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We present high (> 2 T) magnetic field βNMR measurements of 8Li+ implanted in single crystals of sapphire, a commonly used backing material for other samples. From the well-resolved quadrupolar splitting, we extract the electric field gradient (EFG) at the implanted 8Li+ site. Comparison with supercell density functional theory calculations of the EFG allows us to identify the octahedral interstitial site as the most likely candidate. In contrast to the zero field βNQR spectra, where multiple singals are detected, only a single site is evident at high field. We discuss possible explanations for this discrepancy. The spin lattice relaxation is extremely slow (1/T 1 < 0.02 s−1 ) over a broad temperature range from 4 to 300 K, demonstrating that cross relaxation with the 27Al nuclear spins is quenched in such high magnetic fields.

We present the first μ SR measurements ever performed on elemental Pu, and set the most stringent upper limits to date on the magnitude of the ordered moment μ ord in α -Pu and δ -stabilized Pu (alloyed with 4.3 at% Ga). Assuming a nominal hyperfine coupling field of 1 kOe/ μ B we find μ ord ⩽ 10 - 3 μ B at T ≅ 4 K .

We present transverse-field (TF) measurements of the in-plane magnetic-field penetration depth λ ( T ) in single-crystalline PuCoGa 5 ( T c = 18.5 K ) for 0.06 T applied field ( ≈ 2 – 5 × H c 1 ) . We find that the temperature dependence of the superfluid density, and therefore Δ λ ( T ) = λ ( T ) - λ ( 0 ) , is ∝ T for T / T c ⩽ 0.5 . We estimate that the measured λ ( 0 ) = 241 ( 3 ) nm . ZF measurements find no evidence for time-reversal symmetry violation. The ZF and TF measurements are consistent with an even-parity (pseudo-spin singlet), d-wave pairing state.

The effective superconducting penetration depth measured in the vortex state of PrOs 4 Sb 12 using transverse-field muon spin rotation ( TF - μ SR ) exhibits an activated temperature dependence at low temperatures, consistent with a nonzero gap for quasiparticle excitations. In contrast, Meissner-state radiofrequency (rf) inductive measurements of the penetration depth yield a T 2 temperature dependence, suggestive of point nodes in the gap. A scenario based on the recent discovery of extreme two-band superconductivity in PrOs 4 Sb 12 is proposed to resolve this difference. In this picture a large difference between large- and small-gap coherence lengths renders the field distribution in the vortex state controlled mainly by supercurrents from a fully gapped large-gap band. In zero field all bands contribute, yielding a stronger temperature dependence to the rf inductive measurements.

We have measured the temperature dependence and magnitude of the superfluid density ${\ensuremath{\rho}}_{s}(T)$ via the magnetic field penetration depth $\ensuremath{\lambda}(T)$ in $\mathrm{Pu}\mathrm{Co}{\mathrm{Ga}}_{5}$ (nominal critical temperature ${T}_{c0}=18.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$) using the muon spin rotation technique in order to investigate the symmetry of the order parameter, and to study the effects of aging on the superconducting properties of a radioactive material. The same single crystals were measured after $25\phantom{\rule{0.3em}{0ex}}\text{days}$ $({T}_{c}=18.25\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ and $400\phantom{\rule{0.3em}{0ex}}\text{days}$ $({T}_{c}=15.0\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ of aging at room temperature. Penetration depths $\ensuremath{\lambda}(0)=265(5)$ and $\ensuremath{\geqslant}498(10)\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ are derived for the fresh and aged samples, respectively. The temperature dependence of the superfluid density ${\ensuremath{\rho}}_{s}(T)∕{\ensuremath{\rho}}_{s}(0)=\ensuremath{\lambda}{(0)}^{2}∕\ensuremath{\lambda}{(T)}^{2}$ is well described in both materials by a model using $d$-wave gap symmetry. Within the context of a strong-coupling dirty $d$-wave model a zero-temperature gap value ${\ensuremath{\Delta}}_{0}=3.0{k}_{B}{T}_{c0}$ is obtained in the fresh sample for a scattering rate $\ensuremath{\Gamma}=0.005\ensuremath{\pi}{k}_{B}{T}_{c0}$, which is consistent with Abrikosov-Gor'kov (AG) pair-breaking theory. This ${\ensuremath{\Delta}}_{0}$ should be compared to the weak-coupling value for a clean $d$-wave gap ${\ensuremath{\Delta}}_{0}=2.14{k}_{B}{T}_{c0}$. In the aged sample the same model yields ${\ensuremath{\Delta}}_{0}=2.4{k}_{B}{T}_{c0}$ for $\ensuremath{\Gamma}=0.010\ensuremath{\pi}{k}_{B}{T}_{c0}$. This value of $\ensuremath{\Gamma}$ is much less than required by the AG pair-breaking formalism. Furthermore, the aged ${\ensuremath{\rho}}_{s}(0)$ is reduced by at least 70% compared to the fresh sample, which is also incompatible with $\ensuremath{\Delta}{T}_{c}∕{T}_{c0}\ensuremath{\sim}20%$, according to AG theory. We conclude that the data in aged $\mathrm{Pu}\mathrm{Co}{\mathrm{Ga}}_{5}$ support the postulate that the scattering from radiation-induced defects is not in the limit of the AG theory of an order parameter which is spatially averaged over impurity sites, but rather in the limit of short-coherence-length superconductivity. We show that a model calculation consistent with this assumption fits ${\ensuremath{\rho}}_{s}(T)$ in the aged sample rather well.

Longitudinal-field muon spin relaxation experiments have been carried out in the paramagnetic state of single-crystal Gd_2Ti_2O_7 just above the phase transition at T_m = 1.0 K. At high applied fields the exponential relaxation time T_1 is proportional to field, whereas T_1 saturates below a crossover field B_c that is ~2.5 T at 1.5 K and decreases as T_m is approached. At low fields the relaxation rate increases markedly as the freezing temperature is approached, as expected for critical slowing down of the spin fluctuations, but the increase is suppressed by applied field. This behavior is consistent with the very long autocorrelation function cutoff time implied by the low value of B_c., 4 pages, 2 figures, submitted to 10th International Conference on Muon Spin Rotation, Relaxation, and Resonance, Oxford, UK, August 2005

We report muon spin rotation Knight shift and susceptibility studies for 1 T applied field along the crystalline c- and a-axes of the heavy fermion compound Ce2IrIn8. Below a characteristic temperature T* one observes a `Knight-shift anomaly' in which the Knight shift constant K no longer scales linearly with susceptibility chi. This anomaly is consistent with a scaling law in which chi is composed of a high-temperature component corresponding to non-interacting local moments and a low-temperature component chi_cf proportional to (1-T/T*)\ln(T*/T) which characterizes the heavy-electron state below T*. We find that T* is anisotropic, with T_a* = 59(3)K and T_c* = 24(1)K, and derive the magnitudes of chi_cf for H along the a- and c-axes., 4 pages, 5 figures, Submitted to 10th International Conference on Muon Spin Rotation, Relaxation and Resonance, Oxford, UK, August 2005

A new facililty for conducting beta-detected nuclear magnetic resonance (beta-NMR) investigations of condensed matter systems has recently been constucted at TriUniversity Meson Facility in Vancouver, Canada. The unique features of this new facility are described, and some preliminary results on Li-8(+) in GaAs are presented. (C) 2003 Elsevier B.V. All rights reserved.

We report muon spin rotation measurements of the local magnetic susceptibility around a positive muon in the paramagnetic state of the quasi-one-dimensional spin 1/2 antiferromagnet dichlorobis (pyridine) copper (II). Signals from three distinct sites are resolved and have a temperature dependent frequency shift which is significantly different than the magnetic susceptibility. This difference is attributed to a muon induced perturbation of the spin 1/2 chain. The obtained frequency shifts are compared with transfer matrix density-matrix renormalization-group numerical simulations.

Zero-field muon spin-relaxation $(\mathrm{ZF}\ensuremath{-}\ensuremath{\mu}\mathrm{SR})$ measurements were undertaken on under- and overdoped samples of superconducting ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6+x}$ to determine the origin of the weak static magnetism recently reported in this system. The temperature dependence of the muon spin-relaxation rate in overdoped crystals displays an unusual behavior in the superconducting state. A comparison to the results of NQR and lattice structure experiments on highly doped samples provides compelling evidence for strong coupling of charge, spin, and structural inhomogeneities.

Transverse-field muon-spin rotation measurements in the vortex-lattice of the heavy-fermion (HF) superconductor ${\mathrm{P}\mathrm{r}\mathrm{O}\mathrm{s}}_{4}{\mathrm{S}\mathrm{b}}_{12}$ yield a temperature dependence of the magnetic penetration depth $\ensuremath{\lambda}$ indicative of an isotropic or nearly isotropic energy gap. This is not seen to date in any other HF superconductor and is a signature of isotropic pairing symmetry, possibly related to a novel nonmagnetic ``quadrupolar Kondo'' HF mechanism in ${\mathrm{P}\mathrm{r}\mathrm{O}\mathrm{s}}_{4}{\mathrm{S}\mathrm{b}}_{12}$. The $T=0$ relaxation rate ${\ensuremath{\sigma}}_{s}(0)=0.91(1)\text{ }\text{ }\ensuremath{\mu}{\mathrm{s}}^{\ensuremath{-}1}$ yields an estimated magnetic penetration depth $\ensuremath{\lambda}(0)=3440(20)\text{ }\text{ }\AA{}$, which is considerably shorter than in other HF superconductors.