Interference of a first-order transition with the formation of a spin-Peierls state in alpha'-NaV2O5?

TL;DR

This study investigates the complex phase transitions in alpha'-NaV2O5, revealing a first-order transition near 33K and a second-order transition around 34K, linked to structural and spin-Peierls ordering.

Contribution

It provides high-resolution thermal-expansion and specific-heat data showing the interplay of first- and second-order transitions in alpha'-NaV2O5, highlighting the influence of spin-Peierls order on structural transformation.

Findings

Identification of a first-order transition at 33K

Observation of a second-order transition around 34K

Evidence of structural transformation induced by spin-Peierls order

Abstract

We present results of high-resolution thermal-expansion and specific-heat measurements on single crystalline alpha'-NaV2O5. We find clear evidence for two almost degenerate phase transitions associated with the formation of the dimerized state around 33K: A sharp first-order transition at T1=(33+-0.1)K slightly below the onset of a second-order transition at T2onset around (34+-0.1)K. The latter is accompanied by pronounced spontaneous strains. Our results are consistent with a structural transformation at T1 induced by the incipient spin-Peierls (SP) order parameter above T2=TSP.