Charge-Order Pattern of the Low-Temperature Phase of NaV2O5 Uniquely Determined by Resonant X-Ray Scattering from Monoclinic Single Domain

TL;DR

This study unambiguously determines the charge-order pattern in low-temperature NaV2O5 using resonant X-ray scattering, revealing a specific stacking sequence and linking it to theoretical models explaining complex phase behaviors.

Contribution

It provides the first definitive charge-order pattern of NaV2O5's low-temperature phase through resonant X-ray scattering of monoclinic domains.

Findings

Charge-order pattern identified as AAA'A' stacking sequence.

Zig-zag charge-order configurations confirmed in the ab-plane.

The stacking sequence explains the devil's staircase behavior via the ANNNI model.

Abstract

The present resonant x-ray scattering from each of monoclinically-split single domains of NaV2O5 has critically enhanced contrast between V4+ and V5+ ions strong enough to lead to unambiguous conclusion of the charge-order pattern of its low-temperature phase below Tc = 35 K. The zig-zag type charge-order patterns in the $ab$-plane previously confirmed have four kinds of configurations (A, A', B and B') and the stacking sequence along the c-axis is determined as the AAA'A' type by comparison with model calculations. By assigning the A and A' configurations to Ising spins, one can reasonably understand the previously discovered "devil's staircase"-type behavior with respect to the modulation of the layer-stacking sequences at high pressures and low temperatures, which very well resembles the global phase diagram theoretically predicted by the ANNNI model.