7,417 research outputs found

    Spin Tunneling, Berry phases and Doped Antiferromagnets

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    Interference effects between Berry phase factors in spin tunneling systems have been discussed in recent Letters by Loss, DiVincenzo and Grinstein and von Delft and Henley. This Comment points out that Berry phases in spin tunneling are important in another interesting case: the two dimensional doped antiferromagnet. I show that the dispersion of a single hole in the t-J model changes sign as e2πse^{2\pi s} where ss is the size of the spins. This provides an interpretation of the numerical results for the s=\half model, and a prediction for other spin sizes.Comment: 5 pages, LaTe

    Coulomb corrections to superallowed beta decay in nuclei

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    Corrections to the superallowed beta decay matrix elements are evaluated in perturbation theory using the notion of the isovector monopole resonance. The calculation avoids the separation into different contributions and thus presents a consistent, systematic and more transparent approach. Explicit expressions for the Coulomb correction as a function of mass number A, are given.Comment: 10 page

    Nature of an intermediate non-Fermi liquid state in Ge-substituted YbRh2_{2}Si2_{2}: Fermionized skyrmions, Lifshitz transition, Skyrmion liquid, and Gruneisen ratio

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    We propose a skyrmion liquid state for the non-Fermi liquid (NFL) phase in Ge-substituted YbRh2_{2}Si2_{2}, where skyrmions form their Fermi surface, argued to result from the strongly coupled nature between skyrmions and itinerant electrons. The fermionized skyrmion theory identifies the antiferromagnetic (AF) transition with the Lifshitz transition, where the quantum critical point (QCP) is characterized by the dynamical critical exponent z=2z = 2. Nonlocal interactions between skyrmions allow a critical line above the AF QCP, which originates from the Kondo-coupling effect with itinerant electrons. This critical line is described by the skyrmion liquid state, which results in Landau damping for spin fluctuations, thus characterized by z=3z = 3. As a result, the Gruneisen ratio is predicted to change from T1\sim T^{-1} at the AF QCP to T2/3\sim T^{-2/3} in the NFL phase

    Electric charging of magnetic textures on the surface of a topological insulator

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    A three-dimensional topological insulator manifests gapless surface modes, described by two-dimensional Dirac equation. We study magnetic textures, such as domain walls and vortices, in a ferromagnetic thin film deposited on a three-dimensional topological insulator. It is shown that these textures can be electrically charged, ascribed to the proximity effect with the Dirac surface states. We derive a general relation between the electric and the magnetic charges. As a physical consequence, we discuss domain wall motion driven by an applied electric field, which promises magnetic devices with high thermal efficiency.Comment: 5 pages, 2 figure

    "Super-radiance" and the width of exotic baryons

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    It is suggested that the narrow width of the recently observed resonance Θ+(1540)\Theta^{+}(1540) with strangeness S=+1S=+1 could be a result of the super-radiance mechanism of the redistribution of the widths of overlapping resonances due to their coupling through common decay channels.Comment: This is an update of the original version submitted on October 08, 2003; it includes consideration of an additional model and one new figur

    Spin Chains with Periodic Array of Impurities

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    We investigate the spin chain model composed of periodic array of two kinds of spins S1S_1 and S2S_2, which allows us to study the spin chains with impurities as well as the alternating spin chains in a unified fashion. By using the Lieb-Shultz-Mattis theorem, we first study the model rigorously, and then by mapping it to the non-linear sigma model, we extensively investigate low-energy properties with particular emphasis on the competition between the massive and massless phases.Comment: 5 pages, revtex, To appear in PR