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Low temperature structural phase transition and incommensurate lattice modulation in the spin gap compound BaCuSi2O6

E. C. Samulon, Z. Islam, S. E. Sebastian, P. B. Brooks, M. K. McCourt, J. Ilavsky, I. R. Fisher

cond-mat.str-elarXiv:cond-mat/0512560

Abstract

Results of high resolution x-ray diffraction experiments are presented for single crystals of the spin gap compound BaCuSi2O6 in the temperature range from 16 to 300 K. The data show clear evidence of a transition from the room temperature tetragonal phase into an incommensurately modulated orthorhombic structure below 100 K. This lattice modulation is characterized by a resolution limited wave vector qIC=(0,0.13,0) and its 2nd and 3rd harmonics. The phase transition is first order and exhibits considerable hysteresis. This observation implies that the spin Hamiltonian representing the system is more complex than originally thought.

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