89 research outputs found
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
One-dimensional Bose chemistry: effects of non-integrability
Three-body collisions of ultracold identical Bose atoms under tight
cylindrical confinement are analyzed. A Feshbach resonance in two-body
collisions is described by a two-channel zero-range interaction. Elimination of
the closed channel in the three-body problem reduces the interaction to a
one-channel zero-range one with an energy dependent strength. The related
problem with an energy independent strength (the Lieb-Liniger-McGuire model)
has an exact solution and forbids all chemical processes, such as three-atom
association and diatom dissociation, as well as reflection in atom-diatom
collisions. The resonant case is analyzed by a numerical solution of the
Faddeev-Lovelace equations. The results demonstrate that as the internal
symmetry of the Lieb-Liniger-McGuire model is lifted, the reflection and
chemical reactions become allowed and may be observed in experiments.Comment: 5 pages, 4 figure
Magnon-photon coupling in the noncollinear magnetic insulator Cu 2 OSeO 3
Anticrossing behavior between magnons in the noncollinear chiral magnet Cu2OSeO3 and a two-mode X-band microwave resonator was studied in the temperature range 5–100 K. In the field-induced ferrimagnetic phase, we observed a strong-coupling regime between magnons and two microwave cavity modes with a cooperativity reaching 3600. In the conical phase, cavity modes are dispersively coupled to a fundamental helimagnon mode, and we demonstrate that the magnetic phase diagram of Cu2OSeO3 can be reconstructed from the measurements of the cavity resonance frequency. In the helical phase, a hybridized state of a higher-order helimagnon mode and a cavity mode—a helimagnon polariton—was found. Our results reveal a class of magnetic systems where strong coupling of microwave photons to nontrivial spin textures can be observed
Single - particle correlations in events with the total disintegration of nuclei
New experimental data on the behaviour of the single-particle two-dimensional
correlation functions R versus Q (Q is the number of nucleons emitted from nuc-
lei) and Ap (Ap is the mass of projectile nuclei) are presented in this paper.
The interactions of protons, d, 4He and 12C nuclei with carbon nuclei (at a
momentum of 4.2 A GeV/c) are considered.The values of R are obtained separately
for pi minus mesons and protons.In so doing,the values of R are normalized so
that -1=<R=<1.The value of R=0 corresponds to the case of the absence of corre-
lations.It has been found that the Q- and Ap-dependence of R takes place only
for weak correlations (R< 0.3).In the main (90 %),these correlations are con-
nected with the variable pt and have a nonlinear character, that is the regi-
ons with different characters of the Q-dependence of R are separated: there is
a change of regimes in the Q-dependences of R.The correlations weaken with
increasing Ap, and the variable R gets the least values of all the considered
ones in 12CC interactions.Simultaneously with weakening the correlations in the
region of large Q, the character of the Q-dependence of R changes.Comment: 17 pages, submitted to Phys. Rew.
Experimental data on pi-mesons produced in inelastic and central nucleus-nucleus interactions at 4.5-Gev/C momentum per nucleon
Some Properties of the Central pi--Meson Carbon Interactions at 40 Gev/C
We discuss some properties of the central pi--meson carbon reactions at 40
GeV/c. While these results were obtained many years ago they have not been
explained completely. We attempt to interpret following: results regime change
on the behavior of some characteristics of the events as a function of the
centrality; anomaly peak on the angular distributions of the slow protons
emitted in these reactions; charge asymmetry on the pi--mesons production in
the back hemisphere in lcs.
Understanding of the results could help to explain the new ones coming from
the modern central experiments at high and ultrarelativistic energies.Comment: To appear in the proceedings of the 10th nternational Workshop on
Meson Production, Properties and Interaction (MESON 2008), Krakow, Poland, 6
- 10 June 2008. 4 pages and 4 figure
Nonlinear NMR and magnon BEC in antiferromagnetic materials with coupled electron and nuclear spin precession
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