Abstract
Tl2Mo6Se6 represents a model system for quasi-one-dimensional (quasi-1D) superconductors. We investigate its superconducting transition in detail by means of electrical transport experiments on high-quality single crystalline samples with onset Tc = 6.8 K. Our measurements indicate a highly complex superconducting transition that occurs in different stages, with a characteristic bump in the resistivity and distinct plateau structures in the supercurrent gap imaged by V–I curves. We interpret these features as fingerprints of the gradual establishment of global phase coherence in an array of weakly coupled parallel 1D superconducting bundles. In this way, we demonstrate that superconducting Tl2Mo6Se6 behaves like an intrinsic array of proximity or Josephson junctions, undergoing a complex superconducting phase-ordering transition at 4.5 K that shows many similarities to the Berezinskii–Kosterlitz–Thouless transition.
Highlights
1367-2630/11/103018+12$33.00 intrinsic array of proximity or Josephson junctions, undergoing a complex superconducting phase-ordering transition at 4.5 K that shows many similarities to the Berezinskii–Kosterlitz–Thouless transition
Since Tl2 Mo6 Se6 becomes superconducting at low temperature, while Mo6 Se6 remains metallic, a typical crystal will be composed of superconducting bundles of Tl2 Mo6 Se6 chains, several tens of nanometers in diameter, separated by narrow Tl-deficient metallic Mo6 Se6 zones. (Note that it is unclear whether any microscopic phase separation occurs in Tl2−x Mo6 Se6 : this would both increase the size and decrease the number of superconducting and metallic regions.)
4 Å carbon nanotubes grown in the linear channels of AlPO4 -5 zeolite undergo precisely this type of phase transition [9], we have identified Tl2 Mo6 Se6 as a potential candidate to undergo a similar superconducting transition
Summary
1367-2630/11/103018+12$33.00 intrinsic array of proximity or Josephson junctions, undergoing a complex superconducting phase-ordering transition at 4.5 K that shows many similarities to the Berezinskii–Kosterlitz–Thouless transition. The transverse coupling of the bundles via the Josephson effect will trigger phase coherence within the 2D lateral plane, which instantly stabilizes the longitudinal phase and restores a 3D bulk superconducting state. The Josephson coupling between the superconducting islands only becomes important at temperatures below the bump [16, 19] and complete phase coherence is only obtained when the resistance reaches zero.
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