Charge and heat transport in new materials
Complex metallic alloys (CMAs) are formed with crystal structures based on giant unit cells containing many tens, up to more than a thousand atoms per cell. Limiting cases are the quasicrystals for which the unit cells extend to infinity. Most often the structure of the CMAs, and their unit cells, can be considered to be built from, more or less interpenetrating, large atomic clusters which may posses the axes of rotational symmetries of 5, 8, 10 or 12 order. For this reason the properties of CMAs are the result of the interplay between long range order and the local order on the range of the first and second neighbours. As a result, these materials can offer unique combinations of properties, which are excluded in conventional materials.
CMAs are divided into two main groups which are regular crystals and quasicrystals
Regular crystals are described with a finite unit cell which is repeated infinitely through the space and are through this equal to the conventional crystals.
Quasicrystals (QCs) are materials with the sharp diffraction patterns which exhibit the rotational symmetries forbidden for periodic structures. Therefore they are perfectly ordered but do not have a unit cell which is repeated periodically. Quasicrystals are divided into three-dimensional icosahedral quasicrystals, i-QCs which are apperiodic in all three directions in space, and polygonal (decagonal, octagonal, dodecagonal) quasicrystals which are apperiodic in a particular plane but are periodic in a direction perpendicular to that plane.
Our main interest
is in the charge and heat transport in Al-Transition Metal based decagonal quasicrystalls (d-QCs) and a specific class of regular crystals which consists of the approximants to these decagonal quasicrystalls.
Approximant phases are characterized by large unit cells which periodically repeat in space, and by one set of the atomic planes which correspond to the quasiperiodic atomic planes of d-QCs in the sense that they show locally similar patterns. This means that their structure, on the scale of near-neighbor atoms, closely resemble each other. Further, the periodicity lengths along the stacking direction of these planes in the approximant phases are almost identical to those along the periodic direction of d-QCs. Therefore, decagonal approximants offer valid comparison to the d-QCs. Here it is important, that the translational periodicity of decagonal approximants may enable the straightforward theoretical simulation of the physical properties.
A consequence of the anisotropic and layered structure of both d-QCs and their approximants is distinct anisotropy of their physical properties. Here we are particulary interested in electrical and thermal transport properties (electrical resistivity, thermoelectric power, Hall coefficient, thermal conductivity) when measured along different crystalline directions. The research is realized on the high quality single crystals produced by the leading experts in this field.
For some our experimental results for the anisotropic transport properties in Al-TM based approximants to the decagonal quasicrystals see Laboratory equipment & Selected results, and for some interestinf problems see Stil open questions.
The policrystalline samples of these materials with unusal physical properties are, of course, no less interesting particulary because of the unconventional dependence of these properties on the chemical composition and structural disorder.
Selected Links to Qasicrystals
Research is a part of ESF (The European Science Foundation) Program: Highly Frustrated Magnets
For some interesting details of the structure and properties of highly frustrated magnets see and download some Lectures Notes from the HFM - School
Our research is focused on the studies of the heat transport in one-dimensional (1D) spin systems which are of strong current interest. From the theoretical side, there is consensus that the intrinsic spin-mediated heat transport of integrable spin models is ballistic, while the situation in nonintegrable spin models is less clear. Experimentally, such studies were stimulated by the observation of a strong anisotropy of the thermal conductivity κ(T) in some spin 1/2 ladder compounds, which has been explained by a large spin contribution κs along the ladder direction. In order to relate model calculations to experimental data, theory has to incorporate the coupling between spin excitations and the underlying lattice, while experimentally it is necessary to separate κs from the measured total κ. Here, studies of the magnetic-field dependent κ(B,T) can provide much more information than just the zero field κ(T) since strong enough magnetic fields change the spin excitation spectra and cause transitions between different quantum phases.
C-MAC Days 2014
C-MAC Days 2013
Visit of the Nobel Prize Laureate Daniel Shechtman
C-MAC Days 2012
2012 MRS Fall Meeting
Junior Travel Avwards
Physics of Low-Dimensional Conductors:
Problems & Perspectives
With a contribution by