Meissner Effect and Nonreciprocal Charge Transport in Non-Topological 1T-CrTe2/FeTe Heterostructures

Interface-induced superconductivity has recently been achieved by stacking a magnetic topological insulator layer on an antiferromagnetic FeTe layer. However, the mechanism driving this emergent superconductivity remains unclear. Here, we employ molecular beam epitaxy to grow a 1T-CrTe2 layer, a two-dimensional ferromagnet with a Curie temperature up to room temperature, on a FeTe layer. These 1T-CrTe2/FeTe heterostructures show superconductivity with a critical temperature of ~12 K. Through magnetic force microscopy measurements, we observe the Meissner effect on the surface of the 1T-CrTe2 layer. Our electrical transport measurements reveal that the 1T-CrTe2/FeTe heterostructures exhibit nonreciprocal charge transport behavior, characterized by a large magneto-chiral anisotropy coefficient. The enhanced nonreciprocal charge transport in 1T-CrTe2/FeTe heterostructures provides a promising platform for exploring the magnetically controllable superconducting diode effect.

💡 Research Summary

In this work the authors demonstrate that interface‑induced superconductivity does not require a topological overlayer: a non‑topological two‑dimensional ferromagnet, 1T‑CrTe₂, when epitaxially grown on antiferromagnetic FeTe, yields a robust superconducting state with a critical temperature Tc ≈ 12 K. Molecular‑beam epitaxy was used to fabricate a series of heterostructures denoted (m, n), where m is the number of CrTe₂ trilayers and n the number of FeTe unit cells. Structural characterization by in‑situ RHEED, ex‑situ AFM, cross‑sectional STEM‑EDS and X‑ray diffraction confirms high‑quality, atomically sharp interfaces despite the different in‑plane rotational symmetries (six‑fold for CrTe₂ versus four‑fold for FeTe). Superconductivity appears only when m ≥ 1 and n ≥ 4; Tc rises with increasing thickness of either layer and saturates at ~12 K for m ≥ 3 and n ≥ 15. Thin samples (m < 3 or n < 15) display broadened transitions and incomplete zero‑resistance, indicating spatial inhomogeneity of the superconducting condensate.

To directly verify superconductivity, low‑temperature magnetic‑force microscopy (MFM) was employed. At 2.5 K a clear positive frequency‑shift (df‑z) curve demonstrates the Meissner repulsion of magnetic flux, while at 8 K the MFM images reveal bright and dark patches on a ~10 µm length scale. The contrast diminishes with increasing temperature and vanishes above Tc (~11 K), confirming that the observed signal originates from a spatially varying superfluid density rather than extrinsic artifacts. The inhomogeneity is intrinsic, likely stemming from local thickness variations, strain, or defects, and becomes more pronounced in thinner heterostructures, where only isolated superconducting islands are present.

A second major result is the observation of strong non‑reciprocal charge transport (NRC). Because the CrTe₂/FeTe interface breaks inversion symmetry, an in‑plane magnetic field H‖ further breaks time‑reversal symmetry, allowing a quadratic term in the longitudinal voltage Vxx. The authors measured the second‑harmonic resistance R2ω as a function of the angle φ between H‖ and the current direction. R2ω/R1ω follows a sin φ dependence and scales linearly with μ0H‖, in agreement with the theoretical expression Vxx = R1ωI + γμ0H‖I²sin φ. The magneto‑chiral anisotropy coefficient γ is found to be orders of magnitude larger than that reported for (Bi,Sb)₂Te₃/FeTe heterostructures. γ increases as the excitation current I0 is raised, but excessive current suppresses superconductivity, so an optimal I0≈ 500 µA at ~6.45 Hz was used. Temperature dependence shows a Berezinskii‑Kosterlitz‑Thouless transition at TBKT≈ 11.04 K; γ grows as temperature is lowered below TBKT, indicating that the non‑reciprocal effect is strongly tied to the superconducting phase stiffness.

Overall, the study establishes 1T‑CrTe₂/FeTe as a versatile platform where (i) interface‑driven superconductivity can be realized without topological surface states, (ii) the Meissner effect confirms bulk‑like superconductivity despite nanoscale inhomogeneity, and (iii) a large magneto‑chiral anisotropy enables a superconducting diode‑like response that can be tuned by magnetic field orientation and magnitude. These findings broaden the material landscape for superconducting spintronics and suggest that magnetically controllable superconducting diodes can be engineered in purely non‑topological heterostructures.