Related papers: Quantum Spin Systems: From Spin Gaps to Pseudo Gap…
We study a model of two weakly coupled isotropic spin-1/2 Heisenberg chains with an antiferromagnetic coupling along the chains. It is shown that the system always has a spectral gap. For the case of identical chains the model in the…
The pseudogap phase is considered as a new state of matter in the phase string model of the doped Mott insulator, which is composed of two distinct regimes known as upper and lower pseudogap phases, respectively. The former corresponds to…
The low-energy charge excitations of a doped antiferromagnetic ladder are modeled by a system of interacting spinless fermions that live on the same ladder. A relatively large spin gap is assumed to ``freeze out'' all spin fluctuations. We…
A simple interlayer pair tunneling is solved exactly. We find that in the normal state spin-1/2 particle and hole excitations are gapped. But the state is an unusual metal, characterized by novel fermionic spin zero and charge +2e and -2e…
The spin dynamics of high temperature superconductors measured by inelastic neutron scattering is reviewed. The spin susceptibility evolves a lot with increasing doping from the undoped insulating state to the overdoped metallic state. In…
We study the evolution of a Mott-Hubbard insulator into a correlated metal upon doping in the two-dimensional Hubbard model using the Cellular Dynamical Mean Field Theory. Short-range spin correlations create two additional bands apart from…
We describe some antiferromagnetic systems which exhibit spin gaps. We also discuss the effect of doping one such system, namely, the spin-ladders, with holes. Some model antiferromagnetic systems with spin gap are reviewed for which exact…
The magnetic excitation spectrum in the two-dimensional (2D) S=1/2 Heisenberg antiferromagnet copper deuteroformate tetradeuterate (CFTD) has been measured for temperatures up to T\sim J/2, where J=6.31+-0.02 meV is the 2D exchange…
A link is established between the spin-fermion (SF) model of the cuprates and the approach based on the analogy between the physics of doped Mott insulators in two dimensions and the physics of fermionic ladders. This enables one to use…
Using a spin-only model, we compute spin excitation spectra in a bond-centered stripe state with long-range magnetic order. We employ a bond operator formalism, which naturally captures both dimerization and broken spin symmetry in a…
Inelastic neutron scattering is used to identify single-particle and continuum spin excitations in the quasi-one-dimensional $S=1/2$ antiferromagnet \ba. In the data analysis, close attention is given to resolution effects. A gap in the…
The mechanism of the pseudogap observed in hole-doped cuprates remains one of the central puzzles in condensed matter physics. We analyze this phenomenon via a Feynman-diagrammatic inspection of the Hubbard model. Our approach captures the…
This work shows that a strongly correlated phase which is gapped to collective spin excitations but gapless to charge fluctuations emerges as a universal feature in one-dimensional fermionic systems obeying certain symmetries. Namely,…
The evolution of the spin gap of a 2-leg ladder upon doping depends upon the nature of the lowest triplet excitations in a ladder with two holes. Here we study this evolution using various numerical techniques for a t-t'-J ladder as the…
We construct frustrated antiferromagnetic spin ladders with m chains for which the exact ground state can be determined in a particular parameter regime. The excitation spectrum is shown rigorously to be gapless ( with gap ) for odd ( even…
The low energy excitation spectrum of a two-dimensional ferromagnetic material is dominated by single-magnon excitations that show a gapless parabolic dispersion relation with the spin wave vector. This occurs as long as magnetic anisotropy…
We study the ground state and excitation spectrum of a quasi one-dimensional nanostructure consisting of a pole and rungs oriented in the opposite directions ("centipede ladder", CL) at quarter filling. The spin and charge excitation…
The coupling of the spin of electrons to their motional state lies at the heart of recently discovered topological phases of matter. Here we create and detect spin-orbit coupling in an atomic Fermi gas, a highly controllable form of quantum…
We calculate spectral functions within the t-J model as relevant to cuprates in the regime from low to optimum doping. On the basis of equations of motion for projected operators an effective spin-fermion coupling is derived. The self…
We investigate pseudogap phenomena in the 2D electron system. Based on the mode-mode coupling theory of antiferromagnetic (AFM) and $d_{x^2-y^2}$-wave superconducting ($d$SC) fluctuations, single-particle dynamics is analyzed. For the…