EYA · Optical properties of MgB2-based superconductors
FP6 — Marie Curie Actions (Human Resources and Mobility)
- Duration
- 2004-09-01 → 2005-08-31
- EU contribution
- €40,000
- Participants
- 1
- Scheme
- ERG
Lines connect the coordinator with its partners.
Results in brief
Final Activity Report Summary - EYA (Optical properties of MgB2-based superconductors)
Our research interest has been focused on the study of the vibrational and the superconducting properties of various MgB2-based superconductors. This effort includes the synthesis of novel MgB2-based compounds derived from the chemical modification of the parent material and their experimental study with various complementary techniques including Raman spectroscopy both at ambient and high pressure conditions, XRD, muSR, NMR and inelastic neutron scattering. NMR data indicates a considerable increase of Hc2c with carbon doping and a drastic reduction of coherence with respect to pure MgB2. The spin-lattice relaxation rate 1/(T1T) extracted by NMR analysis demonstrates clearly the presence of a coherence peak right below Tc in pure MgB2, followed by a typical BCS decrease on cooling. Also, in the carbon-doped systems both the coherence peak and the BCS temperature dependence of 1/(T1T) weaken, an effect attributed to the gradual shrinking of the hole cylinders of the Fermi surface with electron doping. Raman spectroscopic studies show that significant changes in the Raman spectra of the MgB2xCx compounds occur for carbon concentrations x > 0.04 and these changes can be associated with carbon substitution-induced disorder in the investigated samples. The most prominent feature of our results concerning the Mg1-xAlxB2-yCy compounds is that the co-addition of Al (up to 0.02) and C (up to 0.08) retains the two-band superconductivity in the presence of significant scattering. Complementary Raman measurements show significant evidence of electron-phonon coupling attenuation in these compounds. Furthermore, inelastic neutron scattering measurements on Mg11B2-xCx samples shows that the high energy part of the generalised phonon density-of-states is hardly affected upon boron doping and that the temperature dependence of the phonon spectrum for the MgB1.96C0.04 compound clarifies the importance of certain modes in the superconducting process. Finally, we have extended our studies toward the synthesis and characterisation of carbon nanotube based composites in order to obtain low-weight composites of extraordinary mechanical properties.
Data: CORDIS, © European Union
Project objective
The discovery of superconductivity in MgB2 has initiated a frantic activity worldwide both theoretically and experimentally in order to understand its physical properties and their implications to the observed superconductivity, since the compound is very promising for practical applications. However, despite the great progress to understand the properties of MgB2, there are open questions that have to be addressed concerning the temperature and pressure response of the E2g phonon mode, which is responsible for the superconductivity in MgB2.On the other hand, these systems exhibit unique properties and atomic substitutions may influence the basic properties of MgB2 superconductor making it appropriate for potential applications. In analogy with the high Tc cuprates we will use an alternative approach for the understanding of the properties of MgB2 by following the evolution of properties of doped MgB2-systems under external perturbations like temperature or pressure. Therefore, we plan to extensively study b y means of Raman scattering at ambient conditions as well as under high pressure or low temperatures the vibrational and the super-conducting properties of various doped MgB2-based superconductors.These compounds are synthesized and characterized with various experimental techniques during my initial fellowship in Prof. K. Prassides research group (University of Sussex, UK). Also, we intent to synthesize novel mixed alkali/transition metal borides with stoichiometry, (A,TM)xMg1.xB2 where A=Li+, Na+ and TM=Z n2+, AI3+. By employing the Raman spectroscopic technique on selected doped MgB2 compounds as a function of both temperature and pressure a wealth of information can be provided about:(i) the elucidation of the role of the E2g mode in the super-conducting process,(ii) how the observed decrease of Tc upon doping is related to the reduction of the electron-phonon coupling and the induced changes of the Fermi surface
Original text from CORDIS.
Participants
- University of Patras · PATRASCoordinatorGreece
Links
Data: CORDIS, © European Union