Observation of a first-order pairing phase transition in atomic nuclei

Abstract

Experimental nuclear level densities at excitation energies below the neutron threshold follow closely a constant-temperature shape. This dependence is unexpected and poorly understood. In this work, a fundamental explanation of the observed constant-temperature behavior in atomic nuclei is presented for the first time. It is shown that the experimental data portray a first-order phase transition from a superfluid to an ideal gas of non-interacting quasiparticles. Even-even, odd-$A$, and odd-odd level densities show in detail the behavior of gap- and gapless superconductors also observed in solid-state physics. These results and analysis should find a direct application to mesoscopic systems such as superconducting clusters.

7 pages, 6 figures

References in corpus (2)

• Scissors resonance in the quasi-continuum of Th, Pa and U isotopes
• Constant-temperature level densities in the quasi-continuum of Th and U isotopes

Cited by in corpus (11)

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• Verification of detailed balance for $\gamma$ absorption and emission in Dy isotopes
• First observation of low-energy γ-ray enhancement in the rare-earth region
• Experimental level densities of atomic nuclei
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• Low-energy enhancement in the γ-ray strength functions of ${}^{73,74}$Ge
• ${}^{137,138,139}$La($n$, $\gamma$) cross sections constrained with statistical decay properties of ${}^{138,139,140}$La nuclei
• Quasicontinuum $\gamma$-decay of ${}^{91,92}$Zr: benchmarking indirect ($n,\gamma$) cross section measurements for the $s$-process
• Strong enhancement of level densities in the crossover from spherical to deformed neodymium isotopes
• Nuclear level densities and gamma-ray strength functions of ${}^{180,181,182}$Ta
• Nuclear level density studied in odd-mass nuclei in the framework of the projected shell model