Quantum transport of buried single-crystalline CoSi2 layers in (111)Si and (100)Si substrates

Observation of triplet superconductivity in CoSi2/TiSi2 heterostructures

Unconventional superconductivity and, in particular, triplet superconductivity have been front and center of topological materials and quantum technology research. Here, we report our observation of triplet pairing in nonmagnetic CoSi₂/TiSi₂ heterostructures on silicon. CoSi₂ undergoes a sharp superconducting transition at a critical temperature T _c ≃ 1.5 K, while TiSi₂ is a normal metal. We investigate conductance spectra of both two-terminal CoSi₂/TiSi₂ contact junctions and three-terminal T-shaped CoSi₂/TiSi₂ superconducting proximity structures. Below T _c, we observe (i) a narrow zero-bias conductance peak on top of a broad hump, accompanied by two symmetric side dips in the contact junctions, (ii) a narrow zero-bias conductance peak in T-shaped structures, and (iii) hysteresis in the junction magnetoresistance. These three independent and complementary observations point to chiral p-wave pairing in CoSi₂/TiSi₂ heterostructures. The excellent fabrication compatibility of CoSi₂ and TiSi₂ with present-day silicon-based integrated-circuit technology suggests their potential use in scalable quantum-computing devices.

Ultralow 1/f Noise in a Heterostructure of Superconducting Epitaxial Cobalt Disilicide Thin Film on Silicon

High-precision resistance noise measurements indicate that the epitaxial CoSi₂/Si heterostructures at 150 and 2 K (slightly above its superconducting transition temperature T_c of 1.54 K) exhibit an unusually low 1/f noise level in the frequency range of 0.008-0.2 Hz. This corresponds to an upper limit of Hooge constant γ ≤ 3 × 10^-6, about 100 times lower than that of single-crystalline aluminum films on SiO₂ capped Si substrates. Supported by high-resolution cross-sectional transmission electron microscopy studies, our analysis reveals that the 1/f noise is dominated by excess interfacial Si atoms and their dimer reconstruction induced fluctuators. Unbonded orbitals (i.e., dangling bonds) on excess Si atoms are intrinsically rare at the epitaxial CoSi₂/Si(100) interface, giving limited trapping-detrapping centers for localized charges. With its excellent normal-state properties, CoSi₂ has been used in silicon-based integrated circuits for decades. The intrinsically low noise properties discovered in this work could be utilized for developing quiet qubits and scalable superconducting circuits for future quantum computing.