1/fnoise in the quasi-two-dimensional organic conductorκ−(BEDT-TTF)2Cu[N(CN)2]Cl

Abstract

Resistance noise spectroscopy is applied to bulk single crystals of the quasi-two-dimensional organic conductor $\ensuremath{\kappa}\text{\ensuremath{-}}{(\text{BEDT-TTF})}_{2}\text{Cu}[\text{N}{(\text{CN})}_{2}]\text{Cl}$ both under moderate-pressure and at ambient-pressure conditions. When pressurized, the system can be shifted to the inhomogeneous coexistence region of antiferromagnetic insulating and superconducting phases, where percolation effects dominate the electronic fluctuations [J. M\uller et al., Phys. Rev. Lett. 102, 047004 (2009)]. Independent of the pressure conditions, at higher temperatures we observe generic $1/{f}^{\ensuremath{\alpha}}$-type spectra, typical for this class of quasi-two-dimensional organic charge-transfer salts. The magnitude of the electronic noise is extremely enhanced compared to typical values of homogeneous semiconductors or metals. This indicates that a highly inhomogeneous current distribution may be an intrinsic property of organic charge-transfer salts. The temperature dependence of the nearly $1/f$ spectra can be very well described by a generalized random fluctuation model [P. Dutta, P. Dimon, and P. M. Horn, Rev. Lett. 43, 646 (1979)]. We find that the number of fluctuators and/or their coupling to the electrical resistance depend on the temperature. The phenomenological model explains a pronounced peak structure in the low-frequency noise at around 100 K, which is not observed in the resistivity itself, in terms of the thermally activated conformational degrees of freedom of the BEDT-TTF molecules' ethylene endgroups.