Phonon-induced quadrupolar ordering of the magnetic superconductor TmNi$_2$B$_2$C

TL;DR

This study reveals a lattice distortion in TmNi₂B₂C below 13.5 K linked to quadrupolar ordering, which is significantly enhanced by magnetic fields and correlates with antiferromagnetic order, advancing understanding of magnetic-superconducting interactions.

Contribution

It provides the first detailed synchrotron x-ray diffraction analysis of quadrupolar ordering and its magnetic field dependence in TmNi₂B₂C, with a theoretical model explaining these phenomena.

Findings

Lattice distortion occurs below 13.5 K at zero field.

Magnetic field amplifies the distortion by a factor of 10.

Distortion shares the same wave vector as field-induced antiferromagnetic order.

Abstract

We present synchrotron x-ray diffraction studies revealing that the lattice of thulium borocarbide is distorted below T_Q = 13.5 K at zero field. T_Q increases and the amplitude of the displacements is drastically enhanced, by a factor of 10 at 60 kOe, when a magnetic field is applied along [100]. The distortion occurs at the same wave vector as the antiferromagnetic ordering induced by the a-axis field. A model is presented that accounts for the properties of the quadrupolar phase and explains the peculiar behavior of the antiferromagnetic ordering previously observed in this compound.