Abstract
The study of superconductivity with unconventional order is complicated in condensed matter systems by their extensive complexity. Optical lattices with their exceptional precision and control allow one to emulate superfluidity avoiding many of the complications of condensed matter. A promising approach to realize unconventional superfluid order is to employ orbital degrees of freedom in higher Bloch bands. In recent work, indications were found that bosons condensed in the second band of an optical chequerboard lattice might exhibit px ± i py order. Here we present experiments, which provide strong evidence for the emergence of px ± i py order driven by the interaction in the local p-orbitals. We compare our observations with a multi-band Hubbard model and find excellent quantitative agreement.
Highlights
The study of superconductivity with unconventional order is complicated in condensed matter systems by their extensive complexity
Our theoretical considerations are consistent with a numerical analysis based upon the Gross–Pitaevskii equation [20] and a renormalization group analysis [21]
The phase diagram in figure 2, we show momentum spectra observed in the different areas (I)–(III)
Summary
Using an interferometric lattice set-up [18], we produce a two-dimensional optical potential comprising deep and shallow wells (A and B in figure 1(a) of the main text) arranged as the black and white fields of a chequerboard with an average well depth V0 and an adjustable relative potential energy offset [17]. Adjustment of β with a precision exceeding π/300 permits controlled tuning of V ≡ V0 η(1 + x )(1 + y)cos(β). If η = x = y = 1, the lattice potential possesses perfect C4 rotation symmetry. In contrast to [17], the optical set-up permits controlled adjustment of arbitrary values of y within an interval including y = 1. This is accomplished as follows: the optical standing wave along the y-axis is obtained by a retro-reflected laser beam. The linear polarization of the incoming beam can be rotated with a retardation plate. After retroreflection the polarization is rotated to precisely match with the z-direction, which exclusively contributes to the lattice potential
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