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Two-dimentional Quantum Spin Liquids: Kekule-Kitaev Model

Mirmojarabian, Fatemeh | 2021

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 53669 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Langari, Abdollah; Kargarian, Mehdi
  7. Abstract:
  8. Quantum spin liquids are characterized by the lack of long range magnetic order at zero temperature due to strong quantum fluctuations in frustrated magnets, emergent fractionalized excitations coupled to gauge fields, pattern of long-range entanglements, and topological orders. Since the theoretical predictions dated back to the seventies, a huge amount of both theoretical and experimental efforts put forward to explore these emerging phenomena in real materials. Besides the organic compounds with spin liquid ground states, recent years have witnessed the dawn of new oxide materials such as α - RuCl3 and Na2IrO3 which may host spin liquid at low temperatures. The ground states of the latter are arguably to be described by the exactly solvable Kitaev model.Motivated by recent progress in experimental characterization of spin liquid phase in α - RuCl3, and especially the measured half-quantum plateau in the thermal Hallconductivity in a magnetic field, we focus on another model candidate, yet exactly solvable, known as the Kekule-Kitaev model. We map out the phase diagram of the model and show that the ground state could be characterized by Majorana fermions with trivial and topological band structures. The trivial Majorana band gap has zero Chern number and the topological gap is associated with a nonzero Chern number. Using degenerate perturbation theory, we show that the trivial phase is continuously connected to a variant of the toric code on the Kagome lattice with electric and magnetic charges as low-energy excitations. The nontrivial Chern band arisen in the magnetic field could support non-Abelian anyons in the vortex cores.The model is an insulating Mott phase with no charge response; we then investigate the signature of the phases in thermal Hall measurements. Since the model has multiple bands, the contributions of bands to the thermal Hall effect were investigated. Our findings show that in the topological phase there is stable plateau in the thermal Hall conductivity; the plateau is half quantized signaling the nature of carriers as neutral particles carrying half degrees of freedom of an electron, the so-called Majorana fermions. We further argue that our results are stable at rather high temperatures as the flux excitations are suppressed
  9. Keywords:
  10. Quantum Spin Liquid ; Topological Order ; Frustrated Magnets ; Kitaev Superconductor

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