Observation of Density-Induced Tunneling

Abstract

We study the dynamics of bosonic atoms in a tilted one-dimensional optical lattice and report on the first direct observation of density-induced tunneling. We show that the interaction affects the time evolution of the doublon oscillation via density-induced tunneling and pinpoint its density-and interaction-dependence. The experimental data for different lattice depths are in good agreement with our theoretical model. Furthermore, resonances caused by second-order tunneling processes are studied, where the density-induced tunneling breaks the symmetric behavior for attractive and repulsive interactions predicted by the Hubbard model. PACS numbers: 37.10.Jk, 03.75.Lm, 67.85.Hj, 75.10.Pq The Hubbard model is the primary description for strongly correlated electrons in solids. It takes into account the interaction between the particles at a lattice site and the tunneling between the sites, whereas other interaction processes are neglected. It was pointed out that these additional interactions may have crucial influence in strongly correlated materials such as superconductors or ferromagnets [1][2][3][4]. Of particular importance is the so-called bond-charge interaction that represents a density-induced tunneling of an electron. In solids, this interaction-driven process cannot be studied systematically due to the lack of direct control over the electron density and the interaction strength. Furthermore, the complexity of the investigated materials hinders a direct observation of this interaction effect. Hence, the role of interaction-induced tunneling has remained an open question in condensed matter physics.Ultracold atoms in optical lattices allow the realization of extremely pure lattice systems without defects and phononic excitations. Furthermore, the unique control of both the lattice potential and the interaction strength permits a systematic study of static and dynamic properties. In optical lattices, density-induced tunneling [5][6][7][8][9] is even more pronounced due to the characteristic shape of the Wannier functions [7]. Several indications for density-induced tunneling have been found: It has a strong influence on the superfluid to Mottinsulator transition in bosonic [7,10,11] and multicomponent systems such as Bose-Fermi mixtures of atoms [6,8,[12][13][14][15]. As a tunneling process, it also modifies the effective band structure, which has also been observed in a Bose-Fermi mixture [16]. A direct observation of density-induced tunneling processes was hindered mainly by the fact that the Mott insulator transition depends only on the ratio of on-site interaction and total tunneling and by the averaging over different on-site occupancies in experimental systems.Here, we report on the direct observation of densityinduced tunneling with ultracold atoms in a tilted one dimensional optical lattice. We study the dynamics of a 1D Mott insulator after quenching the tilt energy E between neighboring sites into resonance with the on-site interaction energy U . We show that the resulting resonant particle o...

Ab initiocalculation of Hubbard parameters for Rydberg-dressed atoms in a one-dimensional optical lattice

“…In particular, if restricted to the lowest band the dominant off-site contribution in BHM comes from a DAT term [first processes in figure 2(e)] of the form ∼ iâ † i (n i +n i+1 )â i+1 and is explicitly occupation dependent. The signatures of this term in a deep MOT state are probed in a recent experiment using tilted optical lattices [59]. In figure 2(d) only the dominant DAT coefficients are shown and corresponding processes are depicted in figure 2(e).…”

Transverse collisional instabilities of a Bose-Einstein condensate in a driven one-dimensional lattice

“…A similar analysis can be used for Raman-driven lattices, such as those used to realize the Harper Hamiltonian [16,19]. It also applies to the study of density induced tunnelling [58] and is related to earlier studies of Bloch oscillations [59]. In section III, we study the stability of a BEC loaded in a shaken optical lattice.…”

Nonlocal correlations in the optical conductivity spectra

“…It was mainly considered while elaborating new mechanisms for high temperature superconductivity [4,5], and while describing organic compounds [6] and molecular crystals [7], electron-hole asymmetry [8] and enhancement of magnetic properties [9]. Quite recently, the correlated hopping turned out to be an important puzzle in understanding the behaviour of quantum dots [10][11][12] and fermionic [13,14] and bosonic [15][16][17] atoms on optical lattices.…”