A new probe of quadrupole detection in PrTi₂Al₂₀

The study of higher-order multipoles is gaining significance due to their expected role in setting up various exotic states in quantum materials, such as quantum spin liquids, high-temperature superconductivity, and quantum critical metallicity. However, detecting multipoles presents three primary challenges: (i) they are often masked by magnetic dipoles (ii) they are difficult to detect due to their intricate angular structure, and (iii) their explicit dependence on magnetic fields requires high-field measurements. Hence, detecting higher-order multipoles requires the right technique and material.

We measure the magnetotropic susceptibility -- the curvature of free energy relative to the orientation of an applied magnetic field [1, 2], which has the significant advantage of operating in magnetic fields up to 100 tesla.

We present preliminary measurements on PrTi₂Al₂₀, a non-Kramer doublet lacking dipole ordering possessing only quadrupoles in the ground state. We clearly observed a quadrupolar ordering transition at T_Q ~ 2 K for the field applied along the [111] direction. The angle-dependent measurements show a qualitative agreement with theoretical simulations, highlighting the need for more precise crystal alignment relative to the applied magnetic field. These initial findings demonstrate that resonant torsion magnetometry is a viable tool for detecting higher-order multipoles more broadly.

References:

[1] Modic, K.A., et al. Resonant torsion magnetometry in anisotropic quantum materials. Nat. Commun. 9, 3975 (2018)

[2] Shekhter, A., et al. "The magnetotropic susceptibility." Phys. Rev. B, 108, 035111 (2023)