Phonon Localization and a Boson-Peak-Like Anomaly in Twisted Penta-PdSe Bilayer.

With the emergence of twistronics, twisting has been employed to manipulate phonon-phonon interactions in 2D-layered systems. However, due to the complexity of twisted structures, twisting-induced phonon localization and Boson-peak-like (BP-like) anomalies have not yet been reported. In this work, using machine-learning-supported molecular dynamics, we study the impact of interlayer twisting on the phonon properties in bilayer pentagonal PdSe (penta-PdSe) with multiple twist angles. We find that twisting reduces the in-plane thermal conductivity by up to 78.62%, while significantly enhancing the phonon coherent thermal conductivity contribution from 21.75% to 85.40%. Furthermore, by analyzing the vibrational density of states and localized shear strain distribution, we demonstrate that twisting introduces the inhomogeneous shear modulus distribution, causing phonon localization and a BP-like anomaly in twisted penta-PdSe bilayers. These findings show that twisting becomes a new variable for producing a BP-like anomaly, different from the conventional strategies by using disorder, defects, or doping.