Anisotropic lattice response induced by a linearly-polarized femtosecond optical pulse excitation in interfacial phase change memory material

Abstract

Optical excitation of matter with linearly-polarized femtosecond pulses creates a transient non-equilibrium lattice displacement along a certain direction. Here, the pump and probe pulse polarization dependence of the photo-induced ultrafast lattice dynamics in (GeTe)2/(Sb2Te3)4 interfacial phase change memory material is investigated under obliquely incident conditions. Drastic pump polarization dependence of the coherent phonon amplitude is observed when the probe polarization angle is parallel to the c–axis of the sample, while the pump polarization dependence is negligible when the probe polarization angle is perpendicular to the c–axis. The enhancement of phonon oscillation amplitude due to pump polarization rotation for a specific probe polarization angle is only found in the early time stage (≤2 ps). These results indicate that the origin of the pump and probe polarization dependence is dominantly attributable to the anisotropically-formed photo-excited carriers which cause the directional lattice dynamics.

THz Pulse Detection by Multilayered GeTe/Sb2Te3

“…This result is consistent with the fact that our samples are polycrystalline, in which the a−b planes of each grain are randomly oriented in the THz spot. 25,29 Also note that thermally excited carriers must absorb THz waves at room temperature. Although it is difficult to distinguish between topological and thermal carrier origin, both of them are expected to contribute the THz-induced electrical signal.…”

Phase‐Change Superlattice Materials toward Low Power Consumption and High Density Data Storage: Microscopic Picture, Working Principles, and Optimization

“…Obviously, for this order‐to‐order transition of GST‐SL, the Ge‐atom flipping is suggested to play the critical role. Hase et al and Makino et al studied the transition dynamics in GST‐SLs using coherent phonon spectroscopy, where the femtosecond‐laser induced change of phonon frequency was detected. They attributed the change to the variation of Ge configuration under excitation.…”

Time-dependent density-functional theory molecular-dynamics study on amorphization of Sc-Sb-Te alloy under optical excitation

“…It is generally believed that a laser pulse induces the phase change through thermal effects, such as meltquenched amorphization 4,17 , caused by carrier-phonon coupling. At the same time, the non-thermal effect of a laser, such as coherent optical phonons excitation 18,19 , and plasma annealing [20][21][22] , could also affect the bonding network 23,24 , and offer another driving force 25 for fast phase change in optical data storage.…”