Speaker
Tomislav Ivek
(Institut za fiziku)
Description
Tomislav Ivek [1], Ivan Kovačević [1], Marko Pinterić [1,2], Bojana Korin-Hamzić [1], Silvia Tomić [1], Conrad Clauss [3], Martin Dressel [3], Dieter Schweitzer [4]
[1] Institut za fiziku, P.O.Box 304, HR-10001 Zagreb, Croatia
[2] Faculty of Civil Engineering, Smetanova 17, 2000 Maribor, Slovenia
[3] 1. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70550 Stuttgart, Germany
[4] 3. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70550 Stuttgart, Germany
Much experimental and theoretical attention has been attracted by organic systems with reduced dimensionality and strong Coulomb interactions, and deservedly so due to their novel broken-symmetry phases and corresponding excitations. Here we take a detailed look at the electrodynamics of one of the most prominent charge-ordered systems, the quasi-2D conductor α-(BEDT-TTF)2I3. A semimetal at high temperatures, at 136 K this particular system transitions into an insulating, diamagnetic ground state. Within the insulating phase a long-range commensurate ordering appears in the BEDT-TTF molecular planes, the so-called "horizontal stripe" charge order. [1,2,3] We characterize the charge response of the low-temperature phase using dc resistivity, dielectric and optical spectroscopy in different crystallographic directions within the BEDT-TTF layer. [4,5] Interestingly, two dielectric relaxation modes appear in the kHz-MHz range. The large mode features an anisotropic phason-like behavior, while the small mode presents a soliton-like characteristic. The observed type of excitations agrees with the most relevant physical picture of this charge order as a cooperative bond-charge density wave with ferroelectric-like features. [6] On the other hand, puzzling phenomena including negative differential resistance and voltage oscillations have been reported under application of high electric fields. [7] Our carefully designed electric-field-dependent measurements of conductivity anisotropy within the molecular plane qualitatively confirm these findings; additionally, they reveal novel intriguing behaviors. [8].
[1] Y. Takano et al., J. Phys. Chem. Solids 62, 393 (2001).
[2] Organic Conductors, Special Topics Section, J. Phys. Soc. Jpn. 75, No. 5, (2006).
[3] T. Kakiuchi et al., J. Phys. Soc. Jpn. 76, 113702 (2007).
[4] T. Ivek et al., Phys. Rev. Lett. 104, 206406 (2010)
[5] T. Ivek et al., Phys. Rev. B 83, 165128, (2011).
[6] R. T. Clay et al., J. Phys. Soc. Jpn. 71, 1816 (2002).
[7] K.Tamura et al., J. Appl.Phys.107, 103716(1-5), (2010).
[8] T. Ivek et al., to be submitted (2012).
Primary author
Tomislav Ivek
(Institut za fiziku)
