Switching ferroelectricity in SnSe across phase transition

Abstract

We experimentally investigate transport properties of a hybrid structure, which consists of a thin single crystal SnSe flake on a top of 5 μm spaced Au leads. The structure initially is in highly conductive state, while it can be switched to the low-conductive one at high currents due to the Joule heating of the sample, which should be identified as phase transition to the symmetric β-Cmcm phase in SnSe. For the highly conductive state, there is significant hysteresis in dI/dV (V ) curves at low biases, so the sample conductance depends on the sign of the applied bias change. This hysteretic behavior reflects slow relaxation due to additional polarization current in the ferroelectric SnSe phase, which we confirm by direct measurement of time-dependent relaxation curves. In contrast, we observe no noticeable relaxation or low-bias hysteresis for the quenched low-conductive phase. Thus, the ferroelectric behavior can be switched on or off in transport through hybrid SnSe structure by controllable phase transition to the symmetric β-Cmcm phase. This result can also be important for nonvolatile memory development, e.g., phase change memory for neuromorphic computations or other applications in artificial intelligence and modern electronics.

Current-induced control of the polarization state in a polar metal based heterostructure SnSe/WTe$_2$

“…For the SnSe/WTe 2 heterostructure, our main finding is the abrupt symmetric dI/dV conductance drop at high biases, which can not be observed for the individual SnSe or WTe 2 flakes [14][15][16]. In Fig.…”

“…1), so Au-SnSe or Au-WTe 2 junctions are formed at the bottom surfaces of the individual flakes. This procedure provides electrically stable contacts with highly transparent metal-semiconductor interfaces, which has been verified for the individual flakes [15,16,[27][28][29]. SnSe/WTe 2 heterostructure appears as a small (40 µm×20µm)) overlap of the flakes at the center of the structure in Fig.…”

“…We assemble SnSe/WTe 2 heterostructure on the predefined Au leads pattern to avoid chemical or thermal treatment of the initial materials, similarly to singleflake samples [15,16,[27][28][29]. 5 µm separated leads are formed on the standard SiO 2 substrate by lift-off technique after thermal evaporation of 100 nm Au.…”

“…Even for relatively thick (100-200 nm) flakes, ferroelectric polarization is sensitive to the gate electric field [14], since the relevant (bottom) flake surfaces are adjoined to the SiO 2 surface. ) Inset shows an enlarged low-bias region with small hysteresis around the zero bias, which is known for the individual WTe2 or SnSe flakes [14][15][16]. (b,c) Gate voltage dependence of the dI/dV (V ) regions near positive and the negative thresholds.…”

“…Manipulation of charge transport by ferroelectric polarization is important for ferroelectric fieldeffect transistors (FeFET), as it has been demonstrated for In 2 Se 3 -based structures [2]. Ferroelectric polarization can be controlled also by the in-plane current-induced electric field in WTe 2 and SnSe thin films [14][15][16]. Van der Waals materials also offer strain control of ferroelectric polarization [17].…”