PC9-6

Growth and Characterizations of Iron-based Superconductor
(Ba1-xRbx)Fe2As2 Single Crystals

Dec.3 17:30-17:45 (Tokyo Time)

*Tong Ren1, SunSeng Pyon1, Tsuyoshi Tamegai1

Dept. of Appl. Phys. The Univ. of Tokyo1

Spontaneous C4 symmetry breaking has been widely reported in iron-based superconductors. Such a novel phenomenon named "nematic superconductivity" draws a lot of attention. In particular, novel nematic states with variable direction of the principal axis has been reported in hole-doped 122-type (Ba1-xRbx)Fe2As2 [1]. On the other hand, in contrast to (Ba1-xKx)Fe2As2, not much is known on the normal state and superconducting properties of (Ba1-xRbx)Fe2As2.

In this study, we synthesized high-quality single crystals of (Ba1-xRbx)Fe2As2 close to the optimal composition of x ≈ 0.4, and have characterized normal state and superconducting properties for pristine/proton irradiated samples. The highest Tc was found to be ~38 K for pristine samples. The critical current density (J­c­) in (Ba0.56Rb0.44)Fe2As2 at 2 K under self-field (sf) is ~1.7 MA/cm­2, which is comparable to that in (Ba0.6K0.4)Fe2As2. After the H+ irradiation, Jc(2 K, sf) reaches 12 MA/cm­2 at a dose of 3 × 1016 H+/cm2, which is comparable to (Ba1-xKx)Fe2As2 (11 MA/cm­2 at x = 0.4, 5.8 × 1016 H+/cm2 [2]), but larger than those in Ba(Fe­1-xCox)2As2 (2.5 MA/cm2 at x = 0.07, 1.2 × 1016 H+/cm2 [3]), and BaFe2(As1-xPx2 (4.5 MA/cm2 at x = 0.33, 1.0 × 1016 H+/cm2 [4]). Jc at low temperatures follows the power-law dependence on the magnetic field (Jc H) with α changed from ~ 1/2 to ~ 1/3 after the H+ irradiation. Unusual peak effects with their peaks at around the self-field were observed in H+ irradiated samples. We tentatively interpret this phenomenon as being caused by the one-dimensional correlation among introduced point defects.

In addition, magneto-optical imaging based on the Faraday effect of an indicator garnet film will be employed to image superconducting state at temperatures below Tc. This technique may also allow us to image nematic domains, which will help us further explore its novel nematic state. In preparation for this observation at low temperatures, the presence of twin-boundaries is confirmed optically in underdoped samples below the structural transition.

[1] K. Ishida et al., Proc. Natl. Acad. Sci. USA, 117, 6424 (2020).
[2] T. Taen et al., Supercond. Sci. Technol. 28, 085003 (2015).
[3] T. Taen et al., Phys. Rev. B 86, 094527 (2012).
[4] A. Park et al., Phys. Rev. B 101, 224507 (2020).

Keywords: (Ba1-xRbx)Fe2As2, critical current density, H+ irradiation, nematicity

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