Abstract:
Since its discovery at 4.2 K in 1911, superconductivity remained a low-temperature phenomenon for the first 75 years, during which a microscopic BCS theory revealed phonon-mediated electron pairing. A breakthrough in 1987 raised the transition temperature Tc to 90 K and above in certain cuprate compounds through a different but as-yet unresolved mechanism. Then, recently, some hydrogen-base materials under high pressure were found to exhibit resistive, magnetic, and, in one case, qualitative calorimetric signals of superconductivity near room temperatures. In this talk, we will briefly review the history of specific heat measurements of superconductors prior to the 1957 BCS theory, and our first measurement under pressure in 1966. The thermodynamic data uniquely confirm an observed transition being a bulk effect. The high Tc also provides a broad Tc/T range for detecting fine structures, if any, of the superconducting-state electronic specific heat Ces. Justifications will be given for being able to delineate the electronic component from the total specific heat at room temperatures, intuitively thought to be dominated by the lattice contribution. High-pressure requirements will certainly be the most difficult part of the experiments. But then, looking back to between 1911 and 1956, an exponential temperature dependence of Ces was realized only after 45 years of technological advancements including, e.g., low-temperature thermometry. The challenge was temperature then, and it will be pressure now!