Abstract
A material potentially exhibiting multiple crystalline phases with distinct optoelectronic properties can serve as a phase-change memory material. The sensitivity and kinetics can be enhanced when the two competing phases have large electronic structure contrast and the phase change process is diffusionless and martensitic. In this work, we theoretically and computationally illustrate that such a phase transition could occur in the group-IV monochalcogenide SnSe compound, which can exist in the quantum topologically trivial Pnma-SnSe and nontrivial Fmbar 3m-SnSe phases. Furthermore, owing to the electronic band structure differences of these phases, a large contrast in the optical responses in the THz region is revealed. According to the thermodynamic theory for a driven dielectric medium, optomechanical control to trigger a topological phase transition using a linearly polarized laser with selected frequency, power and pulse duration is proposed. We further estimate the critical optical electric field to drive a barrierless transition that can occur on the picosecond timescale. This light actuation strategy does not require fabrication of mechanical contacts or electrical leads and only requires transparency. We predict that an optically driven phase transition accompanied by a large entropy difference can be used in an “optocaloric” cooling device.
Highlights
Phase change memory (PCM) materials are one of the key components of next-generation information storage[1]
One would like to find a PCM material that can simultaneously satisfy the following requirements: (i) it can exist in at least two structural phases, (ii) these phases have distinct physical properties that can be measured, preferably in a contact-free manner, (iii) the phase transformation is displacive/martensitic, where the atomic motions are diffusionless, and (iv) the directed phase transition preferably occurs within a single phonon oscillation period in the barrier-free limit
In this work, based on thermodynamic analysis and first-principles density functional theory (DFT) calculations, we propose that a group-IV monochalcogenide compound is a good platform to realize nonvolatile topological phase transition by optomechanical stimulation
Summary
Phase change memory (PCM) materials are one of the key components of next-generation information storage[1]. One would like to find a PCM material that can simultaneously satisfy the following requirements: (i) it can exist in at least two structural phases, (ii) these phases have distinct physical properties that can be measured, preferably in a contact-free manner, (iii) the phase transformation is displacive/martensitic, where the atomic motions are diffusionless, and (iv) the directed phase transition preferably occurs within a single phonon oscillation period (picosecond) in the barrier-free limit. The main idea is to strongly bias only the reaction coordinates of the structural transition, instead of exciting all the phonon modes, such as in a temperature-driven transition With these requirements fulfilled, the phase transition would have the benefits of low energy consumption, low heat load and fast switching speed
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