Possible spin-orbit driven spin-liquid ground state in the double perovskite phase of Ba3YIr2O9

TL;DR

This study reveals that high-pressure synthesis of Ba3YIr2O9 results in a cubic phase exhibiting a gapless quantum spin-liquid state, driven by strong spin-orbit coupling, as evidenced by magnetic, heat capacity, and NMR measurements.

Contribution

It demonstrates the realization of a spin-liquid ground state in a 5d double perovskite through pressure-induced structural transformation and highlights the role of spin-orbit coupling in stabilizing this state.

Findings

High-pressure synthesis stabilizes a cubic phase of Ba3YIr2O9.

The high-pressure phase shows no magnetic order down to 2K.

Evidence of a gapless quantum spin-liquid state with spinon Fermi surface.

Abstract

We report the structural transformation of hexagonal Ba3YIr2O9 to a cubic double perovskite form (stable in ambient conditions) under an applied pressure of 8GPa at 1273K. While the ambient pressure (AP) synthesized sample undergoes long-range magnetic ordering at 4K, the high pressure(HP) synthesized sample does not order down to 2K as evidenced from our susceptibility, heat capacity and nuclear magnetic resonance (NMR) measurements. Further, for the HP sample, our heat capacity data have the form gamma*T+beta*T3 in the temperature (T) range of 2-10K with the Sommerfeld coefficient gamma=10mJ/mol-Ir K2. The 89Y NMR shift has no T-dependence in the range of 4-120K and its spin-lattice relaxation rate varies linearly with T in the range of 8-45K (above which it is T-independent). Resistance measurements of both the samples confirm that they are semiconducting. Our data provide evidence for the formation of a 5d based, gapless, quantum spin-liquid (QSL) in the cubic (HP) phase of Ba3YIr2O9. In this picture, the T term in the heat capacity and the linear variation of 89Y 1/T1 arises from excitations out of a spinon Fermi surface. Our findings lend credence to the theoretical suggestion [G. Chen, R. Pereira, and L. Balents, Phys. Rev. B 82, 174440 (2010)] that strong spin-orbit coupling can enhance quantum fluctuations and lead to a QSL state in the double perovskite lattice.