309 research outputs found
Superhyperfine interactions in Ce3+ doped LiYF4 crystal: ENDOR measurements
The first observation of the resolved Mims electron-nuclear double resonance
(ENDOR) spectra from the nearby and remote nuclei of 19F and 7Li nuclei on
impurity Ce3+ ions in LiYF4 crystal is reported. It shows that LiYF4:Ce3+
system can be exploited as a convenient matrix for performing spin
manipulations and adjusting quantum computation protocols while ENDOR technique
could be used for the investigation of electron-nuclear interaction with all
the nuclei of the system and exploited for the electron-nuclear spin
manipulations.Comment: 4 pages, 2 figures, 1 Table. Reported on Theor-2017 (Kazan, Russia)
Conferenc
On the nonlinear NMR and magnon BEC in antiferromagnetic materials with coupled electron-nuclear spin precession
We present a new study of nonlinear NMR and Bose-Einstein Condensation (BEC)
of nuclear spin waves in antiferromagnetic MnCO3 with coupled electron and
nuclear spins. In particular, we show that the observed behaviour of NMR
signals strongly contradicts the conventional description of paramagnetic
ensembles of noninteracting spins based on the phenomenological Bloch
equations. We present a new theoretical description of the coupled
electron-nuclear spin precession, which takes into account an indirect
relaxation of nuclear spins via the electron subsystem. We show that the
magnitude of the nuclear magnetization is conserved for arbitrary large
excitation powers, which is drastically different from the conventional heating
scenario derived from the Bloch equations. This provides strong evidence that
the coherent precession of macroscopic nuclear magnetization observed
experimentally can be identified with BEC of nuclear spin waves with k=0.Comment: 12 pages, 8 figure
On the "spin-freezing" mechanism in underdoped superconducting cuprates
The letter deals with the spin-freezing process observed by means of NMR-NQR
relaxation or by muon spin rotation in underdoped cuprate superconductors. This
phenomenon, sometimes referred as coexistence of antiferromagnetic and
superconducting order parameters, is generally thought to result from randomly
distributed magnetic moments related to charge inhomogeneities (possibly
stripes) which exhibit slowing down of their fluctuations on cooling below
T . Instead, we describe the experimental findings as due to fluctuating,
vortex-antivortex, orbital currents state coexisting with d-wave
superconducting state. A direct explanation of the experimental results, in
underdoped YCaBaCuO and LaSrCuO,
is thus given in terms of freezing of orbital current fluctuations
Inhomogeneity of the intrinsic magnetic field in superconducting YBa 2Cu3OX compounds as revealed by a rare-earth EPR probe
X-band electron paramagnetic resonance experiments on doped Er 3+ and Yb3+ ions in YBa2Cu3O X (6<X<7) compounds with different oxygen contents in a wide temperature range (4-120 K) have been performed. In the superconducting species at temperatures significantly below TC, strong dependences of the linewidth and resonance line position on the sweep direction of the applied magnetic field are revealed. The possible origins of the observed hysteresis are analysed. The applicability of the presented EPR approach to extract information about the dynamics of the flux-line lattice and critical state parameters (critical current density, JC, magnetic penetration depth, λ, and characteristic spatial scale of the inhomogeneity) is discussed. © 2005 IOP Publishing Ltd
Inhomogeneity of the intrinsic magnetic field in superconducting YBa2Cu3OX compounds as revealed by rare-earth EPR-probe
X-band electron paramagnetic resonance on doped Er3+ and Yb3+ ions in
Y0.99(Yb,Er)0.01Ba2Cu3OX compounds with different oxygen contents in the wide
temperature range (4-120)K have been made. In the superconducting species, the
strong dependencies of the linewidth and resonance line position from the sweep
direction of the applied magnetic field are revealed at the temperatures
significantly below TC. The possible origins of the observed hysteresis are
analyzed. Applicability of the presented EPR approach to extract information
about the dynamics of the flux-line lattice and critical state parameters
(critical current density, magnetic penetration depth, and characteristic
spatial scale of the inhomogeneity) is discussedComment: 17 pages, 5 Figures. Renewed versio
Probing the Yb spin relaxation in YYbBaCuO by Electron Paramagnetic Resonance
The relaxation of Yb in YBaCuO () was studied
using Electron Paramagnetic Resonance (EPR). It was found that both electronic
and phononic processes contribute to the Yb relaxation. The phononic
part of the relaxation has an exponential temperature dependence, which can be
explained by a Raman process via the coupling to high-energy (500 K)
optical phonons or an Orbach-like process via the excited vibronic levels of
the Cu ions (localized Slonczewski-modes). In a sample with a maximum
oxygen doping =6.98, the electronic part of the relaxation follows a
Korringa law in the normal state and strongly decreases below .
Comparison of the samples with and without Zn doping proved that the
superconducting gap opening is responsible for the sharp decrease of Yb
relaxation in YBaCuO. It was shown that the electronic
part of the Yb relaxation in the superconducting state follows the same
temperature dependence as Cu and O nuclear relaxations despite
the huge difference between the corresponding electronic and nuclear relaxation
rates.Comment: 8 pages, 6 figure
Coherent manipulation of dipolar coupled spins in an anisotropic environment
We study coherent dynamics in a system of dipolar coupled spin qubits diluted
in solid and subjected to a driving microwave field. In the case of rare earth
ions, anisotropic crystal background results in anisotropic g tensor and thus
modifies the dipolar coupling. We develop a microscopic theory of spin
relaxation in transient regime for the frequently encountered case of axially
symmetric crystal field. The calculated decoherence rate is nonlinear in Rabi
frequency. We show that the direction of static magnetic field that corresponds
to the highest spin g-factor is preferable in order to obtain higher number of
coherent qubit operations. The results of calculations are in excellent
agreement with our experimental data on Rabi oscillations recorded for a series
of CaWO4 crystals with different concentrations of Nd3+ ions.Comment: 16 pages, 9 figure
EPR study of clusters of rare-earth ions in mixed fluoride crystals
The EPR spectra of the (BaF2)1 - x (CeF3) x system are studied for the concentrations x = 0, 0.001, 0.002, 0.005, 0.01, and 0.02. The appearance of new tetragonal centers is detected beginning from x = 0.002, the intensity of these centers being maximal at x = 0.01. The (CaF2)1 - x - y (CeF3) x (YF3) y double solutions with x = 0.001 and y from 0 to 0.02 are also studied. In addition to the ordinary tetragonal center, beginning from y = 0.001, a new tetragonal center appears with the same structure as in the previously studied mixed crystals based on BaF2 - namely, the Ce3+-R3+ chain elongated along the fourfold axis substitutes the Ca2+-Ca2+-Ca2+ and Ba 2+-Ba2+-Ba2+ chains in regular CaF2 and BaF2 crystals (is the cation vacancy, and R3+ is the Ce3+, La3+, or Y3+ trivalent ion). © 2014 Pleiades Publishing, Ltd
Study of the structures of the tetragonal paramagnetic centers in the mixed fluorite crystals with rare-earth ions by EPR
© Springer-Verlag Wien 2014. Electron paramagnetic resonance (EPR) of the mixed fluorite crystals with the general formula (MeF2)1-x-y(REF3)x(RF3)y (Me = Ca, Sr, Ba; R = Y, La, Lu; RE—paramagnetic trivalent rare-earth ions) were studied comprehensively by different authors and several structural models of paramagnetic centers were considered. However, a lot of details of EPR spectra still remain unexplained. In this work some modifications of the simplest models are proposed which allow explaining adequately the variety of the tetragonal centers in crystals grown under the different conditions. The calculated from the proposed models components of g-factors for Ce3+, Nd3+, Sm3+, Er3+ ions are in a good agreement with the experimental values
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