Indirect tunneling enabled spontaneous time-reversal symmetry breaking and Josephson diode effect in TiN/Al2O3/Hf0.8Zr0.2O2/Nb tunnel junctions
Shaoqing Ding, Jinyuan Yao, Zhen Bi, Quyen Tran, Bangzhi Liu, Qi Li, Susan Trolier-McKinstry, Thomas N. Jackson, Ying Liu
DOI 10.1103/b5pl-fcby · Physical Review B
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Abstract
Josephson diode (JD) effect in Josephson tunnel junctions (JTJs) has attracted a great deal of attention due to its importance for developing superconducting-circuitry-based quantum technologies. Even though the preparation of high-quality JTJs by techniques employed in the semiconductor industry has been demonstrated, which was an important milestone because JTJs are the building blocks of superconducting electronics even before the quantum era, the JD effect has not been accomplished in them, nor has the highly desirable electrical control of the effect. We report here the fabrication of JTJs featuring a composite tunnel barrier of Al2O3 and Hf0.8Zr0.2O2 using complementary-metal-oxide-semiconductor compatible atomic layer deposition. These JTJs were found to show the JD effect in nominally zero magnetic fields with nonreciprocity controllable via an electric training current, yielding a surprisingly large diode efficiency. The quasiparticle tunneling, through which the Josephson coupling in a JTJ is established, was found to show theoretically expected gap features but no nonreciprocity. We attribute these observations to the simultaneous presence of positive and negative local Josephson couplings in the JTJs, with the negative Josephson coupling originating from indirect tunneling, which results in spontaneous time-reversal symmetry breaking. The double-minima washboard potential for the ensemble-averaged phase difference in the resistively and capacitively shunted junction model is shown to fully account for the experimentally observed JD effect.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| TiN Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 3.5 | Pressure not reported | onset |
| Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 8.3 | Pressure not reported | onset |
| NbSe2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | — | Pressure not reported | unknown |
| Bi2Sr2CaCu2O8+x Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | — | Pressure not reported | unknown |
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