Study of the symmetry of electronic system of the Weyl semimetal GdBiPt using rotational anisotropy of second harmonic generation

TL;DR

This study uses rotational anisotropy of second harmonic generation to analyze symmetry changes in GdBiPt across its antiferromagnetic transition, revealing detailed symmetry properties and magnetic order parameters.

Contribution

It provides a detailed symmetry analysis of GdBiPt's phase transition using SHG, identifying specific point groups and magnetic contributions, and determines the Néel temperature and critical exponent.

Findings

SHG intensity correlates with antiferromagnetic order parameter

Identified superposition of point groups $3m$ and $m$ above T_N

Determined T_N=9.61 K and critical exponent β=0.346

Abstract

The half-Heusler compound GdBiPt orders antiferromagnetically around $T_\mathrm{N}=8.5$ K which implies breaking the time reversal symmetry as well as the translational symmetry. This combination preserves the global symmetry. Here, we used rotational anisotropy of second harmonic generation (SHG) to study the symmetry changes associated with this phase transition. GdBiPt crystallizes in the space group $F\overline{4}3m$, which does not change through the phase transition. From powder neutron diffraction, the proposed magnetic point group for the magnetic unit cell is $3m$. We carried out a symmetry analysis of the SHG patterns. Above \tn, the SHG data shows a $C_2$ symmetry which excludes the point group $\overline{4}3m$, as well as the $3m$ point group which represents a $[1 1 1]$ facet of the sample. Thus, we considered the point groups $2$ and $m$, but we have to reject the first one as the associated tensor elements poorly represent the angular dependence SHG. Finally, a superposition consisting of the point groups $3m$ and $m$ fit the data correctly. Below \tn, we had to add a third contribution associated with magnetic points group $m'$ in order to properly describe the SHG signal. The SHG intensity is linearly proportional to the antiferromagnetic order parameter. This allows us to determine $T_\mathrm{N}=9.61\pm0.48$ K and a critical exponent $\beta=0.346\pm0.017$, which are in agreement with the values found in the literature.