Topological superconductivity is an exotic phase of matter in which the fully gapped superconducting bulk hosts gapless Majorana surface states protected by topology. Intercalation of copper, strontium, or niobium between the quintuple layers of the topological insulator Bi 2 Se 3 increases the carrier density and leads to superconductivity that is suggested to be topological. Here we study the electronic structure of strontium-intercalated Bi 2 Se 3 using angle-resolved photoemission spectroscopy and Shubnikov-de Haas oscillations. Despite the apparent low Hall number of ∼2 × 10 19 cm −3 , we show that the Fermi surface has the shape of an open cylinder with a larger carrier density of ∼10 20 cm −3 . We suggest that superconductivity in intercalated Bi 2 Se 3 emerges with the appearance of a quasi-two-dimensional open Fermi surface.

Ferroelectric and ferromagnetic orders rarely coexist, and magnetoelectric coupling is even more scarce. A possible avenue for combining these orders is by interface design, where orders formed at the constituent materials can overlap and interact. Using a combination of magneto-transport and scanning SQUID measurements, we explore the interactions between ferroelectricity, magnetism, and the 2D electron system (2DES) formed at the novel LaAlO 3 /EuTiO 3 /Sr 0.99 Ca 0.01 TiO 3 heterostructure. We find that the electrons at the interface experience magnetic scattering appearing along with a diverging Curie-Weiss-type behaviour in the EuTiO 3 layer. The 2DES is also affected by the switchable ferroelectric polarization at the Sr 0.99 Ca 0.01 TiO 3 bulk. While the 2DES interacts with both magnetism and ferroelectricity, we show that the presence of the conducting electrons has no effect on magnetization in the EuTiO 3 layer. Our results provide a first step towards realizing a new multiferroic system where magnetism and ferroelectricity can interact via an intermediate conducting layer.