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American Physical Society, Physical review B, 14(90)

DOI: 10.1103/physrevb.90.140402

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Direct measurement of the spin gap in a quasi-one-dimensional clinopyroxene:NaTiSi2O6

This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

True inorganic spin-Peierls materials are extremely rare, but ${\mathrm{NaTiSi}}_{2}{\mathrm{O}}_{6}$ was at one time considered to be an ideal candidate owing to its well separated chains of edge-sharing ${\mathrm{TiO}}_{6}$ octahedra. At low temperatures, this material undergoes a phase transition from $C2/c$ to $P\overline{1}$ symmetry, where ${\mathrm{Ti}}^{3+}\text{$-${}}{\mathrm{Ti}}^{3+}$ dimers begin to form within the chains. However, it was quickly realized with magnetic susceptibility that simple spin fluctuations do not progress to the point of enabling such a transition. Since then, considerable experimental and theoretical endeavors have been undertaken to find the true ground state of this system and explain how it manifests. Here, we employ the use of x-ray diffraction, neutron spectroscopy, and magnetic susceptibility to directly and simultaneously measure the symmetry loss, spin singlet-triplet gap, and phonon modes. A gap of 53(3) meV was observed, fit to the magnetic susceptibility, and compared to previous theoretical models to unambiguously assign ${\mathrm{NaTiSi}}_{2}{\mathrm{O}}_{6}$ as having an orbital-assisted Peierls ground state.