Ferroelectric Self-Poling in GeTe Films and Crystals

Abstract

Ferroelectric materials are used in actuators or sensors because of their non-volatile macroscopic electric polarization. GeTe is the simplest known diatomic ferroelectric endowed with exceedingly complex physics related to its crystalline, amorphous, thermoelectric, and—fairly recently discovered—topological properties, making the material potentially interesting for spintronics applications. Typically, ferroelectric materials possess random oriented domains that need poling to achieve macroscopic polarization. By using X-ray absorption fine structure spectroscopy complemented with anomalous diffraction and piezo-response force microscopy, we investigated the bulk ferroelectric structure of GeTe crystals and thin films. Both feature multi-domain structures in the form of oblique domains for films and domain colonies inside crystals. Despite these multi-domain structures which are expected to randomize the polarization direction, our experimental results show that at room temperature there is a preferential ferroelectric order remarkably consistent with theoretical predictions from ideal GeTe crystals. This robust self-poled state has high piezoelectricity and additional poling reveals persistent memory effects.

Spin Hall effect in prototype Rashba ferroelectrics GeTe and SnTe

“…The ferroelectric XTe (X=Ge,Sn) monochalcogenides share rhombohedrally distorted rocksalt structure (space group R3m). Both possess spontaneous electric polarization P parallel to [111] direction, but the high Curie temperature of GeTe (T C = 700 K) 12,13 allowed in-depth experimental studies of the ferroelectric phase which proved the polarization switching, 14 electronic structures [15][16][17] and reversible Rashba spin textures. 18 Importantly, spinto-charge conversion has been recently measured via spin pumping experiments in Fe/GeTe bilayers demonstrating high potential of such interfaces for multifunctional spintronics applications.…”

Triple-Point Fermions in Ferroelectric GeTe

“…The origin of these intriguing features in α-GeTe lies in the spontaneous structural phase transition of the inversion symmetric rocksalt β-GeTe structure (fcc, space group 225) into a ferroelectric rhombohedral structure with Ge atoms displaced by ≈0.3 Å and distorted by ≈1.6°(space group 160) [24,26]. This inversion symmetry breaking introduces a spin splitting except for the bands that line up with the high-symmetry ferroelectric h111i axis, which is the main symmetry axis of the C 3v point group.…”

Room-temperature ferroelectric control of spin-to-charge conversion in GeTe

“…The ferroelectric switching of GeTe has been demonstrated only at the nanoscale, by piezoresponse force microscopy (PFM) for thin films 14,20 , transmission electron microscopy (TEM) for nanometrescale crystals 21 and nanowires 22 , and finally using X-ray spectroscopy 23 . The demonstration of the macroscopic gating of GeTe thin films has never been achieved.…”