研究目的
To identify the origin of the suppressed n ? 1 step in Nb–Dirac semimetal Cd3As2 nanowire–Nb junctions and explore the topological superconductivity in Dirac semimetals.
研究成果
The study systematically investigated the rf response of Cd3As2 nanowire-based Josephson junctions, revealing the contribution of the 4π-periodic supercurrent through the suppression of the n ? 1 step and residual supercurrent at the n ? 0 step under low frequency irradiation. By tuning the gate voltage to enhance the surface state contribution, the odd (n ? 1) Shapiro step is further suppressed, indicating the surface origin of the 4π-periodic supercurrent. These findings help to explore topological superconductivity in Dirac semimetals.
研究不足
The suppression of the n ? 1 step can also be observed in the high-power oscillatory regime of the conventional 2π Josephson effect, making it difficult to distinguish the 4π-periodic supercurrent. The bulk conduction is inevitable, and, therefore, the 2π-periodic contribution should always exist and the 4π-periodic supercurrent cannot make the odd steps completely disappear.
1：Experimental Design and Method Selection:
The study involves measurements of radio frequency irradiation on Nb–Dirac semimetal Cd3As2 nanowire–Nb junctions with continuous power dependence at various frequencies to identify the origin of the suppressed n ? 1 step.
2：Sample Selection and Data Sources:
Cd3As2 nanowires were synthesized via the chemical vapor deposition method and transferred on silicon substrate with 285 nm-thick SiO2 layer, serving as a back gate to modulate the carrier density.
3：List of Experimental Equipment and Materials:
The selected nanowire diameter is ～90 nm. After an Ar etching process to remove the oxidized layer, Nb/Pd contacts were deposited by magnetron sputtering.
4：Experimental Procedures and Operational Workflow:
Electrical transport measurements were carried out in a dilution refrigerator with a base temperature of 12 mK. In rf measurements, the involved Josephson junction was irradiated via a coaxial line, in which an rf-driving current was coupled with dc current bias Idc together to induce phase-locked Shapiro steps.
5：Data Analysis Methods:
The evolution of step size for constant voltages Vn ? nhf/2e utilizing the binning method was derived to study the 4π-periodic supercurrent.
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