Field-free Josephson diode and tunable ϕ0-junction in chiral kagome antiferromagnets

Abstract The recent realization of superconducting proximity effects in chiral antiferromagnets (cAFMs) opens a new route to nonreciprocal superconducting transport of fundamental interest and practical importance. Using microscopic modeling and symmetry analysis, we show that Josephson junctions formed by conventional s -wave superconductors (SCs) and cAFMs on the kagome lattice exhibit both Josephson diode effects and anomalous Josephson effects (a ϕ 0 -junction state with a finite supercurrent at zero phase bias) when spacial inversion $${\mathcal{I}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>I</mml:mi> </mml:math> , time-reversal $${\mathcal{T}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>T</mml:mi> </mml:math> , and the combined mirror-time-reversal $${{\mathcal{TM}}}_{z}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow> <mml:mi>TM</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>z</mml:mi> </mml:mrow> </mml:msub> </mml:math> symmetries are simultaneously broken. We propose two setups to realize these phenomena and achieve high diode efficiency. (i) An SC/cAFM/SC junction with spin-orbit coupling, which enables a field-free diode effect together with a tunable anomalous Josephson supercurrent. (ii) An SC/cAFM/ $${{\rm{cAFM}}}^{{\prime} }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow> <mml:mi>cAFM</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>′</mml:mo> </mml:mrow> </mml:msup> </mml:math> /SC junction, where two cAFM layers with different in-plane order orientations, under an out-of-plane Zeeman field, produce a pronounced diode effect and anomalous Josephson response. These results establish a direct link between $${{\mathcal{TM}}}_{z}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow> <mml:mi>TM</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>z</mml:mi> </mml:mrow> </mml:msub> </mml:math> symmetry breaking and nonreciprocal superconductivity, suggesting cAFMs as versatile platforms for symmetry-engineered Josephson diodes and tunable ϕ 0 -junctions.