Thermal signatures of Little-Parks effect in the heat capacity of mesoscopic superconducting rings
Résumé
We present the first measurements of thermal signatures of the Little-Parks effect using a highly sensitive nanocalorimeter. Small variations of the heat capacity $C_p$ of 2.5 millions of non interacting micrometer-sized superconducting rings threaded by a magnetic flux $\Phi$ have been measured by attojoule calorimetry. This non-invasive method allows the measurement of thermodynamic properties --- and hence the probing of the energy levels --- of nanosystems without perturbing them electrically. It is observed that $C_p$ is strongly influenced by the fluxoid quantization (Little-Parks effect) near the critical temperature $T_c$. The jump of $C_p$ at the superconducting phase transition is an oscillating function of $\Phi$ with a period $\Phi_0=h/2e$, the magnetic flux quantum, which is in agreement with the Ginzburg-Landau theory of superconductivity.
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