Anharmonicity-induced excited-state quantum phase transition in the symmetric phase of the two-dimensional limit of the vibron model Carvajal, Miguel Khalouf Rivera, Jamil Pérez Bernal, Francisco We acknowledge useful discussions with José Miguel Arias, Manuel Calixto, Pedro Pérez Fernández, and Lea Santos. This project received funding from the European Union's Horizon 2020 research and innovation program under Marie Skłodowska-Curie Grant Agreement No. 872081 and from Grant No. PID2019-104002GB-C21 funded by MCIN/AEI/ 10.13039/501100011033 and, as appropriate, by ERDF A way of making Europe, by the European Union, or by the European Union NextGenerationEU/PRTR. This work was also partially supported by the Consejería de Transformación Económica, Industria, Conocimiento y Universidades, Junta de Andalucía, and European Regional Development Fund through Grants No. UHU-1262561 (J.K.-R. and F.P.-B.) and No. PY2000764 and by the Ministerio de Ciencia, Innovación y Universidades (Grant No. COOPB20364) (M.C.). Computing resources supporting this work were provided by the CEAFMC and Universidad de Huelva High Performance Computer located at the Campus Universitario el Carmen and funded by FEDER/MINECO Project No. UNHU-15CE-2848. In most cases, excited-state quantum phase transitions can be associated with the existence of critical points (local extrema or saddle points) in a system’s classical limit energy functional. However, an excited-state quantum phase transition might also stem from the lowering of the asymptotic energy of the corresponding energy functional. One such example occurs in the two-dimensional (2D) limit of the vibron model, once an anharmonic term in the form of a quadratic bosonic number operator is added to the Hamiltonian. This case has been studied in the broken-symmetry phase [Pérez-Bernal and Álvarez-Bajo, Phys. Rev. A 81, 050101 (2010)]. In the present work we delve further into the nature of this excited-state quantum phase transition and we characterize it in the symmetric phase of the model, making use of quantities such as the effective frequency, the expected value of the quantum number operator, the participation ratio, the density of states, and the quantum fidelity susceptibility. In addition to this, we extend the usage of the quasilinearity parameter, introduced in molecular physics, to characterize the phases in the spectrum of the anharmonic 2D limit of the vibron model and a practical analysis is included with the characterization of the critical energies for the linear isomers HCN and HNC. 2022-04-22T08:08:20Z 2022-04-22T08:08:20Z 2022-03-30 journal article Khalouf-Rivera, J., Pérez-Bernal, F., & Carvajal, M. (2022). Anharmonicity-induced excited-state quantum phase transition in the symmetric phase of the two-dimensional limit of the vibron model. Physical Review A, 105(3), 032215. [https://doi.org/10.1103/PhysRevA.105.032215] http://hdl.handle.net/10481/74452 10.1103/PhysRevA.105.032215 eng info:eu-repo/grantAgreement/EC/H2020/872081 http://creativecommons.org/licenses/by-nc-nd/3.0/es/ open access Atribución-NoComercial-SinDerivadas 3.0 España American Physical Society