Effect of Li-C and Li-Al codoping in MgB2 single crystals

Nikolai D. Zhigadlo 1Janusz Karpinski 1Sergiy Katrych 1Mauro Tortello 1,2Bertram Batlogg 1Roman Puzniak 1,3K. Rogacki 1,4

1. Laboratory for Solid State Physics ETH (ETH), Schafmatstr. 16, Zürich 8093, Switzerland
2. Dipartimento di Fisica, Politecnico di Torino, Italy, corso Duca degli Abruzzi, 24, Torino 10129, Italy
3. Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, Poland
4. Polish Academy of Sciences, Institute of Low Temperature and Structure Research (INTiBS), Okólna 2, Wrocław 50-422, Poland

Abstract

Two nearly noninteracting π and σ bands of different dimensionality are key ingredients in MgB2. Critical temperature and other superconducting properties of two-band superconductor depend on the doping level and on the interband and intraband scattering and can be modified by chemical substitutions. Due to strongly anisotropic character of MgB2, single crystal studies of its anisotropic properties are very important. In the crystals codoped simultaneously with Li-C and Li-Al one can expect compensation of electron doping with C or Al and increase of Tc. Following this strategy, we synthesized a series of Mg1-xLix(B1-yCy)2 and Mg1-x(Al,Li)xB2 single crystals under high-pressure/high-temperature conditions. Our experimental results show that holes introduced with Li in Li-C codoped crystals cannot counterbalance electrons coming from C. The Tc reduction in Li-C codoped crystals is a sum of Tc reduction of separate Li and C doping. The possible reason of it can be that holes added by Li occupy π band and do not compensate the electrons from C, which fill the σ band. The comparison of the results on Mg1-x(Al,Li)xB2 with previous experiments on Mg1-xAlxB2 crystals shows that Tc reduction is a function of Al concentration alone. This finding suggests that effect of Li in MgB2 is far from trivial and not yet understood. The total influence of codoping on Tc of MgB2 should be understood as a result of the competition of two effects: the first one is a codoping effect related to the changes of the carrier concentration and the second one is related to the introduction of new scattering centers, leading to the modification of the interband and/or intraband scattering.

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Presentation: Poster at Joint Fith International Conference on Solid State Crystals & Eighth Polish Conference on Crystal Growth, by Nikolai D. Zhigadlo
See On-line Journal of Joint Fith International Conference on Solid State Crystals & Eighth Polish Conference on Crystal Growth

Submitted: 2007-01-15 18:47
Revised:   2009-06-07 00:44
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