Showing papers on "Spin-½ published in 1981"
TL;DR: In this paper, it was shown that the spin of a spin wave in the Heisenberg antiferromagnetic chain of spins 1 2 is equal to 1 2 rather than 1 as is generally considered to be true.
542 citations
TL;DR: In this paper, a new set of parameters for skyrme interactions have been determined, including the compression modulus, spin and spin-isospin Landau parameters, and pairing matrix elements.
412 citations
TL;DR: In this paper, the Schrodinger functional differential operator is shown to exist in renormalizable quantum field theory to all orders in the perturbation expansion, including spin-1 2 fermions, and the Casimir potential for disjoint surfaces is computed for a pair of parallel plates to first order in massless φν4.
401 citations
TL;DR: In this paper, the spin-spin relaxation time T2 for an S spin dipolar coupled to an unlike I spin under conditions of random isotropic rotational motion and I spin rf decoupling is calculated.
Abstract: The spin–spin relaxation time T2 for an S spin dipolar coupled to an unlike I spin under conditions of random isotropic rotational motion and I spin rf decoupling is calculated. The results of the analysis form the basis for a method to detect and analyze rotational motions in solids. The technique is sensitive to motions which occur on the time scale of the rotating‐frame Larmor frequency of the applied rf field and is presented in the context of a variable temperature magic‐angle sample‐spinning experiment where the S spins are observed and the I spins are decoupled. The previously well characterized molecules hexamethylbenzene, hexamethylethane, and adamantane are studied (S=13C and I=1H), and the resulting motional parameters are found to be in good agreement with previous results. As well, the theoretically predicted dependence of T2 on the strength of the decoupling field is experimentally borne out. Finally, the question of resolution of heteronuclear coupled spin systems and the role of decoupling...
335 citations
301 citations
TL;DR: In this paper, the spin-flavor-rotation effect of massive Majorana neutrinos is discussed. And the parametrization and calculation of the electromagnetic form factors of Majorana Neutrinos are discussed.
Abstract: It is stressed that if neutrinos are massive they are probably of "Majorana" type. This implies that their magnetic-moment form factor vanishes identically so that the previously discussed phenomenon of spin rotation in a magnetic field would not appear to take place. We point out that Majorana neutrinos can, however, have transition moments. This enables an inhomogeneous magnetic field to rotate both spin and "flavor" of a neutrino. In this case the spin rotation changes particle to antiparticle. The spin-flavor-rotation effect is worked out in detail. We also discuss the parametrization and calculation of the electromagnetic form factors of Majorana neutrinos. Our discussion takes into account the somewhat unusual quantum theory of massive Majorana particles.
249 citations
TL;DR: In this article, the effects of Zeeman splitting and spin-orbit scattering on the resistance in two-dimensional disordered systems are theoretically studied. And the field dependence of the magnetoresistance is shown to have the characteristic anisotropy.
Abstract: Effects of Zeeman splitting and spin-orbit scattering on the resistance in two-dimensional disordered systems are theoretically studied. The field dependence of the magnetoresistance is shown to have the characteristic anisotropy. The present theory explains the qualitative features of the experimental observations by Komori et al. in Cu granular films.
237 citations
TL;DR: In this article, the density matrix formalism with the Magnus expansion of the time evolution operator is used to study the nmr response in a pulsed magnetic field gradient (mfg) spin-echo experiment.
Abstract: The density matrix formalism with the Magnus expansion of the time evolution operator is used to study the nmr response in a pulsed magnetic field gradient (mfg) spin-echo experiment. The results show that the spin-echo cannot only measure the self-diffusion coefficient but can determine the spectrum of the single-particle velocity autocorrelation function as well. The proper combination of rf and mfg pulse sequences are proposed for measuring self-diffusion in spin systems with strong dipolar coupling where the classical method fails.
139 citations
TL;DR: In this article, the spinor symmetries of the interacting boson-fermion model were discussed and closed expressions for energies, electromagnetic (EO, M1, E2) transition rates, static moments and (one and two) nucleon transfer reaction intensities were derived.
83 citations
01 May 1981
TL;DR: In this paper, the authors give a solution of a more general question, namely, the question of interpreting the intersection of two quadrics modulo IISO (n~) when the 2~'s are allowed to have multiplicities n~.
Abstract: Let 2: x[ = 0, 2; 21x[ = 0 be two quadrics in the projective space of dimension (2g q1). Assume that 2~'s are distinct so that these two quadrics determine a generic pencil of quadrios. One cart associate to this pencil, in a natural way, a hyperelliptic curve X of genus g, namely, the double of the projective line parametrising the pencil with ramification at the points corresponding to the singular quadrics. One can easily check that the variety M~ of d dimensional vector subspaces which are isotropic for both the quadrics is nonsingular. M~ is nonempty i f d ~ g and in [1] we gave an interpretation of M o and Mo_l as the Jacobian and the moduli space of vector bundles of rank 2 and fixed determinant of odd degree over X respectively. One might naturally ask if one could obtain similar interpretation for M~ for other d as well. In particular, does M1 ----the intersection of two quadrics have an interpretation as a moduli-space of some sort of bundles over X? This paper answers, among other things, this question. In fact, ~'e give a solution of a more general question, namely, the question of interpreting M~ modulo IISO (n~), when the 2~'s are allowed to have multiplicities n~. The idea of associating a hyperelliptio curve to a pencil of quadrics is nothing new and goes back, at least to Weil [9], who considered the relationship between the intersection of two quadrics (M1 in our notation) and the curve X from the point of view of diophantine equations over finite fields. He computed the zeta function of M1 in terms of that of X and verified the Weil conjectures for this variety. Incidentally he also raised the specific question of the geometrig relationship between M~ and X, which we have investigated here. It must also be mentioned that Gauthier [2] has already noticed the identity of the space M o and the Jacobian of X, although as far as the present author is aware, no proof has been published till recently [6, 1]. The author is thankful to A. Weil for bringing to his attention these references. The method of proof is quite simple and is not basically different from that in [1 ]. However, the greater generality leads to conceptual clarity and we have also made a few techrtical simplifications. I f E is a bundle to which the action of i lifts, the bundle does not nevertheless go down to a bundle on X/i = 1 m. The obstruction to this is the lack of descent data at the fixed points of i, namely, the
80 citations
TL;DR: In this paper, the effects of mutual interactions on conductivity, magnetoresistance and spin-susceptibility have been examined in the weakly localized regime of two-dimensional disordered systems.
Abstract: Effects of mutual interactions on conductivity, magnetoresistance and spin-susceptibility have been examined in the weakly localized regime of two-dimensional disordered systems. Both conductivity and spin-susceptibility have logarithmic correction with respect to temperature. Field dependence of the magnetoresistance, which can be appreciably different from that due to impurity scattering alone, is shown to be sensitive to temperature.
TL;DR: In this article, the density of relaxation times of the spin system was investigated and it was shown that the logarithmic frequency dependence of the freezing temperature observed in low frequency ac susceptibility measurements follows naturally from a uniform density of relaxations at these frequencies.
TL;DR: In this article, it was shown how both qualitative and quantitative features of the asymptotic freedom of quantum chromodynamics can be understood in a rather intuitive way, starting from the spin of the gluon, which makes the vacuum behave like a paramagnetic substance.
Abstract: It is shown how both the qualitative and the quantitative features of the asymptotic freedom of quantum chromodynamics can be understood in a rather intuitive way. The starting point is the spin of the gluon, which because of the gluon self‐coupling makes the vacuum behave like a paramagnetic substance. Combining this result with Lorentz invariance, we conclude that the vacuum exhibits dielectric antiscreening and hence asymptotic freedom. The calculational techniques are with some minor modifications those of the Landau theory on the diamagnetic properties of a free‐electron gas.
TL;DR: In this paper, a comprehensive experimental and theoretical study of the inelastic scattering in the one-dimensional near-Heisenberg antiferromagnet (CD/sub 3/)/sub 4/N MnCl/sub3/ (TMMC) at low temperatures, 0.3 < or =T< or =2.5 K, was carried out.
Abstract: We have carried out a comprehensive experimental and theoretical study of the inelastic scattering in the one-dimensional near-Heisenberg antiferromagnet (CD/sub 3/)/sub 4/N MnCl/sub 3/ (TMMC) at low temperatures, 0.3< or =T< or =2.5 K, in magnetic fields varying between 0 and 70 kOe; the field is applied perpendicular to the chain axis. In zero field at long wavelengths we observe two sets of excitations, a low-energy acoustic branch corresponding to spin motion within the dipolar determined easy plane and a high-energy optical branch corresponding to oscillations out of the plane. For magnetic fields greater than 30 kOe and Tapprox. =2 K we observe as many as four distinct excitations: the two one-magnon modes plus two sharp excitations at higher energies. Our theoretical analysis suggests that the two higher-energy modes correspond to two-magnon processes in the longitudinal response function. The theory, which is done within the harmonic approximation expanding out to fourth order in the magnon operators, gives a good qualitative description of the data but underestimates the two-magnon intensities by a factor of 2 or 3. We also observe a marked anticrossing of the one- and two-magnon branches; this latter result shows that anharmonic effects are quite important in themore » spin dynamics. Finally at T = 0.3 K and zero field we observe a gap of 0.1 meV in the acoustic spin-wave dispersion relation due to a very small in-plane anisotropy field of 71 x 30 Oe.« less
TL;DR: In this paper, the finite-temperature HFB cranking equations were solved for the two-level model and the pair gap, moment of inertia and internal energy were determined as functions of spin and temperature.
TL;DR: In this paper, lower spin systems 0, 1 and 1 2 are characterized by the interchange of rank of potentials and field strengths with respect to ordinary gauge theories and a self-coupled supersymmetric theory of this type is also constructed.
TL;DR: In this article, a mean field theory of spin-density-wave wave vector and polarisation vector rotation induced by the application of a magnetic field to MnSi in its spin density-wave phase, and a prediction of the associated spin reorientation phase transitions, is presented.
Abstract: A mean-field theory of spin-density-wave wavevector and polarisation vector rotation induced by the application of a magnetic field to MnSi in its spin-density-wave phase, and a prediction of the associated spin reorientation phase transitions, is presented. The dependences of the Neel temperature and the homogeneous magnetisation on applied magnetic field strength and orientation are studied, as is the staggered susceptibility which diverges at the spin orientation phase transition.
TL;DR: In this paper, a theory of the magnetic dipolar interaction of two electrostatically coupled carbene triplet states is presented. But the results of this theory are compared with the E.S.R. data of the quintet states observed during low temperature photopolymerization of diacetylene single crystals.
Abstract: We present a theory of the magnetic dipolar interaction of two electrostatically coupled carbene triplet states. Using a model spin hamiltonian of a bicarbene system the spin functions and energy eigenvalues of the singlet (S = 0), triplet (S = 1), quintet (S = 2) and mixed singlet-quintet spin pair states are calculated. The resulting zero field and high field E.S.R. spectra are sensitively dependent on the energy separation ΔeSQ resulting from different electronic configurations of the same symmetry between the individual total singlet and quintet spin pair states. The results of this theory are compared with the E.S.R. data of the quintet states observed during low temperature photopolymerization of diacetylene single crystals.
TL;DR: In this article, the relative stability between the ferromagnetic state (FMS) and the helical spin density wave (HSDW) is discussed phenomenologically, and the arguments are made to the spin systems of which the spin structures are described by the spin density S ( r ) varying slowly with the position r and the SEI is favorable to the FMS.
Abstract: For the spin systems with both the symmetric exchange interaction (SEI) and the antisymmetric exchange interaction (AEI) (the Dzyaloshinsky-Moriya interaction), the relative stability between the ferromagnetic state (FMS) and the helical spin density wave (HSDW) is discussed phenomenologically. The arguments are made to the spin systems of which the spin structures are described by the spin density S ( r ) varying slowly with the position r and the SEI is favorable to the FMS. For the 21 types of crystal symmetry with the isogonal point groups having no inversion symmetry, the characteristics of the instability of the FMS are investigated. By use of the Landau free energy obtained for crystals with the isogonal point groups T and O , the magnetization process, the magnetic phase diagram, and the intensity of the neutron diffuse scattering are calculated. A comparison between the calculated results and the experiments on MnSi is also given.
TL;DR: In this paper, the spin and charge susceptibilities of an intermediate-valence system fluctuating between two magnetic configurations were calculated and shown to be connected with the energy of charge fluctuations.
Abstract: We calculate the spin and charge dynamical susceptibilities of an intermediate-valence system fluctuating between two magnetic configurations. Our results can explain the most important features of the neutron-scattering spectra of TmSe. We show that the energy of the inelastic peak found experimentally is connected with the energy of charge fluctuations.
TL;DR: In this paper, an exact solution of the s-d exchange model with arbitrary impurity spin S (Kondo problem) is proposed, and the magnetic susceptibility as a function of arbitrary magnetic field is calculated in explicit form.
TL;DR: In this article, the four-spin exchange interactions in fcc spin lattice are investigated for the purpose of understanding anomalous magnetic properties of NiS 2 with pyrite structure.
Abstract: Four-spin exchange interactions in fcc spin lattice are investigated for the purpose of understanding anomalous magnetic properties of NiS 2 with pyrite structure. It is shown that a phase transition is possible from the ordered phase with the first-kind spin ordering to the other ordered phase in which the second-kind ordering coexists with the first-kind ordering. Furthermore, this low temperature phase is expected also to have weak ferromagnetism induced by crystal-line anisotropy.
TL;DR: In this article, the effects of spin fluctuations on the paramagnetic spin susceptibility, magnetization and specific heat are calculated in gaussian statistics as a power series of k B T, and the results are applied to nickel and iron.
TL;DR: In this paper, the mean-field approximation for a large class of one-component models with arbitrary ferromagnetic pair interactions was shown to give an upper bound on the magnetization for discrete and continuous spin Ising models.
Abstract: The mean-field approximation is shown to give an upper bound on the magnetization for a large class of one-component models with arbitrary ferromagnetic pair interactions. Specific examples include discrete and continuous spin Ising models. In addition, a new comparison inequality for multicomponent rotators is proven which allows this result to be extended to the plane rotator and classical Heisenberg ferromagnets.