Inelastic neutron scattering is used to study the finite-temperature scaling behavior of the local dynamic structure factor in the quasi-one-dimensional quantum antiferromagnet (NTENP), at its field-induced Ising quantum critical point. The validity and the limitations of the theoretically predicted scaling relations are tested.
DOI:https://doi.org/10.1103/PhysRevB.92.014412
©2015 American Physical Society
Crystal structure of NTENP. The magnetic ions are surrounded by octahedra with ions in the equatorial vertices. This leads to a single-ion anisotropy with a hard axis along . The chains run along , where the ions are linked by groups. Perchlorate anions between the chains are omitted in the figure for clarity. Two unit cells are indicated by dotted lines.
Reuse & PermissionsX-ray diffraction data measured in NTENP in the vicinity of the Bragg peak at 300 and 120 K. Two satellite peaks are clearly visible at 120 K. The inset shows the plane at 120 K where red circles mark the principal Bragg peaks of the room-temperature crystal structure.
Reuse & Permissions(a) The temperature dependence of the satellite-peak intensity measured in NTENP. (b) The specific heat features a maximum at about 170 K. To emphasize the maximum visually, a second-order polynomial function was subtracted from the total specific heat. The inset illustrates the total specific heat (black, solid line) and the fit (red, dotted line).
Reuse & PermissionsPeak intensity of the Bragg reflection at 40 mK versus magnetic field, as measured on FLEXX at HZB. Above a critical magnetic field the system is magnetically ordered and exhibits a magnetic Bragg peak at . The solid line is an empirical power-law fit to the data with fitted exponent 0.5(2) yielding a critical magnetic field of kOe .
Reuse & PermissionsThe low-energy spectra of NTENP at 0.5 K measured on LET at ISIS are shown in zero field (a) and at 113 kOe (b). The zero-field spectrum was used as the background for the measurements in field. In a magnetic field, the triplet states are split due to the Zeeman effect and the excitation energy of the lowest excited state is reduced whereas one mode persists at meV. The residual energy gap which can be observed at 113 kOe is discussed in Sec. 4a.
Reuse & PermissionsBackground-subtracted constant-energy data measured in NTENP at on FLEXX at HZB at 68 mK around the AF wave vector . A constant offset of 100 counts/ is applied between data measured at different energy transfers. Solid black lines are guides to the eye.
Reuse & PermissionsSummary of the neutron-scattering data for NTENP at the critical magnetic field obtained on IN14, FLEXX, and LET. The -integrated dynamic structure factor is shown versus the temperature-scaled energy transfer .
Reuse & PermissionsScaled -integrated dynamic structure factor measured in NTENP and plotted with scaling exponents , 3, and . The scaling exponent with the best data overlap, , was determined by minimizing the function (inset) [29]. For the data with an additional constant prefactor is applied in order to better discern the data with and .
Reuse & PermissionsThe scaling plot for the local dynamic structure factor measured in NTENP with the Ising scaling exponent . The black line corresponds to the predicted universal scaling function for the quantum critical point of an Ising chain in a transverse magnetic field as described in the text, Eq. (10).
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