Fig. 1: Phase diagram of Mott insulators as function of frustration and correlation strength.
From: Chasing the spin gap through the phase diagram of a frustrated Mott insulator
a While the entropy of a paramagnetic Mott insulator exceeds that of the adjacent Fermi liquid (FL), resulting in a positive slope dTMI/dp > 0 of the metal-insulator boundary, AFM order has much smaller entropy and the Clausius-Clapeyron relation yields dTN/dp < 0, as seen in κ-(BEDT-TTF)2Cu[N(CN)2]Cl36,37. b No such 'reentrance' of insulating behavior is expected for a gapless QSL, possibly realized in triangular, kagome or honeycomb lattices2,3. c Similar to AFM, also the transition from a spin-gapped VBS insulator to a metal yields dT⋆/dp < 0, for instance in EtMe3P[Pd(dmit)2]25,6. d Geometrical frustration \({t}^{{\prime} }/t\) controls the magnetic ground state of triangular-lattice Mott insulators, causing pronounced changes in the phase diagram affecting also unconventional superconductivity (SC). Experimentally, AFM has been observed for \({t}^{{\prime} }/t < 1\) in κ-(BEDT-TTF)2Cu[N(CN)2]Cl and \({\beta }^{{\prime} }\)-[Pd(dmit)2]2 salts whereas magnetic order is absent in the QSL candidates κ-(BEDT-TTF)2Cu2(CN)3, κ-(BEDT-TTF)2Ag2(CN)3 and EtMe3Sb[Pd(dmit)2]2 with \({t}^{{\prime} }/t\) close to unity26,38; VBS states were reported for EtMe3P[Pd(dmit)2]2 (\({t}^{{\prime} }/t\approx 1\))4 and κ-(BEDT-TTF)2B(CN)4 (\({t}^{{\prime} }/t\approx 1.4\))8. The frustration dependence of AFM and VBS phases is schematically indicated for these systems, calling for in-depth studies upon controlled variation of \({t}^{{\prime} }/t\).
