Path dependent scaling of geometric phase near a quantum multi-critical   point
  We study the geometric phase of the ground state in a one-dimensional transverse XY spin chain in the vicinity of a quantum multi-critical point. We approach the multi-critical point along different paths and estimate the geometric phase by applying a rotation in all spins about z-axis by an angle $\eta$. Although the geometric phase itself vanishes at the multi-critical point, the derivative with respect to the anisotropy parameter of the model shows peaks at different points on the ferromagnetic side close to it where the energy gap is a local minimum; we call these points `quasi-critical'. The value of the derivative at any quasi-critical point scales with the system size in a power-law fashion with the exponent varying continuously with the parameter $\alpha$ that defines a path, upto a critical value $\alpha = \alpha_{c}=2$. For $\alpha > \alpha_{c}$, or on the paramagnetic side no such peak is observed. Numerically obtained results are in perfect agreement with analytical predictions. 
Ayoti Patra, Victor Mukherjee and Amit Dutta
cond-mat.stat-mech quant-ph