Variational theory of angulons and their rotational spectroscopy Zeng, Zhongda Yakaboylu, Enderalp ; https://orcid.org/0000-0001-5973-0874 Lemeshko, Mikhail ; https://orcid.org/0000-0002-6990-7802 Shi, Tao Schmidt, Richard ddc:530 The angulon, a quasiparticle formed by a quantum rotor dressed by the excitations of a many-body bath, can be used to describe an impurity rotating in a fluid or solid environment. Here, we propose a coherent state ansatz in the co-rotating frame, which provides a comprehensive theoretical description of angulons. We reveal the quasiparticle properties, such as energies, quasiparticle weights, and spectral functions, and show that our ansatz yields a persistent decrease in the impurity’s rotational constant due to many-body dressing, which is consistent with experimental observations. From our study, a picture of the angulon emerges as an effective spin interacting with a magnetic field that is self-consistently generated by the molecule’s rotation. Moreover, we discuss rotational spectroscopy, which focuses on the response of rotating molecules to a laser perturbation in the linear response regime. Importantly, we take into account initial-state interactions that have been neglected in prior studies and reveal their impact on the excitation spectrum. To examine the angulon instability regime, we use a single-excitation ansatz and obtain results consistent with experiments, in which a broadening of spectral lines is observed while phonon wings remain highly suppressed due to initial-state interactions. American Institute of Physics 2023 info:eu-repo/semantics/article doc-type:article text http://purl.org/coar/resource_type/c_2df8fbb1 https://research-explorer.ista.ac.at/record/12831 https://research-explorer.ista.ac.at/download/12831/12841 Zeng Z, Yakaboylu E, Lemeshko M, Shi T, Schmidt R. Variational theory of angulons and their rotational spectroscopy. <i>The Journal of Chemical Physics</i>. 2023;158(13). doi:<a href="https://doi.org/10.1063/5.0135893">10.1063/5.0135893</a> eng info:eu-repo/semantics/altIdentifier/doi/10.1063/5.0135893 info:eu-repo/semantics/altIdentifier/e-issn/1089-7690 info:eu-repo/semantics/altIdentifier/wos/000970038800001 info:eu-repo/semantics/altIdentifier/arxiv/2211.08070 info:eu-repo/semantics/altIdentifier/pmid/37031113 https://creativecommons.org/licenses/by/4.0/ info:eu-repo/semantics/openAccess