A5065779171- Advanced Condensed Matter Physics
- Magnetic and transport properties of perovskites and related materials
- Physics of Superconductivity and Magnetism
- Multiferroics and related materials
- Nuclear materials and radiation effects
- Rare-earth and actinide compounds
- Iron-based superconductors research
- X-ray Diffraction in Crystallography
- Magnetic properties of thin films
- Topological Materials and Phenomena
- High-pressure geophysics and materials
- Crystallization and Solubility Studies
- Perovskite Materials and Applications
- Nuclear Physics and Applications
- Theoretical and Computational Physics
- Crystal Structures and Properties
- Magneto-Optical Properties and Applications
- Advanced Chemical Physics Studies
- Inorganic Fluorides and Related Compounds
- Magnetic Properties of Alloys
- Superconductivity in MgB2 and Alloys
- Electron and X-Ray Spectroscopy Techniques
- Atomic and Subatomic Physics Research
- Solid-state spectroscopy and crystallography
- Semiconductor materials and interfaces
McMaster University
2010-2025
Brockhouse Institute for Materials Research
2020-2025
University of Toronto
2012-2023
Indiana University Bloomington
2012
Pfizer (United States)
1994-1997
Windsor Regional Hospital
1987
Western Hospital
1987
We examine the role of spin-orbit coupling in electronic structure $\ensuremath{\alpha}\ensuremath{-}{\mathrm{RuCl}}_{3}$, which Ru ions $4{d}^{5}$ configuration form a honeycomb lattice. Our x-ray absorption spectroscopy measurements at $L$ edges exhibit distinct spectral features associated with presence substantial coupling, as well an anomalously large branching ratio. Furthermore measured optical spectra can be described very first-principles calculations obtained by taking into account...
We report magnetic and thermodynamic properties of single crystal $\ensuremath{\alpha}\ensuremath{-}{\text{RuCl}}_{3}$, in which the ${\text{Ru}}^{3+}\phantom{\rule{0.28em}{0ex}}(4{d}^{5})$ ion is its low spin state forms a honeycomb lattice. Two features are observed both susceptibility specific heat data; sharp peak at 7 K broad hump near 10--15 K. In addition, we observe metamagnetic transition between 5 10 T. Our neutron diffraction study samples confirms that temperature associated with...
The electronic structure of the honeycomb lattice iridates ${\mathrm{Na}}_{2}{\mathrm{IrO}}_{3}$ and ${\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ has been investigated using resonant inelastic x-ray scattering (RIXS). Crystal-field-split $d\mathrm{\text{\ensuremath{-}}}d$ excitations are resolved in high-resolution RIXS spectra. In particular, splitting due to noncubic crystal fields, derived from ${j}_{\mathrm{eff}}=3/2$ states, is much smaller than typical spin-orbit energy scale iridates,...
We have performed x-ray absorption spectroscopy (XAS) measurements on a series of Ir-based 5$d$ transition metal compounds, including Ir, IrCl${}_{3}$, IrO${}_{2}$, Na${}_{2}$IrO${}_{3}$, Sr${}_{2}$IrO${}_{4}$, and Y${}_{2}$Ir${}_{2}$O${}_{7}$. By comparing the intensity ``white-line'' features observed at Ir L${}_{2}$ L${}_{3}$ edges, it is possible to extract valuable information about strength spin-orbit coupling in these systems. observe remarkably large, nonstatistical branching ratios...
Recently, it was shown that a significant number of erythromycin-resistant Streptococcus pneumoniae and pyogenes strains contain determinant mediates resistance via putative efflux pump. The gene encoding the cloned sequenced from three S. bearing M phenotype (macrolide resistant but clindamycin streptogramin B susceptible). DNA sequences mefE were nearly identical, with only 2-nucleotide differences between genes any two strains. When compared to mefA sequence pyogenes, found be closely...
A fine resolution chopper spectrometer (SEQUOIA) recently received first neutrons at the SNS. The commissioning phase of instrument is underway. SEQUOIA designed to utilize an incident energy (Ei) between 10-2000 meV. monochromatic beam provided on a sample, 20 m from decoupled ambient temperature H2O moderator, by filtering white with Fermi located 18 source. After interacting are detected array 3He linear position sensitive tubes vertical cylinder radius 5.5 m. This contribution presents...
Experiments show that magnons in CoTiO${}_{3}$ have a similar energy-momentum relation to electrons graphene, setting up as good system which study interactions between so-called Dirac bosons.
The Ce3+ pseudospin-1/2 degrees of freedom in the pyrochlore magnet Ce2Zr2O7 are known to possess dipole-octupole character, making it a candidate for novel quantum spin liquid ground states at low temperatures. We report new polarized neutron diffraction temperatures, as well heat capacity (Cp) measurements on single crystal Ce2Zr2O7. former bears both similarities and differences with that measured from canonical dipolar ice compound Ho2Ti2O7, while latter rises sharply initially...
The low energy excitations in ${\mathrm{Na}}_{2}{\mathrm{IrO}}_{3}$ have been investigated using resonant inelastic x-ray scattering (RIXS). A magnetic excitation branch can be resolved, whose dispersion reaches a maximum of about 35 meV at the $\ensuremath{\Gamma}$ point. momentum dependence is much larger along $\ensuremath{\Gamma}\ensuremath{-}X$ direction compared to that $\ensuremath{\Gamma}\ensuremath{-}Y$ direction. observed relation consistent with recent theoretical prediction based...
We have used a combination of resonant magnetic x-ray scattering (RMXS) and absorption spectroscopy (XAS) to investigate the properties doped spin-orbital Mott insulator Sr2Ir(1-x)Rh(x)O4 (0.07 < x 0.70). show that represents unique model system for study dilute magnetism in presence strong spin-orbit coupling, provide evidence doping-induced change structure suppression order at x_c ~ 0.17. demonstrate Rh-doping introduces Rh3+/Ir5+ ions which effectively hole-dope this material. propose...
In the search for topological phases in correlated electron systems, materials with $5d$ transition-metal ions, particular iridium-based pyrochlores ${A}_{2}$Ir${}_{2}$O${}_{7}$, provide fertile grounds. Several states have been predicted but actual realization of such is believed to critically depend on strength local potentials arising from distortions IrO${}_{6}$ cages. We test this hypothesis by measuring resonant inelastic x-ray scattering electronic level splittings $A=\text{Y}$, Eu...
We report resonant inelastic x-ray scattering (RIXS) measurements on ordered double-perovskite samples containing ${\mathrm{Re}}^{5+}$ and ${\mathrm{Ir}}^{5+}$ with $5{d}^{2}$ $5{d}^{4}$ electronic configurations, respectively. In particular, the observed RIXS spectra of ${\mathrm{Ba}}_{2}{\mathrm{YReO}}_{6}$ ${\mathrm{Sr}}_{2}M{\mathrm{IrO}}_{6}$ ($M$ = Y, Gd) show sharp intra-${t}_{2g}$ transitions, which can be quantitatively understood using a minimal ``atomic'' Hamiltonian incorporating...
We report detailed measurements of the low temperature magnetic phase diagram Er2Ti2O7. Heat capacity and time-of-flight neutron scattering studies single crystals reveal unconventional low-energy states. Er3+ ions reside on a pyrochlore lattice in Er2Ti2O7, where local XY anisotropy antiferromagnetic interactions give rise to unique frustrated system. In zero field, ground state exhibits coexisting short long-range order, accompanied by soft collective spin excitations previously believed...
Elastic and inelastic neutron-scattering studies have been carried out on the pyrochlore magnet ${\text{Ho}}_{2}{\text{Ti}}_{2}{\text{O}}_{7}$. Measurements in zero applied magnetic field show that disordered spin-ice ground state of ${\text{Ho}}_{2}{\text{Ti}}_{2}{\text{O}}_{7}$ is characterized by a pattern rectangular diffuse elastic scattering within [HHL] plane reciprocal space, which closely resembles zone-boundary seen its sister compound...
High-resolution x-ray scattering measurements on single crystal Tb2Ti2O7 reveal finite structural correlations at low temperatures. This geometrically frustrated pyrochlore is known to exhibit a spin-liquid or cooperative paramagnetic state temperatures below approximately 20 K. Parametric studies of Bragg peaks appropriate the Fd3[over ]m space group substantial broadening and peak intensity reduction in temperature regime K 300 mK. We also observe small, anomalous lattice expansion cooling...
We report x-ray resonant magnetic scattering and inelastic studies of epitaxially strained ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$ thin films. The films were grown on ${\mathrm{SrTiO}}_{3}$ $({\mathrm{LaAlO}}_{3}{)}_{0.3}({\mathrm{Sr}}_{2}{\mathrm{AlTaO}}_{6}{)}_{0.7}$ substrates, under slight tensile compressive strains, respectively. Although the develop a structure reminiscent bulk ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$, correlations are extremely anisotropic, with in-plane correlation...
The geometrically frustrated double perovskite Ba${}_{2}$YMoO${}_{6}$ is characterized by quantum $s=1/2$ spins at the Mo${}^{5+}$ sites of an undistorted fcc lattice. Previous low-temperature characterization revealed absence static long-range magnetic order and suggested a nonmagnetic spin-singlet ground state. We report unique time-of-flight triple-axis neutron spectroscopy that shows 28 meV spin excitation with bandwidth $\ensuremath{\sim}$4 meV, which vanishes above...
We have investigated the structural, electronic, and magnetic properties of pyrochlore iridates ${\mathrm{Eu}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$ ${\mathrm{Pr}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$ using a combination resonant elastic x-ray scattering, powder diffraction, inelastic scattering (RIXS). The structural parameters been examined as function temperature applied pressure, with particular emphasis on regions phase diagram where electronic transitions reported. find no evidence...
High resolution time-of-flight neutron scattering measurements on Tb(2)Ti(2)0(7) reveal a rich low temperature phase diagram in the presence of magnetic field applied along [110]. In zero at T = 0.4 K, is highly correlated cooperative paramagnet with disordered spins residing pyrochlore lattice corner-sharing tetrahedra. Application small condenses much diffuse scattering, characteristic spins, into new Bragg peak polarized paramagnet. At higher fields, magnetically ordered induced, which...
The electronic ground state in many iridate materials is described by a complex wave-function which spin and orbital angular momenta are entangled due to relativistic spin-orbit coupling (SOC). Such localized carries an effective total momentum of $J_{eff}=1/2$. In with edge-sharing octahedral crystal structure, such as the honeycomb iridates Li2IrO3 Na2IrO3, these $J_{eff}=1/2$ moments expected be coupled through special bond-dependent magnetic interaction, necessary condition for...
The pyrochlore magnet ${\mathrm{Ce}}_{2}{\mathrm{Zr}}_{2}{\mathrm{O}}_{7}$ has attracted much attention as a quantum spin ice candidate whose novelty derives in part from the dipolar-octupolar nature of ${\mathrm{Ce}}^{3+}$ pseudospin-1/2 degrees freedom it possesses. We report heat capacity measurements on single crystal samples down to $T\ensuremath{\sim}0.1\phantom{\rule{4pt}{0ex}}\mathrm{K}$ magnetic field along $[1,\overline{1},0]$ direction. These show that broad hump zero-field moves...
Molecular orbital systems with clusters of heavy transition metal (TM) ions are one the most important classes model materials for studying interplay between local physics and effects itinerancy. Despite a large number candidates identified in family $4d\text{ }\mathrm{TM}$ materials, an understanding their from competing microscopic energy scales is still missing. We bridge this gap by reporting first resonant inelastic x-ray scattering (RIXS) measurement on well-known series Ru cluster...
Brownmillerite oxides with the composition Ca2Fe2-xMnxO5 had been investigated previously for limited range x = 0.5 to 1.0. Mn3+ preferentially occupies octahedral site. This substitution has a strong impact on magnetic properties as ordering temperature, TN, is suppressed from 730 K 0.0 465 and structure changes Gx (x 0.0) Gy 0.5-1.00). In this study, compositions 0.10 0.25 are using single-crystal X-ray neutron diffraction methods. It found that TN decreases linearly 0.5, values of 584(2)K...
A strain of Streptococcus agalactiae displayed resistance to 14-, 15-, and 16-membered macrolides. In PCR assays, total genomic DNA from this contained neither erm nor mef genes. EcoRI-digested was cloned into lambda Zap II construct a library S. DNA. clone, pAES63, expressing erythromycin, azithromycin, spiramycin in Escherichia coli recovered. Deletion derivatives pAES63 which defined functional region on clone that encoded 14- 15-membered, but not 16-membered, macrolides were produced....
We report high resolution single crystal x-ray diffraction measurements of the frustrated pyrochlore magnet Tb2Ti2O7, collected using a novel low temperature pulsed system. This instrument allows characterization structural degrees freedom to temperatures as 4.4 K, and in applied magnetic fields large 30 Tesla. show that Tb2Ti2O7 manifests intriguing effects under application fields, including strongly anisotropic giant magnetostriction, restoration perfect symmetry ultimately phase...