Pressure-dependent optical investigations of α\alpha-(BEDT-TTF)2_2I3_3: tuning charge order and narrow gap towards a Dirac semimetal

Infrared optical investigations of $\alpha$-(BEDT-TTF)$_2$I$_3$ have been performed in the spectral range from 80 to 8000~cm$^{-1}$ down to temperatures as low as 10~K by applying hydrostatic pressure. In the metallic state, $T > 135$~K, we observe a 50\% increase in the Drude contribution as well as the mid-infrared band due to the growing intermolecular orbital overlap with pressure up to 11~kbar. In the ordered state, $T<T_{\rm CO}$, we extract how the electronic charge per molecule varies with temperature and pressure: Transport and optical studies demonstrate that charge order and metal-insulator transition coincide and consistently yield a linear decrease of the transition temperature $T_{\rm CO}$ by $8-9$~K/kbar. The charge disproportionation $\Delta\rho$ diminishes by $0.017~e$/kbar and the optical gap $\Delta$ between the bands decreases with pressure by -47~cm$^{-1}$/kbar. In our high-pressure and low-temperature experiments, we do observe contributions from the massive charge carriers as well as from massless Dirac electrons to the low-frequency optical conductivity, however, without being able to disentangle them unambiguously.Comment: 13 pages, 17 figures, submitted to Phys. Rev.

表紙、奥付、裏表紙

© 2015 Springer Science+Business Media New York. This paper is devoted to a study of the characteristic features of the composition and structure of crude oils from terrigenous Devonian producing deposits in the Minnibaevskii section of the Romashkino and Pervomai fields. Using the SynOil program, we identified the features of the molecular weight distribution of n-paraffins, cyclohexanes, and monoalkylbenzenes associated with the formation and transformation conditions in the crude oil deposits

A new matoniaceous fern from the Upper Triassic of the Caspian Depression in the context of florogenetic processes of transition from the Paleozoic to Mesozoic

© 2015, Pleiades Publishing, Ltd. A new matoniaceous fern species of the genus Phlebopteris Brongniart from the Upper Triassic of the Caspian Depression (Zhylyoiskii District, Atyrau Region, Kazakhstan) is described. It is represented by both sterile and fertile leaves preserved in situ, including the structure of sporangia and spores. The main trends in the evolution of ferns at transition from the Paleozoic to Mesozoic are discussed

Highly anisotropic energy gap in superconducting Ba(Fe0.9_{0.9}Co0.1_{0.1})2_{2}As2_{2} from optical conductivity measurements

We have measured the complex dynamical conductivity, $\sigma = \sigma_{1} + i\sigma_{2}$, of superconducting Ba(Fe$_{0.9}$Co$_{0.1}$)$_{2}$As$_{2}$ ($T_{c} = 22$ K) at terahertz frequencies and temperatures 2 - 30 K. In the frequency dependence of $\sigma_{1}$ below $T_{c}$, we observe clear signatures of the superconducting energy gap opening. The temperature dependence of $\sigma_{1}$ demonstrates a pronounced coherence peak at frequencies below 15 cm$^{-1}$ (1.8 meV). The temperature dependence of the penetration depth, calculated from $\sigma_{2}$, shows power-law behavior at the lowest temperatures. Analysis of the conductivity data with a two-gap model, gives the smaller isotropic s-wave gap of $\Delta_{A} = 3$ meV, while the larger gap is highly anisotropic with possible nodes and its rms amplitude is $\Delta_{0} = 8$ meV. Overall, our results are consistent with a two-band superconductor with an $s_{\pm}$ gap symmetry.Comment: 6 pages, 4 figures, discussion on pair-barking scattering and possible lifting of the nodes is adde

Compositional variation of thin PZT films near morphotropic phase boundary: experiment and simulation

The work was partly supported by the Ministry for Education and Science (Russian Federation) (Grant No 16.2811.2017/4.6) and RFBR (Grant No 16-02-00632)