# Exotic phase transition and superconductivity in layered titanium-oxypnictides implied by a computational phonon analysis

## TL;DR

This study uses ab initio phonon analysis to investigate phase transitions and superconductivity in layered titanium-oxypnictides, revealing a systematic dependence on the pnictogen element that influences the transition mechanism.

## Contribution

It provides the first computational phonon analysis explaining the structural phase transition in titanium-oxypnictides and highlights the pnictogen-dependent shift from conventional to exotic mechanisms.

## Key findings

- Explains experimental structure of Na2Ti2Pn2O with lighter pnictogen using electron-phonon theory.
- Identifies discrepancies with heavier pnictogen, suggesting alternative mechanisms.
- Shows systematic dependence of phase transition on pnictogen element.

## Abstract

We applied $ab$ $initio$ phonon analysis to layered titanium-oxypnictides, Na$_2$Ti$_2Pn_2$O ($Pn$ = As, Sb), and found a clear contrast between the cases with lighter/heavier pnictogen in comparisons with experiments. The result completely explains the experimental structure, $C$2/$m$ for $Pn$ = As, within the conventional electron-phonon framework, while there arise discrepancies when the pnictogen gets heavier, being in the same trend for the BaTi$_2Pn_2$O ($Pn$ = As, Sb, Bi) case. The fact implies a systematic dependence on pnictogen to tune the mechanism of the phase transition and superconductivity from conventional to exotic.