High spin states and pairing vibrations

The Generator-Coordinate-Method is applied to describe yrast-bands and excited vibrational bands of pairing-vibrational orβ-vibrational type in deformed rare earth nuclei. The model wave functions are supplied by the Pairing+Quadrupole-Model with angular momentum — and particle number projection. Results are shown for the nucleus¹⁷⁰Yb. The question if backbending may be produced by the intersection of the ground and the neutron pairing vibrational band is discussed.     

Chiral spin pairing in helical magnets

A concept of chiral spin pairing is introduced to describe a vector-chiral liquid-crystal order in frustrated spin systems. It is found that the chiral spin pairing is induced by the coupling to phonons through the Dzyaloshinskii-Moriya interaction and the four-spin exchange interaction of the Coulomb origin under the edge-sharing network of magnetic and ligand ions. This produces two successive second-order phase transitions upon cooling: an O(2) chiral spin nematic, i.e., spin cholesteric, order appears with an either parity, and then the O(2) symmetry is broken to yield a helical magnetic order. Possible candidate materials are also discussed as new multiferroic systems.     

Hole pairing induced by antiferromagnetic spin fluctuations

The effective interaction induced by antiferromagnetic spin fluctuations is considered in the random phase approximation in the context of the recently discovered highT _c oxide superconductors. This effective attraction favours a triplet pairing of holes. The implications of such pairing mechanism are discussed in connection with the current experimental observations.     

Signatures of spin pairing in chaotic quantum dots

Coulomb blockade resonances are measured in a GaAs quantum dot in which both shape deformations and interactions are small. The parametric evolution of the Coulomb blockade peaks shows a pronounced pair correlation in both position and amplitude, which is interpreted as spin pairing. As a consequence, the nearest-neighbor distribution of peak spacings can be well approximated by a modified bimodal Wigner surmise, in which interactions are taken into account beyond the constant interaction model.     

Quantum computing for the Lipkin model with unitary coupled cluster and structure learning ansatz

We report a benchmark calculation for the Lipkin model in nuclear physics with a variational quantum eigensolver in quantum computing. Special attention is paid to the unitary coupled cluster (UCC) ansatz and structure learning (SL) ansatz for the trial wave function. Calculations with both the UCC and SL ansatz can reproduce the ground-state energy well; however, it is found that the calculation with the SL ansatz performs better than that with the UCC ansatz, and the SL ansatz has even fewer quantum gates than the UCC ansatz.     

Correlations and spin susceptibility of lowst-energy Cooper pairing in an antiferromagnet

Lowest-energy Cooper pairing of electron eigenfunctions in an antiferromagnetic metal is transformed to $\text{k}$-wave or nonmagnetic-Bloch-function space, where the pairing is resolved into wave-vector and spin components. The spin susceptibility is calculated using an eight-component field in Bloch function space.     

Dynamical mean-field theory for pairing and spin gap in the attractive hubbard model

We solve the attractive Hubbard model for arbitrary interaction strengths within dynamical mean-field theory. We compute the transition temperature for superconductivity and analyze electron pairing in the normal phase. The normal state is a Fermi liquid at weak coupling and a non-Fermi-liquid state with a spin gap at strong coupling. Away from half filling, the quasiparticle weight vanishes discontinuously at the transition between the two normal states.     

Model construction and pairing symmetry for the iron-based oxypnictides

PC-19-INV: In order to clarify the mechanism of superconductivity in the iron-based compound recently discovered by Hosono’s group, we have first constructed a tight-binding model in terms of the maximally localized Wannier orbitals from a first-principles electronic structure calculation. The model has turned out to involve all the five Fe 3d bands. This is used to calculate the spin and charge susceptibilities with the five-band random-phase approximation, which are then plugged into the linearised Eliashberg equation. For a doped system we obtain an unconventional s-wave pairing with sign-reversing gap functions. To be more precise, the gap function is a 5×5 matrix, for which the diagonal elements mainly comprise d_x²-y² and d_yz,d_xz orbital components. The strong dependence of the gap between different orbitals may be observed experimentally.     

Muon spin relaxation and isotropic pairing in superconducting PrOs4Sb12

Transverse-field muon-spin rotation measurements in the vortex-lattice of the heavy-fermion (HF) superconductor PrOs4Sb12 yield a temperature dependence of the magnetic penetration depth lambda indicative of an isotropic or nearly isotropic energy gap. This is not seen to date in any other HF superconductor and is a signature of isotropic pairing symmetry, possibly related to a novel nonmagnetic "quadrupolar Kondo" HF mechanism in PrOs4Sb12. The T=0 relaxation rate sigma(s)(0)=0.91(1) micros(-1) yields an estimated magnetic penetration depth lambda(0)=3440(20) A, which is considerably shorter than in other HF superconductors.     

Models of the proton spin structure

A phenomenological model of spin sharing by the constituents of a proton is constructed, based on the recent EMC measurement of the spin dependent structure function and knowledge of the unpolarized parton densities.     

Nucleon spin structure

The present status of the spin of the nucleon is reviewed. The focus will be on inclusive double-spin asymmetry measurements in electron-nucleon (³He) scattering. Recent results from Jefferson Lab will be presented as well as their impact on the transition regime between hadronic and partonic degrees of freedom in the nucleon spin structure.     

The spin structure of the nucleon

An introduction to deep inelastic scattering experiments investigating the spin structure of the proton and the neutron is given. Discussed are measurements with longitudinally polarized targets to determine the spin structure functiong ₁ and sum rules and to do pQCD analyses with inclusive data, while a flavour separation and first extractions of the gluon polarization are performed with semi-inclusive data.     

Distribution of pairing functions in superconducting spin valve SF1F2

The distribution of the spin-singlet component, the short-range spin-triplet component with zero projection, and the long-range spin-triplet component with projection ±1 of the superconducting pairing function has been obtained for different regimes of switching of a spin valve with a three-layer heterostructure (superconductor/ferromagnet/ferromagnet). The distribution of the components is discussed as the main reason for the behavior of the superconducting transition temperature as a function of the angle between the magnetic moments of the ferromagnetic layers in these regimes.     

Intralayer and Interlayer Couplings in the Soliton pairing Model of Superconductivity

Explicit expressions and results for T_c(n) of the layer compounds of Bi and T1 are obtained within the generalized soliton pairing framework, in which T_c, is raised by the cooperation l i of the two couplings, intralayer and interlayer. The calculated values are in good agreement I with the observed T_c's. The maximum possible T_c(∞) is predicted at≈ 200 K.     

Results on the nucleon spin structure

SMC performed an investigation of the spin structure of the nucleon by measuring deep inelastic scattering of polarised mouns off polarised protons and deuterons: Asymmetries and spin structure functions were obtained for x>0.0008 and Q ²>0.2 GeV². Using a next-to-leading order QCD analysis of all experimental results polarised parton distributions and their first moments were determined. All data show a clear violation of the Ellis-Jaffe sum rule. The Bjorken sum rule is found to be valid and is tested to the 10% level.     

Influence of shell structure and pairing correlations on the nuclear state density

A microscopic calculation of nuclear state densities was performed starting from realistic single-particle levels. Within this concept, a correspondence between microscopic ground state energy corrections and microscopic effects on state densities was deduced. It is shown that the approximations introduced by a simple analytical expression for the nuclear state density are comparable to the uncertainties of microscopically calculated state densities for nuclei in their ground state configuration. Guidelines for the determination of the parameters of this analytical expression were deduced from the microscopic computations.