Deformation of the Fermi surface in the Conclusion The idea that the metamagnetism has a connection with the occurrence of spontaneous Fermi surface distortion has been invoked to understand main features of the observations in the ruthenate metal Sr3Ru2O7 . To support this idea, we demonstrate the local density of states dependence of the d-wave Fermi surface distortion, comparing it with the evolution of the differential conductance dI/dV spectra obtained using the STM technique. The sharp features near the Fermi level and the asymmetric weight transfer from the inner peaks to the local minimum cross the metamagnetic transition can be captured by our results. Deformation of the Fermi surface in the two-dimensional extended t-t' Hubbard model Hui-Min Chen, Chang-Qin Wu Phys. Dept., Fudan Univ., Shanghai, People’s Republic of China We study the extended t-t' Hubbard model with the nearest neighbor repulsion V on a two-dimensional square lattice. We investigate the competition between the superconductivity and Fermi surface deformation using the variational cluster approach(VCA). The ground state, from an energy point of view, favors the d-wave superconducting state with isotropic underlying lattice for V<Vc. As $V$ is increased, the system undergoes a first order transition from the superconductivity to d-wave Fermi surface deformation (dFSD) at V=Vc. We find that the low-energy features of the density of states obviously changes in the presence of dFSD. The spectral weight transfers from low-energy peaks to the local minimum very close to the chemical potential. This behavior can be related to the strong critical fluctuations in the vicinity of metamagnetic transition in the bilayer ruthenate Sr3Ru2O7. Experiments Experimental evidence for the formation of a nonsuperconducting phase in the vicinity of a magnetic field–tuned quantum critical point in the ruthenate metal Sr3Ru2O7 Neutron-scattering measurements of the low-frequency spin fluctuations in YBCO samples. V. Hinkov, et al, Science 319, 597 (2008). Experimental evidence potentially supporting the Fermi surface deformation. R map in Na-CCOC observed in one recent STM experiments. S. A. Grigera, et al, Science 306, 1154 (2004). R. A. Borzi, et al, Science 315, 214 (2007). Y. Kohsaka, et al, Science 315, 1380 (2007). Our results Model and method Two-dimensional extended t-t’ Hubbard model along x direction along y direction Variational cluster approximation Same interaction modified single particle term Magnetic field dependence of dI/dV spectra at T 560 mK from 0 to 11 T. Evolution of the density of states K. Iwaya, et al., Phys. Rev. Lett. 99, 057208 (2007).