High spin Chern-number insulator (HSCI) emerges as a novel 2D topological phase of condensed matter that is beyond the classification scheme of topological quantum chemistry. In this work, we report the observation of a semimetallic Sb monolayer with the same band topology as HSCI. Our first-principles calculations further indicate a moderate lattice strain can make Sb monolayer an insulator while retaining the nontrivial topological order. A quantized spin Hall conductivity is found in the HSCI phase of Sb monolayer. The results suggest strained Sb monolayer as a promising platform for exploring intriguing physical properties of the exotic HSCI topological matter
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