**Abstract**
The rich order parameter space of multicomponent Bose-Einstein condensates (BECs) admit various kinds of topological excitations. In this seminar, I will explain the symmetry property of spinor BECs and then show some intrigung spin configurations.

The spin-1 polar phase has a discrete Z2 symmetry and accommodates a half-quantum vortex, in which the quantization unit of the circulation is a half of that in a conventional U(1) vortex. The polar BECs can also accommodate a knot, a three dimensional coreless monopole characterized by a linking number [1]. On the other hand, the ferromagnetic BEC has a spin-gauge symmetry, and therefore, spin texture induces mass current. More interestingly, at low magnetic field the magnetic dipole-dipole interaction between atoms induces spatial variation of spin configurations, leading to spontaneous mass current [2].

[1] YK, M. Nitta, and M. Ueda, PRL 100, 180403 (2008)

[2] YK, H. Saito, and M. Ueda, PRL 97, 130404 (2006)