Single crystals of pure and substituted MgB2: crystal growth and physical properties

Janusz Karpinski 3N. Zhigadlo 3S. M. Kazakov 3J. Jun 3E. Müller 3Manuel Angst 3,6Roman Puzniak 2A. Wisniewski 2M. Eskildsen 4,7R. Gonnelli 5K. Rogacki 1

1. Polish Academy of Sciences, Institute of Low Temperature and Structure Research (INTiBS), Okólna 2, Wrocław 50-422, Poland
2. Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, Poland
3. Solid State Physics Laboratory ETH, Schafmatstr. 16, Zürich CH-8093, Switzerland
4. University of Notre Dame, Notre Dame, IN 46556, United States
5. Politecnico di Torino, Torino 10129, Italy
6. Iowa State University of Science and Technology, Ames, IA 50011, United States
7. University of Geneva, Geneva 1211, Switzerland


MgB2 is a two-gap superconductor with several anomalous properties originating from the existence of two separate sheets of the Fermi surface, one quasi 2D (σ band) and second quasi 3D (π band). This leads to temperature and field dependent anisotropy and high critical temperature of 39K. Prospects of applications of MgB2 depend on a success in increasing the critical parameters such as the upper critical field and critical current. This can be realized via substitutions of B or Mg. Substitutional chemistry is one of the most effective methods to modify the electronic properties of superconductors. Partial replacement of B by C, or Mg by Al in MgB2 single crystals introduces additional electrons which influences superconducting properties, electronic structure and energy gaps. The magnetic properties investigations with torque magnetometer and the transport investigations show twice increase of the upper critical field with carbon substitution. The behavior of two gaps as a function of temperature and field has been studied by the point contact spectroscopy and the scanning tunneling spectroscopy. However, defects introduced by substitutions led to formation of domains, vacancies and inhomogeneities in the structure, which influence the properties as well. Transition electron microscopy and single crystal x-ray investigations show the influence of substitutions on defect formation in the structure.

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Presentation: invited oral at NATO Advanced Research Workshop, by Janusz Karpinski
See On-line Journal of NATO Advanced Research Workshop

Submitted: 2004-08-08 11:50
Revised:   2009-06-08 12:55
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