Spin-vortex Superconductivity

Abstract

We present a theory of superconductivity based on the theoretical prediction that a macroscopic persistent current is generated by spin-vortices. It explains the origin of the phase variable θ that is canonical conjugate to the superfluid density as a Berry phase arising from the spin-vortex formation. This superconductivity does not require Cooperpairs as charge carriers, thus, is not directly related to the standard theory based on the BCS one; however, it exhibits the flux quantization in the unit Φ 0 = hc/2|e|, where h is Planck's constant, c the speed of light, and e the electron charge; and the AC Josephson frequency, f J = 2|e|V /h, where V is the voltage of the battery connected to the superconductor-insulator-superconductor junction. In due course, it is found that the standard derivation of the AC Josephson frequency misses a term arising from the flow of particles through the leads connected to the junction. If this contribution is included, the observed f J indicates that the phase θ is a variable conjugate to the number density of charge e carriers instead of the currently accepted charge 2e carriers. We propose an experiment that discriminates whether it is e or 2e. If the above claim is verified, it means that the BCS theory cannot predict whether a particular compound is a superconductor or not since it does not explain the origin of θ . A connection between the present mechanism and the BCS mechanism is discussed; the fact that the BCS theory gives an excellent estimate of T c is attributed to the fact that it predicts the temperature at which spin-vortices become long-lived due to the energy gap formation; since the stabilization by the electron-pair formation is compatible with the present mechanism, asymmetries observed in the H. Koizumi ( ) Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan e-mail: koizumi@ims.tsukuba.ac.jp even and odd number of electron systems are preserved. The most notable difference is that the persistent current generation is formulated in a strictly particle-number-conserving manner. Thus, it does not violate the superselection rule for the total charge.

Vortex state of topological superconductorCuxBi2Se3

“…However, the doping dependence of the superconducting phase resembles that of the cuprate superconductivity [2]; thus, it is suggested that the recently proposed superconductivity theory for the cuprate based on the spin-twisting itinerant motion of electrons may be relevant [7][8][9][10][11]. The spin-twisting itinerant motion of electrons is stabilized by the strong Rashba spin-orbit interaction in this system [11], and the doped coppers may become the stabilizing centers of the spin-vortices produced by the itinerant electrons.…”

“…It can be shown that the system with the above current density exhibits the flux quantum hc/2e and Josephson frequency 2eV / h (V is the voltage across the Josephson junction) [7,11]. In this mechanism, the superconductivity is connected to the appearance of points ∇ × (∇ψ) = 0, and positions of the doped coppers become such points.…”

“…Considering the similarity between Cu x Bi 2 Se 3 and the cuprate superconductor, the recently proposed superconductivity mechanism based on the spin-vortex formation may be relevant [7][8][9][10][11]. This mechanism will be realized if spin vortices are formed in the real space with the doped coppers as their cores.…”

Magnetic Excitation Spectra from Spin-Vortices and Spin-Vortex-Induced Loop Currents in Hole-Doped Cuprates

“…2,3) Recently, a theory of superconductivity, the spin-vortex superconductivity, is put forward as a theory that explains superconductivity in materials close to antiferromagnetic insulators. 4) In this theory, spin-vortices arise in the background antiferromagnetism, and stable loop currents are induced around the spin-vortices [spin-vortex-induced loop currents (SVILCs)]. [4][5][6][7] Since the existence of spin-vortices is indicated by the magnetic excitation spectrum obtained by neutron scattering experiments, [8][9][10] this theory may be relevant for superconductivity in hole-doped cuprate.…”

“…4) In this theory, spin-vortices arise in the background antiferromagnetism, and stable loop currents are induced around the spin-vortices [spin-vortex-induced loop currents (SVILCs)]. [4][5][6][7] Since the existence of spin-vortices is indicated by the magnetic excitation spectrum obtained by neutron scattering experiments, [8][9][10] this theory may be relevant for superconductivity in hole-doped cuprate. It is also noteworthy that the Kerr effect measurement 11) and the recently observed hidden magnetic excitation spectrum 12) indicate the presence of loop currents.…”