High-pressure superconductivity in yttrium: The strong-coupling approach

Abstract

Abstract In the framework of the Eliashberg formalism, the properties of the superconducting state inducing in yttrium for the pressure at p 1 ≡ 26 GPa and p 2 ≡ 31 GPa ( [ T C ] p 1 = 7.9 K and [ T C ] p 2 = 9.27 K ) have been determined. It has been proven that the value of the Coulomb pseudopotential is high and increases with the increasing pressure: [ μ ⋆ ] p 1 = 0.181 and [ μ ⋆ ] p 2 = 0.251 . Next, the order parameter ( Δ ( T ) ) , the thermodynamic critical field ( H C ( T ) ) , the specific heat in the superconducting state ( C S ( T ) ) , and the specific heat in the normal state ( C N ( T ) ) have been calculated. It has been proven that the values of the dimensionless parameters R Δ ≡ 2 Δ ( 0 ) k B T C , R C ≡ C S ( T C ) − C N ( T C ) C N ( T C ) , and R H ≡ T C C N ( T C ) H C 2 ( 0 ) significantly deviate from the predictions of the classical BCS theory: R Δ ∈ { 3.97 , 4.13 } , R C ∈ { 2.16 , 2.41 } , and R H ∈ { 0.153 , 0.152 } . The electron effective mass is high for both pressures [ m e ⋆ ] p 1 T = T C = 2.16 m e and [ m e ⋆ ] p 2 T = T C = 2.64 m e , where the symbol me denotes the electron band mass.