Superconducting diode effect in selectively grown topological insulator based Josephson junctions

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 <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mi>Nb</a:mi> <a:mo>/</a:mo> <a:msub> <a:mi>Bi</a:mi> <a:mrow> <a:mn>0.8</a:mn> </a:mrow> </a:msub> <a:msub> <a:mi>Sb</a:mi> <a:mrow> <a:mn>1.2</a:mn> </a:mrow> </a:msub> <a:msub> <a:mi>Te</a:mi> <a:mn>3</a:mn> </a:msub> <a:mo>/</a:mo> <a:mi>Nb</a:mi> </a:mrow> </a:math> 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 nonsinusoidal 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.