Giant electron–phonon coupling of the breathing plane oxygen phonons in the dynamic stripe phase of $$\hbox {La}_{1.67}\hbox {Sr}_{0.33}\hbox {NiO}_4$$

Abstract

Doped antiferromagnets host a vast array of physical properties and learning how to control them is one of the biggest challenges of condensed matter physics. La 1.67 Sr 0.33 NiO 4 (LSno) is a classic example of such a material. At low temperatures holes introduced via substitution of La by Sr segregate into lines to form boundaries between magnetically ordered domains in the form of stripes. the stripes become dynamic at high temperatures, but LSno remains insulating presumably because an interplay between magnetic correlations and electron-phonon coupling localizes charge carriers. Magnetic degrees of freedom have been extensively investigated in this system, but phonons are almost completely unexplored. We searched for electron-phonon anomalies in LSno by inelastic neutron scattering. Giant renormalization of plane ni-o bond-stretching modes that modulate the volume around ni appears on entering the dynamic charge stripe phase. other phonons are a lot less sensitive to stripe melting. Dramatic overdamping of the breathing modes indicates that dynamic stripe phase may host small polarons. We argue that this feature sets electron-phonon coupling in nickelates apart from that in cuprates where breathing phonons are not overdamped and point out remarkable similarities with the colossal magnetoresistance manganites. Mott insulators should become metallic when extra charge carriers are introduced by doping. However, many of them remain insulating or become very poor metals with large electrical resistivity and incoherent or diffusive transport 1,2. This behavior is particularly common in transition metal oxides that have the potential to realize novel electronic phases with interesting and exotic properties from nontrivial topologies to superconductivity 3. Poor electrical conductivity is typically associated with charge carrier localization arising from interactions between different quasiparticles 4. Learning how to control these interactions is challenging, especially in the presence of strong electron-electron correlations. Electron-phonon coupling is often involved in localization of charge carriers in crystalline materials. For example, in the case of polaron formation, the carriers locally distort the atomic lattice and the distortions trap the carriers when the electron-phonon coupling strength is large enough 5. A detailed understanding of both electronic and phonon channels is necessary to accurately account for such phenomena. A lot of research focused on the former 4,6 , but the latter is poorly characterized in many interesting materials. Time-of-flight neutron scattering instruments can map the phonon spectra over hundreds of Brillouin zones, but comprehensive analysis of these datasets is extremely difficult and time-consuming. For example, small peaks in the background can be assigned to phonons. A broad peak may arise from a superposition of two or more closely-spaced peaks. Some phonons can be overlooked since most of them have appreciable structure factor only in a few zones, etc. Recently we deve...

Charge Condensation and Lattice Coupling Drives Stripe Formation in Nickelates

“…The pinning effect of CO to the structural disorder also evinces the relevance of EPC in nickelates, which has been illustrated by the discovery of phonon anomalies and nematic behaviors in LSNO [55][56][57][58]. It has been argued theoretically that without EPC CO will remain dynamic and not order [32].…”

Automating Analysis of Neutron Scattering Time-of-Flight Single Crystal Phonon Data

“…To summarize, Phonon Explorer software has been successfully used in three completed research projects spanning a variety of experimental conditions [9,13,14].…”

“…It has been successfully applied to cases where a measurement of all phonons is desired as well as to projects focusing on specific phonons or phonon branches [9,13,14]. Here we focus on phonons mostly because their scattering intensity is greatest at large wavevectors where manually going through every Brillouin zone is especially time-consuming.…”

Charge Condensation and Lattice Coupling Drives Stripe Formation in Nickelates

“…The pinning effect of CO to the structural disorder also evinces the relevance of EPC in nickelates, which has been illustrated by the discovery of phonon anomalies and nematic behaviors in LSNO [51][52][53][54]. It has been argued theoretically that without EPC CO will remain dynamic and not order [32].…”