Odd Spin Research Articles

Quantum phase interference in nanomagnets with tetragonal symmetry

Employing a spin-coherent-state path integral method, we study the spin-parity dependence of the tunnel splitting in the uniaxial system with tetragonal symmetry. The tunnel splitting is found to vanish for magnetic particles with half integer or odd number spin. Applying an external magnetic field along the hard axis, we find that topological effect results in oscillation of the tunnel splitting, and present the relation between the quenching period and the ratio of two anisotropy constants of the nanomaget with any total spin including molecular magnets.

Mixed-parity superconductivity inSr2RuO4

We show that in Sr2RuO4 the Fermi surface geometry as inferred from angle resolved photoemission experiments has important implications for a pairing interaction dominated by incommensurate, strongly anisotropic, spin fluctuations. For a spin fluctuation spectrum consistent with inelastic neutron scattering experiments the system is close to an accidental degeneracy between even parity spin singlet and odd parity spin triplet channels. This opens the possibility of a mixed parity order parameter state in Sr2RuO4. We determine the stable and metastable order parameter phases at low temperatures and discuss especially phases with order parameter nodes.

Phonon-assisted tunneling in the quantum regime of Mn12 acetate

Longitudinal or transverse magnetic fields applied on a crystal of Mn12 acetate allows one to observe independent tunnel transitions between m = -S+p and m = S-n-p ( n = 6-10, p = 0-2 in longitudinal field and n = p = 0 in transverse field). We observe a smooth transition (in longitudinal) from coherent ground-state to thermally activated tunneling. Furthermore, two ground-state relaxation regimes show a crossover between quantum spin relaxation far from equilibrium and near equilibrium, when the environment destroys multimolecule correlations. Finally, we stress that the complete Hamiltonian of Mn12 should contain odd spin operators of low order.

Spin-dependent Coulomb blockade in a silicon-on-insulator-based single-electron transistor

We report low-temperature conductance measurement on a Coulomb-blockaded dot in a silicon-on-insulator-based single-electron transistor with in-plane side gates. The linear conductance for 4.2 K at zero magnetic field exhibits up to three paired peaks, indicating simple alternating odd (spin 1/2)-even(spin 0) filling. Three intrapair spacings are found to be nearly a constant value, corresponding to the single charging energy U, whereas two interpair spacings are different which are associated with U+ΔE1 and U+ΔE2, i.e., successive quantized level spacings added to U. The quantized level spacings were also revealed in the nonlinear current staircases.

The First Nonclassical Distonic Ion

The gaseous and ionized prototype carbonyl ylide, the distonic ion +CH2−O−CH2•, is found to transfer ionized methylene to 1-adamantylphosphaacetylene (1-Ad−C⋮P), a kinetically stabilized phosphaalkyne, thus forming the 1-adamantylphosphaacetylenium P-methylide ion, 1-Ad−C+P−CH2•, a novel phosphorus, and the first nonclassical distonic ion. The ion abstracts CH3S• from CH3SSCH3 and both Br• and C3H5• from allyl bromide, and this characteristic reactivity demonstrates its distonic character. MO calculations at the Becke3LYP/6-311G(d,p) and MCSCF [CAS(3,3)] levels confirm that 1-Ad−C+P−CH2• bears spatially separated charge and odd spin sites. They also reveal for the ion a phosphaallylic radical structure that stabilizes the radical site, and a σ-bridged structure with three-center two-electron bonds that stabilizes the charge site. This unique electronic structure characterizes 1-Ad−C+P−CH2• as the first nonclassical distonic ion.

Acyclic distonic acylium ions: dual free radical and acylium ion reactivity in a single molecule

Three gaseous acyclic distonic acylium ions: •CH 2–CH 2–C +O, •CH 2–CH 2–CH 2–C +O, and •CH 2C(CH 2)–C +O, are found to display dual free radical and acylium ion reactivity; with appropriate neutrals, they react selectively either as free radicals with inert charge sites, or (and more pronouncedly) as acylium ions with inert radical sites. The free radical reactivity of the ions is demonstrated via the Kenttämaa reaction: CH 3S • abstraction with the spin trap dimethyl disulfide; their ion reactivity by two reactions most characteristic of acylium ions: transacetalization with 2-methyl-1,3-dioxolane and the gas-phase Meerwein reaction, that is, expansion of the three-membered epoxide ring of epichlorohydrin to the five-membered 1,3-dioxolanylium ion ring. In “one-pot” reactions with gaseous mixtures of epichlorohydrin and dimethyl disulfide, the ions react selectively at either site, but more readily at the acylium charge site, to form the two mono-derivatized ions. Further reaction at either the remaining free radical or acylium charge site forms a single bi-derivatized ion as the final product. Becke3LYP/6-31G( d) calculations predict the reactions at the acylium charge sites of the three distonic ions to be highly exothermic, and both the “hot” transacetalization and epoxide ring expansion products of •CH 2–CH 2–CH 2–C +O to dissociate rapidly by H 2CCH 2 loss in overall exothermic processes. The calculations also predict highly spatially separate odd spin and charge sites for the novel cyclic distonic ketal ions formed by the reactions at the acylium charge sites.

Towards a supersymmetric classification of D–brane configurations with odd spin structure

We consider the construction of a general tree level amplitude for the interactions between dynamical D-branes where the configurations have non-zero odd spin structure. Using Riemann Theta Identities we map the conditions for the preservation of some supersymmetry to a set of integer matrices satisfying a simple but non-trivial equation. We also show how the regularization of the RR zero modes plays an important role in determining which configurations are permitted.

On a class of consistent linear higher spin equations on curved manifolds

We analyse a class of linear wave equations for odd half spin that have a well-posed initial value problem. We demonstrate consistency of the equations in curved space-times. They generalise the Weyl neutrino equation. We show that there exists an associated invariant exact set of spinor fields indicating that the characteristic initial value problem on a null cone is formally solvable, even for the system coupled to general relativity. We derive the general analytic solution in flat space by means of Fourier transforms. Finally, we present a twistor contour integral description for the general analytic solution and assemble a representation of the group O(4, 4) on the solution space.

Super-Liouville action for Regge surfaces

We compute the super-Liouville action for a two-dimensional Regge surface by exploiting the invariance of the theory under the superconformal group for sphere topology and under the supermodular group for torus topology. For sphere topology and torus topology with even spin structures, the action is completely fixed up to a term which in the continuum limit goes over to a topological invariant, while the overall normalization of the action can be taken from perturbation theory. For the odd spin structure on the torus, due to the presence of the fermionic supermodulus, the action is fixed up to a modular invariant quadratic polynomial in the fermionic zero-modes.

THE LORENTZ FORCE BETWEEN D0 AND D6 BRANES IN STRING AND M(ATRIX) THEORY

We use different techniques to analyze the system formed by a D0-brane and a D6- brane (with background gauge fields) in relative motion. In particular, using the closed string formalism of boosted boundary states, we show the presence of a term linear in the velocity, corresponding to the Lorentz force experienced by the D0-brane moving in the magnetic background produced by the D6-brane. This term, that was missed in previous analyses of this system, comes entirely from the R–R odd spin structure and is also reproduced by a M(atrix) theory calculation.

Electric and magnetic interaction of dyonic D-branes and odd spin structure

We present a general description of electromagnetic RR interactions between pairs of magnetically dual D-branes, focusing on the interaction of a magnetically charged brane with an electrically charged one. In the boundary state formalism, it turns out that while the electric-electric and/or magnetic-magnetic interaction corresponds to the usual RR even spin structure, the magnetic-electric interaction is described by the RR odd spin structure. As representative of the generic case of a dual pair of p and 6- p-branes, we discuss in detail the case of the self-dual 3-brane wrapped on a T 6/ Z 3 , which looks like an extremal dyonic black hole in four dimensions.

The Dimethylene Ketene Radical Cation

Molecular orbital calculations (at the Becke3LYP/6-31G(d) level of theory) indicate that the distonic ion •CH2C(CH2)CO+ is planar and has C2v symmetry. Most of the positive charge resides at the carbonyl carbon while the odd spin is delocalized over the allyl group. A similar spin distribution was calculated for the allyl radical. Hence, the reactivity of •CH2C(CH2)CO+ toward spin traps may be expected to resemble that of the neutral allyl radical. This issue was examined experimentally by using Fourier transform ion cyclotron resonance mass spectrometry. Similar to other carbon-centered free radicals, the gaseous •CH2C(CH2)CO+ abstracts H• from benzeneselenol, CH3Se• from dimethyl diselenide, and I• from allyl iodide. However, some of these reactions occur at efficiencies that suggest catalysis by the charged group. Further, the reaction of •CH2C(CH2)CO+ with dimethyl disulfide was found to proceed in an unprecedented manner. In addition to the expected formation of CH3SCH2C(CH2)CO+ and CH3S• (via CH3S• abstraction), a new distonic ion, CH3SCH•C(CH2)CO+, is generated. This ion is likely produced upon H• abstraction by CH3S• from CH3SCH2C(CH2)CO+ within the collision complex (net CH2S abstraction). The latter reaction has not been reported for distonic radical cations with localized radical sites. Hence, the reaction must be driven by the regeneration of the delocalized allylic radical. This proposal is supported by the observation of CH2S abstraction for the product ion CH3SCH•C(CH2)CO+ that also contains a delocalized radical site.

New aspects in the theory of ? electron systems on the basis of quantum statistical considerations

The electronic properties of π systems are studied under special consideration of the quantum statistical constraints experienced by a fermionic ensemble. In a many-electron basis of atomic occupation numbers these constraints decompose into a formal on-site constraint and a formal intersite constraint. The on-site constraint can be equated with the Pauli exclusion principle (PEP) while the intersite constraint can be equated with the Pauli antisymmetry principle (PAP). Under special molecular topologies the intersite constraints of fermion ensembles are suppressed. In this case the conventional fermionic statistics coincides with a mixed quantum statistics with fermionic on-site and bosonic intersite properties. Such a mixed statistics is realized in the π subspace of polyenes, (4n+2) Hückel annulenes (n=0, 1, 2,…) and the odd spin space of (2n+1) annulenes (n=1, 2, 3,…) if the π electron hoppings are restricted to nearest-neighbor centers. We discuss the topological conditions to conserve this statistical peculiarity at least approximately in two-dimensional (2D) π topologies. The quantities “aromaticity” and “antiaromaticity,” widely used in the chemical literature, are traced back to quantum statistical, topological, and molecular size considerations. The competition between the quantum constraints PEP and PAP, on the one hand, and the strength of the two-electron interaction in a given π Hamiltonian, on the other, is analyzed on the basis of Pariser–Parr–Pople (PPP), Hubbard (Hu), and simple Hückel molecular orbital (HMO) calculations. The influence of the PAP is reduced with increasing correlation strength while the influence of the PEP does not depend on this coupling parameter. The numerical results have been derived by Green's function quantum Monte Carlo (GF QMC) simulations. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 727–752, 1998

Axion production from gravitons off interacting 0-branes

We study axion-graviton scattering from a system of two D0-branes in a Type II superstring theory, a process which does not occur on a single brane. The two D0-branes interact via the exchange of closed string states which form a cylinder joining them. By compactifying on the Z 3 orbifold we find a non-vanishing amplitude coming from the odd spin structure sector, thus from the exchanged RR states. We compute, in particular, the leading term of the amplitude at large distance from the branes, which corresponds to taking a field theory limit. This seems to suggest that the process takes place through the coupling of an axion to the RR states exchanged between the 0-branes.

Bethe ansatz study for ground state of Fateev Zamolodchikov model

A Bethe ansatz study of a self-dual ZN spin lattice model, originally proposed by V. A. Fateev and A. B. Zamolodchikov, is undertaken. The connection of this model to the Chiral Potts model is established. Transcendental equations connecting the zeros of Fateev–Zamolodchikov transfer matrix are derived. The free energies for the ferromagnetic and the anti-ferromagnetic ground states are found for both even and odd spins.

Octupole vibrations and signature splitting in even mass Hg superdeformed bands

The octupole characteristics of excited SD bands in ${}^{190,192,194}$Hg are discussed. In particular we show that for ${}^{194}$Hg, the odd spin sequence is favored at lower spins---in agreement with the assumption these bands contain significant octupole character. The data are compared with a model in which $K$=2 octupole vibrations are predicted to be favored at the low frequencies.

High-spin spectroscopy near the deformed N ≈ Z ≈ 38 shell gap: The light Rb isotopes

Nuclei near the prolate single-particle energy gap at proton number Z = 38 ( ε 2 ≈ +0.38) and neutron number N ≈ Z offer unique possibilities to study the pn-interaction at large quadrupole deformation. In the yrast band of the Z = N = 37 nucleus 74Rb, we have identified a crossing of the T = 1 pn-paired band (even spins) with the T = 0 pn-unpaired band (odd spins). In 77Rb, the positive-parity yrast and yrare bands have been followed over large spin ranges and assigned different 1qp-proton 2qp-neutron structures. These band crossings do not follow the usual pattern of two identical particles aligning in high-j orbits. In addition, an aligned g 9 2 proton-neutron negative-parity sequence with K= 11 2 has been identified in 77Rb Rotational bands with more conventional band crossings have also been found.

The radical cation of trimethylphosphine oxide

The structure of the gaseous long-lived radical cation generated upon electron ionization of trimethylphosphine oxide, (CH 3) 3PO, has been investigated by using ion-molecule reactions in a Fourier transform ion cyclotron resonance mass spectrometer. A radical cation with the connectivity of trimethylphosphine oxide is expected to react by facile electron transfer with triethylamine, pyridine and dimethyl disulfide since all these reactions are highly exothermic. However, no electron transfer reactions were observed. Instead, the radical cation transfers a proton to triethylamine and to pyridine, i.e., acts as a Brønsted acid. Further, the radical cation abstracts CH 3S from dimethyl disulfide and hence demonstrates behavior characteristic of a distonic ion with a carbon radical center. This reactivity is unprecedented for a radical cation such as (CH 3) 3P +-O with the odd spin located at an oxygen atom. These experimental results indicate that the initially generated radical cation (CH 3) 3P +-O undergoes unimolecular isomerization to (CH 3) 2P +(OH)CH 2 within a millisecond time frame. Ab initio molecular orbital calculations carried out at the unrestricted second-order Møller-Plesset (UMP2/6-31G** + ZPVE) level of theory support this conclusion by predicting that (CH 3) 2P +(OH)CH 2 lies 23 kcal mol −1 lower in energy than (CH 3) 3P +-O. The energy barrier for unimolecular [1,3]-hydrogen atom migration in (CH 3) 3P +-O is estimated to be 24 kcal mol −1. This study demonstrates that the PO moiety provides a very strong driving force for hydrogen shifts in phosphorus containing radical cations.

New high-spin band structures in 184Hg.

The high-spin states in $^{184}\mathrm{Hg}$ have been investigated via the $^{154}\mathrm{Gd}$ ${(}^{32}$S,4n) reaction at a beam energy of 160 MeV, with an array of Compton suppressed Ge detectors in the Spin Spectrometer at HHIRF. The ground state oblate band and excited prolate band were extended to ${10}^{+}$ and ${26}^{+}$, respectively, and seven new bands are observed. A new band with odd spins, 13 to 25, has a much larger moment of inertia than the other bands in $^{184}\mathrm{Hg}$. Two of the new bands feed the prolate excited band and are interpreted as quadrupole vibrational bands. Also, two new signature partner bands are observed for which the configuration of \ensuremath{\nu}${\mathit{i}}_{13/2}$${\mathit{f}}_{7/2}$ is proposed. The similarity of the band with odd spins to the band with intermediate deformation (${\mathrm{\ensuremath{\beta}}}_{2}$\ensuremath{\sim}0.34) in $^{186}\mathrm{Hg}$, and signature partner bands to the bands observed in 104 isotones $^{180}\mathrm{Os}$ and $^{182}\mathrm{Pt}$, is discussed.

Spin catalysis: three-spin model

Recently it has been shown that in a radical triad one of the radical partners affects the chemical reactivity of the other pair, catalyzing the spin transformation of this pair. The phenomenon is shown to be caused by the exchange interaction between the radical triad partners which stimulates doublet-doublet spin evolution and produces the oscillating triplet-singlet spin conversion of the selected radical pair in the radical triad under the influence of the odd radical spin. The theory of the phenomenon is developed and the equations for the rate of spin evolution in a three-spin system are derived. A new type of quantum beats is predicted.