Charge Ordering Fluctuation and Optical Pseudogap in La$_{1-x}$Ca$_{x}$MnO$_{3}$

TL;DR

This study uses optical spectroscopy to explore charge ordering and pseudogap phenomena in La$_{1-x}$Ca$_{x}$MnO$_{3}$, revealing large charge gap ratios and enhanced correlations near x=0.5, with implications for understanding complex electronic states.

Contribution

It provides new insights into charge ordering fluctuations and pseudogap behavior in manganites, especially near the critical doping level x=0.5, using optical spectroscopy.

Findings

Large charge gap ratio (2Δ/k_B T_CO) up to 30 near x=0.5

Enhanced pseudogap and charge ordering correlations above T_CO near x=0.5

Systematic increase of T* indicating strong charge fluctuations

Abstract

Optical spectroscopy was used to investigate the optical gap (2$\Delta $) due to charge ordering (CO) and related pseudogap developments with x and temperature (T) in La$_{1-x}$Ca$_{x}$MnO$_{3}$ (0.48 <= x <= 0.67). Surprisingly, we found 2$\Delta $/k_{B}T_{CO} is as large as 30 for x ~0.5, and decreases rapidly with increasing x. Simultaneously, the optical pseudogap, possibly starting from T^* far above T_{CO} becomes drastically enhanced near x=0.5, producing non-BCS T-dependence of 2$\Delta $ with the large magnitude far above T_{CO}, and systematic increase of T^* for x~0.5. These results unequivocally indicate systematically-enhanced CO correlation when x approaches 0.5 even though T_{CO} decreases.