Novel sample-thickness-dependent flux pinning behaviors of KFe ₂ As ₂ intercalations in CaKFe ₄ As ₄ single crystals

Abstract

Abstract We report the strong dependence of critical current density ( J c ) on the sample thickness ( d ) along the crystalline c -axis in CaKFe 4 As 4 single crystals. The J c can be respectively enlarged more than 3 and 50 times in H parallel to c -axis ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mi>J</mml:mi> <mml:mrow> <mml:mtext>c</mml:mtext> </mml:mrow> <mml:mi>c</mml:mi> </mml:msubsup> </mml:math> ) and ab -plane ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mi>J</mml:mi> <mml:mrow> <mml:mtext>c</mml:mtext> </mml:mrow> <mml:mrow> <mml:mi>a</mml:mi> <mml:mi>b</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> ) at temperature of 5 K and high magnetic fields of 8 T when the d is reduced from 88 to 2.0 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>μ</mml:mi> <mml:mrow> <mml:mtext>m</mml:mtext> </mml:mrow> </mml:math> . It is surprising to find that, accompanied by the enhanced J c , the fishtail effect fades away with the decreasing d . We believe that both the origins of enhanced J c and the fishtail effect in CaKFe 4 As 4 may have close relationship with the interlayer coupling between CaKFe 4 As 4 and the intercalations of KFe 2 As 2 . Our results not only demonstrate an encouraging prospect for application of CaKFe 4 As 4 , but also illuminate new light on the origin of fishtail effect in iron-based superconductors.