Spin gap behavior and charge ordering in \alpha^{\prime}-NaV_2O_5 probed by light scattering

TL;DR

This study uses light scattering to investigate the spin gap and charge ordering phenomena in -NaVO, revealing magnetic bound states, charge order onset at 80 K, and associated fluctuations.

Contribution

It provides detailed experimental evidence of spin gap behavior and charge ordering in -NaVO using light scattering, highlighting the nature of phase transitions and fluctuations.

Findings

Detection of magnetic bound states below 34 K.

Observation of charge ordering onset at 80 K.

Pretransitional fluctuations in magnetic and phononic spectra.

Abstract

We present a detailed analysis of light scattering experiments performed on the quarter-filled spin ladder compound $\alpha^\prime$-NaV$_{2}$O$_{5}$ for the temperature range 5 K$\le$T$\le$300 K. This system undergoes a phase transition into a singlet ground state at T=34 K accompanied by the formation of a super structure. For T$\leq$34 K several new modes were detected. Three of these modes are identified as magnetic bound states. Experimental evidence for charge ordering on the V sites is detected as an anomalous shift and splitting of a V-O vibration at 422 cm$^{-1}$ for temperatures above 34 K. The smooth and crossover-like onset of this ordering at T$_{\rm CO}$= 80 K is accompanied by pretransitional fluctuations both in magnetic and phononic Raman scattering. It resembles the effect of stripe order on the super structure intensities in La$_2$NiO$_{4+\delta}$.