Influence of Al doping on the critical fields and gap values in magnesium diboride single crystals

Thierry Klein (1, 2) , L. Lyard (1) , J. Marcus (1) , C. Marcenat (3) , P. Szabo (4) , Z. Holanova (4) , P. Samuely (4) , W. Kang (5) , H.-J. Kim (5) , H.-S. Lee (5) , H.-K. Lee (5) , S.-I. Lee (5)

1 LEPES - Laboratoire d'Etudes des Propriétés Electroniques des Solides
2 IUF - Institut universitaire de France
3 SPSMS - UMR 9001 - Service de Physique Statistique, Magnétisme et Supraconductivité
4 CLTP IEP - Centre of Low Temperature Physics
5 NVCRICS

The lower Hc1 and upper Hc2 critical fields of Mg1−xAlxB2 single crystals for x=0, 0.1, and 0.2 have been deduced from local magnetization and specific heat measurements, respectively. We show that Hc1 and Hc2 are both decreasing with increasing doping content. The corresponding anisotropy parameter Hc2 0 =Hc2 ab 0 /Hc2 c 0 value also decreases from 5 in pure MgB2 samples down to 1.5 for x 0.2 whereas Hc1 0 =Hc1 c 0 /Hc1 ab 0 remains on the order of 1 in all samples. The small and large gap values have been obtained by fitting the temperature dependence of the zero-field electronic contribution to the specific heat to the two-gap model for the three Al concentrations. Very similar values have also been obtained by point contact spectroscopy measurements. The evolution of those gaps with Al concentration suggests that both band filling and interband scattering effects are present.

Domaines: Supraconductivité [cond-mat.supr-con]

Thierry Klein, L. Lyard, J. Marcus, C. Marcenat, P. Szabo, et al.. Influence of Al doping on the critical fields and gap values in magnesium diboride single crystals. Physical Review B: Condensed Matter and Materials Physics (1998-2015), 2006, 73, pp.224528. ⟨10.1103/PhysRevB.73.224528⟩. ⟨hal-00957685⟩