Low-temperature spin-liquid phase in a S = 3/2 undistorted triangular lattice: RbAg${}_2$Cr$[$VO${}_4$$]$${}_2$

We present a series of distorted and undistorted antiferromagnetic triangular lattice (TL) compounds, AAg${}_2$Cr$[$VO${}_4$$]$${}_2$ with A = Ag, K, or Rb. The A-site cation induces slight symmetry changes of the $[$CrO${}_6$$]$ complex and thereby alters the relative orientation of the vanadate with respect to the TL. This aspect of fine-tuning allows for distinct alterations of the magnetic exchange interactions between the Cr${}^{3+}$ (3d${}^3$) ions, J${}^{Ag}$ = 3 K, J${}^K$ = 1 K, J${}^{Rb}$ = 0.5 K. We observe for the distorted TL collinear antiferromagnetic long-range order at T${}_N$ = 10 K (A = Ag), whereas the high-symmetry cases (A = K, Rb) even evade the theoretically predicted 120° long-range order in zero field down to 0.03 K. Our experiments support a spin liquid ground state for the latter compounds which is unconventional for antiferromagnetic TL systems and points towards the relevance of additional competing interaction mechanisms.