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Title: Broken vertex symmetry and finite zero-point entropy in the artificial square ice ground state

In this paper, we study degeneracy and entropy in the ground state of artificial square ice. In theoretical models, individual nanomagnets are typically treated as single spins with only two degrees of freedom, leading to a twofold degenerate ground state with intensive entropy and thus no zero-point entropy. Here, we show that the internal degrees of freedom of the nanostructures can result, through edge bending of the magnetization and breaking of local magnetic symmetry at the vertices, in a transition to a highly degenerate ground state with finite zero-point entropy, similar to that of the pyrochlore spin ices. Finally, we find that these additional degrees of freedom have observable consequences in the resonant spectrum of the lattice, and predict the occurrence of edge “melting” above a critical temperature at which the magnetic symmetry is restored.
Authors:
 [1] ;  [2] ;  [1] ;  [3] ;  [4]
  1. Federal Inst. of Technology, Zurich (Switzerland). Dept. of Materials. Lab. for Mesoscopic Systems; Paul Scherrer Inst. (PSI), Villigen (Switzerland). Lab. for Micro- and Nanotechnology
  2. Helmholtz-Zentrum Dresden-Rossendorf, Dresden (Germany). Inst. of Ion Beam Physics and Materials Research
  3. Univ. of Strasbourg (France). Inst. of Physics and Chemistry of Materials
  4. Argonne National Lab. (ANL), Argonne, IL (United States). Materials Science Division; Northwestern Univ., Evanston, IL (United States). Dept. of Physics and Astronomy
Publication Date:
Grant/Contract Number:
AC02-06CH11357
Type:
Accepted Manuscript
Journal Name:
Physical Review. B, Condensed Matter and Materials Physics
Additional Journal Information:
Journal Volume: 92; Journal Issue: 6; Journal ID: ISSN 1098-0121
Publisher:
American Physical Society (APS)
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States); Paul Scherrer Inst. (PSI), Villigen (Switzerland)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Contributing Orgs:
Federal Inst. of Technology, Zurich (Switzerland); Helmholtz-Zentrum Dresden-Rossendorf, Dresden (Germany); Univ. of Strasbourg (France); Northwestern Univ., Evanston, IL (United States)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 36 MATERIALS SCIENCE; artificial spin ice
OSTI Identifier:
1356660
Alternate Identifier(s):
OSTI ID: 1213106