The low-temperature highly correlated quantum phase in the charge-density-wave 1T-TaS_2 compound

TL;DR

This study investigates the low-temperature magnetic phase of 1T-TaS_2, revealing a short-range correlated quantum spin state with a small magnetic moment, using neutron scattering and muon experiments.

Contribution

It provides experimental evidence for a highly correlated, short-range magnetic order in 1T-TaS_2 at low temperatures, highlighting the role of orphan spins and spin-orbit coupling.

Findings

Presence of short-range magnetic order confirmed.

Magnetic moment upper bound ~0.4 μ_B.

Supports orphan-spin and spin-orbit coupling scenario.

Abstract

A prototypical quasi-2D metallic compound, 1T-TaS_2 has been extensively studied due to an intricate interplay between a Mott-insulating ground state and a charge density-wave (CDW) order. In the low-temperature phase, 12 out of 13 Ta_{4+} 5\textit{d}-electrons form molecular orbitals in hexagonal star-of-David patterns, leaving one 5\textit{d}-electron with \textit{S} = 1/2 spin free. This orphan quantum spin with a large spin-orbit interaction is expected to form a highly correlated phase of its own. And it is most likely that they will form some kind of a short-range order out of a strongly spin-orbit coupled Hilbert space. In order to investigate the low-temperature magnetic properties, we performed a series of measurements including neutron scattering and muon experiments. The obtained data clearly indicate the presence of the short-ranged phase and put the upper bound on ~ 0.4 \textit{\mu}_B for the size of the magnetic moment, consistent with the orphan-spin scenario.