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Title: Magnons and continua in a magnetized and dimerized spin - 12 chain

We examine the magnetic field dependent excitations of the dimerized spin -1/2 chain, copper nitrate, with antiferromagnetic intra-dimer exchange $J_1=0.44$ (1) meV and exchange alternation $$\alpha=J_2/J_1=0.26$$ (2). Magnetic excitations in three distinct regimes of magnetization are probed through inelastic neutron scattering at low temperatures. At low and high fields there are three and two long-lived magnon-like modes, respectively. The number of modes and the anti-phase relationship between the wave-vector dependent energy and intensity of magnon scattering reflect the distinct ground states: A singlet ground state at low fields $$\mu_0H < \mu_0H_{c1} = 2.8$$ T and an $S_z=1/2$ product state at high fields $$\mu_0H > \mu_0H_{c2} = 4.2$$ T. Lastly, in the intermediate field regime, a continuum of scattering for $$\hbar\omega\approx J_1$$ is indicative of a strongly correlated gapless quantum state without coherent magnons.
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [6]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Johns Hopkins Univ., Baltimore, MD (United States). Department of Physics and Astronomy
  2. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States); Johns Hopkins Univ., Baltimore, MD (United States). Department of Physics and Astronomy
  3. Johns Hopkins Univ., Baltimore, MD (United States). Department of Physics and Astronomy
  4. Johns Hopkins Univ., Baltimore, MD (United States). Department of Physics and Astronomy; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)
  5. Brookhaven National Lab. (BNL), Upton, NY (United States). Condensed Matter Physics and Materials Science Dept.; Johns Hopkins Univ., Baltimore, MD (United States). Department of Physics and Astronomy
  6. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)
Publication Date:
OSTI Identifier:
1159418
Grant/Contract Number:
AC05-00OR22725; FG02-08ER46544; DMR-0454672; DMR-0944772
Type:
Accepted Manuscript
Journal Name:
Physical Review. B, Condensed Matter and Materials Physics
Additional Journal Information:
Journal Volume: 90; Journal Issue: 9; Journal ID: ISSN 1098-0121
Publisher:
American Physical Society (APS)
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY