碲烯中依赖于厚度的极化子交叉
Thickness-Dependent Polaron Crossover in Tellurene
AI总结：
本研究发现碲烯厚度低于10 nm时会发生从大极化子到小极化子的交叉，源于其准一维特性下介电屏蔽减弱、电声耦合增强，为低维材料极化子效应研究提供了新见解。
摘要：
极化子是由电子-声子耦合产生的准粒子，对于理解高温超导、庞磁电阻等材料性质至关重要。然而，针对具有声子极性和电子结构转变的低维材料中极化子形成的研究仍十分匮乏。本研究中，我们探究了由碲原子手性链构成的碲烯中的极化子。A₁声子的频率和线宽会随碲烯厚度减小而极性逐渐增强，当碲烯厚度低于10 nm时，该声子的频率和线宽会发生突变。同时，当厚度小于10 nm时，碲烯的场效应迁移率会迅速下降。这些声子与输运特征，结合计算得到的声子极性和能带结构，表明存在从块体碲的大极化子到少层碲烯的小极化子的交叉。有效场理论考虑了强耦合（小极化子）区域的声子重整化，半定量地复现了少层碲烯中观测到的声子硬化和展宽效应。这种极化子交叉源于碲烯的准一维特性：链间距离的调制减弱了介电屏蔽，增强了电子-声子耦合。本研究为理解极化子对低维材料声子、电子和结构性质的影响提供了宝贵见解。
英文摘要：
Polarons, quasiparticles arising from electron-phonon coupling, are crucial in understanding material properties such as high-temperature superconductivity and colossal magnetoresistance. However, scarce studies have been performed to investigate the formation of polarons in low-dimensional materials with phonon polarity and electronic structure transitions. In this work, we studied polarons of tellurene that are composed of chiral chains of tellurium atoms. The frequency and linewidth of the A1 phonon, which becomes increasingly polar for thinner tellurene, exhibit an abrupt change when the thickness of tellurene is below 10 nm. Meanwhile, the field effect mobility of tellurene drops rapidly as the thickness is smaller than 10 nm. These phonon and transport signatures, combined with the calculated phonon polarity and band structure, suggest a crossover from large polarons for bulk tellurium to small polarons for few-layer tellurene. Effective field theory considers the phonon renormalization in the strong coupling (small polaron) regime, and semi-quantitatively reproduces the observed phonon hardening and broadening effects in few-layer tellurene. This polaron crossover stems from the quasi-1D nature of tellurene where modulation of the interchain distance reduces the dielectric screening and promotes electron-phonon coupling. Our work provides valuable insights into the influence of polarons on phononic, electronic, and structural properties in low-dimensional materials.
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