Anomalous charge response in a novel spin-liquid candidate κ-(BEDT-TTF)2Ag2(CN)3

Novel forms of the low-temperature phases in the two-dimensional molecular solids with competing interactions between charges, spins and lattice, in particular those featuring anomalous dielectric relaxation, have been the focus of intense activity in recent years. Open issues concern the nature of collective charge excitations as well as their coupling to applied ac and dc electric fields. Dimer Mott insulator with quantum spin-liquid phase κ-(BEDT-TTF)2Cu2(CN)3 shows variable-range hopping in dc limit and dielectric response featuring relaxor-like ferroelectricity [1, 2] despite missing symmetry-breaking evidences [3]. In this presentation we report our study of the anisotropic dc and ac charge response in a novel spin-liquid candidate κ-(BEDT-TTF)2Ag2(CN)3 [4]. The obtained results indicate the presence of an anomalous dielectric response, and we discuss and compare them with κ-(BEDT-TTF)2Cu2(CN)3. The importance of anion network geometry and cation-anion coupling is emphasized. [1] M. Abdel-Jawad et al., Phys.Rev.B 82, 125119 (2010). [2] M. Pinterić et al., Phys.Rev.B 90, 195139 (2014). [3] K. Sedlmeier et al., Phys.Rev.B 86, 245103 (2012). [4] M. Pinterić et al., in preparation (2015).