From Spin Glass to Quantum Spin Liquid Ground States in Molybdate Pyrochlores

TL;DR

This study investigates how chemical modifications in molybdate pyrochlores influence their magnetic ground states, revealing a transition from spin glass to quantum spin liquid driven by quantum fluctuations, with detailed experimental insights.

Contribution

It demonstrates that tuning the composition from oxide to oxynitride in molybdate pyrochlores changes the ground state from spin glass to quantum spin liquid, highlighting the role of quantum fluctuations.

Findings

Lu$_2$Mo$_2$O$_7$ exhibits a spin glass transition at 16 K.

Lu$_2$Mo$_2$O$_5$N$_2$ shows signs of a quantum spin liquid state.

Estimated spin excitation gap in the quantum spin liquid is approximately 0.05 meV.

Abstract

We present new magnetic heat capacity and neutron scattering results for two magnetically frustrated molybdate pyrochlores: $S=1$ oxide Lu$_2$Mo$_2$O$_7$ and $S={\frac{1}{2}}$ oxynitride Lu$_2$Mo$_2$O$_5$N$_2$. Lu$_2$Mo$_2$O$_7$ undergoes a transition to an unconventional spin glass ground state at $T_f {\sim} 16$ K. However, the preparation of the corresponding oxynitride tunes the nature of the ground state from spin glass to quantum spin liquid. The comparison of the static and dynamic spin correlations within the oxide and oxynitride phases presented here reveals the crucial role played by quantum fluctuations in the selection of a ground state. Furthermore, we estimate an upper limit for a gap in the spin excitation spectrum of the quantum spin liquid state of the oxynitride of ${\Delta} {\sim} 0.05$ meV or ${\frac{\Delta}{|\theta|}}\sim0.004$, in units of its antiferromagnetic Weiss constant ${\theta} {\sim}-121$ K.