Electron transport in a ferromagnet-superconductor junction on graphene

In a usual ferromagnet connected with a superconductor, the exchange potential suppresses the superconducting pairing correlation. We show that this common knowledge does not hold in a ferromagnetsuperconductor junction on a graphene. When the chemical potential of a graphene is close to the conical point of energy dispersion, the exchange potential rather assists the charge transport through a junction interface. The loose-bottomed electric structure causes this unusual effec

Fate of exceptional points under interactions: Reduction of topological classifications

Despite recent extensive studies of the non-Hermitian topology, understanding interaction effects is left as a crucial question. In this paper, we address interaction effects on exceptional points which are protected by the non-trivial point-gap topology unique to non-Hermitian systems. Our analysis in a two-dimensional parameter space elucidates the existence of exceptional points and symmetry-protected exceptional rings fragile against interactions; they are topologically protected only in non-interacting cases. This fragility of exceptional points and symmetry-protected exceptional rings arises from the reduction of non-Hermitian topological classifications, which is elucidated by introducing topological invariants of the second-quantized Hamiltonian for both non-interacting and interacting cases. These topological invariants are also available to analyze the reduction phenomena of gapped systems. The above results strongly suggest similar reduction phenomena of exceptional points in generic cases and open up a new direction of research in the non-Hermitian topology.Comment: 14 pages, 12 figures, published in PR

Kalb-Ramond interaction for a closed p-brane

The Kalb-Ramond action for an interacting string is generalized to the case of a high-dimensional object (p-brane). The interaction is found to be mediated by a gauge boson of a completely antisymmetric tensor of rank $p+1$.Comment: 7 page