ABSTRACT
Superconductivity was observed in the Kagome metals cesium vanadium antimonide (CsV₃Sb₅) or CVS at the critical transition temperature Tc = 2.5K. But the resistivity of the CVS started decreasing even around 4K, and vanished at 1K. In general, for superconductors, the resistivity suddenly drops to zero at Tc. In Kagome metals, such a gradual drop in resistivity starting well above the bulk transition temperature (Tc) was observed in thin superconducting compound signifying existence of a fluctuating regime of superconductivity where Cooper pairs may be present in a disorganized form. In general, charge-2e Cooper pairs should persist from 4K (pre-formation of Cooper pairs before Tc) to Tc and below, and should give rise to (, Quantized flux) resistance oscillations. Instead, the experimental observations led to the existence of oscillations at the flux period of between 2K and 3K; and of between 1K and 2K; and the period becoming dominant in the zero-resistance regime below 1K only. Thus, the periodicities and could emphatically mean that two and/or three Cooper pairs may coalesce into Cooper molecules with Cooper molecules having a total charge of 4e and/or 6e. Since a Cooper pair behaves effectively as a boson, these Cooper molecules can be treated as bosons, and a theory is presented, which describes the condensed state of these bosons. An expression is obtained for the quasi-particle energy in the condensed state, and this is used to calculate the specific heat (Cv), and the transition temperature (Tc). Charges of Cooper molecules will determine the magnitudes and variation of Cv and Tc with T.
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