Dielectric signature of charge order in lanthanum nickelates

TL;DR

This study investigates the dielectric properties of charge-ordered lanthanum nickelates using broadband spectroscopy, revealing colossal dielectric constants and anomalies at charge-order transitions, linked to charge ordering phenomena.

Contribution

It provides new insights into the dielectric signature of charge order in lanthanum nickelates through broadband spectroscopy and complementary measurements.

Findings

Colossal dielectric constants observed in all three compounds

Distinct anomalies at charge-order transition temperatures

Relaxation features partly due to electrode polarization

Abstract

Three charge-ordering lanthanum nickelates La2-xAxNiO4, substituted with specific amounts of A = Sr, Ca, and Ba to achieve commensurate charge order, are investigated using broadband dielectric spectroscopy up to GHz frequencies. The transition temperatures of the samples are characterized by additional specific heat and magnetic susceptibility measurements. We find colossal magnitudes of the dielectric constant for all three compounds and strong relaxation features, which partly are of Maxwell-Wagner type arising from electrode polarization. Quite unexpectedly, the temperature-dependent colossal dielectric constants of these materials exhibit distinct anomalies at the charge-order transitions.