Phase fluctuation dominated superconducting transition in ultrathin Pb films: Berezinskii-Kosterlitz-Thouless transition and incoherent Cooper pairs
Jinyue Wang, Ningning Liu, Xutao Wang, Yanfu Wu, Wenxuan Zhang, Zhan Wang, Dandan Guan, Shiyong Wang, Hao Zheng, Yaoyi Li, Hao Yang, Xiaoxue Liu, Liang Liu, Canhua Liu, Jinfeng Jia
DOI 10.1103/18wq-6jdk · Physical Review B
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Abstract
We present a comprehensive study of phase fluctuation effects in ultrathin Pb films using combined scanning tunneling microscopy and two-coil mutual inductance measurements. In atomically thin films (two to four monolayers), we observe a pronounced separation between the Cooper pair formation temperature (TΔ) and the macroscopic superconducting transition temperature (Tc), signaling the emergence of incoherent Cooper pairs and a pseudogap regime above Tc. The superfluid stiffness Jn(T) exhibits distinct scaling behaviors: a Berezinskii-Kosterlitz-Thouless (BKT)-like transition with renormalized vortex dynamics in 2-ML films, and a crossover from quantum to classical phase fluctuations in 4-ML films. Thicker films (7 to 11 ML) adhere to conventional Bardeen-Cooper-Schrieffer theory, demonstrating negligible phase fluctuations despite their subcoherence-length thickness. Our results establish the dominance of phase fluctuations in low-dimensional superconductors and provide a clean experimental platform to explore BKT and incoherent pairing physics in highly crystalline systems.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| Pb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 2.6 | Pressure not reported | onset |
| Pb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 3.6 | Pressure not reported | onset |
| Pb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 5.8 | Pressure not reported | onset |
| Pb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 5.6 | Pressure not reported | onset |
| Pb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 6.5 | Pressure not reported | onset |
| Pb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 6.1 | Pressure not reported | onset |
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