Time: 10:00am, Nov. 18 (Mon.), 2019

Venue: Rm. N210, UCAS Teaching Building [View Map]

Speaker: Wei Ruan (Berkeley)

Abstract:

Quantum spin liquids (QSLs) are a novel state of matter predicted to arise in quantum antiferromagnets where magnetic frustration or quantum fluctuations are strong enough to prevent magnetically ordered states even down to the lowest temperatures. QSLs are believed to exist in strongly correlated Mott insulators, and are thus related to unconventional superconductivity. Much work on QSLs has focused on triangular lattices where frustration is strong. An example is the bulk Mott insulator 1T-TaS₂ which has attracted attention as a QSL candidate due to localized d-orbitals in the Ta atoms that form a triangular lattice in this material. This scenario, however, is complicated by interlayer coupling and possible different stacking orders in the bulk, thus motivating investigation into related single-layer materials.

I will discuss our recent studies on single-layer (SL) 1T-TaSe₂ that provide evidence for 2D spin-liquid behavior. We have characterized the electronic structure of SL 1T-TaSe₂ (grown via molecular beam epitaxy) by means of scanning tunneling microscopy/spectroscopy (STM/STS), angle-resolved photoemission spectroscopy (ARPES), and first-principles calculations. We observe Mott insulating behavior in SL 1T-TaSe₂, including novel orbital texture not seen in bulk samples. Vertical heterostructures formed by a single 1T-TaSe₂ layer placed on top of metallic 1H-TaSe₂ exhibit Kondo behavior, providing direct evidence for a triangular array of local spins in SL 1T-TaSe₂. Evidence for a spin-liquid-based spinon Fermi surface is observed in STM measurements of SL 1T-TaSe₂. These results will be discussed in the context of recent theoretical predictions.

Speaker invited by: Long Zhang