Prediction of hyperdeformed nuclear states at very high spins

Calculations based on the generalized cranking-Strutinsky method with the deformed Woods-Saxon potential predict the existence of extremely elongated hyperdeformed nuclear shapes with the axis ratios significantly exceeding2:1. The strongest effect is expected to take place for nuclei around ¹⁶⁶Er, ¹⁶⁸Yb, and ¹⁷⁰Hf (Z = 68, 70, 72; N = 98) for spins as high as the fission limit down to I ∼ 10–20. The chances for observing those states in nature are discussed in detail. Systematic occurrences of the superdeformed and hyperdeformed states also in lighter (A ∼ 70, and A ∼ 100) nuclei are suggested as a consequence of the approximate pseudo-oscillator (or pseudo-SU(3) symmetries of the realistic nuclear mean field.     

High-resolution DOSY NMR with spins in different chemical surroundings: influence of particle exchange

The effect of chemical exchange in the diffusion-ordered (DOSY) spectra of a two-site system in the slow-exchange limit with respect to the chemical shift is studied. The problem is addressed both theoretically and experimentally. The relationship between diffusion time (t) and mean lifetimes (tau) is studied by the simulation of the magnetization attenuations as a function of the gradient strength, under PFG conditions. The influence of the difference in populations and diffusion coefficients of the two sites is also considered. In analogy to the limiting cases of fast- and slow-exchange with respect to the chemical shift, limiting cases with respect to the diffusion dimension are defined. The slow-exchange limit in diffusion corresponds to the relation of t and tau that allows us to observe the two spins in exchange associated with the individual diffusion coefficients of the two sites when no exchange is present. The fast-exchange limit in diffusion is reached when the relation of t and tau is such that the two spins present the same apparent diffusion coefficient. By using a model system consisting of water/t-butanol it is shown that by recording several DOSY experiments with increasing diffusion times it is possible to estimate the value of the exchange rate.     

Transfer of CIDNP among coupled spins at low magnetic field

Coherent polarization transfer among groups of dynamically polarized spins is explored and applied to field cycling experiments where spin evolution proceeds at low magnetic field while observation is performed at high field. The case of two nonequivalent spins-1/2 with scalar spin coupling is considered theoretically in detail for the cases of sudden and adiabatic field change. The criterion for efficient polarization transfer is derived theoretically and consistently confirmed experimentally for three photochemical reactions, involving spin systems of increasing complexity that exhibit chemically induced dynamic nuclear polarization: (1) the two polarized protons of the purine base of adenosine monophosphate; (2) four coupled indole protons of tryptophan; and (3) long-range polarization transfer among the aliphatic protons of cycloundecanone. The importance of polarization transfer in other cases with non-equilibrium population of the nuclear spin levels and the possibility of its utilization in field cycling NMR studies are discussed.     

On Heisenberg exchange of high spins

The well-known Kaplan-Alexander equations for chemical exchange are generalized to include Heisenberg exchange of high spins (S > 1/2). General expressions are obtained for the effect of the exchange on the shape and width of lines and on the population of spin eigenstates. The broadening action of an arbitrary spin on a spin of 1/2 is taken as an example.     

Influence of octupole interactions on the behavior of negative-parity states at low spins

The energies of negative-parity levels based on two-particle states exhibit a nonlinear behavior at low spins versus the core-rotation energy because the alignment process has not yet been completed for them. This behavior of negative-parity levels in the low-spin region is satisfactorily described upon the inclusion of octupole-octupole interactions. This is demonstrated within the rotational model involving the Coriolis mixing of states for the even-even isotopes ^162–168Hf.     

Nuclear spins, magnetic moments and α-decay spectroscopy of long-lived isomeric states in 185Pb

Alpha-decay properties of the neutron-deficient isotope ¹⁸⁵Pb were studied at the PSB-ISOLDE (CERN) on-line mass separator using the resonance ionisation laser ion source (RILIS). The nuclei of interest were produced in a 1.4 GeV proton-induced spallation reaction of a uranium graphite target. In contrast to previous studies, two α-decaying isomeric states were identified in ¹⁸⁵Pb. The relative production of the isomers, monitored by their α-counting rates, could be significantly changed when a narrow-bandwidth laser at the RILIS setup was used to scan through the atomic hyperfine structure. Based on the atomic hyperfine structure measurements, along with the systematics for heavier odd-mass lead isotopes, the spin and the parity of these states were interpreted as 3/2^- and 13/2⁺ and their nuclear magnetic moments were deduced. The α-decay energy and half-life value for the I ^π = 13/2⁺ isomer are E _α = 6408(5) keV, T _1/2 = 4.3(2) s, respectively; while for the I ^π = 3/2^- isomer ( T _1/2 = 6.3(4) s) two α-decays with E _α1 = 6288(5) keV, I _α1 = 56(2)% and E _α2 = 6486(5) keV, I _α2 = 44(2)% were observed. By observing prompt α-γ coincidences new information on the low-lying states in the daughter isotope ¹⁸¹Hg was obtained. Received: 7 February 2002 / Accepted: 19 February 2002     

Direct observation of exchange bias related uncompensated spins at the CoO/Cu interface

Magnetization-induced optical second harmonic generation (MSHG) from the exchange-biased CoO/Cu-(X)/Fe multilayer shows the presence of pinned uncompensated spins at the CoO/Cu interface. For increasing Cu spacer thickness, the exchange bias measured via the hysteresis loop shift diminishes and disappears at X = 3.5 nm, while the MSHG signal still shows a strong magnetic contribution from the CoO interface. This indicates that the magnetic interaction between Fe and CoO layers is sufficiently strong to induce order in the antiferromagnetic layer even at a spacer thickness for which there is no observable hysteresis loop shift.     

Extraction of singlet states from noninteracting high-dimensional spins

We present a scheme for the extraction of singlet states of two remote particles of arbitrary quantum spin number. The goal is achieved through post-selection of the state of interaction mediators sent in succession. A small number of iterations is sufficient to make the scheme effective. We propose two suitable experimental setups where the protocol can be implemented.     

Probing the mass degeneracy of particles with different spins

The spin is an important property of a particle. Although it is unlikely, there is still a possibility that two particles with di erent spins share similar masses. In this paper, we propose a method to probe this kind of mass degeneracy of particles with di erent spins. We use the cascade decay B⁺→X(3872)K⁺, X(3872)→D⁺D^- to illustrate our method. It can be seen that the possible mass degeneracy of X(3872) can lead to interesting behavior in the corresponding cascade decay.     

Sub-optical resolution of single spins using magnetic resonance imaging at room temperature in diamond

There has been much recent interest in extending the technique of magnetic resonance imaging (MRI) down to the level of single spins with sub-optical wavelength resolution. However, the signal to noise ratio for images of individual spins is usually low and this necessitates long acquisition times and low temperatures to achieve high resolution. An exception to this is the nitrogen-vacancy (NV) color center in diamond whose spin state can be detected optically at room temperature. Here we apply MRI to magnetically equivalent NV spins and demonstrate fully resolved spectra with resolution well below the optical wavelength of the readout light. In addition, using a microwave version of MRI we achieved a resolution that is 1/270 in size of the coplanar striplines, which define the effective wavelength of the microwaves that were used to excite the transition. This technique can eventually be extended to imaging of large numbers of NVs in a confocal spot and possibly to image nearby dark spins via their mutual magnetic interaction with the NV spin.     

Two magnetic impurities with arbitrary spins in open boundary t-J model

From the open boundary t-J model an impurity model is constructed in which magnetic impurities of arbitrary spins are coupled to the edges of the strongly correlated electron system. The boundary R matrices are given explicitly. The interaction parameters between magnetic impurities and electrons are related to the potentials of the impurities to preserve the integrability of the system. The Hamiltonian of the impurity model is diagonalized exactly. The integral equations of the ground state are derived and the ground state properties are discussed in detail. We discuss also the string solutions of the Bethe ansatz equations, which describe the bound states of the charges and spins. By minimizing the thermodynamic potential we get the thermodynamic Bethe ansatz equations. The finite size correction of the free energy contributed by the magnetic impurities is obtained explicitly. The properties of the system at some special limits are discussed and the boundary bound states are obtained.     

Stability of quantum spins in a magnetic field

Continuous representations of the dynamical group, and the corresponding generalized coherent states, are used to conjugate dynamics of a system of quantum spins to that of a classical Hamiltonian system. Stability of the Hamiltonian system obtained are studied, using linear stability analyses and results from the perturbation theory. Quantum evolution of any of the compound‐spins components is described exactly by classical Hamilton's equations. No semiclassical asymptotics in the analyses or explicit time‐dependence has been involved.     

Indirect magnetic exchange interaction mediated by bound Landau states in 2DES

The possibility of indirect exchange coupling mediated by Landau electrons bound to magnetic impurities in 2DES is studied here. The importance of the resonance scattering of the Landau electrons with the impurities is emphasized due to its spin selectivity which results in strong spin polarization of the localized Landau states. The bound Landau states act as mediators of the superexchange interaction resulting in an antiferromagnetic interaction between the nuclear spins of the impurities. The coupling constant, between these nuclear spins, J, is presented for the case of a weak scattering limit and found to depend strongly on the ratio of the impurity separation over the magnetic length. Possible applications of these results may include a long-range mechanism for coupling between two nuclear spins to be used as a qubits interaction with a spacing distance of the order of the magnetic length.     

Depth profile of uncompensated spins in an exchange bias system

We have used the unique spatial sensitivity of polarized neutron and soft x-ray beams in reflection geometry to measure the depth dependence of magnetization across the interface between a ferromagnet and an antiferromagnet. The net uncompensated magnetization near the interface responds to applied field, while uncompensated spins in the antiferromagnet bulk are pinned, thus providing a means to establish exchange bias.     

Modeling band spectra of compound crystals in the basis of states of their sublattices

A technique for simulation of band spectra of compound crystals in the basis of states of their sublattices is developed. The Hamiltonian of the crystal is written as a sum of sublattice Hamiltonians and a perturbation operator resulting from hybridization of the sublattice states. The simplest models are proposed to account for the sublattice hybridization. The methods for calculating the average crystal potential are discussed to represent the band spectra of sublattices in a common energy scale when calculating band structures by the pseudopotential method. The band spectra of MgO and MgS crystals are calculated to show the application of the methods under consideration. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 81–84, July, 2006.     

Hall crystal states at nu = 2 and moderate landau level mixing

The structure and orientational ordering of N2O molecules physisorbed on graphite (0001) is investigated applying x-ray, neutron, and low-energy electron diffraction techniques. Combining the results of the three techniques, we find that N2O forms a highly ordered, hexagonal, commensurate (sqrt[21]xsqrt[21])R10.89 degrees phase. The unit cell contains seven molecules which are arranged in a seven-sublattice pinwheel structure, unexpected for linear molecules on a hexagonal lattice. Potential energy calculations corroborate these results.     

Inversion of electron spins in CaO with the reversal of the magnetic field

We have obtained population inversion of a system of polarized (P=80%) electron spins in a solid during a very fast (dB _z dt=4·10⁵ T·s ^–1) reversal of the external magnetic field. The electrons were trapped at oxygen vacancies in CaO single crystals. This method, whch does not exploit any high frequency electromagnetic field, has been for the first time successfully used to achieve an inverted state of electron spins in a solid. The negative temperature of an electron spin ensembleT=–23 mK has been obtained.