NEWS OF THE WEEK
SUPERCONDUCTORS: Path to higher temperatures in doubt Superconductivity researchers have arrived at a peculiar juncture in their efforts to raise the transition temperature (Tc) above the current record, 125 K (-148 °C). In recent weeks, widely separated groups investigating new thallium cuprate superconductors have reported conflicting results that may either signal an end to rising Tcs in this chemical family or point to even higher temperatures. One widely pursued goal—synthesis of a thallium cuprate containing four consecutive copper-oxygen layers—has now been achieved by at least three laboratories. Two of them have published their results. In the Aug. 11 issue of Nature [334, 510 (1988)], H. Ihara and coworkers at the Electrotechnical Laboratory, Tsukuba, Japan, announced the preparation of a sample of TlBa2Ca3Cu4On that becomes superconducting at 122 K. Last week, a Boston group led by Bill C. Giessen and Robert S. Markiewicz at Northeastern University made a similar a n n o u n c e m e n t in t h e pages of Science [241, 1198 (1988)]. Their sample of the so-called 1-2-3-4 phase showed a zero-resistance Tc of 122 K. This is a few degrees short of the highest confirmed Tc—125 K— first achieved earlier this year in Tl2Ba2Ca2Cu30io by researchers at
Tc rises as number of copper layers increases TI-Ba-Ca-Cu-0
Copper layers
TC(K)
