Developing two-dimensional multifunctional materials is highly desirable for nanoscale device applications. Herein, by means of first-principles calculations, we demonstrate a promising two-dimensional multifunctional semiconductor with ferroelectricity, ultrahigh carrier mobility, and negative Poisson’s ratio in single-layer $\mathrm{BI}$. We show that single-layer $\mathrm{BI}$ exhibits intrinsic ferroelectricity, derived from its asymmetric structure, and the ferroelectricity features an in-plane electric polarization as large as $3.3\times {10}^{-10}{\mathrm{C}}_{{\mathrm{m}}^{-1}}$, which is beneficial for nonvolatile memories. Owing to its large band dispersion, single-layer $\mathrm{BI}$ is also found to harbor an extremely high carrier mobility ($1.17\times {10}^5\mathrm{c}{\mathrm{m}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$), even comparable to that of graphene, suggesting its potential for high-performance electronics and bulk photovoltaic effect. This, combined with the moderate band gap, renders single-layer $\mathrm{BI}$ with a high absorption coefficient (${10}^5\mathrm{cm}{\mathrm{m}}_{-1}$) from near-infrared to ultraviolet light. In addition, we unveil that single-layer $\mathrm{BI}$ is a long-sought-after auxetic material with a negative Poisson’s ratio of −0.31. All of these findings make single-layer $\mathrm{BI}$ a compelling multifunctional material, offering a versatile platform for diverse nanoscale devices applications.

中文翻译：

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单层BI：具有铁电性，超高载流子迁移率和负泊松比的多功能半导体

开发二维多功能材料对于纳米级设备应用是非常需要的。在这里，通过第一性原理的计算，我们证明了一种有前途的二维多功能半导体，具有单层铁电性，超高载流子迁移率和负泊松比$双$。我们展示了单层$双$ 表现出固有的铁电性（源自其不对称结构），并且铁电性具有高达 $3.3\times {10}^{-10}{\mathrm{C}}_{{\mathrm{米}}^{-\mathrm{1个}}}$，这对于非易失性存储器是有益的。由于其宽带分散，单层$双$ 也被发现具有极高的载具流动性（$1.17\times {10}^5\mathrm{C}{\mathrm{米}}^2{\mathrm{V}}^{-\mathrm{1个}}{\mathrm{s}}^{-\mathrm{1个}}$），甚至可以与石墨烯媲美，表明其在高性能电子学和体光伏效应方面的潜力。结合适度的带隙，可形成单层$双$ 具有高吸收系数（${10}^5\mathrm{厘米}{\mathrm{米}}_{-\mathrm{1个}}$）从近红外到紫外光。此外，我们揭开了单层$双$是一种广受欢迎的消泡材料，泊松比为-0.31。所有这些发现使单层$双$ 一种引人注目的多功能材料，可为各种纳米级设备应用提供多功能平台。