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

TL;DR

This study reveals a first-order structural phase transition in BaCuSi2O6 around 100 K, involving incommensurate lattice modulation, which suggests a more complex spin Hamiltonian than previously assumed.

Contribution

The paper provides high-resolution x-ray diffraction evidence of a temperature-induced incommensurate phase transition in BaCuSi2O6, highlighting the complexity of its spin interactions.

Findings

Transition from tetragonal to incommensurate orthorhombic phase below 100 K

Presence of incommensurate lattice modulation with wave vector q_IC

First order transition with hysteresis

Abstract

Results of high resolution x-ray diffraction experiments are presented for single crystals of the spin gap compound BaCuSi$_2$O$_6$ 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 $\sim$100 K. This lattice modulation is characterized by a resolution limited wave vector {\bf q}$_{IC}$=(0,$\sim$0.13,0) and its 2$^{nd}$ and 3$^{rd}$ 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.