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Complex States, Emergent Phenomena & Superconductivity in Intermetallic & Metal-like Compounds

FWP/Project Description: 

The specific scientific question to be addressed by this FWP is: how can we develop, discover, understand and ultimately control and predictably modify new and extreme examples of complex states, emergent phenomena, and superconductivity? Over the next review period we will study materials manifesting specifically clear or compelling examples (or combinations) of superconductivity, strongly correlated electrons, quantum criticality, and exotic, bulk magnetism because of their potential to lead to revolutionary steps forward in our understanding of their complex, and potentially energy relevant, properties. For example, part of our effort will focus on the understanding and control of FeAs‐based superconductors as well as searching for other examples of novel, or high temperature, superconductivity. This work will be leveraged via highly collaborative interactions between the scientists within this FWP as well as through extensive collaborations with other Ames Laboratory FWPs, other DOE laboratories, and other universities and labs throughout the world. Experiment and theory will be implemented synergistically. The experimental work will consist of new materials development and crystal growth, combined with detailed and advanced measurements of microscopic, thermodynamic, transport, and spectroscopic properties, as well as electronic structure, at extremes of pressure, temperature, magnetic field and resolution. The theoretical work will focus on modeling transport, thermodynamic and spectroscopic properties using world‐leading, phenomenological approaches to superconductors and modern quantum many‐body theory.

To accomplish our goals, three highly interacting classes of research operate both in series and in parallel:

  • Design and Growth: (Canfield, Bud’ko, Johnston, Kogan)
  • Advanced Characterization: (Bud’ko, Furukawa, Kaminski, Prozorov, Tanatar)
  • Theory and Modeling: (Kogan, Johnston, Prozorov)

This research is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering.

Correlations & Competition Between the Lattice, Electrons, & Magnetism

FWP/Project Description: 
Research Project Overview

The properties of novel materials, such as high-temperature superconductors, charge/orbital ordering systems, and multiferroics, are all sensitively controlled by correlations and competition among the lattice, electronic, and magnetic degrees-of-freedom.  A complete understanding of the interrelations between these systems and the necessary conditions for enhancing or tailoring desirable physical properties have been identified as a Grand Challenge to the scientific community. Neutron and x-ray scattering are powerful techniques that directly probe the structural, electronic, and magnetic aspects of complex ground states, phase transitions, and corresponding excitations. Within this FWP, the varied expertise of the PIs in different scattering methods is employed in a synergistic approach and systems are studied using a wide range of neutron and x-ray techniques. The experimental program is supported by a closely coupled effort in ab initio band structure calculations, theoretical modeling, and scattering simulations. We also enjoy strong collaborations with many of the other FWPs in the Ames Laboratory, especially Complex States, Emergent Phenomena Superconductivity in Intermetallic & Metal-like Compounds, Extraordinary Responsive Rare Earth Magnetic Materials, Innovative & Complex Metal-Rich Materials, and Magnetic Nanosystems: Making, Measuring, Modeling and Manipulation

Some Recent Projects

Iron Pnictides: Over the last two years, we have continued our investigations of the iron-based superconductors and our major emphasis has turned to understanding the nature of spin fluctuations and their connection with superconductivity.

  • In CaFe2As2, for example, the wide Q and high energy capabilities of ARCS at the SNS allowed us to conclusively show that the Fe moment is completely quenched in the non-superconducting collapsed tetragonal phase.
  • We have demonstrated that the onset of superconductivity in Ba(Fe1-xCox)2As2 coincides with a crossover from well-defined spin waves to overdamped and diffusive spin excitations. This crossover occurs despite the presence of long-range stripe-like antiferromagnetic (AFM) order for samples in a compositional range from x = 0.04 to 0.055, and is a consequence of the shrinking spin-density wave gap and a corresponding increase in the particle-hole (Landau) damping.
  • We have also investigated the dispersion of the spin resonance below Tc that appears at QAFM = (1/2 1/2 1) in the 122 iron arsenide compounds.  In the cuprates, the dispersion of the resonance is downwards towards the nodes in the d-wave superconducting gap forming the characteristic hourglass shape below Tc.  For Ba(Fe0.963Ni0.037)2As2, however, we found that the resonance disperses upwards and showed, with the assumption of an s± superconducting order parameter, that the details of the resonance’s dispersion are determined by the normal state spin fluctuations (e.g. the in-plane anisotropic magnetic correlation length).
  • Our inelastic neutron scattering measurements on a set of co-aligned samples of antiferromagnetic LaFeAsO demonstrated that the magnetic interactions are essentially two-dimensional .  The spin-wave velocities, within the Fe layer, and the magnitude of the spin gap, are similar to the AFe2As2 based materials. However, the ratio of interlayer and intralayer exchange is found to be less than ∼10-4 in LaFeAsO, very similar to the cuprates, and ∼100 times smaller than that found in AFe2As2 compounds.

Manganese and cobalt arsenides: A closely related effort focuses on the manganese and cobalt arsenides.

  • Low levels of K substitutions for Ba induce metallic behavior in BaMn2As2. However strong AFM ordering (TN > 500 K) remains, suggesting that charge conductivity and AFM order are independent of one another. In recent work we have shown: (1) the local-moment AFM ordering is very robust up to at least 40% K substitution; and (2) using polarized neutron diffraction, we demonstrated that itinerant ferromagnetism coexists with the AFM order below 100 K. These results are consistent the weak coupling described above.
  • Dilute substitutions of Co for Fe in the AFe2As2 compounds (A = Ca, Ba, Sr) destabilizes the stripe-like AFM ordering by shrinking (enlarging) the hole (electron) pockets and detuning the nesting condition. Ultimately, the suppression of stripe AFM ordering upon Co substitutions of a only few percent allows a superconducting ground state to appear in the presence of substantial spin fluctuations at QAFM. Further Co substitutions (> 12% Co) lead to a complete suppression of both stripe-like spin fluctuations and superconductivity. We have found that, at the other end of the compositional range, SrCo2As2 is close to an instability toward stripe-like AFM order, exhibiting steeply dispersing and quasi-two-dimensional paramagnetic excitations near QAFM. This is quite surprising for several reasons: (1) The sister compound, CaCo2As2, orders antiferromagnetically in the A-type AFM structure (ferromagnetic planes antiferromagnetically coupled along the c-axis; (2) Band-structure calculations find a large density of states at the Fermi energy that was proposed to drive a ferromagnetic instability or A-type AFM ordering; and (3) There is no clear nesting feature favoring stripe AFM order in SrCo2As2, raising the general issue of what drives the stripe-like magnetic ordering in the iron pnictides. The ACo2As2 compounds manifest other interesting behaviors as well. For example, both BaCo2As2 and SrCo2As2 manifest negative c-axis thermal expansion coefficients, which is unusual for paramagnetic metals.

Magnetic oxides: We have grown a high quality single crystal FeV2O4 and conducted elastic and inelastic neutron scattering to determine the phase diagram of this unique spinel oxide.

  • FeV2O4 features two transition metal ions that both possess spin and orbital degrees of freedom that are strongly coupled, giving rise to unique properties that are manifested by three structural transitions of which two are accompanied by magnetic transitions.  Fe2+ occupies the diamond-like A-site in the cubic spinel structure whereas V3+ occupies the pyrochlore B-site. FeV2O4 is an excellent candidate to investigate the roles of orbital ordering at not only the B site, but also at the A site. The recent discovery of multiferroicity in FeV2O4 with a coexistence of ferroelectricity and non-collinear ferrimagnetism, in contrast to the antiferromagnetism in most of the multiferroics, further motivates us to focus on this system. FeV2O4 undergoes three transitions from the high temperature cubic phase to Tetragonal-I at TS = 140 K (due to Fe orbital ordering); Tetragonal-I to Orthorhombic at TN1 = 110 K accompanied by ferrimagnetic ordering (iron up-spin – vanadium down-spin); and Orthorhombic to Tetragonal-II accompanied by non-collinear ferrimagnetic order at TN2 = 70 K (vanadium spins canted) and the emergence of ferroelectricity.  Our neutron scattering studies elucidated the different roles of the two orbital-active Fe2+ and V3+ species in the magnetic excitations.   For example, the strong spin-orbit coupling for Fe2+ induces a significant energy gap below TN1 with little contribution from the V3+. The absence of a change in the energy gap below TN2 is evidence for either a very weak spin-orbit coupling or significantly quenched orbital moment of the V3+.

Magnetic quasicrystals and related compounds: We have started a new program to investigate magnetism in quasiperiodic crystals.

  • In a close collaboration with the Complex States, Emergent Phenomena & Superconductivity in Intermetallic & Metal-like Compounds FWP in the Ames Laboratory we discovered a new family of local-moment bearing binary quasicrystals, i-R-Cd (R = Gd through Tm + Y).  The discovery is particularly exciting because these quasicrystals represent the compositionally simplest system for the study of the magnetic interactions in aperiodic systems. Furthermore, the existence of a corresponding set of cubic approximants, RCd6, to the icosahedral phase allows for direct comparison between the low-temperature magnetic states of crystalline and quasicrystalline phases with fundamentally similar local structures, since RCd6 may be described as a body-centered cubic packing of the same clusters of atoms as found in the newly discovered i-R-Cd icosahedral phase.
  • Using x-ray resonant magnetic scattering and neutron diffraction on 114Cd  enriched samples, we have demonstrated that the RCd6 approximants manifest long-range magnetic order at low temperatures, whereas the related icosahedral phase exhibits only spin-glass-like freezing at low temperatures.

Publications

2014

Kong T; Budko S L; Jesche A; McArthur J; Kreyssig A; Goldman A I; Canfield P C . 2014. Magnetic and transport properties of i-R-Cd icosahedral quasicrystals (R=Y, Gd-Tm). Physical Review B. 90:014424.

Pathak A K; Paudyal D; Jayasekara W T; Calder S; Kreyssig A; Goldman A I; Gschneidner K A; Pecharsky V K . 2014. Unexpected magnetism, Griffiths phase, and exchange bias in the mixed lanthanide Pr0.6Er0.4Al2. Physical Review B. 89:224411.

Taufour V; Foroozani N; Tanatar M A; Lim J; Kaluarachchi U; Kim S K; Liu Y; Lograsso T A; Kogan V G; Prozorov R; Bud'ko S L; Schilling J S; Canfield P C . 2014. Upper critical field of KFe2As2 under pressure: A test for the change in the superconducting gap structure. Physical Review B. 89:220509.

Tucker G S; Fernandes R M; Pratt D K; Thaler A; Ni N; Marty K; Christianson A D; Lumsden M D; Sales B C; Sefat A S; Bud'ko S L; Canfield P C; Kreyssig A; Goldman A I; McQueeney R J . 2014. Crossover from spin waves to diffusive spin excitations in underdoped Ba(Fe1-xCox)(2)As-2. Physical Review B. 89:180503.

Ueland B G; Kreyssig A; Prokes K; Lynn J W; Harriger L W; Pratt D K; Singh D K; Heitmann T W; Sauerbrei S; Saunders S M; Mun E D; Bud'ko S L; McQueeney R J; Canfield P C; Goldman A I . 2014. Fragile antiferromagnetism in the heavy-fermion compound YbBiPt. Physical Review B. 89:180403.

Weber F; Pintschovius L; Reichardt W; Heid R; Bohnen K P; Kreyssig A; Reznik D; Hradil K . 2014. Phonons and electron-phonon coupling in YNi2B2C. Physical Review B. 89:104503.

Jesche A; McCallum R W; Thimmaiah S; Jacobs J L; Taufour V; Kreyssig A; Houk R S; Bud'ko S L; Canfield P C . 2014. Giant magnetic anisotropy and tunnelling of the magnetization in Li-2(Li1-xFex)N. Nature Communications. 5:3333.

Siemons W; Beekman C; MacDougall G J; Zarestky J L; Nagler S E; Christen H M . 2014. A complete strain-temperature phase diagram for BiFeO3 films on SrTiO3 and LaAlO3 (001) substrates. Journal of Physics D-Applied Physics. 47:034011.

2013

Quirinale D G; Anand V K; Kim M G; Pandey A; Huq A; Stephens P W; Heitmann T W; Kreyssig A; McQueeney R J; Johnston D C; Goldman A I . 2013. Crystal and magnetic structure of CaCo1.86As2 studied by x-ray and neutron diffraction. Physical Review B. 88:174420.

Roy B; Pandey A; Zhang Q; Heitmann T W; Vaknin D; Johnston D C; Furukawa Y . 2013.Experimental evidence of a collinear antiferromagnetic ordering in the frustrated CoAl2O4 spinel. Physical Review B. 88:174415.

Soh J H; Tucker G S; Pratt D K; Abernathy D L; Stone M B; Ran S; Bud'ko S L; Canfield P C; Kreyssig A; McQueeney R J; Goldman A I . 2013. Inelastic Neutron Scattering Study of a Nonmagnetic Collapsed Tetragonal Phase in Nonsuperconducting CaFe2As2: Evidence of the Impact of Spin Fluctuations on Superconductivity in the Iron-Arsenide Compounds. Physical Review Letters. 111:227002.

Zhang Q; Tian W; Li H F; Kim J W; Yan J Q; McCallum R W; Lograsso T A; Zarestky J L; Bud'ko S L; McQueeney R J; Vaknin D . 2013. Magnetic structures and interplay between rare-earth Ce and Fe magnetism in single-crystal CeFeAsO. Physical Review B. 88:174517.

Kogan V G . 2013. Elastic contribution to interaction of vortices in uniaxial superconductors. Physical Review B. 88:144514. 

Kreyssig A; Beutier G; Hiroto T; Kim M G; Tucker G S; De Boissieu M; Tamura R; Goldman A I . 2013. Antiferromagnetic order and the structural order-disorder transition in the Cd6Ho quasicrystal approximant. Philosophical Magazine Letters. 93:512-520.

Goldman A I; Kong T; Kreyssig A; Jesche A; Ramazanoglu M; Dennis K W; Bud'ko S L; Canfield P C . 2013. A family of binary magnetic icosahedral quasicrystals based on rare earths and cadmium. Nature Materials. 12:714-718. 

Zimmermann A S; Sondermann E; Li J Y; Vaknin D; Fiebig M . 2013. Antiferromagnetic order in Li(Ni1-xFex)PO4 (x=0.06, 0.20). Physical Review B. 88:014420.

Pandey A; Ueland B G; Yeninas S; Kreyssig A; Sapkota A; Zhao Y; Helton J S; Lynn J W; McQueeney R J; Furukawa Y; Goldman A I; Johnston D C . 2013. Coexistence of Half-Metallic Itinerant Ferromagnetism with Local-Moment Antiferromagnetism in Ba0.60K0.40Mn2As2. Physical Review Letters. 111:047001. 

Pandey A; Quirinale D G; Jayasekara W; Sapkota A; Kim M G; Dhaka R S; Lee Y; Heitmann T W; Stephens P W; Ogloblichev V; Kreyssig A; McQueeney R J; Goldman A I; Kaminski A; Harmon B N; Furukawa Y; Johnston D C . 2013. Crystallographic, electronic, thermal, and magnetic properties of single-crystal SrCo2As2. Physical Review B. 88:014526.

Kim M G; Soh J; Lang J; Dean M P M; Thaler A; Bud'ko S L; Canfield P C; Bourret-Courchesne E; Kreyssig A; Goldman A I; Birgeneau R J . 2013. Spin polarization of Ru in superconducting Ba(Fe0.795Ru0.205)(2)As-2 studied by x-ray resonant magnetic scattering. Physical Review B. 88:014424.

Hahn S E; Tucker G S; Yan J Q; Said A H; Leu B M; McCallum R W; Alp E E; Lograsso T A; McQueeney R J; Harmon B N . 2013. Magnetism dependent phonon anomaly in LaFeAsO observed via inelastic x-ray scattering. Journal of Applied Physics. 113:17e153.

Kim M G; Tucker G S; Pratt D K; Ran S; Thaler A; Christianson A D; Marty K; Calder S; Podlesnyak A; Bud'ko S L; Canfield P C; Kreyssig A; Goldman A I; McQueeney R J . 2013.Magnonlike Dispersion of Spin Resonance in Ni-doped BaFe2As2. Physical Review Letters. 110:177002.

Lamsal J; Tucker G S; Heitmann T W; Kreyssig A; Jesche A; Pandey A; Tian W; McQueeney R J; Johnston D C; Goldman A I . 2013. Persistence of local-moment antiferromagnetic order in Ba1-xKxMn2As2. Physical Review B. 87:144418.

Ramazanoglu M; Lamsal J; Tucker G S; Yan J Q; Calder S; Guidi T; Perring T; McCallum R W; Lograsso T A; Kreyssig A; Goldman A I; McQueeney R J . 2013. Two-dimensional magnetic interactions in LaFeAsO. Physical Review B. 87:140509.

Zhang Q; Wang W J; Kim J W; Hansen B; Ni N; Bud'ko S L; Canfield P C; McQueeney R J; Vaknin D . 2013. Magnetoelastic coupling and charge correlation lengths in a twin domain of Ba(Fe1-xCox)(2)As-2 (x=0.047): A high-resolution x-ray diffraction study. Physical Review B. 87:094510.

Hahn S E; Tucker G S; Yan J Q; Said A H; Leu B M; McCallum R W; Alp E E; Lograsso T A; McQueeney R J; Harmon B N . 2013. Magnetism-dependent phonon anomaly in LaFeAsO observed via inelastic x-ray scattering. Physical Review B. 87:104518.

Zhang Q; Wang W J; Kim J W; Hansen B; Ni N; Bud'ko S L; Canfield P C; McQueeney R J; Vaknin D . 2013. Magnetoelastic coupling and charge correlation lengths in a twin domain of Ba(Fe1-xCox)(2)As-2 (x=0.047): A high-resolution x-ray diffraction study. Physical Review B. 87:094510.

Pratt D K; Chang S; Tian W; Taskin A A; Ando Y; Zarestky J L; Kreyssig A; Goldman A I; McQueeney R J . 2013. Checkerboard to stripe charge ordering transition in TbBaFe2O5. Physical Review B. 87:045127.

Previous Years

Exploratory Development of Theoretical Methods

FWP/Project Description: 
The purpose of this FWP is to generate new theories, models, and algorithms that will be beneficial to the research programs at the Ames Laboratory and to the mission of DOE. This FWP will lead the development of theoretical tools to study a broad range of problems in physics, materials science, and chemical as well as biological systems. The generality of these tools allows the cross-fertilization of ideas from one problem to problems in an entirely different area through the common link of the mathematical formulation. Such leaps across topic areas and in some cases across disciplines are characteristic of the power of a fundamental physics-based approach to the development of new theoretical methods, facilitated by the availability of general theoretical tools applicable to very different sets of problems.  Current efforts of this FWP includes (1) methods for accurate calculation of correlated electron systems;  (2) methods for spin dynamics and quantum control of spin; and (3) methods for computational prediction and design of complex structures and materials.

This research is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering.

Extraordinary Responsive Rare Earth Magnetic Materials

FWP/Project Description: 
Responsive systems, where a small change of an extrinsic thermodynamic variable, such as temperature, pressure, or magnetic field, triggers an intrinsic phase change, have both fundamental and technological significance.  Alloys and compounds that exhibit strong field-, temperature-, or pressure-controlled reactions, tunable by chemistry, crystallography, and processing, provide broad benefits to energy-related applications, such as sensors and smart materials, and materials for energy conversion, generation, and utilization devices.  Responsive materials, therefore, have the potential to make transformative changes that can be used to help meet our Nation’s future energy demands.  Conventional (and strong) stimuli are temperature and pressure, but a magnetic field is weak and often an underappreciated trigger, whose role in initiating strong changes in solids is much less understood.  Knowledge of the mechanisms delivering minor-stimulus driven phase change that is then followed by a major perturbation of properties is crucial for guiding the discovery of new materials, and is the focus of this research.  Our goal is to uncover the underlying electronic, atomic and microscopic interactions that result in an extraordinarily strong coupling of the magnetic and crystal lattices in chosen model systems representing rare earth-based intermetallic materials.  Development and validation of phenomenological models of transformations that range from magneto-volume to magnetic-martensitic is one of our prime objectives.

This research is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering.

Innovative & Complex Metal-Rich Materials

FWP/Project Description: 
This project strives (i) to uncover and ultimately design new families of intermetallic phases; (ii) to understand the factors that stabilize both new and known metal-rich phases by combining exploratory synthesis and temperature-dependent structure determinations with electronic structure theory; and (iii) to establish structure-property relationships for complex metal-rich materials as related to both practical as well as fundamental issues, e.g., thermoelectric, magnetocaloric, catalytic, and magnetic behavior. Targeted compound classes include, but are not limited to, Hume-Rothery types, polar intermetallics, quasicrystalline and approximant phases, and complex metallic alloys of transition metals.  Significant focus includes (i) compounds involving reduced environments for elements of the late 5th and 6th period transition elements (Pd, Pt, Ag, Au), which offer filled d-bands and relativistic enhancements of chemical bonding; (ii) Li-rich intermetallics, taking advantage of Li’s dual role of both an active as well as an electronegative metal in chemically reduced environments; and (iii) 3d metal systems grown in reactive and eutectic fluxes. 

This research is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering.

Metamaterials

FWP/Project Description: 
Many of the technologies that underpin our economy and enable our standard of living depend on advanced materials. Therefore, the engine for progress in many scientific disciplines is the discovery and understanding of new materials. Metamaterials are novel artificial materials that enable the realization of innovative properties unattainable in naturally existing materials. This research project will explore the theoretical understanding, analysis, development, fabrication, and experimental characterization of metamaterials, and investigate their feasibility for applications. In view of the complexity of electromagnetic interactions in metamaterials, state-of-the-art computational techniques to understand these materials, and collaboration with experimentalists to fabricate and characterize them, are essential. Finding and understanding mechanisms that minimize loss and increasing the operating frequency will be critical for future applications, such as solar energy harvesting and biomedical/terahertz imaging. We will develop new 3D nanofabrication techniques such as direct laser writing and experimentally realize dynamic and tunable metamaterials employing nonlinear and gain materials. Finally, we will characterize the physical properties of metamaterials and develop unique optical characterization techniques.

This research is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering.

Magnetic Nanosystems: Making, Measuring, Modeling and Manipulation

FWP/Project Description: 

The scientific goal of this effort is to investigate pathways that connect quantum mechanical mechanisms governing nano-scale magnetism with macroscopic magnetic properties emerging as the system size increases from nano- to macro- length scales. The focus ranges from low-dimensional (confined and restricted geometries) magnetic systems to homogeneous systems exhibiting magnetic texture, from modeling to fabrication, measurement and manipulation. The key goals are to examine effects of quantum confinement and reduced dimensionality in magnetic nano- and meso-scale structures, study quantum coherence and spin coupling to the environment, investigate charge and spin currents in topologic insulators and examine out of equilibrium dynamics of quantum magnetism in these systems. Advanced experimental probes, such as novel optical magnetic field sensor based on nitrogen–vacancy (NV) centers in diamond (NV-magnetoScope) and spin-polarized scanning tunneling spectroscopy (SP-STM) are used to map magnetic and electronic properties, while x-ray magnetic circular dichroism and ultra-fast magneto-optical spectroscopies provide information on element-resolved local moment and non-equilibrium charge and spin dynamics, respectively.

This research is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering.

Novel Materials Preparation & Processing Methodologies

FWP/Project Description: 
The growth, control and modification of novel materials in single crystal and polycrystalline form, represent a national core competency that is essential for scientific advancement within and across traditional disciplinary boundaries, and are critical components of the Basic Energy Sciences’ mission. In support of this mission, the Novel Materials Preparation and Processing Methodologies FWP focuses on developing synthesis protocols for energy-relevant materials that contain volatile, reactive or toxic components such as the rare earth metals, Mg-based and RE containing thermoelectric alloys and Fe-As based superconductors.  The objective of Novel Materials is to advance the ability to synthesize and characterize high purity, high quality materials, primarily in single crystal form; to quantify and control processing-structure-property relationships between chemical inhomogeneities and structural defects and  functionality of highly responsive materials; to develop unique capabilities and processing knowledge in the preparation, purification, and fabrication of metallic elements and alloys. Single crystals are often required to achieve scientific understanding of the origin of various phenomena, whether from intrinsic or extrinsic origins, to elucidate its properties as well as to evaluate a material’s full functionality.

This research is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering.

Photonic Systems

FWP/Project Description: 
Since ~1990, the Ames Laboratory has conducted pioneering development and studies of 3D photonic crystals (PCs), developed forefront organic light-emitting diodes (OLEDs) and procedures for characterizing them, and conducted pioneering optically detected magnetic resonance (ODMR) studies on organic semiconductors and OLEDs. PCs, artificial periodic dielectrics or metallic structures, have revolutionized control and manipulation of photons, similar to the control of electrons in semiconduc-tors. Photon diffraction by PCs has opened new vistas to control spontaneous emission, chemical reactions, optical communications, sensing, energy-efficient lighting, displays, and, in particular, solar cells. In parallel, OLEDs and organic electronics are developing rapidly, with particular relevance for solid state lighting. These research areas are combined into four interrelated tasks that will be performed in the next three years. Besides continuing studies in each of these areas, we will use our vast expertise to enhance light emission from OLEDs, thereby combining the PC expertise with (organic) light-emitting structures. We will explore new functionalities of PCs, including lasing and non-linear effects and utilize low-cost methods to design and fabricate large-area PC and OLED structures relevant to energy-related applications. In close relation to ODMR, we will also explore organic spintronics. There will be a close synergy between theory, simulation, fabrication, and experimental studies in these interrelated tasks.

This research is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering.

Structures and Dynamics in Condensed Systems

FWP/Project Description: 
The research effort proposed here entails bringing simulation methods together with theory and critical experiments to investigate structural selection dynamics in highly driven systems. Building on our past efforts aimed at understanding the structure and properties of highly undercooled liquids and glasses, the structural dynamics of solidification and devitrification, and the fundamental behavior of interfaces, we are developing a research program that is focused on the multi-scale structural dynamics of metallic liquids, glasses, and crystalline phases under far-from-equilibrium conditions. By exploring this realm of material dynamics in earnest, we aim to open vast untapped domains of materials structures and physical behaviors, with an equally broad scope of potential functionality in magnetic, electric, elastic, thermal, and optical properties, and the critical coupled-response behaviors that may be strongly influenced by using far-from-equilibrium conditions to influence phase selection, crystallographic orientation, polycrystalline scale and texture, multiphase architectures, interface structure, solute distribution, and defect concentrations.

This research is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering.

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