is not prone to some of the problems (solid air plugs, etc.) of helium in piping. Many other cuprate superconductors have since been discovered, and the theory of superconductivity in these materials is one of the major outstanding challenges of theoretical condensed-matter physics. In March 2001, superconductivity of magnesium diboride () was found with Tc = 39 K. In 2008, the oxypnictide or iron-based superconductors were discovered, which led to a flurry of work in the hope that studying them would provide a theory of the cuprate superconductors. In 2013, room-temperature superconductivity was attained in YBCO for picoseconds, using short pulses of infrared laser light to deform the material's crystal structure. In 2017 it was suggested that undiscovered superhard materials (e.g. critically doped beta-titanium Au) might be a candidate for a new superconductor with Tc, substantially higher than HgBaCuO (138 K), possibly up to 233 K, which would be higher even than H2S. A lot of research suggests that additionally nickel could replace copper in some perovskites, offering another route to room temperature. Li+ doped materials can also be used, i.e. the spinel battery material LiTi2Ox and the lattice pressure can increase Tc to over 13.8 K. Also LiHx has been theorized to metallise at a substantially lower pressure than H and could be a candidate for a Type 1 superconductor. Historical publications Papers by H.K. Onnes "The resistance of pure mercury at helium temperatures". Comm. Leiden. April 28, 1911. "The disappearance of the resistivity of mercury". Comm. Leiden. May 27, 1911. "On the sudden change in the rate at which the resistance of mercury disappears". Comm. Leiden. November 25, 1911. "The imitation of an ampere molecular current or a permanent magnet by means of a supraconductor". Comm. Leiden. 1914. BCS theory Other key papers F. London and H. London, "The electromagnetic equations of the supraconductor," Proc. Roy. Soc. (London) A149, 71 (1935), ISSN 0080-4630. V.L. Ginzburg and L.D. Landau, Zh. Eksp. Teor. Fiz. 20, 1064 (1950) A.A. Abrikosov, "On the magnetic properties of superconductors of the second group," Soviet Physics JETP 5, 1174 (1957) Patents Tesla, Nikola, "Means for Increasing the Intensity of Electrical Oscillations", March 21, 1900. See also Superconductivity Macroscopic quantum phenomena Timeline of low-temperature technology Technological applications of superconductivity High-temperature superconductivity External links and references Heike Kamerlingh Onnes, "Investigations into the properties of substances at low temperatures, which have led, amongst other things, to the preparation