text: 4 
  3  3 
  
  1  2 
  2 
  (a)  (b) 
  
  3 
  4 
  3  2  3 
  
  QE 
  2 
  
  2 
  1  4  1 
  1  (a)  (b)  (c) 
  
  Illustration of the tetragonal to orthorhombic 
  FIG. 3: 
  QE 
  2 (bottom) distortion modes. (a) Perspective 
  view of the tetrahedron. 1, . . . , 4 label the spins. Arrows in- 
  dicate the motion of each spin under the distortion mode. (b) 
  Top view of (a). (c)(d) Side view of (a). 
  
  1 (top) and QE 