A5070714748- Advanced Condensed Matter Physics
- Advanced NMR Techniques and Applications
- Muon and positron interactions and applications
- Physics of Superconductivity and Magnetism
- Rare-earth and actinide compounds
- Magnetic and transport properties of perovskites and related materials
- Advancements in Battery Materials
- Magnetic properties of thin films
- Graphene research and applications
- Atomic and Subatomic Physics Research
- Solid-state spectroscopy and crystallography
- NMR spectroscopy and applications
- Superconducting Materials and Applications
- Superconductivity in MgB2 and Alloys
- Electronic and Structural Properties of Oxides
- Ammonia Synthesis and Nitrogen Reduction
- Iron-based superconductors research
- Magnetism in coordination complexes
- Quantum and electron transport phenomena
- Advanced Battery Materials and Technologies
- Inorganic Chemistry and Materials
- Particle accelerators and beam dynamics
- Material Dynamics and Properties
- Magnetic Properties of Alloys
- Fullerene Chemistry and Applications
University of British Columbia
2015-2024
TRIUMF
2013-2024
Simon Fraser University
1992-2023
University of Victoria
2023
Humboldt-Universität zu Berlin
2022
Walter de Gruyter (Germany)
2022
Translational Research Platform for Veterinary Biologicals (India)
2022
Vancouver Biotech (Canada)
2018
University of Alberta
2007-2011
Newcastle University
2010
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...
We report microwave surface resistance (${\mathit{R}}_{\mathit{s}}$) measurements on two very-high-quality ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.95}$ crystals which exhibit extremely low residual loss at 1.2 K (2-6 \ensuremath{\mu}\ensuremath{\Omega} 2 GHz), a broad, reproducible peak around 38 K, and rapid increase in loss, by 4 orders of magnitude, between 80 93 K. These data provide one ingredient the determination temperature dependence real part conductivity,...
Step‐pool streams dissipate flow energy primarily through spill resistance. We compared the geometry, step characteristics, and hydraulics of 20 step‐pool reaches without large woody debris (LWD) to with LWD. Non‐LWD exhibited significantly shallower flows, lower steps, shorter spacings, greater percentages water‐surface drop created by larger grain sizes, smaller Darcy‐Weisbach friction factors. Grain resistance was negligible in both stream types. Form irregularities channel shape...
We report muon-spin-rotation (\ensuremath{\mu}SR) measurements of the a-b magnetic penetration depth (${\ensuremath{\lambda}}_{\mathit{a}\mathit{b}}$) in vortex state high quality single crystals ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.95}$. Contrary to earlier \ensuremath{\mu}SR studies on powders and crystal mosaics, 1/${\ensuremath{\lambda}}_{\mathit{a}\mathit{b}}^{2}$ shows a strong linear temperature dependence below 50 K which weakens with increasing field. These...
We present a study of the electronic ultrasound attenuation alpha in unconventional superconductor Sr(2)RuO(4). The power law behavior at temperatures down to T(c)/30 clearly indicates presence nodes gap. In normal state, we find an enormous anisotropy basal plane tetragonal structure. superconducting temperature dependence also exhibits significant anisotropy. discuss these results relation possible gap functions.
We compare the effects of in-plane non magnetic Li$^{+}$ and Zn$^{2+}$ impurities on normal state high-T$_{c}$ cuprates. Y NMR shows that extra hole introduced by Li is not localized in its vicinity. The Tc depression induced moments near neighbour Cu sites Zn or are found identical. These universal spinless establish major influence spin perturbation with respect to charge defect. susceptibility moment measured displays a 1/(T+Theta) behavior. Theta increases doping up about 200 K overdoped...
Positive muons injected into solid ${\mathrm{C}}_{60}$, ${\mathrm{K}}_{4}$${\mathrm{C}}_{60}$, and ${\mathrm{K}}_{6}$${\mathrm{C}}_{60}$ form vacuumlike muonium (${\mathrm{\ensuremath{\mu}}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$) with a (6--12)% probability. Observation of coherent spin precession establishes that all three materials are nonmagnetic nonconducting at low temperatures. From the temperature dependence signals we estimate electronic band gaps in...
The spin dynamics of geometrically frustrated pyrochlore antiferromagnets Y2Mo2O7 and Tb2Mo2O7 have been investigated using muon relaxation. A dramatic slowing down the moment fluctuations occurs as one approaches freezing temperatures (TF=22 K 25 respectively) from above. Below TF there is a disordered magnetic state similar to that found in glass but with residual relaxation rate at low temperatures. These results show large density states for excitations these systems near zero energy.
We report the observation of weak magnetism in superlattices LaAlO3/SrTiO3 using beta-detected nuclear magnetic resonance. The spin lattice relaxation rate 8 Li with a spacer layers and 6 unit cells LaAlO3 exhibits strong peak near ~35 K, whereas no such is observed superlattice layer thickness 3 cells. attribute temperature dependence to slowing down weakly coupled electronic moments at interface. These results show that interface depends strongly on layer, minimal ~4-6 required for...
Superconductivity is a striking example of quantum phenomenon in which electrons move coherently over macroscopic distances without scattering. The high-temperature superconducting oxides (cuprates) are the most studied class superconductors, composed two-dimensional CuO2 planes separated by other layers that control electron concentration planes. A key unresolved issue cuprates relationship between superconductivity and magnetism. Here we report sharp phase boundary static three-dimensional...
Depth-controlled $\ensuremath{\beta}$-NMR can be used to probe the magnetic properties of thin films and interfaces on a nanometer length scale. A 30 keV beam highly spin-polarized $^{8}\mathrm{L}\mathrm{i}^{+}$ ions was slowed down implanted into 50 nm film Ag deposited ${\mathrm{S}\mathrm{r}\mathrm{T}\mathrm{i}\mathrm{O}}_{3}$ substrate. novel high field spectrometer observe two well resolved resonances which are attributed Li occupying substitutional octahedral interstitial sites in...
Muon spin relaxation resulting from exchange scattering of endohedral muonium (${\mathrm{\ensuremath{\mu}}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$) with thermal electronic excitations has been observed in the fullerene superconductor ${\mathrm{Rb}}_{3}$${\mathrm{C}}_{60}$. The temperature dependence ${\mathit{T}}_{1}^{\mathrm{\ensuremath{-}}1}$ shows a coherence peak just below ${\mathit{T}}_{\mathit{c}}$ and can be fit to conventional Hebel-Slichter theory for broadened BCS density...
Using 7Li NMR shift data, the anomalous local moment induced by spinless Li impurities persists below T(c) in YBa 2Cu 3O6+y. In underdoped regime, moments retain their Curie law Tc. contrast, near optimal doping, large Kondo screening observed above Tc (TK = 135 K) is strongly reduced as expected theoretically when superconducting gap develops. The limited spatial extent of (on first neighbor Cu) not drastically modified Tc, which allows a comparison with STM determination density states....
Muon-spin rotation spectroscopy has been used to measure the internal magnetic field distribution in NbSe2 for Hc1 << H < 0.25 Hc2. The deduced profiles of supercurrent density indicate that vortex-core radius bulk decreases sharply with increasing field. This effect, which is attributed increased vortex-vortex interactions, does not agree dirty-limit microscopic theory. A simple phenomenological equation core depends on intervortex spacing model this behaviour. In addition, we find first...
We demonstrate that zero-field $\beta$-detected nuclear quadrupole resonance and spin relaxation of low energy $^8$Li can be used as a sensitive local probe structural phase transitions near surface. find the transition surface SrTiO$_3$ single crystal occurs at $T_c \sim 150$ K, i.e., 45 K higher than $T^{bulk}_c$, tetragonal domains formed below $T_c$ are randomly oriented.
The molecular dynamics and electronic structure of the ${\mathrm{\ensuremath{\mu}}}^{+}$-${\mathrm{C}}_{60}$ radical in crystalline ${\mathrm{C}}_{60}$ have been studied using muon spin rotation relaxation. At room temperature appears to be a state quasifree rotation. critical ${\mathit{T}}_{\mathit{S}}$=260 K local change discontinuously as expected for first-order phase transition. correlation times reorientation are remarkably close those determined by recent NMR experiments on...
The magnetic properties of a monolayer Mn12 single molecule magnets grafted onto silicon (Si) substrate have been investigated using depth-controlled β-detected nuclear resonance. A low-energy beam spin-polarized radioactive 8Li was used to probe the local static field distribution near in Si substrate. resonance line width varies strongly as function implantation depth result dipolar fields generated by electronic moments. temperature dependence indicates that moments this low-dimensional...
Currently, no known material retains its photoinduced metallic conductivity over a long time while also exhibiting repeatable metal-to-insulator recovery. Here, we demonstrate such highly insulator-to-metal transition in yttrium oxyhydride (YOxHy) epitaxial thin films. The temperature (T) dependence of the electrical resistivity (ρ) films transforms from insulating to state (dρ/dT > 0) under ultraviolet laser illumination. YOxHy film recovers original when heated (125 °C) an Ar atmosphere...
A new high field spectrometer has been built to extend the capabilities of $\beta$-detected nuclear magnetic resonance ($\beta$-NMR) facility at TRIUMF. This beamline extension allows $\beta$-NMR spectroscopy be performed with fields up 200 mT parallel a sample's surface (perpendicular ion beam), allowing depth-resolved studies local electromagnetic spin polarized probes much higher applied than previously available in this configuration. The primary motivation and application is allow...
Muon spins precess in transverse magnetic fields and emit a positron preferentially the spin direction at instant of decay, enabling muon rotation ( μ SR) as precise probe local matter. SR has been used to characterize superconducting radio-frequency (SRF) materials since 2010. At TRIUMF, beam 4.2 MeV + is implanted material-dependent depth approximately 150 m. A dedicated spectrometer was developed measure field first vortex penetration pinning strength SRF parallel up 300 mT. low-energy...
The low temperature spin dynamics of the geometrically frustrated antiferromagnet Gd 3Ga 5O (12) (GGG) have been investigated using muon relaxation. No evidence for static order is seen down to a 25 mK or few percent Curie-Weiss temperature. Instead there linear decrease in fluctuation rate below 1 K which extrapolates small but finite value 2 GHz at zero In terms fluctuations system appears essentially remain dynamic temperatures (T>0.02 K) and magnetic fields up 1.8 T.
A nuclear quadrupole resonance (NQR) spectrum of $^{8}\mathrm{Li}$ has been observed in a single crystal $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ using beam low-energy highly polarized radioactive $^{8}\mathrm{Li}^{+}$. The resonances were detected by monitoring the $\ensuremath{\beta}$-decay anisotropy as function small audio frequency magnetic field. These results demonstrate that low energy spin can be used sensitive probe local and electronic environment nanostructures ultrathin films...
The vortex state of a type-II superconductor produces distinctive ${\mathrm{\ensuremath{\mu}}}^{+}$SR line shape with features determined by the average internal field ${\mathit{B}}_{\mathit{o}}$, magnetic penetration depth \ensuremath{\lambda}, superconducting coherence length \ensuremath{\xi}, and degree disorder in lattice. Only high regime (\ensuremath{\lambda}\ensuremath{\gg}L>\ensuremath{\xi}, where L is intervortex spacing) do cores (of radius \ensuremath{\approxeq}\ensuremath{\xi})...