoelectron spectroscopy, spin-resolved spectroscopies, and high-resolution microscopy. Our work is highly collaborative. Several groups in our own department have inter-related projects in this area and we have established external collaborations with Brookhaven National Laboratory, the University of Konstanz in Germany, the Pennsylvania State University, and the Advanced Light Source (Berkeley).
There are a variety of oxides of metallic species that show complex and inter-related properties. Chief among this group are the transition metal oxides. One important member of this group is the copper oxides, which under certain conditions become high temperature superconductors and are listed separately above. However, in other oxides small variations of the same physical interactions lead to a variety of remarkable phenomena, including complex magnetism, metal-insulator transitions, colossal magneto-resistance, and tunable dielectric properties. There is a long and constantly changing list of materials in this category that are under active investigation. Following are a few examples of the exciting developments that UConn scientists are pursuing in this area. Ca1 - xSrxRuO3 with variable x forms an interesting set of compounds. SrRuO3 (x = 1) is a ferromagnetic metal. However, CaRuO3 (x = 0) does not order down to 50 mK. Ca and Sr are electronically and chemically similar, differing mainly in their ionic radii. Yet this difference is enough to radically affect the magnetic state. At UConn we are trying to understand the origin of these changes concentrating on muon spin resonance studies, nuclear magnetic resonance experiments, and x-ray spectroscopy.
Another interesting example is NiO. This material is predicted to be a nonmagnetic metal by standard theory, yet it is in fact an insulator and an ordered antiferromagnet. Furthermore, when grown as a thin film, the antiferromagnetic properties appear to change due to stresses in the film. However, both antiferromagnetism and thin films are difficult to study. Researchers at the University of Connecticut are developing new experimental techniques that allow us to study and understand this phenomenon.
Almost any application of these materials in devices will rely on building structures as thin films. However the properties of these oxides depend strongly on the strains introduced in the film growth process. In our department there are several experimental efforts aimed at understanding film versus bulk properties of oxides. One new area is producing thin films grown by pulsed laser deposition (PLD). PLD is a relatively new and extremely powerful technique for growing quality oxide films. An important direction for this effort is developing new analysis tools for measuring and characterizing the films. Collaborators in this area include UConn's Institute of Materials Science, the University of Maryland, and Brookhaven National Laboratory.
Research in magnetism covers a broad range of materials and systems from metals to insulators and from bulk properties to ultra-thin films, nano-structures, nanoparticles and surfaces.
Studies of magnetic properties in confined geometries (multilayers, nano-structures and nanoparticles) have, in the last decade, led to discoveries of exciting new magnetic properties like giant magneto-resistance (GMR), exchange biasing and spin-dependent tunneling which have attracted much attention because of their importance in information technologies. Some of these novel properties have already found use in real devices (hard drives), some have the potential to do so (Magnetic-RAM) and are opening a new frontier of spin-electronics (spintronics). The development of nanoscale devices based on electron spin requires both a fundamental understanding of magnetic interactions and practical solutions to a variety of challenges. The work is performed in collaboration with IBM, Princeton University and New York University and involves a number of disciplines. We are engaged in several projects including: 1) understanding electronic bases of high spin-polarized current materials (half-metallic ferromagnets) using spin-resolved photoemission at the National Synchrotron Light Source (NSLS), 2) study of magnetic metal/oxide interfaces which forms the basis of spin-dependent tunneling and exchange biasing, 3) study of magnetic domain pattern formation in ferromagnetic and antiferromagnetic nanostructures to investigate the fundamental size-limits of magnetic storage and sensor elements, carried out at the Advanced Light Source (ALS, Berkeley). The research utilizes state-of-the-art Photoemission Electron Microscope (PEEM) and tunable polarization insertion devices. We are a member of a team to develop 1-nm resolution PEEM capability at ALS. This research also involves development of novel spin-resolved electron-emission techniques that provide new insight into the magnetic properties of complex oxides (see above).
Research on metals and alloys focuses on small magnetic particles and new permanent magnetic materials and it is being conducted through experimental investigations by nuclear magnetic resonance, magnetization and x-ray absorption and diffraction spectroscopy. The x-ray absorption investigations are carried out using a dedicated beam line at NSLS at the Brookhaven National Laboratory (BNL). Some work on new magnetic nanophase materials is carried out in cooperation with members of the Institute of Materials Science. Students in condensed matter physics have the opportunity to use the extensive resources of the Institute of Materials Science, as well as other facilities and institutes with missions in materials research. A new state-of-the-art x-ray diffraction facility has been installed in the Institute of Materials Science, which includes three new diffractometers and associated computer-analysis facilities. There is also a Surface Characterization Laboratory whose capabilities include x-ray and uv photoemission spectroscopy, Auger spectroscopy and SIMS, and a 2 MV van de Graaf accelerator facility for Rutherford Back Scattering (RBS) analysis and surface modification. These facilities are being used by members of our Department to characterize thin films and interfaces, nanophase materials, and to study disorder in high-temperature alloys. Additional information on surface characterization work can be found in the AMO section of this brochure.
Recently, the Institute of Materials Science has been awarded funding from NSF for the purchase of an automated digital 200 keV transmission electron microscope with parallel electron energy loss spectroscopy. This instrument will be used for the study of the microstructure and chemical properties of magnetic and alloy nanostructures.
Study of growth and properties of atomically engineered ultra-thin magnetic oxide films and their surfaces addresses some of the key issues of these important but complex systems: i) how does the crystal structure influence the magnetic properties? ii) how do properties of a single-component (atomic species) contribute to the overall property of the system? iii) stability of polar magnetic surfaces, and iv) formation of magnetic metal/oxide interface. Most of this work is performed on campus in a surface-science laboratory employing a dedicated multi-technique UHV chamber for in-situ growth and characterization of electronic, structural and magnetic properties.
Semiconductor lasers, optoelectronic devices and optical communication systems are important areas of research in the Physics Department. Among the current research activities are: (i) Tera-bit optical communication systems employing multiple channels at 100 Gb/s or higher data rate; (ii) wavelength transparent all-optical networks; (iii) optical transmission using plastic optical fibers; (iv) investigation of nonradiative recombination in far infrared lasers; (v) fiber lasers; and (vi) optical coherence tomography.
The research on very high speed transmission involves optical multiplexing and demultiplexing for data generation and data decoding after transmission. It includes investigation of high speed and mode-locked semiconductor lasers, investigation of fiber nonlinearities, investigation of short pulse propagation characteristics, optical amplification, and investigation of gain and phase modulation in semiconductor amplifiers for optical demultiplexing. The research on all optical networks involves investigation of various wavelength translation/conversion mechanisms, including gain modulation and four wave mixing in semiconductor amplifiers. The research on plastic optical fiber transmission includes (i) investigation of noise for analog, digital and subcarrier modulated multichannel transmission in plastic optical fibers, and (ii) investigation of fiber designs that would lead to low dispersion fibers.
The research on fiber laser includes (i) investigation of suitable co-dopants and materials for high power emission at 940 nm and (ii) generation of very short pulses near 1550 nm for high speed fiber communication. The research on optical coherence tomography involves the development of a suitable technique including instrumentation which can be used for clinical testing of periodontal tissues. Please see the Laser Physics section for additional information.
The experimental techniques utilized to investigate insulating solids include electron spin resonance, optical absorption, and laser spectroscopy including excited-state absorption, energy-transfer, and laser-induced photoluminescence. Subjects of investigation include crystal growth, point defects and radiation damage processes in insulating crystals, as well as fundamental processes in potential solid-state laser and scintillator materials. These studies qualify as components of both the condensed matter physics activity and the laser and optical physics activity. Additional information can be found in the section on Laser Physics.
X-ray absorption fine structure and near edge studies are being carried out at beamline X-11A at the National Synchrotron Light Source to explore specific local structures in a wide variety of interesting systems including high TC oxides, magnetic nitrides and transition metal aluminide systems. In addition, a novel method for obtaining x-ray absorption-edge fine structure on dilute materials in the presence of x-ray noise has been developed. This method is being used at the NSLS and will also be used at the Advanced Photon Source at Argonne National Laboratory, and has stimulated interest in its application to the characterization of environmental soil pollutants, studies of catalysis and of metal-insulator transitions, and of biological processes. In addition, in cooperation with the Departments of Mechanical Engineering and Metallurgy, novel methods have been developed for performing x-ray strain measurements in high temperature materials, such as refractory alloys covered with thermal barrier coatings.
Research in this area focuses on the molecular processes that govern the mechanical properties of amorphous solids. Unlike the crystalline state, which is by now understood at an impressive level of detail, many fundamental questions are still unanswered for the glassy state of matter. Specifically, our efforts concentrate on the following objectives: 1) development of methods and tools for the structural and dynamic investigation of amorphous solids, particularly glassy polymers; 2) characterization of structural changes induced by plastic deformation in such materials; and 3) establishment of relationships between the structure of amorphous materials and their mechanical properties, using both experimental data and extensive computer simulation. The pursuit of these research goals requires the application of a broad spectrum of experimental, numerical and theoretical methods, such as solid-state NMR and optical spectroscopy, mechanical testing, synthetic and preparative polymer chemistry, statistical mechanics, molecular simulation, and quantum chemistry.
The theoretical condensed matter program in our department focuses on several important and current areas of research. One area of investigation involves non-equilibrium thermal properties of solids including transport properties, surface acoustic-wave scattering and attenuation. There is also an effort in optical and magnetic properties of point defects and impurities in solids carried out in close collaboration with experimentalists.
Phonon scattering and transport are studied theoretically with emphasis on the thermal conductivity of solids. Recent investigations address phonon transport in two dimensional systems, including graphite and quantum wells. Phonon scattering by grain boundaries, and the thermal conductivity of ceramic materials composed of nanometer-scale crystallites, are also included.
There is also an active program in first principles studies of condensed matter systems, with emphasis on both formal and computational aspects. Alternatives to Density Functional Theory are being investigated in order to address various inadequacies of the present formalism. State-of-the-art electronic structure work as well as simple physical models are being used to gain a better understanding of the structural, magnetic and conducting properties of bulk solids (such as binary alloys and permanent magnets), surfaces/interfaces (of metals and oxides) and nanostructured devices. There is also an interest in Statistical Mechanics based studies combined with first principles work that can be used to develop parameter-free theories to examine, for example, disordered phases of materials.
Interaction with experimentalists is a highly valued, integral part of these theoretical efforts that is beneficial to all those involved.