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Register a new userNovel vortex structures in the three-dimensional superconductor under the helical magnetic field from the chiral helimagnet
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We have investigated vortex structures in three-dimensional superconductors under a helical magnetic field from a chiral helimagnet numerically. In order to obtain vortex structures, we solve three-dimensional Ginzburg-Landau equations with the finite element method. The distribution of the helical magnetic field is assumed to be proportional to the distribution of the magnetic moments in the chiral helimagnet. Then, the magnetic field is the same direction in the yz-plane and helical rotation along the helical axis. Under this helical magnetic field, vortices appear to be perpendicular to the surface of the superconductor. But we have found that there are tilted vortices toward the helical axis, although there is no component of the magnetic field along the helical axis. This vortex structure depends on the chirality of the distribution of the helical magnetic field.
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We have investigated vortex states in two-dimensional superconductors under a oscillating magnetic field from a chiral helimagnet. We have solved the two-dimensional Ginzburg-Landau equations with finite element method. We have found that when the magnetic field from the chiral helimagnet increases, vortices appear all at once in all periodic regions. This transition is different from that under the uniform magnetic field. Under the composite magnetic field with the oscillating and uniform fields (down-vortices), vortices antiparallel to the uniform magnetic field disappear. Then, the small uniform magnetic field easily remove down-vortices.
The site-selective nuclear spin-lattice relaxation rate T1^{-1} is theoretically studied inside a vortex core in a chiral p-wave superconductor within the framework of the quasiclassical theory of superconductivity. It is found that T1^{-1} at the vortex center depends on the sense of the chirality relative to the sense of the magnetic field. Our numerical result shows a characteristic difference in T1^{-1} between the two chiral states, k_x + i k_y and k_x - i k_y under the magnetic field.
The zero temperature phase diagram of the mono-axial chiral helimagnet in the magnetic field plane formed by the components parallel and perpendicular to the helical axis is thoroughly analyzed. The nature of the transition to the commensurate state depends on the angle between the field and the helical axis. For field directions close to the directions parallel or perpendicular to the helical axis the transition is continuous, while for intermediate angles the transition is discontinuous and the incommensurate and commensurate states coexist on the transition line. The continuous and discontinuous transition lines are separated by two tricritical points with specific singular behaviour. The location of the continuous and discontinuous lines and of the tricritical points depend strongly on the easy-plane anisotropy, the effect of which is analyzed. For large anisotropy the conical approximation locates the transition line very accurately, although it does not predict the continuous transitions nor the tricitical behaviour. It is shown that for large anisotropy, as in CrNb3S6, the form of the transition line is universal, that is, independent of the sample, and obeys a simple equation. The position of the tricritical points, which is not universal, is theoretically estimated for a sample of CrNb3S6
In discussing the phase transition of the three-dimensional complex |psi|^4 theory, we study the geometrically defined vortex-loop network as well as the magnetic properties of the system in the vicinity of the critical point. Using high-precision Monte Carlo techniques we investigate if both of them exhibit the same critical behavior leading to the same critical exponents and hence to a consistent description of the phase transition. Different percolation observables are taken into account and compared with each other. We find that different connectivity definitions for constructing the vortex-loop network lead to different results in the thermodynamic limit, and the percolation thresholds do not coincide with the thermodynamic phase transition point.
In the novel stoichiometric iron-based material RbEuFe4As4 superconductivity coexists with a peculiar long-range magnetic order of Eu 4f states; their coexistance is puzzling and represents a challenge for both experiment and theory. Using angle-resolved photoemission spectroscopy, resonant photoemission spectroscopy, Andreev reflection spectroscopy and scanning tunneling spectroscopy we have addressed this puzzle and unambigously shown that Fe- and Eu-derived states are largely decoupled and that superconducting and a long range magnetic orders exist almost independently from each other.
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