Faraday patterns, spin textures, spin-spin correlations and competing instabilities in a driven spin-1 antiferromagnetic Bose-Einstein condensate

We study the formation of transient Faraday patterns and spin textures in driven quasi-one-dimensional and quasi-two-dimensional spin-1 Bose-Einstein condensates under the periodic modulation of $s$-wave scattering lengths $a_0$ and $a_2$, starting from the anti-ferromagnetic phase. This phase is characterized by a Bogoliubov spectrum consisting of three modes: one mode is gapped, while the other two are gapless. When $a_0$ is modulated and half of the modulation frequency lies below the gapped mode, density and spin Faraday patterns emerge. In that case, in quasi-one-dimension, the spin texture is characterized by periodic domains of opposite $z$-polarizations. When driven above the gap, the spin texture is characterized by random orientations of spin vectors along the condensate axis. Qualitatively new features appear in the driven quasi-two-dimensional condensate. For instance, when driven above the gap, the spin textures are characterized by anomalous vortices and antivortices that do not exhibit phase winding in individual magnetic components. Below the gap, the spin texture exhibits irregular ferromagnetic patches with opposite polarizations. The spatial spin-spin correlations in quasi-one-dimension exhibit a Gaussian envelope, whereas they possess a Bessel function dependence in quasi-two-dimension. Under the $a_2$-modulation, the density patterns dominate irrespective of the driving frequency, unless the spin-dependent interaction strength is sufficiently smaller than that of the spin-independent interaction. The intriguing scenario of competing instability can emerge when both scattering lengths are simultaneously modulated. Finally, we show that the competing instabilities result in a complex relationship between the population transfer and the strength of the quadratic Zeeman field, while keeping all other parameters constant.

💡 Research Summary

The paper investigates the emergence of transient Faraday patterns, spin textures, spin‑spin correlations, and competing instabilities in a driven spin‑1 antiferromagnetic Bose‑Einstein condensate (BEC). The authors consider a homogeneous condensate initially prepared in the antiferromagnetic (AF) phase, characterized by three Bogoliubov excitation branches: one gapped mode (associated with population transfer to the $m=0$ component) and two gapless modes (density and magnon excitations). By periodically modulating the $s$‑wave scattering lengths $a_0$ and $a_2$, they explore how the system responds in quasi‑one‑dimensional (Q1D) and quasi‑two‑dimensional (Q2D) geometries under a quadratic Zeeman field $q$.

Model and Linear Stability:
The spinor Gross‑Pitaevskii equations (GPEs) for the three Zeeman components are written with spin‑independent interaction $c_0$ and spin‑dependent interaction $c_1$. The scattering lengths are modulated as $a_F(t)=\bar a_F