Interaction of Magnetic Fields with Spinons in a Fractionalized State

TL;DR

This study reveals how magnetic fields induce localization of spinons in a quantum spin liquid, dramatically affecting thermal properties without altering magnetic susceptibility or electrical resistivity.

Contribution

It demonstrates a novel field-induced localization mechanism of spinons in a QSL, leading to significant changes in heat capacity and thermal conductivity.

Findings

Magnetic field causes a 5000% increase in heat capacity below 150 mK.

Thermal conductivity is suppressed by up to 40% below 4 K.

AC susceptibility and resistivity remain nearly unchanged.

Abstract

The 4d-electron trimer lattice exhibits either a quantum spin liquid (QSL) or a heavy-fermion strange metal (HFSM) phase, depending on Nb content. In the QSL state, itinerant spinons act as effective heat carriers, enhancing thermal conductivity. Strikingly, applying a magnetic field up to 14 T causes an abrupt increase in heat capacity by as much as 5000% below 150 mK, disrupting the linear temperature dependence characteristic of both phases. Meanwhile, AC magnetic susceptibility and electrical resistivity remain nearly unchanged, while thermal conductivity is suppressed by up to 40% below 4 K. These observations suggest that spinons, though charge-neutral, are highly sensitive to magnetic fields at low temperatures. We propose that the field induces Anderson localization of spinons, leading to emergent non-magnetic two-level systems that account for the rapid rise in heat capacity. These findings uncover a previously unexplored regime of spinon dynamics, governed by field-induced localization and distinct from conventional magnetic or transport signatures. Comments: To appear in npj Quantum Materials.