Quantum Criticality by Interaction Frustration in a Square-Planar Lattice

TL;DR

This study investigates a square-planar lattice compound showing quantum critical behavior driven by magnetic frustration, with experimental evidence of non-Fermi-liquid properties and theoretical insights into competing exchange interactions.

Contribution

It provides a rare example of zero-field, ambient pressure quantum criticality caused by interaction frustration in a square lattice, combining experimental and theoretical analysis.

Findings

No magnetic order down to 70 mK.

Logarithmic divergences indicating quantum criticality.

Non-Fermi-liquid resistivity behavior.

Abstract

We report experimental and theoretical investigations on ThCr$_2$Ge$_2$C, a metallic compound in which Cr$_2$C planes form a square-planar lattice. Neutron powder diffraction, magnetization, and specific heat measurements reveal no evidence of long-range magnetic order or short-range spin freezing down to 70~mK. Quantum critical behavior was indicated through logarithmic divergences in both the magnetic susceptibility and the specific heat divided by temperature. Resistivity measurements exhibit non-Fermi-liquid behavior, with a Fermi liquid recovered under magnetic fields or high pressures. First-principles calculations identify competing nearest-neighbor ($J_1$) and next-nearest-neighbor ($J_2$) exchange interactions, with $J_2/J_1 \sim -0.5$, pointing to strong magnetic frustration. The interaction frustration is reduced, and magnetically ordered phases are stabilized upon the application of negative or positive pressures. This work offers a rare example of zero-field, ambient pressure quantum criticality mainly driven by interaction frustration in a square lattice.