Random exchange Heisenberg behavior in the electron-doped quasi-1D spin-1 chain AgVP₂S₆

Enhanced quantum fluctuations in lower dimensional materials can produce interesting states of matter such as superconductivity or the gapped Haldane phase. Recent theoretical work suggests that a pair‑density wave superconducting state can be realized by doping a one‑dimensional spin‑1 chain. Here, we investigate these claims by reporting the physical properties of single crystals of Mg_xAg_1‑xVP₂S₆ (x = 0, x = 0.017(6), x = 0.067(8), and 0.098(11)) prepared by solid-state synthesis. Single crystal X‑ray Diffraction measurements confirm that Mg²⁺ is substituting for Ag⁺ to electron dope the V³⁺ zigzag chains. Magnetization measurements reveal that electron doping breaks up the V³⁺ chains, resulting in unpaired spins at the chain ends. The Mg_xAg_1‑xVP₂S₆ series is consistent with random exchange Heisenberg antiferromagnetic chain behavior and can be well described by the exchange coupled pair model at low temperatures. Transport measurements show Mg_xAg_1‑xVP₂S₆ remains insulating in the range 0 <= x <= 0.098(11), with the band gap decreasing to 0.2 eV at x = 0.098(11). This work motivates further theoretical work for understanding the low temperature thermodynamics of doped Haldane chains as well as further experimental work for discovering superconductivity in doped Haldane chains.