Nanoscale inhomogeneity of charge density waves dynamics in La$_{2-x}$Sr$_x$NiO$_4$

TL;DR

This study reveals nanoscale heterogeneity and phase separation in charge density wave dynamics in La$_{2-x}$Sr$_x$NiO$_{4+y}$, showing how CDW motion correlates with correlation length at low temperatures.

Contribution

It provides direct visualization of nanoscale spatial inhomogeneity and phase separation of charge density waves using advanced X-ray techniques.

Findings

Nanoscale inhomogeneity of CDW relaxation dynamics observed.

Decreasing correlation length correlates with increased CDW motion.

Nanoscale phase separation of short-range and quasi-static CDW puddles.

Abstract

While stripe phases with broken rotational symmetry of charge density appear in many complex correlated systems, the heterogeneity of spatial ordering and dynamics remains elusive. This missing info is at the heart of understanding the structure and function relation in quantum complex materials. We focus here on the spatial heterogeneity of the motion of charge density wave (CDW) at nanoscale in the archetypal case of La$_{2-x}$Sr$_x$NiO$_{4+y}$ perovskite at low temperature. We report compelling evidence that the unconventional increasing motion of CDW at T < 50K is related with the decreasing of its correlation length using resonant soft X-ray photon correlation spectroscopy (XPCS). The key result of this work is the direct visualization of nanoscale spatial inhomogeneity of CDW relaxation dynamics by scanning micro X-ray diffraction (SmXRD) showing a nanoscale landscape of percolating short range dynamic CDW puddles competing with large quasi-static CDW puddles giving rise to a novel form of nanoscale phase separation of the incommensurate stripes order landscape.