# Polar State induced by Block-type Lattice Distortions in BaFe2Se3 with Quasi-One-Dimensional Ladder Structure

## TL;DR

This study investigates the temperature-dependent crystal structures of BaFe2Se3, revealing a polar low-temperature phase with block-type lattice distortions and a loss of inversion symmetry, linked to electronic and magnetic property changes.

## Contribution

It provides detailed structural analysis of BaFe2Se3's low-temperature phase, highlighting the role of block-type lattice distortions and symmetry breaking in its properties.

## Key findings

- Low-temperature phase has Pmn2_1 space group with broken inversion symmetry.
- Emergence of macroscopic polarization along the rung direction.
- Structural transition affects electronic and magnetic properties.

## Abstract

Temperature dependent crystal structures of the quasi-one-dimensional ladder material BaFe2Se3 are examined. Combining the optical second harmonic generation (SHG) experiments and neutron diffraction measurements, we elucidate the crystal structure with Pmn2_1 space group in the low-temperature phase below Ts2 = 400 K, further above Neel temperature. This low-temperature phase loses the spatial inversion symmetry, where a resultant macroscopic polarization emerges along the rung direction. The transition is characterized by block-type lattice distortions with the magneto-striction mechanism. Change in the electrical resistivity and the magnetic susceptibility across the polar-nonpolar transition also suggests a modification of the electronic states reflecting the structural instability. Consistency and discrepancy with the existing theory are discussed.