title: Blue Phosphorene Oxide: Strain-Tunable Quantum Phase Transitions and Novel 2D Emergent Fermions.
abstract: Tunable quantum phase transitions and novel emergent fermions in solid-state materials are fascinating subjects of research. Here, we propose a new stable two-dimensional (2D) material, the blue phosphorene oxide (BPO), which exhibits both. On the basis of first-principles calculations, we show that its equilibrium state is a narrow-bandgap semiconductor with three bands at low energy. Remarkably, a moderate strain can drive a semiconductor-to-semimetal quantum phase transition in BPO. At the critical transition point, the three bands cross at a single point at Fermi level, around which the quasiparticles are a novel type of 2D pseudospin-1 fermions. Going beyond the transition, the system becomes a symmetry-protected semimetal, for which the conduction and valence bands touch quadratically at a single Fermi point that is protected by symmetry, and the low-energy quasiparticles become another novel type of 2D double Weyl fermions. We construct effective models characterizing the phase transition and these novel emergent fermions, and we point out several exotic effects, including super Klein tunneling, supercollimation, and universal optical absorbance. Our result reveals BPO as an intriguing platform for the exploration of fundamental properties of quantum phase transitions and novel emergent fermions and also suggests its great potential in nanoscale device applications.
authors.affiliation: School of Physics and Electronic & Electrical Engineering, and Jiangsu Key Laboratory of Modern Measurement Technology and Intelligent Systems, Huaiyin Normal University , Huai'an, Jiangsu 223300, P. R. China.
authors.forename: Liyan
authors.initials: L
authors.lastname: Zhu
authors.affiliation: Research Laboratory for Quantum Materials, Singapore University of Technology and Design , Singapore, 487372, Singapore.
authors.forename: Shan-Shan
authors.initials: SS
authors.lastname: Wang
authors.affiliation: Research Laboratory for Quantum Materials, Singapore University of Technology and Design , Singapore, 487372, Singapore.
authors.forename: Shan
authors.initials: S
authors.lastname: Guan
authors.affiliation: Research Laboratory for Quantum Materials, Singapore University of Technology and Design , Singapore, 487372, Singapore.
authors.forename: Ying
authors.initials: Y
authors.lastname: Liu
authors.affiliation: School of Physics and Electronic & Electrical Engineering, and Jiangsu Key Laboratory of Modern Measurement Technology and Intelligent Systems, Huaiyin Normal University , Huai'an, Jiangsu 223300, P. R. China.
authors.forename: Tingting
authors.initials: T
authors.lastname: Zhang
authors.affiliation: School of Physics and Electronic & Electrical Engineering, and Jiangsu Key Laboratory of Modern Measurement Technology and Intelligent Systems, Huaiyin Normal University , Huai'an, Jiangsu 223300, P. R. China.
authors.forename: Guibin
authors.initials: G
authors.lastname: Chen
authors.affiliation: Research Laboratory for Quantum Materials, Singapore University of Technology and Design , Singapore, 487372, Singapore.
authors.forename: Shengyuan A
authors.initials: SA
authors.lastname: Yang
keywords: Two-dimensional material; emergent fermion; first-principles calculations; quantum phase transition; strain engineering; universal optical absorbance