Appearance of new lines and change in line shape in the IR spectrum of a NaV_2O_5 single crystal at the spin-Peierls transition

TL;DR

This study reports the first observation of new infrared spectral lines and line shape changes in NaV_2O_5 crystals at the spin-Peierls transition, revealing insights into magnetic excitation gap formation.

Contribution

First detection of spectral line emergence and shape change associated with unit-cell doubling at the spin-Peierls transition in NaV_2O_5.

Findings

New lines appear in IR spectrum at transition

Line shape changes from Fano to symmetric

Evidence of magnetic excitation gap opening

Abstract

We report the first observation of new lines in the infrared spectrum of a crystal due to unit-cell doubling at the spin-Peierls transition (in NaV_2O_5). The change in the shape of the spectral lines at the spin-Peierls transition is recorded for the first time. A contour characteristic of a Fano resonance is observed above the transition temperature Tsp and the standard symmetric contour is observed below Tsp. We attribute this effect to the opening of a gap in the magnetic-excitation spectrum at the spin-Peierls transition.