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arXiv:1109.1241 · Physical Review Letters

Quasiparticle Dynamics in a Bose Insulator Probed by Interband Bragg Spectroscopy

Nicole Fabbri, Sebastian D. Huber, David Clément, L. Fallani, C. Fort, M. Inguscio, Ehud Altman

Published Jul 31, 2012• 38 citations
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Abstract

We investigate experimentally and theoretically the dynamical properties of a Mott insulator in decoupled one-dimensional chains. Using a theoretical analysis of the Bragg excitation scheme, we show that the spectrum of interband transitions holds information on the single-particle Green's function of the insulator. In particular, the existence of particle-hole coherence due to quantum fluctuations in the Mott state is clearly seen in the Bragg spectra and quantified. Finally, we propose a scheme to directly measure the full, momentum-resolved spectral function as obtained in the angle-resolved photoemission spectroscopy of solids.

DOI
10.1103/physrevlett.109.055301

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We analyze the spectral properties of a very general two-channel fermion-boson transport model in the insulating and metallic regimes and the signatures of the metal-insulator quantum phase transition in between. To this end we determine the single-particle spectral function related to angle-resolved photoemission spectroscopy, the momentum distribution function, the Drude weight, and the optical response by means of a dynamical (pseudosite) density-matrix renormalization group technique for the one-dimensional half-filled band case. We show how the interplay of correlations and fluctuations in the background medium controls the charge dynamics of the system, which is a fundamental problem in a great variety of advanced materials.
We use the density-matrix renormalization group method to investigate ground-state and dynamic properties of the one-dimensional Bose-Hubbard model, the effective model of ultracold bosonic atoms in an optical lattice. For fixed maximum site occupancy n b = 5, we calculate the phase boundaries between the Mott insulator and the "superfluid" phase for the lowest two Mott lobes. We extract the Tomonaga-Luttinger parameter from the density-density correlation function and determine accurately the critical interaction strength for the Mott transition. For both phases, we study the momentum distribution function in the homogeneous system, and the particle distribution and quasi-momentum distribution functions in a parabolic trap. With our zero-temperature method we determine the photoemission spectra in the Mott insulator and in the "superfluid" phase of the one-dimensional Bose-Hubbard model. In the insulator, the Mott gap separates the quasi-particle and quasi-hole dispersions. In the "superfluid" phase the spectral weight is concentrated around zero momentum.