Quantum Elliptic Vortex in a Nematic-Spin Bose-Einstein Condensate

Abstract

We find a novel topological defect in a spin-nematic superfluid theoretically. A quantized vortex spontaneously breaks its axisymmetry, leading to an elliptic vortex in nematic-spin Bose-Einstein condensates with small positive quadratic Zeeman effect. The new vortex is considered the Joukowski transform of a conventional vortex. Its oblateness grows when the Zeeman length exceeds the spin healing length. This structure is sustained by balancing the hydrodynamic potential and the elasticity of a soliton connecting two spin spots, which are observable by in situ magnetization imaging. The theoretical analysis clearly defines the difference between half quantum vortices of the polar and antiferromagnetic phases in spin-1 condensates.

Spin-current instability at a magnetic domain wall in a ferromagnetic superfluid: A generation mechanism of eccentric fractional skyrmions

“…The bulk ordered state is suppressed in the core of the DW, in which the macroscopic wave functions vary continuously between the two states. The core of a topological defect in spin-1 BECs has been revealed to exhibit complicated states [32,[39][40][41][42][43][44][45][46][47][48][49]. Similarly, there are different possibilities for the local states at the wall in our system.…”

“…To approach the problem systematically, we introduce a general rule on the mass and spin currents along a DW. This rule is a natural extension of the vortex winding rule for a rotational flow around an axisymmetric vortex [32,48,50]. The rule is applicable when all Zeeman components have finite population.…”

“…Energetics are of fundamental importance because the relationship between the skyrmion charge and the vortex state with off-centered or eccentric spin singularity in Fig. 5(f) reminds us of that between the vortex winding rule and the nonaxisymmetic vortex [32,48], which is related to the stability of the eccentric skyrmions. It is noted that similar objects have been discussed in superfluid 3 He-A; "SV" (singular vortex) in the phase diagram of vortices [75,86] (see, also, [87][88][89][90][91]).…”

“…Recently, composite defects of nematic-spin DWs and half-quantum vortices have been experimentally realized * takeuchi@osaka-cu.ac.jp; http://hiromitsu-takeuchi.appspot.com through the symmetry breaking phase transition in spin-1 Bose-Einstein condensates (BECs) of 27 Na atoms [31]. The mass-current field around a composite defect is theoretically shown to form an anomalous elliptic structure in equilibrium [32]. Magnetic-domain formation has been realized in a strongly ferromagnetic spinor BEC of 7 Li atoms [33].…”

Phase diagram, stability and magnetic properties of nonlinear excitations in spinor Bose–Einstein condensates

“…It is relevant to mention here that the properties of specific vortex structures such as the elliptic one characterized by broken axisymmetry were recently discussed for the PO phase in Refs. [56,57] and the so-called nematic spin vortices in the EP of AF condensates were analyzed in Ref. [58].…”