Quantum Magnetic Properties in Perovskite with Anderson Localized Artificial Spin-1/2.

Jagath Gunasekera,Yiyao Chen,Jose A Rodriguez-Rivera,Ashutosh Dahal,Deepak K Singh,Vitalii Dugaev,Thomas W Heitmann,Arthur Ernst,Leland W Harriger,Stefan Thomas

doi:10.1002/advs.201700978

Abstract

Quantum magnetic properties in a geometrically frustrated lattice of spin‐1/2 magnet, such as quantum spin liquid or solid and the associated spin fractionalization, are considered key in developing a new phase of matter. The feasibility of observing the quantum magnetic properties, usually found in geometrically frustrated lattice of spin‐1/2 magnet, in a perovskite material with controlled disorder is demonstrated. It is found that the controlled chemical disorder, due to the chemical substitution of Ru ions by Co‐ions, in a simple perovskite CaRuO3 creates a random prototype configuration of artificial spin‐1/2 that forms dimer pairs between the nearest and further away ions. The localization of the Co impurity in the Ru matrix is analyzed using the Anderson localization formulation. The dimers of artificial spin‐1/2, due to the localization of Co impurities, exhibit singlet‐to‐triplet excitation at low temperature without any ordered spin correlation. The localized gapped excitation evolves into a gapless quasi‐continuum as dimer pairs break and create freely fluctuating fractionalized spins at high temperature. Together, these properties hint at a new quantum magnetic state with strong resemblance to the resonance valence bond system.

Highlights

1/2 magnet, such as quantum spin liquid or solid and the associated spin partitioning of nearest neighbor spins fractionalization, are considered key in developing a new phase of matter
The enhancement in ΘCW is much more pronounced in compounds with x > 0.15, i.e., when the Co ions occupy more than one site per unit lattice
Our experimental results provide new perspective to the study of quantum magnetism in spin-1/2 system for three reasons: first, the absence of any type of magnetic order rules out the ordered dimer arrangement of artificial spin-1/2, responsible for the valence bond solid (VBS) state

Summary

Results and Discussion

The collective gapped excitation at low temperature (Figure 6a–c), centered at E = 5.9 meV, is comparable to the mean field exchange constant of Co–Co interaction, JCo–Co ≃ 6 meV. The broad continuous tail in both energy and the momentum space is reminiscent of the quasi-continuum spectrum, observed in geometrically frustrated lattice of spin-1/2.[9,26] The quasi-continuum excitation at high temperature complements the ac dynamic susceptibility measurements in x > 0.15 (Figure 3, and Figure S2, Supporting Information). The localized excitation gradually melts and the spectral weight is transferred to low energy It is as if the dimer pairs break and the freely fluctuating spins occupy the low energy spectrum between the singlet ground state and the triplet excited state in a continuous fashion, making it a gapless continuum.

Conclusion

Experimental Section

Conflict of Interest