Two-dimensional (2D) boron has been predicted to exhibit various structural polymorphs and interesting physics, including superconductivity, ideal strength, negative Possion's ratio, and a higher thermal conductivity than graphene, etc. However, the difficulty in experimental synthesis of 2D boron has further reduced its exploration and applications. In this work we have used a crystal structure search method and first-principles calculations. We have proposed a scheme of "synthesize under high pressure and peel off at ambient conditions" to first predict a bulk phase of KB4, and then peel off free standing 2D boron from it. Based on electron-phonon coupling calculations, we estimated that 2D boron is an intrinsic superconductor with T-c = 17.9 K. In addition we found a strong anisotropy of the electron-phonon coupling strength in 2D boron, thus the superconductivity in 2D boron possesses a quasi-1D feature. Our proposed scheme for the synthesis of free standing 2D boron will stimulate further studies of superconductivity in low dimensional materials, both theoretically and experimentally.
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