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1.
We investigate analytically and numerically the Multiple Quantum (MQ) NMR dynamics in dipolar ordered spin systems of nuclear spins 1/2 at low temperatures. We consider two different methods of MQ NMR. One of them is based on the measurement of the dipolar energy. The other method uses an additional resonance (π/4)y-pulse after the preparation period of the standard MQ NMR experiment in solids and allows one to measure the Zeeman energy. Both considered methods are sensitive to the contribution of remote spins in the interaction and to the spin system structure. The QS method is sensitive to the spin number in the molecule while the PS method gives very similar time dependencies of the intensities of MQ coherences for different spin numbers. It is shown that the use of the dipolar ordered initial state has the advantage of exciting the highest order MQ coherences in clusters of 4m identical spins, where m=1,2,3,…, that is impossible to do with the standard MQ method. MQ NMR methods based on the dipolar ordered initial states at low temperatures complement the standard NMR spectroscopy for better studying structures and dynamic processes in solids. 相似文献
2.
S. I. Doronin E. B. Fel’dman A. I. Zenchuk 《Journal of Experimental and Theoretical Physics》2011,113(3):495-501
The multiple quantum (MQ) NMR dynamics in the system of equivalent spins with the dipolar ordered initial state is considered.
The high symmetry of the Hamiltonian responsible for the MQ NMR dynamics (the MQ Hamiltonian) is used to develop analytic
and numerical methods for the investigation of the MQ NMR dynamics in systems consisting of hundreds of spins from the “first
principles.” We obtain the dependence of the intensities of the MQ NMR coherences on their orders (profiles of the MQ NMR
coherences) for systems of 200–600 spins. It is shown that these profiles may be well approximated by exponential distribution
functions. We also compare the MQ NMR dynamics in the systems of equivalent spins having two different initial states, the
dipolar ordered state and the thermal equilibrium state in a strong external magnetic field. 相似文献
3.
An analytical expression I(ω) is obtained for a normalized function of the shape of an idealized nuclear quandrupole resonance
nutation line of a powdered sample for spins I=3/2 (η≠0). Calculations are made of the initial moments <ωn> of the nutation spectrum of the powder in the form of functions of ω0=γB1 and the asymmetry parameter η of the electric field gradient tensor. A method is proposed for determining the spectral parameters
η and eQqzz from the experimentally measured values of <ω>, <ω2>, <ω4>, and ω1/2 of the nuclear quadrupole resonance nutation spectrum of the powder.
State University, Kaliningrad. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 3–8, July, 1997. 相似文献
4.
We investigate the evolution of entanglement in multiple-quantum (MQ) NMR experiments in crystals with pairs of close nuclear
1/2-spins. The initial thermodynamic equilibrium state of the system in a strong external magnetic field evolves under the
nonsecular part of the dipolar Hamiltonian. As a result, MQ coherences of the zeroth and plus/minus second orders appear.
A simple condition for the emergence of entanglement is obtained. We show that the measure of the spin-pair entanglement—concurrence—coincides
qualitatively with the intensity of MQ coherences of the plus/minus second order and, hence, the entanglement can be studied
with MQ NMR methods. We introduce an entanglement witness using MQ NMR coherences of the plus/minus second order.
The text was submitted by the authors in English. 相似文献
5.
Dipolar relaxation of multiple quantum (MQ) nuclear magnetic resonance (NMR) coherence is investigated on the evolution period of the MQ NMR experiment in chains of 19F nuclei in a single crystal of calcium fluorapatite. The dependence of the relaxation time of the MQ coherence of the second order on the size of the coherent spin cluster formed on the preparation period is obtained. The dipolar relaxation of MQ NMR coherences is considered as a model for the investigation of decoherence of quantum states of many-qubit spin clusters. 相似文献
6.
Vytautas Balevicius Alexandar Gacesa Janez Plavec 《Central European Journal of Physics》2004,2(1):120-131
An origin of narrow 1H NMR signals in pyridine-N-oxide (PyO)...HCl crystal has been investigated by means of MAS, SPEDAS, NOESY and COSY techniques.
Spectra of crystalline samples are compared with those of solid phase obtained from liquid PyO...HCl solutions (in acetonitile/H2O) after the heterogeneous phase separation. It has been concluded that partially resolved peaks in 1H NMR spectra of solids are related with heterogeneity of spin system and presence of different H-bond clusters of water molecules.
NOESY spectra show no cross-peaks even at very long mixing time (500 ms). This indicates there is no exchange process between
spins causing different peaks, and thus the corresponding molecular aggregates are captured in “islands of mobility8 without
any channels sufficient for exchange. Appearance of MAS side bands as “pseudo8 cross-peaks in 2D NMR spectra using MAS/COSY
technique is reported. In the case of accidental coincidence of spinning frequency (ω
MAS
) with spectral distances between some diagonal signals, intensive non-diagonal peaks are observed at the corresponding cross-positions.
A misleading conclusion concerning spin coupling is easy to avoid using various ω
MAS
.
This work is dedicated to Professor Robert Blinc on the occasion of his 70th birthday. 相似文献
7.
《Current Applied Physics》2014,14(3):383-388
The magnetic properties and the electronic structures of a rare-earth aluminum intermetallic compound CeAl2 are investigated by magnetic susceptibility measurements and 27Al pulsed nuclear magnetic resonance (NMR) techniques. The magnetic susceptibility is strongly temperature-dependent, following a Curie–Weiss law down to ∼12 K, and shows an antiferromagnetic transition at 4 K. The 27Al NMR spectra show a typical powder pattern for a nuclear spin I of 5/2 with the second-order nuclear quadrupole interaction at high temperature and an additional large dipolar broadening between the 4f electron spins of cerium and the 27Al nuclear spins at low temperature. The 27Al NMR Knight shift follows the same temperature dependence as the magnetic susceptibility, suggesting that the 27Al NMR Knight shift originates from the transferred hyperfine field of the Ce 4f electron spins with the hyperfine coupling constant of A = +5.7 kOe/μB. The spin-lattice relaxation rate 1/T1 is roughly proportional to temperature, as with most non-magnetic metals at high temperature, and then strongly temperature-dependent, increasing rapidly with a peak near the antiferromagnetic transition temperature and decreasing at lower temperature. The temperature dependence of the Korringa ratio K, however, suggests that the antiferromagnetic spin fluctuation signature, which is an enhancement in the Korringa ratio, is washed out owing to the geometrical cancellation of Ce 4f fluctuations at the Al sites. 相似文献
8.
A. Goto T. Shimizu R. Miyabe K. Hashi H. Kitazawa G. Kido K. Shimamura T. Fukuda 《Applied Physics A: Materials Science & Processing》2002,74(1):73-77
We have performed 7Li and 19F nuclear magnetic resonance (NMR) in two lithium fluorides BaLiF3 and YLiF4 to explore the possibility of a crystal NMR quantum computing device. We find that (1) both the absolute values and the angular
dependences of the line widths can primarily be accounted for by the nuclear dipolar fields, and (2) the spin–lattice relaxation
times are long enough for quantum computations. These characteristics indicate that these crystals can be possible candidates
for quantum computing devices. We also find that, in the perovskite structures like BaLiF3, magic angles are quite effective to diminish the nuclear dipole fields, which enables us to treat some nuclei as ‘isolated’.
We propose using this feature to create low-dimensional nuclear-spin networks in the crystals.
Received: 29 January 2001 / Accepted: 6 February 2001 / Published online: 3 April 2001 相似文献
9.
A study was made of lattice defects in hep Co metal using the technique of perturbed γ-γ angular correlations. Lattice sites
of111Cd impurities were characterized by their nuclear magnetic dipole and electric quadrupole interaction frequencies, respectively
ωL and ωO. The signal for defect-free substitutional Cd impurities was found to have collinear interactions at 77K, with ωL=438 Mrad/s and ωO=7 Mrad/s. Analysis of measurements after heavy deformation at 100 K and after annealings up to 700 K gave little evidence
of thermal trapping of point defects. However, in all spectral measured after deformation, a highly stable defect site with
ωL=418 and ωO Mrad/s, and showing collinear interactions, was also observed. It is attributed to a111Cd probe in a stacking fault (SF). Assuming a random distribution of proble atoms and SF's, a SF density of 20% was estimated. 相似文献
10.
The low-frequency part of the magnetic resonance spectrum of the hexagonal six-sublattice quasi-one-dimensional antiferromagnet
CsMnBr3 at temperatures which are low compared with T
N
=8.3 K is investigated experimentally. A temperature-dependent gap Δ(T) is found in the spectrum ω
e
(H) of the lower AFMR branch; this gap is due to the hyperfine interaction of the nuclear spins with the electronic spins of
the (55Mn)2+ ions. The spectrum of the low-lying resonance frequencies of such a system is calculated taking this interaction into acount
in the approximation of fluctuationless spin hydrodynamics for the electronic branch of the oscillations. The computational
results are in good qualitative and satisfactory quantitative agreement with experiment.
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 6, 433–437 (25 September 1996) 相似文献
11.
Poynor A. N. Cumblidge S. E. Rasera R. L. Catchen G. L. Motta A. T. 《Hyperfine Interactions》2001,136(3-8):549-553
We have measured nuclear electric–quadrupole interactions (EQI) at 181Ta impurities substituted as Hf atoms into the Zr site in Zr2Ni. Using perturbed-angular-correlation (PAC) spectroscopy, we measured the EQI over temperatures ranging from 10 to 1200
K. Over the entire range of temperature, the Zr2Ni crystal has a bct Al2Cu structure that includes a single Zr site. The crystal field symmetry surrounding this site is rather low, giving rise to
a highly asymmetric electric-field gradient tensor. At 10 K, the EQI is characterized by an angular frequency ω0=601(3) Mrad s−1, and an asymmetry parameter η=0.835(2). At 1200 K, ω0 decreases to 516(3) Mrad s−1, and η also decreases to 0.790(4). Although weak, the temperature dependence of ω0 is consistent with a (1−BT
3/2) power law, in which B=6×10−6 K−3/2. The EQI also manifests a very narrow linewidth. We observed no evidence either for magnetic ordering or for structural phase
transitions in the temperature range covered by this experiment. Moreover, the sharpness of the EQI indicates that the samples
as prepared are remarkably free of strain and defects. These results indicate that the Zr2Ni structure does not promote the formation of defects and that the power-law dependence of ω0 on T is insensitive to the asymmetric nature of the crystal.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
12.
K.C. Chung C.S. Wang A.J. Santiago J.W. Zhang 《The European Physical Journal A - Hadrons and Nuclei》2001,11(2):137-141
The σ-ω coupling is introduced phenomenologically in the linear σ-ω model to study the nuclear matter properties. It is shown
that not only the effective nucleon mass M* but also the effective σ meson mass m
σ
* and the effective ω meson mass m
ω
* are nucleon-density-dependent. When the model parameters are fitted to the nuclear saturation point, with the nuclear radius
constant r
0 = 1.14 fm and volume energy a
1 = 16.0 MeV, as well as to the effective nucleon mass M
* = 0.85M, the model yields m
σ
* = 1.09m
σ and m
ω
* = 0.90m
ω at the saturation point, and the nuclear incompressibility K
0 = 501 MeV. The lowest value of K0 given by this model by adjusting the model parameters is around 227 MeV.
Received: 23 March 2001 / Accepted: 8 June 2001 相似文献
13.
Hamid Arian Zad 《理论物理通讯》2016,66(6):629-637
We analytically investigate Multiple Quantum (MQ) NMR dynamics in a mixed-three-spin (1/2,1,1/2) system with XXX Heisenberg model at the front of an external homogeneous magnetic field B. A single-ion anisotropy property ζ is considered for the spin-1. The intensities dependence of MQ NMR coherences on their orders (zeroth and second orders) for two pairs of spins (1,1/2) and (1/2,1/2) of the favorite tripartite system are obtained. It is also investigated dynamics of the pairwise quantum entanglement for the bipartite (sub)systems (1,1/2) and (1/2,1/2) permanently coupled by, respectively, coupling constants J1 and J2, by means of concurrence and fidelity. Then, some straightforward comparisons are done between these quantities and the intensities of MQ NMR coherences and ultimately some interesting results are reported. We also show that the time evolution of MQ coherences based on the reduced density matrix of the pair spins (1,1/2) is closely connected with the dynamics of the pairwise entanglement. Finally, we prove that one can introduce MQ coherence of the zeroth order corresponds to the pair spins (1,1/2) as an entanglement witness at some special time intervals. 相似文献
14.
O. S. Barišić S. Barišić 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(1):1-9
The translationally invariant diagrammatic quantum perturbation theory (TPT) is applied to the polaron problem on the 1D lattice,
modeled through the Holstein Hamiltonian with the phonon frequency ω0, the electron hopping t and the electron-phonon coupling constant g. The self-energy diagrams of the fourth-order in g are
calculated exactly for an intermittently added electron, in addition to the previously known second-order term. The corresponding
quadratic and quartic corrections to the polaron ground state energy become comparable at t/ω0>1 for g/ω0∼(t/ω0) 1/4 when the electron self-trapping and translation become adiabatic. The corresponding non adiabatic/adiabatic crossover occurs
while the polaron width is large, i.e. the lattice coarsening negligible. This result is extended to the range (t/ω0)1/2>g/ω0>(t/ω0)1/4>1 by considering the scaling properties of the high-order self-energy diagrams. It is shown that the polaron ground state
energy, its width and the effective mass agree with the results found traditionally from the broken symmetry side, kinematic
corrections included. The Landau self-trapping of the electron in the classic self-consistent, localized displacement potential,
the restoration of the translational symmetry by the classic translational Goldstone mode and the quantization of the polaronic
translational coordinate are thus all encompassed by a quantum theory which is translationally invariant from the outset.
This represents the first example, open to various generalizations, of the capability of TPT to hold through the adiabatic
symmetry breaking crossover. Plausible arguments are also given that TPT can describe the g/ω0>(t/ω0)1/2 regime of the small polaron with adiabatic or non-adiabatic translation, i.e., that TPT can cover the whole g/ω0, t/ω0 parameter space of the Holstein Hamiltonian. 相似文献
15.
Louise Odgaard Mads Bak Hans J. Jakobsen Niels Chr. Nielsen 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2001,148(2):298
This work explores the utility of simple rotary resonance experiments for the determination of the magnitude and orientation of 13C chemical shift tensors relative to one or more 13C–14N internuclear axes from 13C magic-angle-spinning NMR experiments. The experiment relies on simultaneous recoupling of the anisotropic 13C chemical shift and 13C–14N dipole–dipole coupling interactions using 2D rotary resonance NMR with RF irradiation on the 13C spins only. The method is demonstrated by experiments and numerical simulations for the 13Cα spins in powder samples of
-alanine and glycine with 13C in natural abundance. To investigate the potential of the experiment for determination of relative/absolute tensor orientations and backbone dihedral angles in peptides, the influence from long-range dipolar coupling to sequential 14N spins in a peptide chain (14Ni–13Cαi–14Ni+1 and 14Ni+1–13C′i–14Ni three-spin systems) as well as residual quadrupolar–dipolar coupling cross-terms is analyzed numerically. 相似文献
16.
G.I. Lykasov W. Cassing A. Sibirtsev M.V. Rzjanin 《The European Physical Journal A - Hadrons and Nuclei》1999,6(1):71-81
We calculate the elastic and inelastic ωN→ωN, →πN, →ρN, →ρπN, →ππN, →σN reactions within a boson exchange approximation where the ωρπ coupling constant and form factor are fixed by the reaction
πN→ωN in comparison to the experimental data. We find rather large ωN cross sections at low relative momenta of the ω-meson which
leads to a substantial broadening of the ω-meson width in nuclear matter. The implications of the ωN final state interactions are studied for ω production in 12C +12C, 40Ca +40Ca and 58Ni +58Ni reactions at about 2 · A GeV within the HSD transport approach; the drastic changes of the transverse mass spectra relative
to a general m
T-scaling (for π0 and η mesons) might be controlled experimentally by the TAPS Collaboration.
Received: 28 April 1999 / Revised version: 7 June 1999 相似文献
17.
5 s; the polarizing field was varied from 10 V/cm to 10 kV/cm, and the temperature between -190 °C and 25 °C.
The results confirm that the depolarization current in TGS follows the formula Id∼[(ωpt)n+(ωpt)m]-1, where n<1 and m>1. The values of the parameters n and m depend on both the electric field strength and the polarization
time as well as on the temperature of the experiment. The loss peak frequency ωp exhibits activation character: ωp∼exp(-E/kBT) with E=0.34 eV at temperatures directly below room temperature and E=0.013 eV in the range of liquid nitrogen temperatures.
Received: 1 April 1997/Accepted: 7 April 1997 相似文献
18.
Y.J. Uemura R.S. Hayano J. Imazato N. Nishida T. Yamazaki 《Solid State Communications》1979,31(10):731-734
The zero-field spin relaxation function of μ+ observed in ZrH2 has revealed that the second moment of the nuclear dipolar broadening is five times larger than the high-field value. This experiment clearly demonstrates the recovery of the non-secular part of dipolar interaction between unlike spins. A general expression of zero-field relaxation function is presented to account for a slow modulation of random fields on μ+ found at room temperature. 相似文献
19.
M. R. Galpin D. E. Logan 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(2):129-145
We develop a non-perturbative local moment approach (LMA) for the gapped Anderson impurity model (GAIM), in which a locally
correlated orbital is coupled to a host with a gapped density of states.
Two distinct phases arise, separated by a level-crossing quantum phase transition: a screened singlet phase, adiabatically
connected to the non-interacting limit and as such a generalized Fermi liquid (GFL); and an incompletely screened, doubly
degenerate local moment (LM) phase.
On opening a gap (δ) in the host, the transition occurs at a critical gap δc, the GFL [LM] phase occurring for δ<δc [ δ>δc] . In agreement with numerical renormalization group (NRG) calculations, the critical
δc = 0 at the particle-hole symmetric point of the model, where the LM phase arises immediately on opening the gap. In the generic
case by contrast δc > 0, and the resultant LMA phase boundary is in good quantitative agreement with NRG results. Local single-particle dynamics
are considered in some detail.
The major difference between the two phases resides in bound states within the gap: the GFL phase is found to be characterised
by one bound state only, while the LM phase contains two such states straddling the chemical potential. Particular emphasis
is naturally given to the
strongly correlated, Kondo regime of the model. Here,
single-particle dynamics for both phases are found to exhibit universal scaling as a function of scaled frequency ω/ωm
0 for fixed gaps
δ/ωm
0, where ωm
0 is the characteristic Kondo scale for the gapless (metallic) AIM; at particle-hole symmetry in particular, the
scaling spectra are obtained in closed form. For frequencies
|ω|/ωm
0 ≫δ/ωm
0, the
scaling spectra are found generally to reduce to those of the gapless, metallic Anderson model;
such that for small gaps δ/ωm
0≪ 1 in particular, the Kondo resonance that is the spectral hallmark of the usual metallic Anderson model persists more or
less in its entirety in the GAIM. 相似文献
20.
N. V. Zavaritskii I. S. Solodovnikov 《Journal of Experimental and Theoretical Physics》1998,87(3):546-552
The evolution of the longitudinal magnetization of nuclear spins in a cw high-frequency magnetic field has been measured using
a SQUID magnetometer at liquid-helium temperatures in magnetic fields H
0 of up to 57 Oe. The time T
m for thermal mixing of the Zeeman and dipolar systems has been found to range between 0.05 and 4×102 s. For T
m>1 s the function T
m(H
0) is exponential. The proton NMR spectra near the fundamental and twice the Larmor frequency have been obtained. The shift
in the resonance with respect to the Larmor frequency is close to the theoretical prediction.
Zh. éksp. Teor. Fiz. 114, 1006–1017 (September 1998)
Deceased. 相似文献