Tuning the multiorbital Mott transition of BaCoS2

In this thesis we tune the Mott insulating phase of BaCoS2, a playground for the study of electronic correlations in a multiorbital system. We first developed a novel self-flux technique to grow single crystals of improved quality and size. We then confirmed a stable orthorhombic Cmma phase at ambient conditions where the orthorhombic distortion is concomitant to a long-range AFM order, suggesting a scenario of orbital ordering that stabilises this order. Next, we explored the possibility of inducing a metallic state in BaCoS2 using chemical pressure and electronic doping as control parameters. For this goal, we successfully applied HP technique to the synthesis of Ba1−xSrxCoS2 and Ba1−xKxCoS2 samples with x up to 0.07. The partial substitution of Ba for Sr or K is expected to produce chemical pressure or hole-doping, respectively, thus favouring a metallic phase in both cases. We find that both substitutions induce similar structural changes, and a full suppression of the orthorhombic distortion and of the AFM order. However, no indication of metallic properties is found in the Ba1−xSrxCoS2 samples. However, a sizeable value of Sommerfeld coefficient,γ= 5.7mJ mol−1K−2 is found at 7% of K-substitution suggesting a metallic state induced by hole doping.