Topological phases in narrow-band systems

• Main Author: Tang, Evelyn (Evelyn May Yin)
• Other Authors: Xiao-Gang Wen.
• Format: Others
• Language: English
• Published: Massachusetts Institute of Technology 2016
• Subjects: Physics.
• Online Access: http://hdl.handle.net/1721.1/103220

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2015. === Cataloged from PDF version of thesis. === Includes bibliographical references (pages 64-72). === I discuss several novel topological phases in correlated electron systems, realized through spin-orbit interactions and lattice effects especially narrow-band systems. The first realizes the fractional quantum Hall effect using geometric frustration and ferromagnetism to obtain a nearly flat band with a large bandgap and non-zero Chern number. This system can support this effect at high temperatures upon partial filling of the flat band. The second proposal builds upon this system: as the ground state is a fractional quantum Hall state, excitations of this state are anyons when there is an incommensurate filling. The underlying lattice allows access to a new regime in which the anyon gas can form a charged superfluid, including states with intrinsic topological order or that similar to a BCS-type state. The third proposal studies topological crystalline insulators and strain as an effective gauge field on the surface state Dirac fermions. The zero-energy Landau orbitals form a flat band where the high density of states gives rise to the interface superconductivity observed in IV-VI semiconductor multilayers at high temperatures, with non-BCS behavior. A discussion of superconductivity in flat band systems concludes and is contrasted with classic results for a typical electron gas. This work closely parallels that in references [1, 2, 3]. === by Evelyn Tang. === Ph. D.