Orbital-dependent singlet state observed in quantum antiferromagnet chain BaCoTe₂O₇

Motivated by recent theories on orbital effect by Linet al(2024Phys. Rev. B109155163), we propose an orbital-dependent singlet state for spin-3/2 systems on a zigzag spin antiferromagnetic (AFM) chain BaCoTe₂O₇. 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 belowT_N∼ 6 K. Thec-axis magnetization exhibits a phase transition from singlet ground state to triplet state, accompanied with two boundaries atHc1∼8.2 T andHc2∼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 BaCoTe₂O₇is possibly originated from forming a Heitler-London state. The current results indicate that BaCoTe₂O₇is the candidate material for the observation of the orbital-selective phase due to the largeU.