Field-Free Superconducting\nDiode Effect and Magnetochiral\nAnisotropy in FeTe<sub>0.7</sub>Se<sub>0.3</sub> Junctions with the\nInherent Asymmetric Barrier

Nonreciprocal electrical transport, characterized by\nan asymmetric\nrelationship between the current and voltage, plays a crucial role\nin modern electronic industries. Recent studies have extended this\nphenomenon to superconductors, introducing the concept of the superconducting\ndiode effect (SDE). The SDE is characterized by unequal critical supercurrents\nalong opposite directions. Due to the requirement on broken inversion\nsymmetry, the SDE is commonly accompanied by electrical magnetochiral\nanisotropy (eMCA) in the resistive state. Achieving a magnetic-field-free\nSDE with field tunability is pivotal for advancements in superconductor\ndevices. Conventionally, field-free SDE has been achieved in Josephson\njunctions by intentionally intercalating an asymmetric barrier layer.\nAlternatively, internal magnetism was employed. Both approaches pose\nchallenges in the selection of superconductors and fabrication processes,\nthereby impeding the development of SDE. Here, we present a field-free\nSDE in FeTe<sub>0.7</sub>Se<sub>0.3</sub> (FTS) junction with eMCA,\na phenomenon absent in FTS single nanosheets. The field-free property\nis associated with the presence of a gradient oxide layer on the upper\nsurface of each FTS nanosheet, while eMCA is linked to spin splitting\narising from the absence of inversion symmetry. Both SDE and eMCA\nrespond to magnetic fields with distinct temperature dependencies.\nThis work presents a versatile and straightforward strategy for advancing\nsuperconducting electronics.