Anomalous carrier density independent superconductivity in iron pnictides

TL;DR

This study reports a novel form of high-temperature superconductivity in iron pnictides that remains constant across a range of doping levels, likely due to interfacial effects rather than traditional carrier density mechanisms.

Contribution

It reveals anomalous doping-independent superconductivity in iron pnictides, emphasizing the role of interface effects over carrier density in high-Tc superconductivity.

Findings

Superconductivity at ~35 K induced by TM doping in Ca0.94La0.06Fe2As2.

Superconducting transition temperature remains constant across a wide doping range.

Superconductivity exhibits two-dimensional characteristics consistent with interfacial effects.

Abstract

Dome-shape superconductivity phase diagram can commonly be observed in cuprate and iron-based systems via tuning parameters such as charge carrier doping, pressure, bond angle, and etc. We report doping electrons from transition-metal elements (TM = Co, Ni) substitution can induce high-Tc superconductivity around 35 K in Ca0.94La0.06Fe2As2, which emerges abruptly before the total suppression of the innate spin-density-wave/anti-ferromagnetism (SDW/AFM) state. Unexpectedly, the onset critical temperature for the high-Tc superconductivity stays constant for a wide range of TM doping. Possible extrinsic factors like phase separation, chemical inhomogeneity, and charge carrier cancelation effect are all excluded. This anomalous charge carrier density independent SC is very similar to the interface superconductivity in La2-xSrxCuO4-La2CuO4 bilayer system. The further verified two-dimensional (2D) nature of superconductivity by the Tinkham's angular-dependent critical field model as well as by the angle-resolved magneto-resistance measurements jointly supports the idea of interfacial effect induced high-Tc superconductivity.