Photostrictive Two-Dimensional Materials in the Monochalcogenide Family

Abstract

Photostriction is predicted for SnS and SnSe monolayers, two-dimensional ferroelectrics with rectangular unit cells (the lattice vector a1 is larger than a2) and an intrinsic dipole moment parallel to a1. Photostriction in these two-dimensional materials is found to be related to the structural change induced by a screened electric polarization in the photoexcited electronic state (i.e., a converse piezoelectric effect) that leads to a compression of a1 and a comparatively smaller increase of a2 for a reduced unit cell area. The structural change documented here is ten times larger than that observed in BiFeO3, making monochalcogenide monolayers an ultimate platform for this effect. This structural modification should be observable under experimentally feasible densities of photexcited carriers on samples that have been grown already, having a potential usefulness for light-induced, remote mechano-opto-electronic applications.A truly novel opto-mechanical coupling in twodimensional (2D) ferroelectric materials awaits to be discovered.Photostriction -the creation of nonthermal strain upon illumination [1-4]-has been welldocumented in three-dimensional ferroelectrics such as SbSI [5] and BiFeO 3 [6,7]. It has been suggested to be driven by the large voltage build-up caused by a photovoltaic effect and the resulting converse piezoelectricity [8], and it may be useful for applications such as remotely-switchable memory devices [9] and lightinduced actuators [10]. The earliest studied photostrictive material, SbSI, transitions from a ferroelectric onto a paraelectric at a critical temperature T c < 300 K. As photostrictive effects are larger in the ferroelectric phase, T c can be increased above 300 K on SbSI ceramics which have smaller domain sizes and display a non-uniform stoichiometry nevertheless. The photostriction response time increases with sample thickness due to a reduced penetration depth, being a few seconds on bulk samples [5]. On the other hand, ferroelectric films show photostriction within a few picoseconds [11][12][13][14][15], and even when the photoexcited electron-hole pair is localized [16,17].The growing interest on the interactions of light with 2D materials [18-21] makes a study of illumination leading to non-trivial structural deformations an interesting and timely endeavor. As long as a photoexcited state induces some amount of charge redistribution -which is a quite reasonable physical assumption-any material is expected to change shape as the structure is let to relieve the stress induced by the photoexcited carriers. Here, the surprising result is the rather large magnitude of such structural change for 2D ferroelectrics, that originates from an inverse piezoelectric effect upon illumination.Two-dimensional ferroelectrics in the group IV monochalcogenide family (GeS, GeSe, SnS, SnSe, among others) [22][23][24][25][26][27][28][29][30][31] undergo a ferroelectric-to-paraelectric transition with a transition temperature that is tunable by atomic number [25]. Following the numerical approach...

Electronic and optical properties of strained graphene and other strained 2D materials: a review

“…In brief, linearly polarized light can address individual valleys and create a population of excited carriers that screen the underlying dipole moment characteristic of these materials. In turn, the structure compresses anisotropically [36]. This finding means that illumination can play an active role in creating non-uniform strain in this barely explored material, showing promising ways ahead concerning the interrelation among strain and material properties in 2D materials.…”

The rise of two‐dimensional van der Waals ferroelectrics

“…The coupling of ferroelectric (FE) and ferroelasticity in group IV monochalcogenide monolayers which renders efficient data reading due to the anisotropy (left, Reprinted with permission from Wu and Zeng (). Copyright 2016 American Chemical Society) and related phenomena like photostriction and optical second harmonic generation (right, Reprinted with permission from Haleoot et al () and Wang and Qian (). Copyright 2017 American Physical Society and American Chemical Society).…”

Shift-current bulk photovoltaic effect influenced by quasiparticle and exciton

“…However, these conclusions were drawn from calculations neglecting quasiparticle corrections and excitonic effects, and should be revised with these many-body effects taken into account. Similarly, * rappe@sas.upenn.edu many theoretical predictions of shift current in new materials are routinely made without these many-body effects taken into account.In the present Letter, we study the shift current with quasiparticle GW corrections and excitonic effects in the typical perovskite oxide BaTiO 3 and large BPVE two-dimensional monochalcogenide SnSe [28][29][30]. These many-body effects work to redistribute the spectral weight of the shift current response.…”