Chiral spin condensation in a double-valley optical lattice

Clarina dela Cruz, Jiannis K. Pachos

Ying-Hai Wu, Xiaopeng Li, S. Das Sarma

We study a spinor (two-component) Bose gas confined in a one-dimensional double-valley optical lattice which has a double-well structure in momentum space. Based on field theory analysis, it is found that spinor bosons in the double-valley band may form a spin-charge mixed chiral spin quasicondensate under certain conditions. Our numerical calculations in a concrete $\ensuremath{\pi}$-flux triangular ladder system confirm the robustness of the chiral spin order against interactions and quantum fluctuations. This exotic atomic Bose-Einstein condensate exhibits spatially staggered spin loop currents without any charge dynamics despite the complete absence of spin-orbit coupling in the system, creating an interesting approach to atom spintronics. The entanglement entropy scaling allows us to extract conformal-field-theory central charge and establish the low-energy effective field theory for the chiral spin condensate as a two-component Luttinger liquid. Our predictions should be detectable in atomic experiments through spin-resolved time-of-flight techniques.

Zhongcheng Yu, Chengyang Wu, Chi Zhang +2 more

All data for the article "Vestigial Order Melting of a Chiral Atomic Superfluid in a Double-Valley Optical Lattice" This work is supported by the National Natural Science Foundation of China (Grants No. 92365208), Innovation Program for Quantum Science and Technology of China (Grant No. 2024ZD0300100), the National Basic Research Program of China (Grants No. 2021YFA0718300 and No. 2021YFA1400900), Shanghai Municipal Science and Technology (Grant No. 25TQ003, 2019SHZDZX01, 24DP2600100), and the Space Application System of China Manned Space Program.

Sara Bergkvist, Ian P. McCulloch, Anders Rosengren

Annica M. Black‐Schaffer, Wéi Wú, Karyn Le Hur

We study superconductivity on the honeycomb lattice close to the Mott state at half filling. Due to the sixfold lattice symmetry and disjoint Fermi surfaces at opposite momenta, we show that several different fully gapped superconducting states naturally exist on the honeycomb lattice, of which the chiral $d+i{d}^{\ensuremath{'}}$-wave state has previously been shown to appear when superconductivity appears close to the Mott state. Using renormalized mean-field theory to study the $t\ensuremath{-}J$ model and quantum Monte Carlo calculations of the Hubbard-$U$ model we show that the $d+i{d}^{\ensuremath{'}}$-wave state is the favored superconducting state for a wide range of on-site repulsion $U$, from the intermediate to the strong coupling regime. We also investigate the possibility of a mixed chirality $d$-wave state, where the overall chirality cancels. We find that a state with $d+i{d}^{\ensuremath{'}}$-wave symmetry in one valley but $d\ensuremath{-}i{d}^{\ensuremath{'}}$-wave symmetry in the other valley is not possible in the $t\ensuremath{-}J$ model without reducing the translational symmetry, due to the zero-momentum and spin-singlet nature of the superconducting order parameter. Moreover, any extended unit cells result either in disjoint Dirac points, which cannot harbor this mixed chirality state, or the two valleys are degenerate at the zone center, where valley hybridization prevents different superconducting condensates. We also investigate extended unit cells where the overall chirality cancels in real space. For supercells containing up to eight sites, including the Kekul\'e distortion, we find no energetically favorable $d$-wave solution with an overall zero chirality within the restriction of the $t\ensuremath{-}J$ model.

Marcel A. Pinto, Giovanni Luca Sferrazza, Silvia Casulleras +3 more

Valleytronics and valley photonics exploit the valley degree of freedom to encode and manipulate information. Here we show that photonic valleys can be selectively addressed in quantum optics using a simple two-level emitter, provided it is coupled nonlocally to the field, thereby realizing a so-called giant atom. Specifically, we consider a qubit coupled at multiple points to an engineered honeycomb lattice of resonators with detuned sublattice frequencies. By tailoring the geometry of the coupling points, the giant atom can be made to emit selectively into a single valley. The emitted photons thereby acquire a well-defined valley character and inherit the associated Berry curvature. By placing the qubit near a domain wall between regions of opposite sublattice detuning, whose interface supports valley-polarized edge modes, emission becomes chiral along the domain wall. This provides a promising route toward implementation of single-photon disorder-robust chiral emission without breaking time-reversal symmetry of the electromagnetic medium in platforms such as circuit QED.