Exploratory Materials Synthesis & Characterization
Our research program concentrates on the synthesis and characterization of the new model materials of current interest in condensed matter physics. We put strong effort in the discovery of new phenomena associated with the correlated behavior of electrons, superconductivity and magnetism. Most often materials are made in the single crystal form since many observables of interest are tensor quantities and since this allows for the investigation of properties that are free of grain boundaries influence.
New materials are prepared by variety of crystal growth and materials synthesis methods: conventional arc melting and powder metallurgical techniques, solution methods, high temperature intermetallic, oxide, sulfide or salt fluxes, chemical vapor transport and deposition. Automated physical and structural characterization is the essential component of the lab. In order to optimize synthesis parameters, it is necessary to characterize structural and physical properties of materials. Quite often the same methods are used to probe and perturb crystal structure, transport, thermodynamic and magnetic properties, sometimes at the extreme conditions. Besides our lab instruments, we use environment of high magnetic fields and low temperatures at NHMFL Tallahassee and HZDR Dresdena>. We also use NSLS EXAFS beamlines in collaboration with Anatoly Frenkel. There is considerable synergy and overlap with BNL X-ray scattering group. We are actively engaged in the constant buildup of our synthesis and characterization capabilities by custom designing and/or building of both materials synthesis and physical characterization tools.
Our research portfolio consists of several general themes relevant to Experimental Condensed Matter Physics (CMP) Core Research Area of the Office of BES:
1. Fe based high-Tc superconductivity
We pursue activities associated with studies of the Fe based superconductors and related materials within Center for Emergent Superconductivity. We focus on exploratory synthesis and improvement of known iron selenide and iron telluride superconductors. Exploratory synthesis includes new materials design, structure-property relations in similar materials and search for crystal chemical environment where superconductivity may exist. Improvement of known materials includes growth of crystals suitable for particular experimental probes such as neutron scattering or ARPES.
2. Quantum criticality
Heavy fermion superconductors with low dimensional electronic systems and highly anisotropic magnetic interactions offer a model material for the study of superconductivity near Quantum Critical Point (QCP) in parameter space that is not accessible in cuprate oxides (e.g. above Hc2) or free from other phenomena which may or may not be related to superconductivity (e.g. disorder, charge and/or magnetic ordering, etc..). We are also exploring superconducting materials near putative charge density wave (CDW) QCP in low dimensional chalcogenide conductors.
3. Correlated electron semiconductors
We have an interest in exploring correlated electron metallic states in materials where there are no localized and well defined 4f moments and where the large enhancement of the quasiparticle mass is not related to Abrikosov – Suhl resonance. Such materials of interest are correlated electron semiconductors with 3d transition metal elements (FeSi – like) and variety of other materials with residual and frustrated magnetic interactions, charge and/or orbital order. Prominent examples are materials such as FeSi and FeSb2, Kondo-insulator-like narrow band semiconductors with large pileup of states at the gap edges. Since the thermopower S is very sensitive to variations in density of states in the vicinity of the Fermi level, very large values (|S|~100 µV/K) can be expected.
4. Dirac states in bulk crystals
We have embarked recently on the exploration of Dirac states in bulk crystals. Quasi two-dimensional electronic transport and magnetotransport phenomena were observed in single crystals of materials such as SrMnBi2 and CaMnBi2. The linear energy dispersion in bulk bands leads to nonsaturated linear magnetoresistance (MR) since all Dirac fermions occupy the lowest Landau level in the quantum limit. The effective magnetoresistant mobility up to μMR~3400 cm2/Vs is derived. Angular-dependent magnetoresistance and quantum oscillations suggest dominant 2D Fermi surfaces. Our results imply that bulk crystals with Bi square nets can be used to study low-dimensional electronic transport commonly found in 2D materials such as graphene.