10.26165/JUELICH-DATA/EDX1CD Behner, Gerrit0000-0002-7218-3841(Peter Grünberg Institute 9)Jalil, Abdur Reman0000-0003-1869-2466(Peter Grünberg Institute 9)Grützmacher, Detlev0000-0001-6290-9672(Peter Grünberg Institute 9)Schäpers, Thomas0000-0001-7861-5003(Peter Grünberg Institute 9) Jülich DATA 2025 Abstract: 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. Schäpers, Thomas(Peter Grünberg Institute 9)