Hiroyuki Yamase

Possible quasi-one-dimensional Fermi surface in La2-xSrxCuO4

To reconcile the two experimental findings on La 2- x Sr x CuO 4 , namely, Fermi surface (FS) observed by angle-resolved photoemission spectroscopy and sharp incommensurate magnetic peaks by neutro...

Instability toward Formation of Quasi-One-Dimensional Fermi Surface in Two-Dimensional t-J Model.

We show within the slave-boson mean field approximation that the two-dimensional t - J model has an intrinsic instability toward forming a quasi-one-dimensional (q-1d) Fermi surface. This q-1d state competes with, and is overcome by, the d -wave pairing state for a realistic parameter choice. However, we find that a small spatial anisotropy in t and J exposes the q-1d instability which has been hidden behind the d -wave pairing state, and brings about the coexistence with the d -wave pairing. We argue that this coexistence can be realized in La 2- x Sr x CuO 4 systems.

Mean-field theory for symmetry-breaking Fermi surface deformations on a square lattice

We analyze a mean-field model of electrons with pure forward scattering interactions on a square lattice which exhibits spontaneous Fermi surface symmetry breaking with a d-wave order parameter: the surface expands along the kx-axis and shrinks along the ky-axis (or vice versa). The symmetry-broken phase is stabilized below a dome-shaped transition line Tc(mu), with a maximal Tc near van Hove filling. The phase transition is usually first order at the edges of the transition line, and always second order around its center. The d-wave compressibility of the Fermi surface is however strongly enhanced even near the first order transition down to zero temperature. In the weak coupling limit the phase diagram is fully determined by a single non-universal energy scale, and hence dimensionless ratios of different characteristic quantities are universal. Adding a uniform repulsion to the forward scattering interaction, the two tricritical points at the ends of the second order transition line are shifted to lower temperatures. For a particularly favorable choice of hopping and interaction parameters one of the first order edges is replaced completely by a second order transition line, leading to a quantum critical point.

Van Hove Singularity and Spontaneous Fermi Surface Symmetry Breaking in Sr3Ru2O7

The most salient features observed around a metamagnetic transition in Sr 3 Ru 2 O 7 are well captured in a simple model for spontaneous Fermi surface symmetry breaking under a magnetic field, with...

Competition of Fermi surface symmetry breaking and superconductivity

We analyze a mean-field model of electrons on a square lattice with two types of interaction: forward scattering favoring a d-wave Pomeranchuk instability and a BCS pairing interaction driving d-wave superconductivity. Tuning the interaction parameters a rich variety of phase diagrams is obtained. If the BCS interaction is not too strong, Fermi surface symmetry breaking is stabilized around van Hove filling, and coexists with superconductivity at low temperatures. For pure forward scattering Fermi surface symmetry breaking occurs typically via a first order transition at low temperatures. The presence of superconductivity reduces the first order character of this transition and, if strong enough, can turn it into a continuous one. This gives rise to a quantum critical point within the superconducting phase. The superconducting gap tends to suppress Fermi surface symmetry breaking. For a relatively strong BCS interaction, Fermi surface symmetry breaking can be limited to intermediate temperatures, or can be suppressed completely by pairing.

Turning a First Order Quantum Phase Transition Continuous by Fluctuations: General Flow Equations and Application to d-Wave Pomeranchuk Instability

We derive renormalization group equations which allow us to treat order parameter fluctuations near quantum phase transitions in cases where an expansion in powers of the order parameter is not possible. As a prototypical application, we analyze the nematic transition driven by a d-wave Pomeranchuk instability in a two-dimensional electron system. We find that order parameter fluctuations suppress the first order character of the nematic transition obtained at low temperatures in mean-field theory, so that a continuous transition leading to quantum criticality can emerge.

Possible charge instabilities in two-dimensional doped Mott insulators

Motivated by the growing evidence of the importance of charge fluctuations in the pseudogap phase in high-temperature cuprate superconductors, we apply a large-

Superconductivity from orbital nematic fluctuations

N

Spontaneous Fermi surface symmetry breaking in bilayer systems

expansion formulated in a path integral representation of the two-dimensional

Theory of reduced singlet pairing without the underlying state of charge stripes in the high-temperature superconductor YBa2CU3O6.45

t