Critical Spin Superflow in a Spinor Bose-Einstein Condensate

Joon Hyun Kim, Sang Won Seo, and Y. Shin

Phys. Rev. Lett. 119, 185302 – Published 31 October 2017

Abstract

We investigate the critical dynamics of spin superflow in an easy-plane antiferromagnetic spinor Bose-Einstein condensate. Spin-dipole oscillations are induced in a trapped condensate by applying a linear magnetic field gradient and we observe that the damping rate increases rapidly as the field gradient increases above a certain critical value. The onset of dissipation is found to be associated with the generation of dark-bright solitons due to the modulation instability of the counterflow of two spin components. Spin turbulence emerges as the solitons decay because of their snake instability. We identify another critical point for spin superflow, in which transverse magnon excitations are dynamically generated via spin-exchanging collisions, which leads to the transient formation of axial polar spin domains.

Received 8 July 2017

DOI:https://doi.org/10.1103/PhysRevLett.119.185302

Physics Subject Headings (PhySH)

Superfluidity

Spinor Bose-Einstein condensates

Atomic, Molecular & OpticalCondensed Matter, Materials & Applied Physics

Authors & Affiliations

Joon Hyun Kim¹, Sang Won Seo^1,2, and Y. Shin^1,2,*

¹Department of Physics and Astronomy, and Institute of Applied Physics, Seoul National University, Seoul 08826, Korea
²Center for Correlated Electron Systems, Institute for Basic Science, Seoul 08826, Korea

^*yishin@snu.ac.kr

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 119, Iss. 18 — 3 November 2017

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
Spin-dipole oscillations in a trapped antiferromagnetic spinor Bose-Einstein condensate. Spatial distribution of axial magnetization of the condensate at various hold times $t$ (a)–(d) for magnetic field gradient $B_{q} \approx 0.6 mG / cm$ and (e)–(h) $1.3 mG / cm$ . The oscillation period is $T \approx 1230 ms$ (840 ms) for $B_{q} \approx 0.6 mG / cm$ ( $1.3 mG / cm$ ). The magnetization images were taken after 24 ms time of flight [5].
Reuse & Permissions
Figure 2
Damping rate $γ$ as a function of the magnetic field gradient $B_{q}$ . $γ$ was determined based on a damped sinusoidal function fit to the time evolution data of the relative displacement $Δ D$ of the center-of-mass positions of the $m_{z} = \pm 1$ spin components (inset); the error bar indicates the fitting error. The dashed and solid lines denote a two-line fit to the $γ$ data. The top axis shows the ratio of the trap displacement $x_{0}$ for $B_{q}$ to the Thomas-Fermi radius $R_{x}$ of the condensate.
Reuse & Permissions
Figure 3
Generation of dark-bright solitons. (a) Density distributions of the $m_{z} = \pm 1$ components for various hold times $t$ for $B_{q} \approx 1.3 mG / cm$ slightly above the critical point. The two spin components move to opposite directions, and dark-bright solitons are generated in the boundary of the two-component overlap region. The insets in the right column show enlarged images of the boxed regions, where the first dimple-shaped solitons are located. The dashed line indicates the condensate boundary. The optical depths (ODs) of the two spin components are different because of the optical pumping effect that occurred during the imaging [34]. (b) Density profiles of the two spin components along the $x$ axis in the central region. The gray arrows indicate the positions of the first solitons.
Reuse & Permissions
Figure 4
Images of the $m_{z} = - 1$ spin component at various hold times for $B_{q} \approx 1.6 mG / cm$ . Solitons are progressively generated along the boundary of the overlap region. As the solitons decay into small segments due to their snake instability, a spin turbulence state forms in the center region.
Reuse & Permissions
Figure 5
Generation of transverse magnon excitations. Fractional population $η_{0}$ of the $m_{z} = 0$ spin component as a function of the product of $t$ and $B_{q}$ . When the spin flow velocity is high to overcome the quadratic Zeeman energy, spin-exchanging collisions occur to generate the $m_{z} = 0$ spin components. The vertical dashed line indicates the onset point for $η_{0}$ at $t B_{q} \approx 0.4 s mG / cm$ . The inset images show the density distributions of the spin components for $B_{q} \approx 2.2 mG / cm$ at (i) $t = 200 ms$ , (ii) 250 ms, and (iii) 300 ms.
Reuse & Permissions

Physical Review Letters