Emergent Random Spin Singlets in Disordered Spin-1/2 perovskite BaCu$_{1/3}$Ta$_{2/3}$O$_3$

TL;DR

This study explores a disordered perovskite material where random magnetic interactions lead to a novel disordered quantum ground state, characterized by emergent random spin singlets without magnetic order down to very low temperatures.

Contribution

It demonstrates the realization of a bounded exchange randomness disordered quantum state, differing from the traditional infinite-randomness fixed point in spin systems.

Findings

No magnetic order observed down to 0.1 K

Presence of a broad distribution of exchange couplings

Evidence for a disordered quantum ground state

Abstract

We investigate the disordered perovskite BaCu$_{1/3}$Ta$_{2/3}$O$_3$, where Cu (spin-1/2) and Ta randomly occupy a pseudo-cubic lattice. Synchrotron X-ray diffraction and X-ray absorption spectroscopy establish the local nature of the disorder, revealing the presence of structurally constrained magnetic exchange paths. No magnetic ordering or spin freezing is observed down to 0.1 K. The low-temperature magnetic and thermodynamic behavior is captured by a broad but non-singular distribution $P(J)$ of exchange couplings $J$. These results open the possibility of realizing a disordered quantum ground state where the exchange randomness is broad yet intrinsically bounded, departing from the conventional infinite-randomness fixed point driven random-singlet phase.