Identifying the Transition Order in an Artificial Ferroelectric van der Waals Heterostructure

Abstract

Two-dimensional semiconducting ferroelectrics can enable new technology for low-energy electronic switching. However, conventional ferroelectric materials are usually electrically insulating and suffer from severe depolarization effects when downscaled to atomic thickness. Following recent work, we show that robust ferroelectricity can be obtained from nonferroelectric semiconducting 2H-WSe2 by creating R-stacked bilayers with broken inversion symmetry. Here, we identify that the phase transition order of this artificial ferroelectric heterostructure is first-order, with a discontinuous jump in the order parameter across the phase transition temperature. The Curie temperature has been experimentally determined as 353 K. Using the Landau-Devonshire theory, we further determine the Curie–Weiss temperatures to be 351.2 K. We additionally demonstrate the robustness of this artificial ferroelectric material using consecutive polarization measurements, where no appreciable deterioration was detected.

Slippery Paraelectric Transition-Metal Dichalcogenide Bilayers

“…And thus, the ferroelectic to paraelectric phase transition for a family of ferroelectrics created by the thinning down of their layered bulk and known as group-IV monochalcogenide monolayers (IVMMLs) 3,[11][12][13] is facilitated by the rotation of individual metal-chalcogen dimers within a given monolayer 14 taking place within a sub-picosecond timeframe. 11,[15][16][17] On the other hand, experimental work on ferroelectrics created by the relative rotation and/or sliding of two monolayers [18][19][20][21][22][23] (type (b) ferroelectrics) is relatively newer, 9,10 but Liu and coworkers have demonstrated a transition from a ferroelectric configuration (one in which the intrinsic electric dipole moment P is finite) onto a paraelectric one (in which P = 0) at finite temperature unequivocally, creating electronic devices based on 3R transition metal dichalcogenide bilayers (TMDBs) 24,25 for this purpose. 9 What must atoms do to turn those bilayers from ferroelectric (P = 0) to paraelectric (P = 0)?…”

“…11,[15][16][17] On the other hand, experimental work on ferroelectrics created by the relative rotation and/or sliding of two monolayers [18][19][20][21][22][23] (type (b) ferroelectrics) is relatively newer, 9,10 but Liu and coworkers have demonstrated a transition from a ferroelectric configuration (one in which the intrinsic electric dipole moment P is finite) onto a paraelectric one (in which P = 0) at finite temperature unequivocally, creating electronic devices based on 3R transition metal dichalcogenide bilayers (TMDBs) 24,25 for this purpose. 9 What must atoms do to turn those bilayers from ferroelectric (P = 0) to paraelectric (P = 0)? In other words, what is the atomistic structure of the experimentally verified paraelectric phase of TMDBs 9 ?…”

“…This picture is markedly different from the one presented on Figure 2(a) and employed in Refs. 9 and, 23 in which a double-well energy functional is still being considered and for which a single, definite paraelectric atomistic configuration can be created. Such realization is the main point of this…”

“…Ferroelectrics are ubiquitous within capacitors and could also be of use on neuromorphic computers . Ferroelectricity arises on materials lacking a center of inversion, and layered materials offer two novel pathways to induce ferroelectricity: (a) by thinning down − or (b) by applying a relative rotation and/or sliding. − Sustained experimental and theoretical efforts to characterize layered ferroelectrics focus on (i) the atomistic nature of the ferroelectric-to-paraelectric two-dimensional phase transition and (ii) the deployment of critical temperature ( T C ) trends.…”

“…On the other hand, experimental work on ferroelectrics created by the relative rotation and/or sliding of two monolayers − (type b ferroelectrics) is relatively newer, , but Liu and co-workers have demonstrated a transition from a ferroelectric configuration (one in which the intrinsic electric dipole moment P is finite) onto a paraelectric one (in which P = 0) at finite temperature unequivocally, creating electronic devices based on 3 R transition-metal dichalcogenide bilayers (TMDBs) , for this purpose …”