Anisotropic physical properties and large critical current density in KCa2Fe4As4F2 single crystal

Abstract

We present a systematic study of electrical resistivity, Hall coefficient, magneto-optical imaging, magnetization, and STEM analyses of KCa 2 Fe 4 As 4 F 2 single crystals. Sharp diamagnetic transition and magneto-optical imaging reveal homogeneity of single crystal and prominent Bean-like penetrations of vortices. Large anisotropy of electrical resistivity, with  c / ab > 100, and semiconductor-like  c suggest that the electronic state is quasi two-dimensional. Hall effect measurements indicate that KCa 2 Fe 4 As 4 F 2 is a multiband system with holes as main carriers.Magnetization measurements reveal significantly larger J c compared with that in other iron-based superconductors with different values of J c depending on the direction of magnetic field. Origin of these J c characteristics is discussed based on microstructural observations using STEM. In addition, further enhancement of J c in KCa 2 Fe 4 As 4 F 2 for future application is demonstrated in terms of heavy-ion irradiation.

Critical Current Density and Vortex Dynamics in Pristine and Irradiated KCa2Fe4As4F2

“…In KCa 2 Fe 4 As 4 F 2 , quasi two-dimensional electronic behavior, which is similar to that of cuprate superconductors, has been revealed by neutron spin resonance [15]. The quasi two-dimensional electronic state was also suggested from the large anisotropy of electrical resistivity, with ρ c /ρ ab > 100, and semiconductor-like ρ c [16]. Furthermore, a large anisotropy parameter, γ (= H c2 ab /H c2 c )~8, was also evaluated near T c [12,16].…”

“…The quasi two-dimensional electronic state was also suggested from the large anisotropy of electrical resistivity, with ρ c /ρ ab > 100, and semiconductor-like ρ c [16]. Furthermore, a large anisotropy parameter, γ (= H c2 ab /H c2 c )~8, was also evaluated near T c [12,16]. Notable features of this highly anisotropic KCa 2 Fe 4 As 4 F 2 are moderate T c of~34 K, and larger J c , and H c2 compared with 122-type IBSs.…”

“…Notable features of this highly anisotropic KCa 2 Fe 4 As 4 F 2 are moderate T c of~34 K, and larger J c , and H c2 compared with 122-type IBSs. Large H c2 //ab above 700 kOe at low temperatures has been evaluated [17], although the irreversibility field (H irr ), which separate zero and finite J c regions, is relatively low [12,16]. The in-plane J c evaluated from the measurement of irreversible magnetization at 2 K under the self-field is 8.2 MA/cm 2 , which is significantly larger compared with that of 122-type IBSs [16].…”

“…One of the most intriguing topics in KCa 2 Fe 4 As 4 F 2 is how the significantly high J c is enhanced by adding artificial pinning centers. It is well known that J c in superconductors, such as cuprates and IBSs, can be enhanced by introducing defects using swift particle irradiations, and significant effects on physical properties, such as remarkable enhancements of J c by irradiations of heavy ions and protons have been demonstrated [16,[18][19][20][21][22][23][24][25][26][27][28][29][30]. For KCa 2 Fe 4 As 4 F 2 , enhancement of J c up to 19 MA/cm 2 at 2 K under self-field is also demonstrated by introducing columnar defects in terms of heavy-ion irradiation, although the irradiation dose is limited [16].…”

“…It is well known that J c in superconductors, such as cuprates and IBSs, can be enhanced by introducing defects using swift particle irradiations, and significant effects on physical properties, such as remarkable enhancements of J c by irradiations of heavy ions and protons have been demonstrated [16,[18][19][20][21][22][23][24][25][26][27][28][29][30]. For KCa 2 Fe 4 As 4 F 2 , enhancement of J c up to 19 MA/cm 2 at 2 K under self-field is also demonstrated by introducing columnar defects in terms of heavy-ion irradiation, although the irradiation dose is limited [16]. It is also well known that introducing point defects by proton irradiation is effective at enhancing J c in cuprate superconductors [31,32] and IBSs [24,27].…”