Novel shape evolution in Sn isotopes from magic numbers 50 to 82

TL;DR

This paper uses advanced Monte Carlo Shell Model calculations to reveal a novel shape evolution in Sn isotopes, explaining key experimental puzzles and identifying a quantum phase transition around N=66.

Contribution

It introduces a comprehensive shell model analysis of Sn isotopes, elucidating shape changes and phase transitions driven by proton excitations and neutron number variations.

Findings

Explains the increase in B(E2) around 110Sn as shape evolution due to proton excitations.

Identifies a second-order quantum phase transition near N=66.

Describes shape and shell evolution from 100Sn to 138Sn.

Abstract

A novel shape evolution in the Sn isotopes by the state-of-the-art application of the Monte Carlo Shell Model calculations is presented in a unified way for the 100-138Sn isotopes. A large model space consisting of eight single-particle orbits for protons and neutrons is taken with the fixed Hamiltonian and effective charges, where protons in the 1g9/2 orbital are fully activated. While the significant increase of the B(E2; 0+1 -> 2+1) value, seen around 110Sn as a function of neutron number (N), has remained a major puzzle over decades, it is explained as a consequence of the shape evolution driven by proton excitations from the 1g9/2 orbital. A second-order quantum phase transition is found around N=66, connecting the phase of such deformed shapes to the spherical pairing phase. The shape and shell evolutions are thus described, covering topics from the Gamow-Teller decay of 100Sn to the enhanced double magicity of 132Sn.