Orbital-dependent singlet state observed in quantum antiferromagnet chain BaCoTe 2 O 7

Abstract Motivated by recent theories on orbital effect by Lin et al (2024 Phys. Rev. B 109 155163), we propose an orbital-dependent singlet state for spin-3/2 systems on a zigzag spin antiferromagnetic (AFM) chain BaCoTe 2 O 7 . Here, this compound is systematically studied by single crystal growth, magnetic susceptibility, specific heat, magnetization and density functional theory (DFT). Magnetic susceptibility and specific heat demonstrate that the compound develops AFM ordering below T N ∼ 6 K. The c -axis magnetization exhibits a phase transition from singlet ground state to triplet state, accompanied with two boundaries at H c1 ∼ 8.2 T and H c2 ∼ 11.2 T at 1.7 K. Further, the block magnetic structure is reproduced by the first-principles DFT with linear combination of atomic orbitals. Hence, the spin gap uncovered in BaCoTe 2 O 7 is possibly originated from forming a Heitler–London state. The current results indicate that BaCoTe 2 O 7 is the candidate material for the observation of the orbital-selective phase due to the large U .