{"oa":1,"dataavailabilitystatement":"There are no publicly available research data or software supporting this manuscript. Requests for further information or data should be sent to the authors.","file_date_updated":"2026-09-09T07:00:24Z","volume":16,"status":"public","title":"Eigenstate thermalization in thermal first-order phase transitions","arxiv":1,"month":"08","_id":"22755","scopus_import":"1","date_published":"2026-08-18T00:00:00Z","corr_author":"1","quality_controlled":"1","DOAJ_listed":"1","date_updated":"2026-09-09T07:01:47Z","date_created":"2026-08-24T06:57:25Z","OA_place":"publisher","fulldoi":"https://doi.org/10.1103/4zs8-7kf4","file":[{"file_size":2537492,"checksum":"8bf0d88f17783dc1e6bf4c754534d734","success":1,"date_updated":"2026-09-09T07:00:24Z","relation":"main_file","file_name":"2026_PhysicalReviewX_Serbyn.pdf","date_created":"2026-09-09T07:00:24Z","creator":"dernst","content_type":"application/pdf","access_level":"open_access","file_id":"22862"}],"acknowledgement":"A. A. acknowledges discussions and prior collaboration on related topics with Anatoly Dymarsky. M. S. acknowledges Ashwin Vishwanath for introducing him to the idea of thermal first-order phase transitions in quantum systems. This research was supported in part by Grant No. NSF PHY-2309135 to the Kavli Institute for Theoretical Physics (KITP) and by the Erwin Schrödinger International Institute for Mathematics and Physics (ESI). O. K. D. acknowledges support from the NSF through a grant for ITAMP at Harvard University. D. A. H. was supported in part by NSF QLCI Grant No. OMA-2120757.","das_tickbox":"1","article_type":"original","article_number":"031042","publication_identifier":{"issn":["2160-3308"]},"abstract":[{"lang":"eng","text":"The eigenstate thermalization hypothesis (ETH) posits how isolated quantum many-body systems thermalize, assuming that individual eigenstates at the same energy density have identical expectation values of local observables in the limit of large systems. While the ETH apparently holds across a wide range of interacting quantum systems, in this work, we show that it may require generalization in the presence of thermal first-order phase transitions. We introduce a class of all-to-all spin models, featuring first-order thermal phase transitions that stem from two distinct local maxima of entropy (two mean-field solutions that we dub “branches”) that exchange dominance in the many-body density of states as the energy is varied. We argue that, for energies in the vicinity of the thermal phase transition, eigenstate expectation values do not need to converge to the same thermal value. The system has a regime with coexistence of two classes of eigenstates corresponding to the two branches with distinct expectation values at the same energy density and another regime with Schrödinger-cat-like eigenstates that are interbranch superpositions; these two regimes are separated by an eigenstate phase transition. We propose a more general form of the ETH , support our results by semiclassical calculations and an exact diagonalization study of a microscopic spin model, and argue that the structure of eigenstates in the vicinity of thermal first-order phase transitions can be experimentally probed via nonequilibrium dynamics."}],"researchdata_availability":"upon request","ddc":["530"],"author":[{"full_name":"Serbyn, Maksym","id":"47809E7E-F248-11E8-B48F-1D18A9856A87","last_name":"Serbyn","orcid":"0000-0002-2399-5827","first_name":"Maksym"},{"first_name":"Alexander","last_name":"Avdoshkin","full_name":"Avdoshkin, Alexander"},{"last_name":"Diessel","full_name":"Diessel, Oriana K.","first_name":"Oriana K."},{"first_name":"David A.","full_name":"Huse, David A.","last_name":"Huse"}],"OA_type":"gold","supplementarymaterial":"yes","citation":{"mla":"Serbyn, Maksym, et al. “Eigenstate Thermalization in Thermal First-Order Phase Transitions.” <i>Physical Review X</i>, vol. 16, no. 3, 031042, American Physical Society, 2026, doi:<a href=\"https://doi.org/10.1103/4zs8-7kf4\">10.1103/4zs8-7kf4</a>.","ama":"Serbyn M, Avdoshkin A, Diessel OK, Huse DA. Eigenstate thermalization in thermal first-order phase transitions. <i>Physical Review X</i>. 2026;16(3). doi:<a href=\"https://doi.org/10.1103/4zs8-7kf4\">10.1103/4zs8-7kf4</a>","ieee":"M. Serbyn, A. Avdoshkin, O. K. Diessel, and D. A. Huse, “Eigenstate thermalization in thermal first-order phase transitions,” <i>Physical Review X</i>, vol. 16, no. 3. American Physical Society, 2026.","chicago":"Serbyn, Maksym, Alexander Avdoshkin, Oriana K. Diessel, and David A. Huse. “Eigenstate Thermalization in Thermal First-Order Phase Transitions.” <i>Physical Review X</i>. American Physical Society, 2026. <a href=\"https://doi.org/10.1103/4zs8-7kf4\">https://doi.org/10.1103/4zs8-7kf4</a>.","short":"M. Serbyn, A. Avdoshkin, O.K. Diessel, D.A. Huse, Physical Review X 16 (2026).","apa":"Serbyn, M., Avdoshkin, A., Diessel, O. K., &#38; Huse, D. A. (2026). Eigenstate thermalization in thermal first-order phase transitions. <i>Physical Review X</i>. American Physical Society. <a href=\"https://doi.org/10.1103/4zs8-7kf4\">https://doi.org/10.1103/4zs8-7kf4</a>","ista":"Serbyn M, Avdoshkin A, Diessel OK, Huse DA. 2026. Eigenstate thermalization in thermal first-order phase transitions. Physical Review X. 16(3), 031042."},"publication":"Physical Review X","tmp":{"short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png"},"article_processing_charge":"Yes","has_accepted_license":"1","department":[{"_id":"MaSe"}],"year":"2026","issue":"3","type":"journal_article","publisher":"American Physical Society","doi":"10.1103/4zs8-7kf4","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","publication_status":"published","language":[{"iso":"eng"}],"intvolume":"        16","oa_version":"Published Version","day":"18","PlanS_conform":"1","external_id":{"arxiv":["2601.08347"]}}