Evidence for Anisotropic Superconductivity Beyond Pauli Limit in Infinite‐Layer Lanthanum Nickelates

Abstract

After being expected to be a promising analog to cuprates for decades, superconductivity has recently been discovered in infinite-layer nickelates, providing new opportunities to explore mechanisms of high-temperature superconductivity. However, in sharp contrast to the single-band and anisotropic superconductivity in cuprates, nickelates exhibit a multi-band electronic structure and an unexpected isotropic superconductivity as reported recently, which challenges the cuprate-like picture in nickelates. Here, it is shown that strong anisotropic magnetotransport behaviors exist in La-based nickelate films with enhanced crystallinity and superconductivity ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msubsup><mml:mi>T</mml:mi> <mml:mi>c</mml:mi> <mml:mi>onset</mml:mi></mml:msubsup> <mml:annotation>$T_{\rm{c}}^{{\rm{onset}}}$</mml:annotation></mml:semantics> </mml:math> = 18.8 K, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msubsup><mml:mi>T</mml:mi> <mml:mi>c</mml:mi> <mml:mi>zero</mml:mi></mml:msubsup> <mml:annotation>$T_{\rm{c}}^{{\rm{zero}}}$</mml:annotation></mml:semantics> </mml:math> = 16.5 K). The upper critical fields are anisotropic and violate the estimated Bardeen-Cooper-Schrieffer (BCS) Pauli limit ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:mrow><mml:msub><mml:mi>H</mml:mi> <mml:mrow><mml:mi>Pauli</mml:mi> <mml:mo>,</mml:mo> <mml:mi>μ</mml:mi> <mml:mo>=</mml:mo> <mml:mn>1</mml:mn> <mml:msub><mml:mi>μ</mml:mi> <mml:mi>B</mml:mi></mml:msub> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>1.86</mml:mn> <mml:mo>×</mml:mo> <mml:mrow></mml:mrow> <mml:msub><mml:mi>T</mml:mi> <mml:mrow><mml:mi>c</mml:mi> <mml:mo>,</mml:mo> <mml:mi>H</mml:mi> <mml:mo>=</mml:mo> <mml:mn>0</mml:mn></mml:mrow> </mml:msub> </mml:mrow> <mml:annotation>${H}_{\mathrm{Pauli},\mu =1{\mu}_{B}}=1.86\ensuremath{\times{}}{T}_{\mathrm{c},H=0}$</mml:annotation></mml:semantics> </mml:math> ) for in-plane magnetic fields. Moreover, the anisotropic superconductivity is further manifested by the cusp-like peak of the angle-dependent T_c and the vortex motion anisotropy under external magnetic fields.