Phase fluctuations dominated superconductivity in a thick Granular Boron-Doped Diamond film

Sulagna Dutta; Subhajit Chatterjee; Vivas Bagwe; Pritam Das; S. Anantha Bharathi; C. Nikhil; M. S. Ramachandra Rao; Pratap Raychaudhuri

arXiv · 2610.34319

Phase fluctuations dominated superconductivity in a thick Granular Boron-Doped Diamond film

Sulagna Dutta·Subhajit Chatterjee·Vivas Bagwe·Pritam Das·S. Anantha Bharathi·C. Nikhil·M. S. Ramachandra Rao·Pratap Raychaudhuri

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Abstract

We investigate the superconducting properties of a 1.2-μm-thick granular boron-doped diamond film, where tightly packed grains form a disordered network of Josephson junctions. The film exhibits a sharp superconducting transition at a critical temperature, T_c ~ 3 K. Its transport properties are well described by the Ambegaokar-Halperin theory of phase fluctuations. Direct measurements of the penetration depth using a two-coil mutual inductance technique reveal classic phase-fluctuation-dominated behavior: below T_c, the superfluid density (n_s) varies linearly over a wide temperature range - a hallmark of thermal phase fluctuations - before crossing over to a T^2 dependence at ultra-low temperatures. Both the large low-temperature penetration depth, λ(0) ~ 8.8 μm, and the slope of the linear ns variation in the thermal regime reveal a remarkably low superfluid stiffness in the range of 0.5-0.8 K. These results establish granular boron-doped diamond films as an excellent model system for investigating the role of long-wavelength phase fluctuations in three-dimensional superconductors.

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Sulagna Dutta, Subhajit Chatterjee, Vivas Bagwe, Pritam Das, S. Anantha Bharathi, C. Nikhil, M. S. Ramachandra Rao, Pratap Raychaudhuri. 2026-10-25. Phase fluctuations dominated superconductivity in a thick Granular Boron-Doped Diamond film. https://arxiv.org/abs/2610.34319

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