In a study published in Advanced Materials, researchers from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences, along with the collaborators from Nanjing University and Yanshan University, directly observed the Meissner effect in two-dimensional (2D) superconductors using a high-sensitivity magnetic measurement technique.

2D van der Waals superconductors have rich low-dimensional quantum phenomena and unconventional properties. However, their extremely small volume and ultralow magnetic signals make it challenging to directly observe the Meissner effect. As a result, superconductivity in these systems has long been inferred primarily from zero-resistance transport measurements, which limits a comprehensive understanding of their intrinsic properties.

In this study, the researchers developed a high-sensitivity magnetic measurement technique and a theoretical framework tailored for anisotropic superconducting systems. This technique is based on their previously developed compact dynamic cantilever magnetometry technique, and it enables the quantitative extraction of key physical quantities, including magnetization, magnetic susceptibility, and diamagnetic screening efficiency.

The researchers found that this technique is much more sensitive than those for detecting magnetic signals. It achieved a magnetic moment sensitivity of approximately 1.1×10^-17 A·m²@1T and an AC susceptibility sensitivity of 9.4×10^-17 A·m²/T@1T, exceeding the detection limits of existing techniques.

Using 2M-WS₂, a specific structural phase of layered tungsten disulfide, as a model system, the researchers observed clear magnetic hysteresis loops for the first time in microscale, hundred-nanometer-thick 2D superconducting samples, revealing the characteristic behavior of type-II superconductors.

In addition, in ultrathin samples down to 4 nm thickness, the researchers achieved precise measurements of magnetic susceptibility and diamagnetic screening efficiency, providing direct experimental evidence of the Meissner effect in 2D superconductors.

This work addresses a key challenge in detecting magnetic signatures of superconductivity in low-dimensional systems, and provides a general platform for high-sensitivity magnetic characterization.

Ultrasensitive detection of the Meissner effect in two-dimensional superconductors. (Image by WANG Kang)