---
DOAJ_listed: '1'
OA_place: publisher
OA_type: gold
PlanS_conform: '1'
_id: '22755'
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.
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.
article_number: '031042'
article_processing_charge: Yes
article_type: original
arxiv: 1
author:
- first_name: Maksym
  full_name: Serbyn, Maksym
  id: 47809E7E-F248-11E8-B48F-1D18A9856A87
  last_name: Serbyn
  orcid: 0000-0002-2399-5827
- first_name: Alexander
  full_name: Avdoshkin, Alexander
  last_name: Avdoshkin
- first_name: Oriana K.
  full_name: Diessel, Oriana K.
  last_name: Diessel
- first_name: David A.
  full_name: Huse, David A.
  last_name: Huse
citation:
  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>
  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>
  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>.
  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.
  ista: Serbyn M, Avdoshkin A, Diessel OK, Huse DA. 2026. Eigenstate thermalization
    in thermal first-order phase transitions. Physical Review X. 16(3), 031042.
  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>.
  short: M. Serbyn, A. Avdoshkin, O.K. Diessel, D.A. Huse, Physical Review X 16 (2026).
corr_author: '1'
das_tickbox: '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.
date_created: 2026-08-24T06:57:25Z
date_published: 2026-08-18T00:00:00Z
date_updated: 2026-09-09T07:01:47Z
day: '18'
ddc:
- '530'
department:
- _id: MaSe
doi: 10.1103/4zs8-7kf4
external_id:
  arxiv:
  - '2601.08347'
file:
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  date_created: 2026-09-09T07:00:24Z
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fulldoi: https://doi.org/10.1103/4zs8-7kf4
has_accepted_license: '1'
intvolume: '        16'
issue: '3'
language:
- iso: eng
month: '08'
oa: 1
oa_version: Published Version
publication: Physical Review X
publication_identifier:
  issn:
  - 2160-3308
publication_status: published
publisher: American Physical Society
quality_controlled: '1'
researchdata_availability: upon request
scopus_import: '1'
status: public
supplementarymaterial: yes
title: Eigenstate thermalization in thermal first-order phase transitions
tmp:
  image: /images/cc_by.png
  legal_code_url: https://creativecommons.org/licenses/by/4.0/legalcode
  name: Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)
  short: CC BY (4.0)
type: journal_article
user_id: 2DF688A6-F248-11E8-B48F-1D18A9856A87
volume: 16
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...