Engineering nodal topological phases in Ising superconductors by magnetic superstructures

Recently it was discovered that superconductivity in transition metal dichalcogenides (TMDs) is strongly affected by an out-of-plane spin-orbit coupling (SOC). In addition, new techniques of fabricating 2d ferromagnets on van der Waals materials are rapidly emerging. Combining these breakthroughs, we propose a realization of nodal topological superconductivity in TMDs by fabricating nanostructured ferromagnets with an in-plane magnetization on the top surface. The proposed procedure does not require application of external magnetic fields and applies to monolayer and multilayer (bulk) systems. The signatures of the topological phase include Majorana flat bands that can be directly observed by Scanning Tunneling Microscopy (STM) techniques. We concentrate on NbSe$_2$ and argue that the proposed structures demonstrating the nodal topological phase can be realized withing existing technology.Comment: 8 pages, 7 figure

Superlattice platform for chiral superconductivity with tuneable and high Chern numbers

Finding concrete realizations for topologically nontrivial chiral superconductivity has been a long-standing goal in quantum matter research. Here we propose a route to a systematic realization of chiral superconductivity with nonzero Chern numbers. This goal can be achieved in a nanomagnet lattice deposited on top of a spin-orbit coupled two-dimensional electron gas (2DEG) with proximity s-wave superconductivity. The proposed structure can be regarded as a universal platform for chiral superconductivity supporting a large variety of topological phases. The topological state of the system can be electrically controlled by, for example, tuning the density of the 2DEG.Comment: 5+6 pages, 4 figure

Chern mosaic - topology of chiral superconductivity on ferromagnetic adatom lattices

In this work we will explore the properties of superconducting surfaces decorated by two-dimensional ferromagnetic adatom lattices. As discovered recently [R\"ontynen and Ojanen, Phys. Rev. Lett. \textbf{114}, 236803 (2015)], in the presence of a Rashba spin-orbit coupling these systems may support topological superconductivity with complex phase diagrams and high Chern numbers. We show how the long-range hopping nature of the effective low-energy theory generically gives rise to a phase diagram covered by a \emph{Chern mosaic} -- a rich pattern of topological phases with large Chern numbers. We study different lattice geometries and the dependence of energy gaps and abundance of different phases as a function of system parameters. Our findings establish the studied system as one of the richest platforms for topological matter known to date.Comment: 9 pages, 8 figure

Quantum detectors for the third cumulant of current fluctuations

We consider the measurement of the third cumulant of current fluctuations arising from a point contact, employing the transitions that they cause in a quantum detector connected to the contact. We detail two generic detectors: a quantum two-level system and a harmonic oscillator. In these systems, for an arbitrary relation between the voltage driving the point contact and the energy scales of the detectors, the results can be expressed in terms of an effective detector temperature T_eff. The third cumulant can be found from the dependence of T_eff on the sign of the driving voltage. We find that proper ordering of the fluctuation operators is relevant in the analysis of the transition rates. This is reflected in the effective Fano factor for the third cumulant measured in such setups: it depends on the ratio of the voltage and an energy scale describing the circuit where the fluctuations are produced.Comment: 12+ pages, 8 figure