Anomalous Enhancement of Critical Current Density in Superconductors with Various Configurations of Columnar Defects*

Significant enhancement of critical current density (J_c) by columnar defects (CDs) introduced by heavy-ion irradiation has been demonstrated in cuprate and iron-based superconductors (IBSs) [1,2]. Recently, we have discovered that J_c shows a broad peak (anomalous peak effect: APE) at around 1/3 of B_Φ (dose equivalent matching field) in IBSs with splayed CDs, [3]. Similar broad enhancement of J_c was also reported in a conventional superconductors 2H-NbSe₂ when tilted CDs are introduced at an angle from the c-axis [4]. The relationship between the two kinds of J_c enhancements induced by CDs in different superconductors with different configurations of CDs remains elusive. To clarify their relationship, we introduced splayed CDs into NbSe₂ and tilted CDs into IBSs and studied the evolution of APE as functions of the angle of CDs (θ_CD) and B_Φ.

It turns out that APE shows up in both of the above cases. Due to very large J_c and resulting large self-field, B_Φ dependence of APE in IBSs is difficult to follow. On the other hand, detailed B_Φ dependence of APE is clarified in NbSe₂. H_p/B_Φ increases more or less linearly at low B_Φ, and it shows a tendency of saturation at higher B_Φ before it is suppressed at very large B_Φ, possibly due to significant suppression of superconductivity in NbSe₂.

 

[1] L. Civale et al., Phys. Rev. Lett. 67, 648 (1991).

[2] Y. Nakajima et al., Phys. Rev. B 80, 012510 (2009).

[3] A. Park et al., Phys. Rev. B 97, 064516 (2018).

[4] S. Eley et al., Sci. Rep. 8, 13162 (2018).