Pressure tuning of competing interactions on a honeycomb lattice

Exchange interactions are mediated via orbital overlaps across chemical bonds. Thus, modifying the bond angles by physical pressure or strain can tune the relative strength of competing interactions. Here we present a remarkable case of such tuning between the Heisenberg (J) and Kitaev (K) exchange, which respectively establish magnetically ordered and spin liquid phases on a honeycomb lattice. We observe a rapid suppression of the Néel temperature (T_N) with pressure in Ag₃LiRh₂O₆, a spin-1/2 honeycomb lattice with both J and Kcouplings. 

Using a combined analysis of x-ray data and first-principles calculations, we find that pressure modifies the bond angles in a way that increases the ∣K/J∣ ratio and thereby suppresses T_N. Consistent with this picture, we observe a spontaneous onset of muon spin relaxation (μSR) oscillations below T_N at low pressure, whereas in the high pressure phase, oscillations appear only when T < T_N/2. Unlike other candidate Kitaev materials, Ag₃LiRh₂O₆is tuned toward a quantum critical point by pressure while avoiding a structural dimerization in the relevant pressure range.