10.26165/JUELICH-DATA/EDX1CDBehner, GerritGerritBehner0000-0002-7218-3841Peter Grünberg Institute 9Jalil, Abdur RemanAbdur RemanJalil0000-0003-1869-2466Peter Grünberg Institute 9Grützmacher, DetlevDetlevGrützmacher0000-0001-6290-9672Peter Grünberg Institute 9Schäpers, ThomasThomasSchäpers0000-0001-7861-5003Peter Grünberg Institute 9Jülich DATA2025PhysicsTopological insulators, Josephson diode effectSchäpers, ThomasThomasSchäpersPeter Grünberg Institute 92025-11-192025-11-252502.08220173240520989115765202579840555606199750996351176403508816435613253418335688795176554798381424488080012499815926815956011826012819516754817670487654237003150905text/csvtext/csvtext/csvapplication/pdfimage/pngapplication/pdfimage/pngapplication/pdfimage/pngapplication/pdfimage/pngapplication/pdfimage/pngapplication/pdfimage/pngapplication/pdfimage/pngapplication/pdfimage/pngapplication/pdfimage/pngapplication/pdfimage/pngapplication/pdfimage/pngapplication/pdfimage/png1.0CC0 WaiverAbstract: The Josephson diode effect, where the switching current magnitude depends on its direction, arises when both time-reversal and inversion symmetries are broken - often achieved by a combination of spin-orbit interaction and applied magnetic fields. Taking advantage of the strong spin-orbit coupling inherent in three-dimensional topological insulators, we study this phenomenon in Nb/Bi0.8Sb1.2Te3/Nb Josephson weak-link junctions. Under an in-plane magnetic field perpendicular to the current direction, we observe a pronounced Josephson diode effect with efficiencies up to 7%. A crucial component of this behavior is the non-sinusoidal current-phase relationship and an anomalous phase shift, which we attribute to the presence of a ballistic supercurrent component due to the surface states. These findings open up new avenues for harnessing and controlling the Josephson diode effect in topological material systems.