Superconductor-insulator transition (SIT) and its phase diagram

Phase boundary (dashed line) in Rn/L versus Rn representation
Phase boundary (dashed line) in Rn/L versus Rn representation. Click to enlarge.
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Phase diagram of a superconductor-insulator transition that appears in short and thin superconducting wires was investigated. A set of wires of various lengths is used for the first time. The boundary line we can draw across the diagram in the (R_N, R_N / L) coordinate plane representation that separates exactly the superconducting and the insulating samples: Fig.4 in The expression for this empirical phase boundary is R_N / L = (2*R_Q - R_N) / 112 nm (here R_Q = R_K / 4 = 6.45 kOhms). Wires above this line happen to be insulating, while the wires below the line are all superconducting. This line has two intercepts: (1) with the abscissa at R_N = 2*R_Q and (2) with the ordinate at R_N / L = 2 * R_Q / 112 nm. The first intercept just means all wires with R_N >2*R_Q are insulating. The second intercept means all wires with R_N / L >= 2R_Q / 112 nm are insulating. Te first conduction can be explained by the localization of electronic states and the second one by the surface effects causing superconductivity suppression. A detailed discussion of the SIT phase diagram is given in

See also images:
Chakravarty-Schmid (CS) type of the SIT phase diagram.
Chakravarty-Schmid (CS) type of the SIT phase diagram.

Related Links:
  • cond-mat archive paper on SIT
  • The substrate is dried off with forced nitrogen gas, and those nanotubes that settled onto the surface of the susbstrate may remain (highlighted). Some of these nanotubes my span the trench.
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