Physics Department -  Field-free Superconducting Diode Effect in Cuprates and Kagome Superconductors

Abstract

The superconducting diode effect (SDE), which requires the simultaneous breaking of time-reversal symmetry (TRS) and inversion symmetry, is characterized by nonreciprocal critical currents and holds potential for next-generation non-dissipative electronics. However, the operating temperature of the SDE is typically low and/or the sample structure is rather complex. For the potential applications in non-dissipative electronics, efficient superconducting diode working in zero magnetic field with high operating temperature and simple configuration is highly desired. Furthermore, zero-field SDE serves as a crucial probe for spontaneous TRS and inversion symmetry breakings. Here, we report the observation of robust zero-field SDE in two distinct unconventional superconducting systems. First, we demonstrate a zero-field SDE in simple Bi2Sr2CaCu2O8+δ (BSCCO) flake devices that operates at zero magnetic field and temperatures up to 72 K [1]. A stable half-wave rectification effect, persisting beyond two hundred sweeping cycles, is demonstrated under square-wave excitation in these devices. The high operating temperature, absence of an applied magnetic field, and simple flake configuration significantly enhance the practicability of superconducting electronic devices based on high-Tc cuprate superconductors. Furthermore, the observation of the zero-field SDE in BSCCO devices suggests the possible breaking of inversion and time-reversal symmetries in cuprates. Our findings not only advance the development of practical superconducting electronics but also stimulate further theoretical and experimental investigations into spontaneous symmetry breaking in cuprates.
Second, we report SDE at zero magnetic field in kagome superconductor CsV3Sb5 nanodevices [2]. The polarity of the SDE changes randomly in repeated thermal cycling to 300 K, consistent with spontaneous TRS breaking. Crucially, on applying a perpendicular magnetic field above the charge density wave (CDW) transition temperature and then removing it to zero above the superconducting onset temperature (Tc), the polarity of the SDE follows the field direction, ascertaining that the CDW state has a macroscopic and trainable TRS-breaking directionality. The symmetry breaking continues into the superconducting state and generates the nonreciprocal critical currents. These results provide evidence for the loop-current CDW normal state with TRS breaking in CsV3Sb5.

Reference
[1]Shichao Qi et al. Nat. Commun. 16, 531 (2025).
[2]Jun Ge et al. arXiv:2506.04601 (Nature Communications 2026) https://www.nature.com/articles/s41467-026-72799-6.