Resolution of zigzag magnetic correlations in Na-deficient NaxIrO3 without long-range ordering

• Published in: Physical review. B 2022-08, Vol.106 (7)
• Main Authors: Kim, Jungho, Zhao, Hengdi, Cao, Gang
• Format: Article
• Language: English
• Subjects: CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; honeycomb lattice; iridates; Kitaev-Heisenberg model; quantum spin liquid; resonant inelastic x-ray scattering; RIXS
• ISSN: 2469-9950; 2469-9969
• DOI: 10.1103/PhysRevB.106.075157

The materials search for Kitaev quantum spin liquids led to the discovery of many honeycomb lattice materials. Much attention has been paid to materials without magnetic order down to the lowest temperatures. The newly synthesized Na-deficient NaxIrO3 has been found to bear no sign of long-range magnetic order above 1 K from physical property measurements. In this paper, we report momentum-and energy-resolved excitation spectra in Na-deficient NaxIrO3 measured using a resonant inelastic x-ray scattering spectrometer. Orbital excitation spectra show that the octahedral and trigonal crystal field splittings are larger in NaxIrO3 than in Na2IrO3. On the other hand, the low-energy spectrum at low temperature shows a wave-vector dispersion and a spectral weight distribution that are similar to those of Na2IrO3, revealing that the two-dimensional zigzag magnetic correlations in NaxIrO3 are similar to those in Na2IrO3 in terms of the ordered magnetic moment direction and three dynamically fluctuating zigzag orders. The azimuth angle dependence of the low-energy spectrum corroborates these results. The two-dimensional zigzag magnetic correlations rapidly weaken until 50 K. At high temperatures, the spectral weight distribution of the low-energy excitation resembles that of the pure Kitaev model, indicating that the Kitaev interaction dominates the dynamic magnetic response at high temperature. Here we suggest that the larger crystal field and distortion and the weakened longer-range Heisenberg exchange interactions due to the Na deficiency in NaxIrO3 contribute to bring NaxIrO3 away from the zigzag long-range magnetic order phase.