The emergence of superconductivity and correlated insulators in magic-angle twisted bilayer graphene (MATBG) has raised the intriguing possibility that its pairing mechanism is distinct from that of conventional superconductors^1,2,3,4, as described by the Bardeen–Cooper–Schrieffer (BCS) theory. However, recent studies have shown that superconductivity persists even when Coulomb interactions are partially screened^5,6. This suggests that pairing in MATBG might be conventional in nature and a consequence of the large density of states of its flat bands. Here we combine tunnelling and Andreev reflection spectroscopy with a scanning tunnelling microscope to observe several key experimental signatures of unconventional superconductivity in MATBG. We show that the tunnelling spectra below the transition temperature T_c are inconsistent with those of a conventional s-wave superconductor, but rather resemble those of a nodal superconductor with an anisotropic pairing mechanism. We observe a large discrepancy between the tunnelling gap Δ_T, which far exceeds the mean-field BCS ratio (with 2Δ_T/k_BT_c ~ 25), and the gap Δ_AR extracted from Andreev reflection spectroscopy (2Δ_AR/k_BT_c ~ 6). The tunnelling gap persists even when superconductivity is suppressed, indicating its emergence from a pseudogap phase. Moreover, the pseudogap and superconductivity are both absent when MATBG is aligned with hexagonal boron nitride. These findings and other observations reported here provide a preponderance of evidence for a non-BCS mechanism for superconductivity in MATBG.

魔角扭曲双层石墨烯 (MATBG) 中超导性和相关绝缘体的出现提出了一种有趣的可能性，即它的配对机制不同于传统超导体^1,2,3,4，正如 Bardeen–Cooper–Schrieffer 所描述的(BCS) 理论。然而，最近的研究表明，即使库仑相互作用被部分屏蔽，超导性仍然存在^5,6. 这表明 MATBG 中的配对在本质上可能是常规的，并且是其平带状态密度大的结果。在这里，我们将隧道和 Andreev 反射光谱与扫描隧道显微镜相结合，以观察 MATBG 中非常规超导性的几个关键实验特征。我们表明低于转变温度Tc的隧道谱与传统s波_超导体的隧道谱不一致，而是类似于具有各向异性配对机制的节点超导体的隧道谱。我们观察到隧道间隙Δ _T之间存在很大差异，它远远超过平均场 BCS 比率（2 Δ _T / k_B T _c  ~ 25)，以及从 Andreev 反射光谱中提取的间隙Δ _{AR (2} Δ _AR / k _B T _c  ~ 6)。即使超导性受到抑制，隧道间隙仍然存在，表明它是从赝能隙阶段出现的。此外，当 MATBG 与六方氮化硼对齐时，赝能隙和超导性都不存在。这些发现和此处报告的其他观察结果为 MATBG 中超导性的非 BCS 机制提供了优势证据。