Crossover From Cooper-Pair Hopping to Single-Electron Hopping in Pb_x(TiO_2)_1-x Granular Films
arxiv(2023)
摘要
The electrical transport properties of Pb_x(TiO_2)_1-x (x being the
Pb volume fraction and ranging from ∼0.45 to ∼0.69) granular films
are investigated experimentally. The charging energy of the Pb granules is
reduced to less than the superconducting gap of Pb granules for the low
temperature insulating films by using high-k dielectric TiO_2 as the
insulating matrix. For the insulating films in the vicinity of the
superconductor-insulator transition, Cooper-pair hopping governs the
low-temperature hopping transport. For these films, the low-temperature
magnetoresistance is positive at low field and the resistivity vs temperature
for Cooper-pair hopping obeys an Efros-Shklovsii-type variable-range-hopping
law. A crossover from Cooper-pair-dominated hopping to
single-electron-dominated hopping is observed with decreasing x. The
emergence of single-electron-dominated hopping in the more insulating films is
due to the causation that the intergrain Josephson coupling becomes too weak
for Cooper pairs to hop between adjacent superconducting Pb granules.
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