Proximity-Induced Odd-Frequency Superconductivity in a Topological Insulator

At an interface between a topological insulator (TI) and a conventional superconductor (SC), superconductivity has been predicted to change dramatically and exhibit novel correlations. In particular, the induced superconductivity by an $s$-wave SC in a TI can develop an order parameter with a $p$-wave component. Here we present experimental evidence for an unexpected proximity-induced novel superconducting state in a thin layer of the prototypical TI, Bi$_2$Se$_3$, proximity coupled to Nb. From depth-resolved magnetic field measurements below the superconducting transition temperature of Nb, we observe a local enhancement of the magnetic field in Bi$_2$Se$_3$ that exceeds the externally applied field, thus supporting the existence of an intrinsic paramagnetic Meissner effect arising from an odd-frequency superconducting state. Our experimental results are complemented by theoretical calculations supporting the appearance of such a component at the interface which extends into the TI. This state is topologically distinct from the conventional Bardeen-Cooper-Schrieffer state it originates from. To the best of our knowledge, these findings present a first observation of bulk odd-frequency superconductivity in a TI. We thus reaffirm the potential of the TI-SC interface as a versatile platform to produce novel superconducting states.Comment: Accepted version for publication in Physical Review Letter

Atomistic models and time-dependent simulations of spin dynamics in isolated and current-carrying systems

THESIS 10028Understanding and ultimately controlling the dynamics of electrons and their spins is an important aspect of spin-based electronics. Recent experimental advances open up new possibilities for probing spin dynamics with very high spatial and temporal resolution, i.e. in atomic-sized systems and at sub-picosecond time scales. At these lengths and times quantum effects and atomistic details can not be neglected and the applicability of classical models is limited. Therefore, there is a need to develop new methodologies and computational tools for atomistic modeling of spin dynamics, in particular in the presence of electric currents. In this Thesis we construct a computational scheme, capable of describing the time evolution of spin systems both in isolation and under current-carrying conditions. The method has been developed in the spirit of the tightbinding model but it is transferable to more accurate first-principles methods such as density functional theory. This computational tool is then used to investigate timedependent phenomena in the systems of interest