Can η mesons have a magnetic moment?

The response of pseudoscalar and vector mesons to strong magnetic fields is studied within a simple constituent quark model using analogy with bound states of Positronium. Magnetic moments of charged vector mesons K*, D*, B* are predicted and it is found that η mesons have magnetic polarizability. In extremely strong magnetic fields, behaviour of J/Ψ mesons is discussed. We speculate on the existence of an induced magnetic moment of η meson.     

Search for the neutrino magnetic moment in the elastic νe scattering

The possibility of detecting the anomalous neutrino magnetic moment from comparison of the “electromagnetic” and “electroweak” contributions to the differential and total cross sections of neutrino-electron scattering is considered. The results of quantitative analysis and a graphical image of the cross sections are presented for the case of scattering of beryllium solar neutrinos by an electronic target.     

Localized 5f electrons in superconducting PuCoIn?: consequences for superconductivity in PuCoGa?

The physical properties of the first In analog of the PuMGa(5) (M = Co, Rh) family of superconductors, PuCoIn(5), are reported. With its unit cell volume being 28% larger than that of PuCoGa(5), the characteristic spin-fluctuation energy scale of PuCoIn(5) is three to four times smaller than that of PuCoGa(5), which suggests that the Pu 5f electrons are in a more localized state relative to PuCoGa(5). This raises the possibility that the high superconducting transition temperature T(c) = 18.5 K of PuCoGa(5) stems from the proximity to a valence instability, while the superconductivity at T(c) = 2.5 K of PuCoIn(5) is mediated by antiferromagnetic spin fluctuations associated with a quantum critical point.     

Observation of Cooper pairs in high-temperature superconductors by 67Cu(67Zn) Mössbauer spectroscopy

A Mössbauer emission spectroscopy study on the ⁶⁷Cu(⁶⁷Zn) isotope showed that the superconducting transition in the Nd_1.85Ce_0.15CuO₄, La_1.85Sr_0.15CuO₄, and Tl₂Ba₂CaCu₂O₈ compounds is accompanied by an electron density redistribution in the crystal, which is considered evidence of Cooper-pair Bose condensation.     

Coboson formalism for Cooper pairs and its application to Richardson’s equations

We propose a many-body formalism for Cooper pairs which has similarities to the one we recently developed for composite boson excitons (coboson in short). Its Shiva diagram representation evidences that N Cooper pairs differ from N single pairs through electron exchange only: no direct coupling exists due to the very peculiar form of the reduced BCS potential. As a first application, we here use this formalism to derive Richardson’s equations for the exact eigenstates of N Cooper pairs. This derivation gives hints on why the N(N-1)N(N-1) dependence of the N-pair ground state energy we recently obtained by solving Richardson’s equations analytically in the low density limit, stays valid up to the dense regime. No higher order dependence exists under large overlap, a surprising result hard to accept at first. We also briefly question the BCS wave function ansatz compared to Richardson’s exact form, in the light of our understanding of coboson many-body effects.     

High-temperature superconductivity in transition metal oxypnictides: A rare-earth puzzle?

Extensive ab initio LDA and LSDA + U calculations of an electronic structure of newly discovered high-temperature superconducting series ReO_{1 − x} F _x FeAs (Re = La, Ce, Pr, Nd, and Sm and the hypothetical case of Re = Y) have been performed. In all cases, almost identical electronic spectrum (both energy dispersions and the densities of states) has been obtained in a rather wide energy interval (about 2 eV) around the Fermi level. This fact is unlikely to be changed by strong correlations. This leads inevitably to the same critical temperature T _c of a superconducting transition in any theoretical BCS-like mechanism of the Cooper pair formation. The experimentally observed variations of the T _c for different rare-earth substitutions are either due to the disorder effects or less probably because of possible changes in the spin-fluctuation spectrum of FeAs layers caused by magnetic interactions with rare-earth spins in ReO layers. The text was submitted by the authors in English.     

Highly conductive polymers: superconductivity in nanochannels or an experimental artifact?

There is a significant body of literature concerning the potential formation of electrically conductive moieties in polymeric materials. The conductive path is not associated with conjugation (such as in the case of ‘conductive polymers’) but rather associated with a new conductivity route. The objective of the experiments reported herein was to provide insight into the phenomenon of unusually high electrical conductivity in polymers that have been reported by several research groups. In some experiments, the test apparatus did indeed indicate high levels of conductance. Arguments pro and con for high conductivity based on known physical phenomena and the collected data were examined.     

Multiple bands: A key to high-temperature superconductivity in iron arsenides?

In the framework of four-band model of superconductivity in iron arsenides proposed by Barzykin and Gor’kov we analyze the gap ratios on hole—like and electron—like Fermi—surface cylinders. It is shown that experimentally observed (ARPES) gap ratios can be obtained only within rather strict limits on the values of pairing coupling constants. The difference of T _c values in 1111 and 122 systems is reasonably explained by the relative values of partial densities of states. The multiple bands electronic structure of these systems leads to a significant enhancement of effective pairing coupling constant determining T _c , so that high enough T _c values can be achieved even for the case of rather small intraband and interband pairing interactions. The article is published in the original.     

Singlet—triplet oscillations of spin-correlated radical pairs due to the Larmor precession in low magnetic fields

Singlet—triplet oscillations in spin-correlated radical pairs have been studied at magnetic field strengths low for one radical and high for the other. Oscillations with frequencies close to the Larmor frequency ω₀ of electron spin precession have been predicted under these conditions. Both numerical and exact analytical solutions in arbitrary magnetic fields are presented for three cases of hyperfine couplings in wide-spectrum radical. For the case of unresolved spectrum, singlet—triplet evolution was found to contain a single oscillating term with frequency ω₀. In the case of one spin-I magnetic nucleus, there are two low frequency oscillating terms with frequencies ω_? = ω₀ ? ω₀/(2I + 1) and ω₊ = ω₀ + ω₀/(2I + 1), the amplitude of the first term being larger than that of the second. The case of a number of equivalent protons also has been analysed as a superposition of one-nucleus oscillations. The predicted oscillations were observed in a time resolved magnetic field effect for several radical ion pairs produced by X-ray irradiation of alkane solutions with charge acceptors. For pairs (p-terphenyl-d ₁₄)^?./(isooctane)^+. and (p-terphenyl-d ₁₄)^?./(2,4-dimethylpentane)^+. the oscillation frequency in a field B ₀ of 0.5–4mT is about 20% lower than ω₀. Oscillations were observed also in pairs with equivalent nuclei: (p-terphenyl-d ₁₄)^+./(C₆F₆)^?. and (p-terphenyl-d ₁₄)^?./(hexamethylethane)^+.     

W-induced anomalous magnetic moment of leptons,calculated with ξ-limiting formalism

The influence on the anomalous magnetic moment of leptons of a charged intermediate vectorboson, mediating weak interactions is discussed, using theξ-limiting formalism ofLee andYang.     

Nuclear magnetic moment of 12 d 11/2− 131mXe

NMR-ON measurements were performed on^131mXe (I=11/2^–; T_1/2=12.0 d) in Fe, the sample being prepared by recoil implantation after the¹³⁰Te(,3n)^131mXe compound reaction at E=40 Mev. The hyperfine splitting _NB_HF/h¦, extrapolated to zero external magnetic field, was found to be 209.9(1) MHz. Taking B_HF=+1523(8) kG for the hyperfine field of XeFe, the magnetic moment of^131mXe is deduced to be (–)0.994(5) _N. As a byproduct, the zero-field hyperfine splitting of^129mXe (I=11/2^–; T_1/2=8.9d) in Fe was measured as 188.1(1) MHz, with which a magnetic moment of (–)0.891(5) _N is deduced for^129mXe.     

Hidden quasi-one-dimensional superconductivity in Sr₂RuO₄

We show that the interplay between spin and charge fluctuations in Sr?RuO? leads unequivocally to triplet pairing which has a hidden quasi-one-dimensional character. The resulting superconducting state spontaneously breaks time-reversal symmetry and is of the form Δ ~(p(x)+ip(y))z(^) with sharp gap minima and a d vector that is only weakly pinned. The superconductor lacks robust chiral Majorana fermion modes along the boundary. The absence of topologically protected edge modes could explain the surprising absence of experimentally detectable edge currents in this system.     

Novel superconducting semiconducting superlattices: dislocation-induced superconductivity?

Novel superconducting superlattices with transition temperature in the range 2.5-6.4 K consisting only of semiconducting materials are discovered. Among them there are multilayers, including a wide-gap semiconductor as one of the components. It is shown that superconductivity is connected with the interfaces between two semiconductors containing regular grids of the misfit dislocations. The possibility of the dislocation-induced superconductivity is discussed.     

What is spin-magnetic moment of electron?

We investigate the problem about what the spin-magnetic moment is. The magnetic moment of the Dirac electron in the frame along z-axis is evaluated. This is identified with the spin-magnetic moment of the electron, because there is not any z-component of magnetic moment caused by orbital angular momentum in our frame. The correct value of the spin-magnetic moment and the correct ratio of the spin-magnetic moment to the spin (i.e. g=2) are obtained explicitly. In deriving them, the negative energy solutions of the Dirac equation perform essential roles. We find that the transition current from a positive energy state to a negative energy state causes spin-magnetic moment of the electrons in vacuum. This fact implies that the ratio of the spin-magnetic moment to the spin may change depending on the environments. For example, it may have different values in materials.