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

T. Klein; L. Lyard; J. Marcus; C. Marcenat; P. Szabó; Z. Hol’anová; P. Samuely; B. W. Kang; H-J. Kim; H-S. Lee; H-K. Lee; S-I. Lee

doi:10.1103/PhysRevB.73.224528

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

T. Klein, L. Lyard, J. Marcus, C. Marcenat, P. Szabó, Z. Hol’anová, P. Samuely, B. W. Kang, H-J. Kim, H-S. Lee, H-K. Lee, S-I. Lee

DOI 10.1103/PhysRevB.73.224528 · Physical Review B

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Abstract

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 ΓHc2(0)=Hc2ab(0)∕Hc2c(0) value also decreases from ∼5 in pure MgB2 samples down to ∼1.5 for x≳0.2 whereas ΓHc1(0)=Hc1c(0)∕Hc1ab(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.

Source-reported materials — not catalogue approval

Formula	Reported Tc (K)	Pressure (GPa)	Type
MgB2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	36.5	Pressure not reported	midpoint
Mg0.9Al0.1B2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	31	Pressure not reported	midpoint
Mg0.8Al0.2B2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	19.5	Pressure not reported	midpoint
Mg0.8Al0.2B2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	22.5	Pressure not reported	midpoint