Proximity effect in multilayer heterostructures allows the creation of electronic excitations or quasiparticles with mixed physical characters that is usually impossible to be obtained in a single material. For example, it allows quasiparticles with combined characters of superconductivity, ferromagnetism, and spin-orbit etc. As a result, unconventional electronic excitations can be built. In particular, inducing superconductivity into well-defined surface bands with giant spin-obit and Zeeman splitting have been shown as candidates for Majorana fermions. In this talk, I will first present our results in building novel ferromagnetic ground states of Dirac electrons in graphene, as well as inducing ferromagnetic order in topological insulators (TI). They further exemplify a precise and clean approach in modulating the spins of two-dimensional materials using the local exchange magnetic field. These experiments are done in heterostructures of graphene/EuS or TI/EuS with EuS a typical ferromagnetic insulator. Secondly, I will present our device based heterostructure platform for creating and detecting Majorana fermions using epitaxial gold nanowires. By means of electron tunneling spectroscopy, I will demonstrate the unconventional superconductivity induced in the two-dimensional surface states of gold, in one dimensional gold nanowires, as well as possible tunneling signatures that may hint the Majorana fermions.
[1.] Wei, P., Katmis, F., Assaf, B. A., Steinberg, H., Jarillo-Herrero, P., Heiman, D. & Moodera, J. S., Exchange-Coupling-Induced Symmetry Breaking in Topological Insulators, Phys Rev Lett 110, 186807, (2013).
[2.] Wei, P., Lee, S., Lemaitre, F., Pinel, L., Cutaia, D., Cha, W., Heiman, D., Hone, J., Moodera, J. S. & Chen, C.-T., Giant Interfacial Exchange Field in a 2D Material/Magnetic-Insulator Heterostructure: Graphene/EuS, arXiv:1510.05920 (under review by Nature Materials) (2015).