Three distinctive temperatures of normal-to-superconductive phase transition detected by the unique SFCO method: their crucial role for proper identification of the nature of superconductivity

Abstract

A low-power stable tunnel diode oscillator with non-traditional single-layer flat pick-up coil is an excellent MHz-range instrument with which one may study weakly expressed peculiarities of the superconductive (SC) state in tiny plate-like high-Tc superconductive (HTSC) materials. It enables to detect changes about 1 pH of the HTSC film's magnetic inductance (changes about 1 Angstrom of the SC-magnetic penetration depth, lambda) with about 6 orders relative resolution. Due to detecting coil's flat design, relatively low operation frequency, so high relative resolution and an ability of this technique to operate also in high magnetic fields the method has advantages over others. They become crucial at non-destructive studies in thin flat HTSC materials with small signals - especially near the normal-to-superconductive (N/S) phase transition (at start of formation of electron-pairs). Just due to such advantages a fine 'paramagnetic' peculiarity of the SC-transition was detected by this method in YBaCuO film recently, which precedes well-known Meissner expel. The method enabled to detect also a little absorption of a power by the HTSC film upon its SC transition, with a peak located after the onset of Meissner push-out - close to its center. Extracted from so complicated fluctuation region these subtle effects (1-st is precursor, whereas the 2-nd - posterior to the Meissner expel) indicate an existence of 3 distinctive temperatures at N/S transition. Crucial role of these specific temperatures for understanding of a real nature of the whole SC-phenomenon is discussed. Possible relation between these temperatures and the 'singlet'/'triplet' behavior of electron-pairs is pointed out and argued.