Ground State of the Easy-Axis Rare-Earth Kagom\'e Langasite Pr3_3Ga5_5SiO14_{14}

We report muon spin relaxation ($\mu$SR) and $^{69,71}$Ga nuclear quadrupolar resonance (NQR) local-probe investigations of the kagom\'e compound Pr$_3$Ga$_5$SiO$_{14}$. Small quasi-static random internal fields develop below 40 K and persist down to our base temperature of 21 mK. They originate from hyperfine-enhanced $^{141}$Pr nuclear magnetism which requires a non-magnetic Pr$^{3+}$ crystal-field (CF) ground state. Besides, we observe a broad maximum of the relaxation rate at $\simeq 10$ K which we attribute to the population of the first excited magnetic CF level. Our results yield a Van-Vleck paramagnet picture, at variance with the formerly proposed spin-liquid ground state.Comment: minor change

Spin coherence lifetime extension in Tm3+^{3+}:YAG through dynamical decoupling

We report on spin coherence lifetime extension on Tm$^{3+}$:YAG obtained through dynamically decoupling the thulium spins from their magnetic environment. The coherence lifetime reached with a Carr-Purcell-Meiboom-Gill sequence revealed a 450-fold extension [$\sim$$(230 \pm 30)$ ms] with respect to previously measured values. Comparison to a simple theoretical model allowed us to estimate the correlation time of the fluctuations of the ground level transition frequency to $(172 \pm 30)$ $\mu$s at 1.7 K. For attaining efficient decoupling sequences, we developed a strategy inspired by the \emph{zero-first-order Zeeman} effect to minimize the large inhomogeneous broadening of the ground level spin transition.Comment: 10 pages, 7 figure

Medium-modified fragmentation of b-jets tagged by a leading muon in ultrarelativistic heavy ion collisions

The possibility to observe the medium-modified fragmentation of hard b-quarks tagged by a leading muon in ultrarelativistic heavy ion collisions is analyzed. We have found that reasonable statistics, ~20000 events per 1 month of LHC run with lead beams, can be expected for the realistic geometrical acceptance and kinematic cuts. The numerical estimates on the effect of the medium-induced softening b-jet fragmentation function are given.Comment: 12 pages in LaTeX (including 3 figures in EPS-format

DIPOLE WIDTH OF THE NMR LINE OF **1**6**9Tm IN THULIUM ETHYL SULFATE.

The authors analyze the width of the NMR line of **1**6**9Tm (spin I equals 1/2) in a model crystals of Tm(C//2H//5SO//4)//3:9H//2O at 4. 2 K. In the case of rare-earth ethyl sulfates LnES the only interaction between magnetic particles is of the dipole-dipole type so that it is easy to calculate the second moments of the NMR lines. The positions of atoms in the ethyl sulfate lattice have already been determined so that the only unknowns are the lattice parameters of TmES at 4. 2 K. The latter can be obtained simply by determining the coordinates of the hydrogen atoms and the positions of the lines in the NMR spectrum of H in a field H perpendicular to the c axis of the crystal. The results of the analysis are presented and discussed

Nuclear magnetic relaxation in rare-earth compound crystals due to fluctuations of hyperfine magnetic fields

Some results on NMR and relaxation studies of the Van Vleck paramagnet TmES (thulium ethylsulphate) and the Ising ferromagnet DyES are summarized. Complicated but regular quasistatic internal magnetic fields are created by Tm and Dy ions in these compounds. These fields fluctuate due to the thermal excitation of tne ions and the energy transfer from one ion to another. Fluctuations give rise to NMR line shifts, broadening of the lines and spin-lattice relaxation, the shifts, linewidth and spin-lattice relaxation rate being proportional to exp(-Δ/kT) at low temperatures (kT≪Δ, Δ is an excitation energy). Pre-exponential factors depend on fluctuating fields in a definite but complicated manner, so estimates of the correlation time (electron spin-spin relaxation time) can be obtained from measurements of nuclear relaxation rates. © 1990 J.C. Baltzer A.G., Scientific Publishing Company

Reducing decoherence in optical and spin transitions in rare-earth-ion doped materials

In many important situations the dominant dephasing mechanism in cryogenic rare-earth-ion doped systems is due to magnetic field fluctuations from spins in the host crystal. Operating at a magnetic field where a transition has a zero first-order-Zeeman (ZEFOZ) shift can greatly reduce this dephasing. Here we identify the location of transitions with zero first-order Zeeman shift for optical transitions in Pr3+:YAG and for spin transitions in Er3+:Y2SiO5. The long coherence times that ZEFOZ would enable would make Pr3+:YAG a strong candidate for achieving the strong coupling regime of cavity QED, and would be an important step forward in creating long-lived telecommunications wavelength quantum memories in Er3+:Y2SiO5. This work relies mostly on published spin Hamiltonian parameters but Raman heterodyne spectroscopy was performed on Pr3+:YAG to measure the parameters for the excited state.Comment: 10 pages, 5 figure

Estimating the size spectrum of lower ionosphere irregularities from oblique-sounding data

A procedure for reducing experimental ionospheric oblique-sounding data is considered. This procedure allows the size spectrum of scattering lower ionosphere irregularities and the rms value of the neutral wind to be estimated from the power spectrum of a scattered radio signal. The problem reduces to solving a Fredholm equation of the first kind; an empirical model of the scattered-signal spectrum is used for its reguiarization. The experimental data obtained on the mid-latitude Moscow-Kazan path in 1986-1990 are used to test its efficiency. The internal scale of turbulence in the E region of the ionosphere is estimated. Copyright © 1999 by MAHK "Hayka/Interperiodica"

Decrease of the homogeneous width of the Tm3+ electron energy levels in TmBa2CCu3 O6+x at the superconducting transition

Enhanced NMR of 169Tm (I= 1 2) enhanced NMR has been studied in TmBa2Cu3O6+x, x=0, 0.2, 0.4, at temperatures 1.2-40K. The nuclear magnetic relaxation rates at T>20K increase exponentially as 1 T1(2) = R1(2)exp(-Δ/kT), with Δ = 176 K being the energy of the first excited state of the Tm3+ ion, while the R1(2) pre-exponential factors are inversely proportional to the homogenous width Γo of this doublet state. The pre-exponential factors measured at the frequencies of 48 and 69 MHz show homogeneous broadening of the 4f-levels due to the decreasing dipole-dipole transfer of the electron excitations from ion to ion at increasing because of crystal structure disordering. A sharp decrease of Γo (by about 0.9K) is observed in the superconducting compound with x=0.4 (Tc onset at 20K) at low temperatures and is attributed to the weakening of the 4f-electron-phonon interaction. At the temperatures around 6K the same sample displays enhancement of the transverse relaxation due to the relatively slow (W ≈ 109s-1) fluctuations of the internal magnetic fields caused by Cu2+ ions in CuO2 planes. © 1992