Dimensionality control and rotational symmetry breaking superconductivity in square-planar layered nickelates

TL;DR

This study reveals how dimensionality and rotational symmetry breaking influence superconductivity in square-planar layered nickelates, showing controllable crossover between 2D and 3D states and a new symmetry-breaking phase.

Contribution

It demonstrates highly tunable dimensionality and a broken rotational symmetry state in nickelate superconductors, providing insights into pairing mechanisms and symmetry effects.

Findings

Superconductivity exhibits a $C_2$ rotational symmetry breaking from the lattice's $C_4$ symmetry.

A crossover from two-dimensional to three-dimensional superconducting states was observed.

Ionic size fluctuations in the spacer layer can manipulate the superconducting dimensionality.

Abstract

The interplay between dimensionality and various phases of matter is a central inquiry in condensed matter physics. New phases are often discovered through spontaneously broken symmetry. Understanding the dimensionality of superconductivity in the high-temperature cuprate analogue $-$ layered nickelates and revealing a new symmetry-breaking state are the keys to deciphering the underlying pairing mechanism. Here, we demonstrate the highly-tunable dimensionality and a broken rotational symmetry state in the superconductivity of square-planar layered nickelates. The superconducting state, probed by superconducting critical current and magnetoresistance within superconducting transition under direction-dependent in-plane magnetic fields, exhibits a $C_2$ rotational symmetry which breaks the $C_4$ rotational symmetry of the square-planar lattice. Furthermore, by performing detailed examination of the angular dependent upper critical fields at temperatures down to 0.5 K with high-magnetic pulsed-fields, we observe a crossover from two-dimensional to three-dimensional superconducting states which can be manipulated by the ionic size fluctuations in the rare-earth spacer layer. Such a large degree of controllability is desired for tailoring strongly two/three-dimensional superconductors and navigating various pairing landscapes for a better understanding of the correlation between reduced dimensionality and unconventional pairing. These results illuminate new directions to unravel the high-temperature superconducting pairing mechanism.