Evidence for the weakly coupled electron mechanism in an Anderson-Blount polar metal

Abstract

Over 50 years ago, Anderson and Blount proposed that ferroelectric-like structural phase transitions may occur in metals, despite the expected screening of the Coulomb interactions that often drive polar transitions. Recently, theoretical treatments have suggested that such transitions require the itinerant electrons be decoupled from the soft transverse optical phonons responsible for polar order. However, this decoupled electron mechanism (DEM) has yet to be experimentally observed. Here we utilize ultrafast spectroscopy to uncover evidence of the DEM in LiOsO 3, the first known band metal to undergo a thermally driven polar phase transition ( T c ≈ 140 K). We demonstrate that intra-band photo-carriers relax by selectively coupling to only a subset of the phonon spectrum, leaving as much as 60% of the lattice heat capacity decoupled. This decoupled heat capacity is shown to be consistent with a previously undetected and partially displacive TO polar mode, indicating the DEM in LiOsO 3 .

Electronically driven spin-reorientation transition of the correlated polar metal Ca 3 Ru 2 O 7

“…ruthenate | magnetism | correlated oxide | Rashba spin-orbit | angle-resolved photoemission P olar distortions in solids give rise to the well-known functionality of switchable macroscopic polarization in ferroelectrics (1,2) and, when combined with strong spin-orbit coupling, can mediate giant spin splittings of electronic states (3,4). While typically found in insulators, ferroelectric-like distortions can remain robust against increasing itineracy, giving rise to so-called "polar metals" (5)(6)(7)(8)(9)(10). Ca3Ru2O7 is the bilayer member of the Can+1Run O3n+1 Ruddlesden-Popper series.…”

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

“…4(b)]. No measurable change in the linear optical response at 1.5 eV or 3 eV has been detected over the temperature range studied here [29,30]. The change in bond directionsb n alone based on neutron diffraction data [2] is also too small to account for the observed changes in χ EQ i jkl within the SHBM (see Appendix E).…”

“…To fit our SHG-RA data we include all three types of bonds in the unit cell of LiOsO 3 : the Os-O bonds, the long Li-O bonds between adjacent c planes, and the short Li-O bonds in the same c planes [11]. Based on the lack of marked temperature dependence in the reported linear optical response [29,30], we assume that the values of γ ω n are temperature independent. We also keepb n values constant, leaving only the γ 2ω n as fit parameters (Fig.…”

Prediction of Strong Converse Magnetoelectric Effect in Nb‐Doped BaTiO3‐Based Polar Metals

“…The metallicity and FE in polar metals conform to the weak‐coupling mechanism. [ 39,40 ] Similarly, the compression strain strengthens FE while weakens FM, so the FE and FM in polar metals also conform to the weak‐coupling mechanism, resulting in a weak ME coupling effect. Yet, the compressive strain can enhance the electrically controlled magnetism in the NBTO system with compressive strain.…”