High temperature collective spin-photon coupling in a microwave cavity

An ensemble of N noninteracting spins being in thermal equilibrium and coupled to the resonant mode of a lossless microwave cavity is studied as the function of the spin temperature τ. Near τ = 0 the system is known to be in a coupled spin-photon state that manifests itself by the splitting of the cavity mode (vacuum Rabi splitting). The cavity emission spectrum is simulated for arbitrary τ. A critical temperature τC = ωS √N/2, where ωS is the spin excitation energy, is related to the destruction of the strong coupling regime as a consequence of thermal excitations arising within the spin ensemble. © 2014 Pleiades Publishing, Ltd

Transient nutations in magnetically diluted solids: An account of the spin flip-flop transitions

Transient nutations of the dipolar-coupled spins in solids are studied theoretically. The spins have either electronic (paramagnetic ions or defects in crystals) or nuclear origin and are subjected to the external resonant magnetic field that continually drives the total magnetization. For an ensemble of spins that have equal resonance frequencies, the flip-flop transitions are possible. The existing microscopic model of the magnetic relaxation in transient regime is modified in order to obtain the decay rate of the transient nutations in this particular case. © Springer Science+Business Media 2012

Decay of rabi oscillations induced by magnetic dipole interactions in dilute paramagnetic solids

Decay of Rabi oscillations of equivalent spins diluted in diamagnetic solid matrix and coupled by magnetic dipole interactions is theoretically studied. It is shown that these interactions result in random shifts of spin transient nutation frequencies and thus lead to the decay of the transient signal. Averaging over random spatial distribution of spins within the solid and over their spectral positions within magnetic resonance line, we obtain analytical expressions for the decay of Rabi oscillations. The rate of the decay in the case when the half-width of magnetic resonance line exceeds Rabi frequency is found to depend on the intensity of resonant microwave field and on the spin concentration. The results are compared with the literature data for E′ 1 centers in glassy silica and [AlO 4] 0 centers in quartz. © 2011 Pleiades Publishing, Ltd

Rabi oscillations of paramagnetic ions in solids: Role of electrostatic interactions

© Springer-Verlag Wien 2014. We study the decay of Rabi oscillations of magnetically coupled impurity ions diluted in the solid. Electrostatic interactions between the ions treated as charged defects shift their g-factors and result in valuable correlations of their Larmor frequencies if the ions are close enough. We find an increase in the decay time of Rabi oscillations in comparison with the case of uncharged defects. The magnitude of the effect depends on the ratio between the impurity and the total defect concentrations, as well as on the type of the electron paramagnetic resonance line broadening mechanism (by random electric fields, electric field gradients, etc.). We present results in the arbitrary order of multipole expansion with respect to valence electron coordinates of the paramagnetic ion. Corresponding corrections to the decay times of Rabi oscillations of Nd3+ ions in CaWO4 crystal are obtained

Multiphonon relaxation of optical excitations in CsCdBr3:Pr3+ and LiYF4:Nd3+ crystals

The technique of calculation of the n-phonon transition rates between electronic sublevels of impurity rare earth ions in dielectric crystals is developed in the case when n>2. The n-phonon transition probabilities are calculated according to the 1st and 2nd orders of perturbation theory. The Hamiltonian of the electron-phonon interaction is constructed in the framework of the exchange charge model and developed as series in relative displacements of the rare earth ion and ligands. The contribution of the lattice anharmonicity on the probabilities of n-phonon transitions is taken into account. On the basis of the developed technique, the nonradiative relaxation rates of 4G7/2 multiplet of Nd3+ ions in LiYF4:Nd3+crystal and 3P1 multiplet of Pr3+ ions in CsCdBr3:Pr3+ crystal were computed. The results of our calculations show that the 2nd order terms in the expressions for the probabilities studied here are comparable with, and in some cases prevail over the 1st order terms. An account of lattice anharmonicity in case of LiYF4:Nd3+ crystal substantially modifies the corresponding multiphonon relaxation rates. The calculated nonradiative relaxation rates for both crystals agree well with the experimental data. © 2010 Pleiades Publishing, Ltd

Coherence Times of Large-Spin Ensemble in Transient Regime

© 2016, Springer Science+Business Media New York.Rabi oscillations in the ensemble of weakly interacting electron or nuclear spins in solids are theoretically studied. A statistical theory which allows for calculation of the coherence times in the transient regime is presented in the general case of arbitrary spin value ≥ 1/2. Analytical expressions of the coherence times depending on the spin, temperature, spin concentration, and the Rabi frequency are obtained

Inhomogeneous broadening of ESR lines of rare earth impurities in scheelite CaWO 4 induced by internal electric field gradients

The inhomogeneous broadening of ESR line in erbium-doped CaWO 4 crystal is studied both theoretically and experimentally in the special case when external magnetic field is parallel to crystal c axis. Lorenzian shapes of ESR lines are observed and ascribed to the broadening from random electric field gradients produced by charged defects. The defect concentrations are estimated on the grounds of a simple statistical model and crystal-field calculations of impurity-defect coupling constants. Samples with different concentrations of erbium ions are used in order to find out how Er 3+ impurities affect the linewidth