Ivo Batistić

Investigation of the charge transport through disordered organic molecular heterojunctions

We present a three-dimensional multiparticle Monte Carlo (3DMPMC) simulation of hopping transport in disordered organic molecular media. We used this approach in order to study the charge transport across an energetically disordered organic molecular heterojunction which is known to strongly influence the characteristics of the multilayer devices based on thin organic films. The role of the energetic disorder and its spatial correlations, which govern the transport in the bulk, are examined here for the bilayer homopolar system where the heterojunction represents the bottleneck for the transport. We study the effects of disorder on both sides of the heterojunction, including the effects of the spatial correlation within each material and among the layers. The 3DMPMC approach allowed us to correctly tackle the effects of the Coulomb interaction among carriers in the region where the charge accumulation in the device is particularly important and the Coulomb interaction most pronounced. The Coulomb interact...

Scattering-dominated high-temperature phase of 1T−TiSe2: An optical conductivity study

The controversy regarding the precise nature of the high-temperature phase of 1T -TiS_e2 lasts for decades. It has intensified in recent times when new evidence for the excitonic origin of the low-temperature charge-density wave state started to unveil. Here we address the problem of the high-temperature phase through precise measurements and detailed analysis of the optical response of 1T -TiS_e2 single crystals. The separate responses of electron and hole subsystems are identified and followed in temperature. We show that neither semiconductor nor semimetal pictures can be applied in their generic forms as the scattering for both types of carriers is in the vicinity of the Ioffe-Regel limit with decay rates being comparable to or larger than the offsets of band extrema. The nonmetallic temperature dependence of transport properties comes from the anomalous temperature dependence of scattering rates. Near the transition temperature the heavy electrons and the light holes contribute equally to the conductivity; this surprising coincidence is regarded as the consequence of dominant intervalley scattering that precedes the transition. The low-frequency peak in the optical spectra is identified and attributed to the critical softening of the L-point collective mode.

Thermal conductivity of Taylor phase T-Al73Mn27 complex metallic alloy

Thermal conductivity, κ, of Taylor phase T-Al73Mn27-xPdx (x = 0 ; 2 ; 4 ; 6) complex metallic alloys (CMAs) has been studied in the temperature interval from 2 K to 300 K. Characteristic of κ are typical for CMAs: relatively small in magnitude, change of slope at about 50 K and increase above 100 K. At room temperature the magnitude of κ is between 2.7 W/mK and 3.7 W/mK. Such a low thermal conductivity originates in complex structure: aperiodic in short length scale, that leads to frequent electron scattering (i.e. to low electronic contribution to the thermal conductivity), while large lattice constant defines a small Brillouin zone that enhances Umklapp scattering of extended phonons. Above 100 K non-extended (localized) lattice vibrations are thermally excited, the hopping gives a new heat carrying channel resulting in the typical increase of the thermal conductivity with temperature.