Magnetic field effects in an octupolar quantum spin liquid candidate

TL;DR

This study investigates how magnetic fields influence an octupolar quantum spin liquid in Ce2Zr2O7, revealing a transition to ferromagnetic order and providing evidence for octupolar interactions as the origin of the QSL state.

Contribution

It demonstrates the magnetic field-induced transition in Ce2Zr2O7 and identifies it as a strong candidate for an octupolar U(1) quantum spin liquid, highlighting the role of octupolar interactions.

Findings

Magnetic field induces an Anderson-Higgs transition in Ce2Zr2O7.

Octupolar spin waves are invisible to neutrons but affect heat capacity.

Ce2Zr2O7 is a candidate for an octupolar U(1) quantum spin liquid.

Abstract

Quantum spin liquid (QSL) is a disordered state of quantum-mechanically entangled spins commonly arising from frustrated magnetic dipolar interactions. However, QSL in some pyrochlore magnets can also come from frustrated magnetic octupolar interactions. Although the key signature for both dipolar and octupolar interaction-driven QSL is the presence of a spin excitation continuum (spinons) arising from the spin quantum number fractionalization, an external magnetic field-induced ferromagnetic order will transform the spinons into conventional spin waves in a dipolar QSL. By contrast, in an octupole QSL, the spin waves carry octupole moments that do not couple, in the leading order, to the external magnetic field or to neutron moments but will contribute to the field dependence of the heat capacity. Here we use neutron scattering to show that the application of a large external magnetic field to Ce2Zr2O7, an octupolar QSL candidate, induces an Anderson-Higgs transition by condensing the spinons into a static ferromagnetic ordered state with octupolar spin waves invisible to neutrons but contributing to the heat capacity. Our theoretical calculations also provide a microscopic, qualitative understanding for the presence of octupole scattering at large wavevectors in Ce2Sn2O7 pyrochlore, and its absence in Ce2Zr2O7. Therefore, our results identify Ce2Zr2O7 as a strong candidate for an octupolar U (1) QSL, establishing that frustrated magnetic octupolar interactions are responsible for QSL properties in Ce-based pyrochlore magnets.