Gap Structure of 12442-Type KCa₂(Fe_1-xCo_x)₄As₄F₂（x=0,0.1） Revealed by Temperature Dependence of Lower Critical Field

【摘要】 We report an in-depth investigation on the out-of-plane lower critical field H_c1 of the KCa₂(Fe_1-xCo_x)₄As₄F₂（12442-type,x=0,0.1）.The multi-gap feature is revealed by the kink in the temperature-dependent H_c1（T）curve for the two samples with different doping levels.Based on a simplified two-gap model,the magnitudes of the two gaps are determined to be Δ₁=1.2 meV and Δ₂=5.0 meV for the sample with x=0,Δ₁=0.86 meV and Δ₂=2.8 meV for that with x=0.1.With the cobalt doping,the ratio of energy gap to critical transition temperature（Δ/k_BT_c） remains almost unchanged for the smaller gap and is suppressed by 20% for the larger gap.For the undoped KCa₂Fe₄As₄F₂,the obtained gap sizes are generally consistent with the results of angle-resolved photoemission spectroscopy experiments.更多还原

【Abstract】 We report an in-depth investigation on the out-of-plane lower critical field H_c1 of the KCa₂(Fe_1-xCo_x)₄As₄F₂（12442-type,x=0,0.1）.The multi-gap feature is revealed by the kink in the temperature-dependent H_c1（T）curve for the two samples with different doping levels.Based on a simplified two-gap model,the magnitudes of the two gaps are determined to be Δ₁=1.2 meV and Δ₂=5.0 meV for the sample with x=0,Δ₁=0.86 meV and Δ₂=2.8 meV for that with x=0.1.With the cobalt doping,the ratio of energy gap to critical transition temperature（Δ/k_BT_c） remains almost unchanged for the smaller gap and is suppressed by 20% for the larger gap.For the undoped KCa₂Fe₄As₄F₂,the obtained gap sizes are generally consistent with the results of angle-resolved photoemission spectroscopy experiments.更多还原