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Title: Pseudopotential approach to superconductivity in MgB<sub>2</sub>
Authors: Sharma, K S
Bhargava, Nidhi
Jain, Ritu
Goyal, Varsha
Sharma, Ritu
Sharma, Smita
Keywords: Superconductivity
Transition temperature
Isotope effect
Electron-phonon interaction
Issue Date: Jan-2010
Publisher: CSIR
Abstract: Superconductivity in MgB<sub>2</sub> has been re-examined in BCS-Eliashberg framework by employing Mc-Millan’s [<i style="">Phys Rev</i>, 167 (1968) 331] <i style="">T</i><sub>c</sub>-equation and form factors of MgB<sub>2</sub> computed from the form factors of component metals (Model-I). The empty core model pseudopotential due to Ashcroft [<i style="">Phys Lett</i>, 23 (1966) 48] and random phase approximation form of dielectric screening due to Gellmann and Brueckner [<i style="">Phys Rev</i>, 106 (1958) 364] are used in the present work. An excellent agreement between the present values and other theoretically computed values of <i style="">T</i><sub>c</sub> and with the relevant experimental data for MgB<sub>2 </sub>confirms the validity of the present approach.<sub> </sub>The explicit dependence of λ and <i style="">T</i><sub>c</sub> on the isotopic masses of Mg and B, as revealed from the present work, confirms the role of lattice vibrations in the superconducting behaviour of MgB<sub>2 </sub>and the high value of <i style="">T</i><sub>c</sub> in it may be attributed to the phonon mediated e-e interaction coupled with higher values of phonon frequencies due to light mass of B atoms. It has also been observed that the pseudo-atom model (Model-II) with appropriate choice of the potential parameter <i style="">r</i><sub>c</sub> successfully explains high value of <i style="">T</i><sub>c</sub> and isotope effect in MgB<sub>2</sub>, confirming the prominent role played by electron-phonon interaction in the high-<i style="">T</i><sub>c</sub><i style=""> </i>superconductivity observed in MgB<sub>2</sub>. The isotope effect exponent <img src='/image/spc_char/alpha.gif' border=0>-values obtained from the two models are in complete agreement with each other and the present value <img src='/image/spc_char/alpha.gif' border=0> = 0.46 is also much closer to the BCS value of 0.5. Interaction strength <i style="">N</i><sub>0</sub><i style="">V</i> values obtained from the two models are also in perfect agreement with each other and the present value <i style="">N</i><sub>0</sub><i style="">V</i> = 0.48 suggests that MgB<sub>2</sub> is a strong coupling superconductor.
Description: 59-66
ISSN: 0975-1041 (Online); 0019-5596 (Print)
Appears in Collections:IJPAP Vol.48(01) [January 2010]

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