Extended quantum critical phase in a magnetized spin-1/2 antiferromagnetic chain.
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< or =0.025 for H=0 and H=8.7 T, where the system is approximately 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.
Stone
M B
MB
Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA.
Reich
D H
DH
Broholm
C
C
Lefmann
K
K
Rischel
C
C
Landee
C P
CP
Turnbull
M M
MM