arXiv subjects

M. G. Rudavets

Publications and source records attributed to M. G. Rudavets.

4 recordsLinked to original sources

arXiv2010

Giant enhancement of the NMR resolution and sensitivity of the critical solutions of hyperpolarized fluids within closed carbon nanotubes

We predict the effect of the nuclear spin density fluctuations on NMR spectra of critical solutions of spin-carrying atoms in closed carbon nanotubes (CNTs). The total effective dipolar coupling of nuclear spin-carrying of 129^Xe atoms is the sum of 2 terms i.e. g_0 of non-correlated 129^Xe atoms and g_1 depending on density fluctuations of Xe atoms. The coupling g_0 falls off to 0 as 1/V with increasing the volume V of CNTs, while the g_1 remains finite for long CNTs containing critical solution of Xe atoms. The g_1 is derived within the Landau-Ginzburg framework. When temperature T goes to critical temperature T_c, the g_1 is about 10 Hz for 129^Xe fluid in closed long tubes. To achieve the g_1>> g_0, 3 conditions should be met: (1) the large mobility of 129^Xe atoms, (2) the maximal isothermal compressibility of Xe nanofluid within CNTs that have to be (3) long and closed. We discuss 3 applications of such a behavior. First, when T goes to T_c, the FID from N magnetically equivalent 129^Xe atoms is broadened so wide that the FID splits into lattice of N equidistant resonances with finite spacing G=3g_1. Second, the absorption line shape of 129^Xe atoms in spin state I=N/2, m=N/2 has a single delta peak at frequency with the large shift N*G/2 from Larmor frequency W for N>>1. The dipolar field of nanofluid in the spin state I=N/2, m=-N/2 inverts the total magnetic field if N>1+2W/G. Third, we discuss the spontaneous superradiation of the nanofluid in course of depolarization I_x(t) in low-field resonator. At CP of the nanofluid, the I_x(t) causes the bursts of dissipated power ~(g_1)^2*N^3. In the opposite limiting case of the strong field resonator, the depolarization I_x(t) has the Dicke's power ~(W*N)^2. Far from the CP of Xe nanofluid, the dissipated power scales linear with N for fixed density of 129^Xe atoms.

cond-mat.mes-hall↗

arXiv2004

Exact results on spin dynamics and multiple quantum dynamics in alternating spin-1/2 chains with XY-Hamiltonian at high temperatures

We extend the picture of a transfer of nuclear spin-1/2 polarization along a homogeneous one-dimensional chain with the XY-Hamiltonian to the inhomogeneous chain with alternating nearest neighbour couplings and alternating Larmor frequencies. To this end, we calculate exactly the spectrum of the spin-1/2 XY-Hamiltonian of the alternating chain with an odd number of sites. The exact spectrum of the XY-Hamiltonian is also applied to study the multiple quantum (MQ) NMR dynamics of the alternating spin-1/2 chain. MQ NMR spectra are shown to have the MQ coherences of zero and $\pm$ second orders just as in the case of a homogeneous chain. The intensities of the MQ coherences are calculated.

cond-mat.stat-mech↗

arXiv2004

NMR line shapes of a gas of nuclear spin-1/2 molecules in fluctuating nano-containers

Reported in this paper is the impact of the fluctuations of the geometry of the nano-meter gas containers in the medium on the NMR line shape of the gas inside of the nano-containers. We calculate exactly the NMR line shape of the gas of spin-1/2 carrying molecules for two typical dynamics of the nano-container volume and the orientation with respect to the external magnetic field: (i) for a Gaussian stochastic dynamics, and (ii) for the regular harmonic vibrations. For the Gaussian ensemble of static disordered containers having an infinite correlation time, $τ_{\sf c} \to \infty $, the overall line shape is shown to obey a logarithmic low frequency asymptotics, $ I(ω) = {const} \times \ln (\frac{1}ω)$, at $ω\to 0$, and exponentially decaying asymptotics in a high frequency domain. For the Gaussian ensemble of the rapidly fluctuating containers of a finite $τ_{\sf c}$, the overall line shape has a bell-shaped profile with $\sim ω^{-4}$ far wing behaviour. In addition, we calculate exactly a satellite structure of the NMR line shape when the nano-bubbles in a liquid are affected by the harmonic deformations due to the acoustic waves.

quant-ph↗

arXiv2003

Non-Ergodic Nuclear Depolarization in Nano-Cavities

Recently, it has been observed that the effective dipolar interactions between nuclear spins of spin-carrying molecules of a gas in a closed nano-cavities are independent of the spacing between all spins. We derive exact time-dependent polarization for all spins in spin-1/2 ensemble with spatially independent effective dipolar interactions. If the initial polarization is on a single (first) spin,$P_1(0)= 1$ then the exact spin dynamics of the model is shown to exhibit a periodical short pulses of the polarization of the first spin, the effect being typical of the systems having a large number, $N$, of spins. If $N \gg 1$, then within the period $4π/g$ ($2π/g$) for odd (even) $N$-spin clusters, with $g$ standing for spin coupling, the polarization of spin 1 switches quickly from unity to the time independent value, 1/3, over the time interval about $(g\sqrt{N})^{-1}$, thus, almost all the time, the spin 1 spends in the time independent condition $P_1(t)= 1/3$. The period and the width of the pulses determine the volume and the form-factor of the ellipsoidal cavity. The formalism is adopted to the case of time varying nano-fluctuations of the volume of the cavitation nano-bubbles. If the volume $V(t)$ is varied by the Gaussian-in-time random noise then the envelope of the polarization peaks goes irreversibly to 1/3. The polarization dynamics of the single spin exhibits the Gaussian (or exponential) time dependence when the correlation time of the fluctuations of the nano-volume is larger (or smaller) than the $<(δg)^2 >^{-1/2} $, where the $<(δg)^2>$ is the variance of the $g(V(t))$ coupling. Finally, we report the exact calculations of the NMR line shape for the $N$-spin gaseous aggregate.

quant-ph↗