Probing Majorana Wave Functions in Kitaev Honeycomb Spin Liquids with Second-Order Two-Dimensional Spectroscopy

Two-dimensional coherent terahertz spectroscopy (2DCS) emerges as a valuable tool to probe the nature, couplings, and lifetimes of excitations in quantum materials. It thus promises to identify unique signatures of spin liquid states in quantum magnets by directly probing properties of their exotic fractionalized excitations. Here, in this study, we calculate the second-order 2DCS of the Kitaev honeycomb model and demonstrate that distinct spin liquid fingerprints appear already in this lowest-order nonlinear response $\chi^{(2)}_{yzx}$⁡($ω_1$, $ω_2$) when using crossed light polarizations. We further relate the off-diagonal 2DCS peaks to the localized nature of the matter Majorana excitations trapped by $\mathbb{Z}_2$ flux excitations and show that 2DCS thus directly probes the inverse participation ratio of Majorana wave functions. By providing experimentally observable features of spin liquid states in the 2D spectrum, our Letter can guide future 2DCS experiments on Kitaev magnets.. Authors: Qiang, Yihua [Iowa State Univ., Ames, IA (United States); Ames Laboratory (AMES), Ames, IA (United States)] (ORCID:0000000308903450); Quito, Victor L. [Iowa State Univ., Ames, IA (United States); Ames Laboratory (AMES), Ames, IA (United States); Univ. of Sao Paulo (Brazil)] (ORCID:0000000160194829); Trevisan, Thaís V. [Iowa State Univ., Ames, IA (United States); Ames Laboratory (AMES), Ames, IA (United States); Univ. of Sao Paulo (Brazil)] (ORCID:0000000169126347); Orth, Peter P. [Iowa State Univ., Ames, IA (United States); Ames Laboratory (AMES), Ames, IA (United States); Saarland University Campus, Saarbrücken (Germany)] (ORCID:0000000321838120). DOE Contract: AC02-07CH11358; AC02-07CH11359. Subjects: 46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY