Local Density of States of One-Dimensional Mott Insulators and Charge-Density Wave States with a Boundary (original) (raw)
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Physical Review B, 2011
We determine the local density of states (LDOS) for spin-gapped one-dimensional charge density wave (CDW) states and Mott insulators in the presence of a hard-wall boundary. We calculate the boundary contribution to the single-particle Green function in the low-energy limit using field theory techniques and analyze it in terms of its Fourier transform in both time and space. The boundary LDOS in the CDW case exhibits a singularity at momentum 2kF, which is indicative of the pinning of the CDW order at the impurity. We further observe several dispersing features at frequencies above the spin gap, which provide a characteristic signature of spin-charge separation. This demonstrates that the boundary LDOS can be used to infer properties of the underlying bulk system. In presence of a boundary magnetic field mid-gap states localized at the boundary emerge. We investigate the signature of such bound states in the LDOS. We discuss implications of our results on STM experiments on quasi-1D systems such as two-leg ladder materials like Sr14Cu24O41. By exchanging the roles of charge and spin sectors, all our results directly carry over to the case of one-dimensional Mott insulators.
Local Density of States induced near Impurities in Mott Insulators
arXiv: Strongly Correlated Electrons, 2018
The local density of states near dopants or impurities has recently been probed by scanning tunneling microscopy in both the parent and very lightly doped compounds of the high-$T_c$ cuprate superconductors. Our calculations based on a slave-rotor description account for all the following key features of the observed local density of states: i) positions and amplitudes of the in-gap spectral weights of a single impurity; ii) the spectral weight transfer from the upper Hubbard band to the lower Hubbard band; iii) the difference between the cases of single and multiple impurities. For multiple impurities, our study explains the complete suppression of spectral weight observed at precisely the Fermi energy and links this property to zeros of the underlying bulk Green's function of the Mott insulating phase.
Localized in-gap state in a single-electron doped Mott insulator
Physical Review B, 2014
Motivated by the recent atomic-scale scanning tunneling microscope (STM) observation for a spatially localized in-gap state in an electron doped Mott insulator, we evaluate the local electronic state of the Hubbard model on the square lattice using the cluster perturbation theory. An in-gap state is found to exist below the upper Hubbard band around the dopant lattice site, which is consistent with the STM measurements. The emergence of this local in-gap state is accompanied with a rapid reduction of the double occupancy of electrons. A similar in-gap state is also found to exist on the triangular lattice. These results suggest that the in-gap state is an inherent feature of Mott insulators independent of the lattice structure.
Weakly coupled one-dimensional Mott insulators
Physical Review B, 2002
We consider a model of one-dimensional Mott insulators coupled by a weak interchain tunnelling t ⊥ . We first determine the single-particle Green's function of a single chain by exact field-theoretical methods and then take the tunnelling into account by means of a Random Phase Approximation (RPA). In order to embed this approximation into a well-defined expansion with a small parameter, the Fourier transform T ⊥ (k) of the interchain coupling is assumed to have a small support in momentum space such that every integration over transverse wave vector yields a small factor κ 2 0 ≪ 1. When T ⊥ (0) exceeds a critical value, a small Fermi surface develops in the form of electron and hole pockets. We demonstrate that Luttinger's theorem holds both in the insulating and in the metallic phases. We find that the quasi-particle residue Z increases very fast through the transition and quickly reaches a value of about 0.4 − 0.6. The metallic state close to the transition retains many features of the one-dimensional system in the form of strong incoherent continua.
Momentum-Resolved Charge Excitations in a Prototype One-Dimensional Mott Insulator
Physical Review Letters, 2002
We report momentum resolved charge excitations in a one dimensional (1-D) Mott insulator studied using high resolution (∼ 325 meV) inelastic x-ray scattering over the entire Brillouin zone for the first time. Excitations at the insulating gap edge are found to be highly dispersive (momentum dependent)compared to excitations observed in two dimensional Mott insulators. The observed dispersion in 1-D is consistent with charge excitations involving holons which is unique to spin-1/2 quantum chain systems. These results point to the potential utility of inelastic x-ray scattering in providing valuable information about electronic structure of strongly correlated insulators.
Observing separate spin and charge Fermi seas in a strongly correlated one-dimensional conductor
Science Advances
An electron is usually considered to have only one form of kinetic energy, but could it have more, for its spin and charge, by exciting other electrons? In one dimension (1D), the physics of interacting electrons is captured well at low energies by the Tomonaga-Luttinger model, yet little has been observed experimentally beyond this linear regime. Here, we report on measurements of many-body modes in 1D gated wires using tunneling spectroscopy. We observe two parabolic dispersions, indicative of separate Fermi seas at high energies, associated with spin and charge excitations, together with the emergence of two additional 1D “replica” modes that strengthen with decreasing wire length. The interaction strength is varied by changing the amount of 1D intersubband screening by more than 45%. Our findings not only demonstrate the existence of spin-charge separation in the whole energy band outside the low-energy limit of the Tomonaga-Luttinger model but also set a constraint on the valid...
Spin gap in low-dimensional Mott insulators with orbital degeneracy
We consider the exchange Hamiltonian HST = −J <rr ′ > (2Sr · S r ′ − 1 2 )(2Tr · T r ′ − 1 2 ) , describing two isotropic spin-1/2 Heisenberg antiferromagnets coupled by a quartic term on equivalent bonds. The model is relevant for systems with orbital degeneracy and strong electron-vibron coupling in the large Hubbard repulsion limit. To investigate the ground state properties we use a Green's Function Monte Carlo, calculating energy gaps and correlation functions, the latter through the forward walking technique. In one dimension we find that the ground state is a "crystal" of valence bond dimers. In two dimensions, the spin gap appears to remain finite in the thermodynamic limit, and, consistently, the staggered magnetization -signal of Néel long range order -seems to vanish. From the analysis of dimer-dimer correlation functions, however, we find no sign of a valence bond crystal. A spin liquid appears as a plausible scenario compatible with our findings.
Spin and charge dynamics of stripes in doped Mott insulators
Europhysics Letters (epl), 2003
We study spin and charge dynamics of stripes in doped Mott insulators by considering a twodimensional Hubbard model with N fermion flavors. For N = 2 we recover the normal one-band model while for N → ∞ a spin density wave mean-field solution. For all band fillings, lattice topologies and N = 4n the model may be solved by means of Monte Carlo methods without encountering the sign problem. At N = 4 and in the vicinity of the Mott insulator, the single particle density of states shows a gap. Within this gap and on rectangular topologies of sizes up to 30 × 12 we find gapless spin collective modes centered around q = (π ± ǫx, π ± ǫy) as well as charge modes centered around q = (±2ǫx, ±2ǫy), q = (±ǫx, ±ǫy) and q = (0, 0). ǫx,y depends on the lattice topology and doping.
Nature of Spin Excitations in Two-Dimensional Mott Insulators: Undoped Cuprates and Other Materials
Physical Review Letters, 2001
We investigate the excitation spectrum of a two-dimensional resonating valence bond (RVB) state. Treating the π-flux phase with antiferromagnetic correlations as a variational ground state, we recover the long wavelength magnon as an "RVB exciton". However, we find that this excitation does not exhaust the entire spectral weight and the high energy spectrum is dominated by fermionic excitations. The latter can be observed directly by inelastic neutron scattering and we predict their characteristic energy scales along different high symmetry directions in the magnetic Brillouin zone. We also interpret experimental results on two magnon Raman scattering and mid-infrared absorption within this scenario.