# Terahertz Vibrational Dynamics and DFT Calculations for the Quantum Spin Chain Linarite, PbCuSO4(OH)2

## TL;DR

This study uses terahertz spectroscopy and DFT calculations to investigate the vibrational behavior of the quantum magnet linarite and how it changes with temperature.

## Contribution

The paper reveals an unexpected infrared spectral feature in linarite linked to high-temperature lattice distortions.

## Key findings

- Anisotropic THz vibrational motion is strongly correlated with the crystallographic b-axis in linarite.
- High-temperature lattice distortions break the centro-symmetry of linarite, causing a new spectral feature.
- The observed effects are likely due to anharmonicity in lattice oscillations.

## Abstract

The low-dimensional
quantum-magnet, linarite, PbCuS4(OH)2, has been
investigated using terahertz (THz) spectroscopy
coupled with detailed density functional theory (DFT) calculations
in order to explore the effects of the temperature on its lattice
vibrations. Linarite is characterized by largely isolated CuO chains
propagating along the crystallographic b-axis, which
at very low temperatures are responsible for exotic, quasi-1D magnetism
in this material. To better understand the synergy between the structural
bonds and lattice oscillations that contribute to these chains, polarized
THz spectroscopic measurements were performed. Consolidating these
results with detailed DFT calculations has revealed that the anisotropic
vibrational motion for the THz modes is correlated with extreme motion
associated with the crystallographic b-axis. An unexpected
feature observed in the infrared spectrum is attributed to subtle
lattice distortions which break the centro-symmetry in linarite at
high temperatures. This phenomenon has not previously been observed
in linarite and likely results from anharmonicity in lattice oscillations.