Extended Quantum Critical Phase in a Magnetized Spin-$\frac{1}{2}$ Antiferromagnetic Chain

Extended Quantum Critical Phase in a Magnetized Spin- $\frac{1}{2}$ Antiferromagnetic Chain

M. B. Stone, D. H. Reich, C. Broholm, K. Lefmann, C. Rischel, C. P. Landee, and M. M. Turnbull

Phys. Rev. Lett. 91, 037205 – Published 17 July 2003

Abstract

Measurements are reported of the magnetic field dependence of excitations in the quantum critical state of the spin $S = 1 / 2$ linear chain Heisenberg antiferromagnet copper pyrazine dinitrate (CuPzN). The complete spectrum was measured at $k_{B} T / J \leq 0.025$ for $H = 0$ and $H = 8.7 T$ , where the system is $\sim 30 %$ magnetized. At $H = 0$ , the results are in agreement with exact calculations of the dynamic spin correlation function for a two-spinon continuum. At $H = 8.7 T$ , there are multiple overlapping continua with incommensurate soft modes. The boundaries of these continua confirm long-standing predictions, and the intensities are consistent with exact diagonalization and Bethe ansatz calculations.

Received 18 March 2003

DOI:https://doi.org/10.1103/PhysRevLett.91.037205

Authors & Affiliations

M. B. Stone^1,*, D. H. Reich¹, C. Broholm^1,2, K. Lefmann³, C. Rischel⁴, C. P. Landee⁵, and M. M. Turnbull⁵

¹Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA
²National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
³Materials Research Department, Risø National Laboratory, DK-4000 Roskilde, Denmark
⁴Ørsted Laboratory, Niels Bohr Institute, University of Copenhagen, DK-2100, København Ø, Denmark
⁵Carlson School of Chemistry and Department of Physics, Clark University, Worcester, Massachusetts 01610, USA

^*Currently at Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA.

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Vol. 91, Iss. 3 — 18 July 2003

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Physical Review Letters

Extended Quantum Critical Phase in a Magnetized Spin-12 Antiferromagnetic Chain

M. B. Stone, D. H. Reich, C. Broholm, K. Lefmann, C. Rischel, C. P. Landee, and M. M. Turnbull

Phys. Rev. Lett. 91, 037205 – Published 17 July 2003

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Extended Quantum Critical Phase in a Magnetized Spin- $\frac{1}{2}$ Antiferromagnetic Chain