A5068745592- Advanced Condensed Matter Physics
- Physics of Superconductivity and Magnetism
- Rare-earth and actinide compounds
- Magnetic and transport properties of perovskites and related materials
- Iron-based superconductors research
- X-ray Diffraction in Crystallography
- Crystallization and Solubility Studies
- Multiferroics and related materials
- High-pressure geophysics and materials
- Nuclear Physics and Applications
- Corporate Taxation and Avoidance
- Magnetic Properties of Alloys
- Crystal Structures and Properties
- Nuclear materials and radiation effects
- Perovskite Materials and Applications
- Inorganic Fluorides and Related Compounds
- Catalysis and Oxidation Reactions
- Solid-state spectroscopy and crystallography
- Magnetism in coordination complexes
- Theoretical and Computational Physics
- Atomic and Subatomic Physics Research
- Intellectual Capital and Performance Analysis
- Organic and Molecular Conductors Research
- Magnetic properties of thin films
- Advanced Chemical Physics Studies
Oak Ridge National Laboratory
2014-2024
Quantum Science Center
2012-2017
Physical Sciences (United States)
2016
University of Tennessee at Knoxville
2016
Karlsruhe Institute of Technology
2014
Mahidol University
2011
McMaster University
1996-2000
St. Francis Xavier University
1995
University of Alberta
1995
Sighting of magnetic Majorana fermions? Quantum spin liquids—materials whose spins do not settle into order even at absolute zero temperature—have long captured the interest physicists. A particularly lofty goal is finding a material that can be described by so-called Kitaev model, network on honeycomb lattice harbors fermions as its excitations. Banerjee et al. present comprehensive inelastic neutron scattering study single crystals α-RuCl 3 , which has been predicted to host liquid. The...
Neutron scattering, muon spin relaxation, and dc susceptibility studies have been carried out on polycrystalline ${\mathrm{Tb}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$, a pyrochlore antiferromagnet in which the ${\mathrm{Tb}}^{3+}$ moments reside network of corner-sharing tetrahedra. Unlike other geometrically frustrated systems, ${\mathrm{Tb}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ remains paramagnetic down to $\ensuremath{\sim}0.07\mathrm{K}$, rather than ordering into conventional N\'eel or...
Single crystals of the Kitaev spin-liquid candidate $\alpha$-RuCl$_3$ have been studied to determine low-temperature bulk properties, structure and magnetic ground state. Refinements x-ray diffraction data show that low temperature crystal is described by space group $C2/m$ with a nearly-perfect honeycomb lattice exhibiting less than 0.2 \% in-plane distortion. The as-grown single exhibit only one sharp transition at $T_{N}$ = 7~K. order below this exhibits propagation vector $k$ (0, 1,...
The Kitaev model on a honeycomb lattice predicts paradigmatic quantum spin liquid (QSL) exhibiting Majorana Fermion excitations. insight that physics might be realized in practice has stimulated investigations of candidate materials, recently including alpha-RuCl3. In all the systems studied to date, non-Kitaev interactions induce magnetic order at low temperature. However, in-plane fields roughly 8 Tesla suppress long-range alpha-RuCl3 raising intriguing possibility field-induced QSL...
We present results from a detailed experimental investigation of LaFeAsO, the parent material in series ``FeAs'' based oxypnictide superconductors. Upon cooling, this undergoes tetragonal-orthorhombic crystallographic phase transition at $\ensuremath{\sim}160\text{ }\text{K}$ followed closely by an antiferromagnetic ordering near 145 K. Analysis these transitions using temperature dependent powder x-ray and neutron-diffraction measurements is presented. A magnetic moment...
Inelastic neutron scattering measurements on single crystals of superconducting BaFe1.84Co0.16As2 reveal a magnetic excitation located at wave vectors (1/2 1/2 L) in tetragonal notation. On cooling below T_{C}, clear resonance peak is observed this vector with an energy 8.6(0.5) meV, corresponding to 4.5(0.3) k_{B}T_{C}. This good agreement the canonical value 5 k_{B}T_{C} cuprates. The spectrum shows strong dispersion plane but very weak along c axis, indicating that fluctuations are two...
In this review, we present a summary of experimental studies magnetism in Fe-based superconductors. The doping dependent phase diagram shows strong similarities to the generic cuprates. Parent compounds exhibit magnetic order together with structural transition both which are progressively suppressed allowing superconductivity emerge. stripe-like spin arrangement Fe moments magnetically ordered state identical in-plane structure for RFeAsO (R=rare earth) and AFe2As2 (A=Sr, Ca, Ba, Eu K)...
Intrinsic, two-dimensional ferromagnetic semiconductors are an important class of materials for overcoming the limitations dilute magnetic spintronics applications. CrSiTe$_3$ is a particularly interesting member this class, since it can likely be exfoliated down to single layers, where T$_C$ predicted increase dramatically. Establishing nature magnetism in bulk necessary precursor understanding behavior thin film samples and possible applications material. In work, we use elastic inelastic...
We report neutron scattering measurements on single crystals of BaFe$_{1.92}$Co$_{0.08}$As$_2$. The magnetic Bragg peak intensity is reduced by 6 % upon cooling through T$_C$. spin dynamics exhibit a gap 8 meV with anisotropic three-dimensional (3d) interactions. Below T$_C$ additional appears at an energy $\sim$4.5(0.5) similar to previous observations resonance in other Fe-based superconductors. No further gapping the excitations observed below for energies down 2 meV. These suggest...
Inelastic neutron scattering measurements of individual phonon lifetimes and dispersion at 295 1200 K have been used to probe anharmonicity thermal conductivity in $\mathrm{U}{\mathrm{O}}_{2}$. They show that longitudinal optic modes carry the largest amount heat, contrast past simulations total demonstrates a quantitative correspondence between microscopic macroscopic physics. We further performed first-principles for $\mathrm{U}{\mathrm{O}}_{2}$ showing semiquantitative agreement with K,...
The metal-insulator transition (MIT) is one of the most dramatic manifestations electron correlations in materials. Various mechanisms producing MITs have been extensively considered, including Mott (electron localization via Coulomb repulsion), Anderson (localization disorder), and Peierls distortion a periodic one-dimensional lattice) mechanisms. One additional route to MIT proposed by Slater, which long-range magnetic order three dimensional system drives MIT, has received relatively...
A central issue in material science is to obtain understanding of the electronic correlations that control complex materials. Such frequently arise because competition localized and itinerant degrees freedom. Although respective limits well-localized or entirely ground states are well understood, intermediate regime controls functional properties materials continues challenge theoretical understanding. We have used neutron spectroscopy investigate plutonium, which a prototypical at brink...
An external magnetic field can induce a transition in $\alpha$-RuCl$_3$ from an ordered zigzag state to disordered that is possibly related the Kitaev quantum spin liquid. Here we present new dependent inelastic neutron scattering and magnetocaloric effect measurements implying existence of additional out liquid phase at upper limit $B_u$. The shows three distinct regimes response. In low response magnon peaks; intermediate regime only continuum scattering, above $B_u$ sharp peaks lower...
Using inelastic neutron scattering, we map a 14 meV coherent resonant mode in the topological Kondo insulator ${\mathrm{SmB}}_{6}$ and describe its relation to low energy insulating band structure. The intensity is confined $X$ $R$ high symmetry points, repeating outside first Brillouin zone dispersing less than 2 meV, with $5d$-like magnetic form factor. We present slave-boson treatment of Anderson Hamiltonian third neighbor dominated hybridized This approach produces spin exciton below...
Abstract Low dimensional quantum magnets are interesting because of the emerging collective behavior arising from strong fluctuations. The one-dimensional (1D) S = 1/2 Heisenberg antiferromagnet is a paradigmatic example, whose low-energy excitations, known as spinons, carry fractional spin 1/2. These modes can be reconfined by application staggered magnetic field. Even though considerable progress has been made in theoretical understanding such magnets, experimental realizations this...
We present single crystal neutron diffraction measurements on multiferroic ${\mathrm{LuFe}}_{2}{\mathrm{O}}_{4}$. Magnetic reflections are observed below transitions at 240 and 175 K indicating that the magnetic interactions in ${\mathrm{LuFe}}_{2}{\mathrm{O}}_{4}$ three-dimensional character. The structure is refined as a ferrimagnetic spin configuration transition. Below significant broadening of peaks along with buildup diffuse component to scattering.
We use powder neutron diffraction to study the spin and lattice structures of polycrystalline samples nonsuperconducting PrFeAsO superconducting ${\text{PrFeAsO}}_{0.85}{\text{F}}_{0.15}$ ${\text{PrFeAsO}}_{0.85}$. find that exhibits abrupt structural phase transitions at 153 K followed by static long-range antiferromagnetic order 127 K. Both distortion magnetic are similar other rare-earth oxypnictides. Electron doping system with either fluorine or oxygen deficiency suppresses order,...
X-ray scattering by multiferroic ${\mathrm{LuFe}}_{2}{\mathrm{O}}_{4}$ is reported. Below 320 K, superstructure reflections indicate an incommensurate charge order with propagation close to $(\frac{1}{3}\frac{1}{3}\frac{3}{2})$. The corresponding configuration, also found electronic structure calculations as most stable, contains polar $\mathrm{Fe}/\mathrm{O}$ double layers antiferroelectric stacking. Diffuse at 360 $(\frac{1}{3}\frac{1}{3}0)$ propagation, indicates ferroelectric short-range...
Magnetic correlations in the paramagnetic phase of CaFe2As2 (T_N=172 K) have been examined by means inelastic neutron scattering from 180 K (~ 1.05 T_N) up to 300 (~1.8 T_N). Despite first-order nature magnetic ordering, strong but short-range antiferromagnetic (AFM) are clearly observed. These correlations, which consist quasi-elastic centered at wavevector Q_{AFM} low-temperature AFM structure, observed highest measured temperature and high energy transfer (E> 60 meV). The L dependence...