Evidence for an extended critical fluctuation region above the polar ordering transition in LiOsO3

Abstract

Metallic LiOsO 3 undergoes a continuous ferroelectric-like structural phase transition below T c = 140 K to realize a polar metal. To understand the microscopic interactions that drive this transition, we study its critical behavior above T c via electromechanical coupling-distortions of the lattice induced by short-range dipoledipole correlations arising from Li off-center displacements. By mapping the full angular distribution of second harmonic electric-quadrupole radiation from LiOsO 3 and performing a simplified hyper-polarizable bond model analysis, we uncover subtle symmetry-preserving lattice distortions over a broad temperature range extending from T c up to around 230 K, characterized by nonuniform changes in the short and long Li-O bond lengths. Such an extended region of critical fluctuations may explain anomalous features reported in specific heat and Raman scattering data and suggests the presence of competing interactions that are not accounted for in existing theoretical treatments. More broadly, our results showcase how electromechanical effects serve as a probe of critical behavior near inversion symmetry-breaking transitions in metals.

Free-Carrier-Induced Ferroelectricity in Layered Perovskites

“…The first observation of polarization switching in a ferroelectric (semi-)metal is even more recent [11,12]. The interest in polar and ferroelectric-like metals is continuing to increase in both bulk and heterostructures [13][14][15][16][17][18][19][20][21][22][23][24] and they continue to promise both a fertile playground for interesting emergent phenomena (including, but not limited to mixed singlet-triplet superconductivity [25] and novel optical effects [26]), and immediate relevance to applications as polar electrodes [27].…”

Extreme Ultraviolet Second Harmonic Generation Spectroscopy in a Polar Metal

“…Open questions for future investigation are highlighted in three recent works. Shan et al 34 observed SHG due to electric quadrupolar effects above the polar ordering temperature up to 230 K, as a result of an extended critical fluctuation region. Such effects were not visible in XUV-SHG at 160 K, but may have been below the detection limit of this experiment.…”