Ferroelectricity, Superconductivity and Non-Trivial Topology in PbSnTe Heterostructures

Combination of broken inversion symmetry and spin-orbit coupling gives rise to a wide range of exotic superconducting states, such as mixed-parity superconductivity, superconducting Weyl state, and superconducting diode effect. Incipient ferroelectrics e.g., PbTe, are near a polar instability. The emergence of superconductivity has been reported in some of these incipient ferroelectrics upon doping. Many unconventional superconductors, such as the cuprates, pnictides, and heavy fermion systems, occur in close proximity to magnetic fluctuations or magnetic orders, suggesting that these are important ingredients in the superconductivity in these materials. Here, ferroelectricity and superconductivity could be connected or accidental neighbors. Furthermore, the intersection of superconductivity and topologically nontrivial states is a fertile landscape for exciting quantum phenomena, including non-abelian excitations.<br/>IV-VI compounds show a wide range of electronic and polar instabilities. Pb_1-xSn_xTe demosntrates a highly tunable superconductivity and ferroelectricity which are dependent on carrier density and Sn(Pb) concentration. Furthermore, a topological phase transition is expected at <i>x</i>~0.4, which inverts the conduction and valence bands for Sn rich compounds. I will report on our recent growth efforts of high quality Pb_1-xSn_xTe heterostructures, using a chalcogenide molecular beam epitaxy (Veeco 930) near the topological phase transition (<i>x</i>~0.4). The cross-section high-angle annular dark-field (HAADF) imaging in scanning transmission electron microscopy (STEM) shows abrupt interfaces. X-ray diffraction demonstrates single oriented films. The sheet resistance v.s. temperature demosntrates a metallic-like behavior, dR/dT &gt;0, in doped samples extending to 2 K. The Hall carrier density was measured at various temperatures, resolving the carrier mobility. The carrier mobility is inversely proportional to doping concentration. We report on superconductivity in electron and hole doped Pb_1-xSn_xTe heterostructures and its relation to neighboring ferroelectric and topological phase transitions.