One of my favorite "dark horse" superconductor candidates came and went (and was more that 50% likely a scam) the "Ultraconductor".[1] I think it fits into this category as a 1 dimensional superconductor. I mention it here for completeness in the discussion.<p>The theory is that using a strong voltage gradient and UV light to grow a fiber of bipolarons in what is otherwise an insulator, results in a fiber with the conductivity of about 10,000,000 times that of copper, but a very, very narrow cross section. The growth rate is incredibly slow, so I doubt it'll be easy to commercialize.<p>[1] <a href="https://patents.google.com/patent/US5777292A/en" rel="nofollow">https://patents.google.com/patent/US5777292A/en</a><p>From the patent<p><pre><code> The most remarkable feature of these films is that the room temperature conductance through the films has been directly measured by several different techniques to be at least five orders of magnitude greater than that of metal, i.e. σ≧1011 S/cm. Moreover, indirect magnetic techniques estimate that σ≧1020 S/cm.</code></pre>