Fig. 5
Spin textures in TI surfaces. An illustration of a gapless Dirac surface state for the top surface, a magnetically gapped surface state with hedgehog spin texture for the bottom surface, and top-gated TI/(Ga,Mn)As heterostructure devices with VG = −5 V and VG = +1 V. Green arrows represent the magnetization of the (Ga,Mn)As layer and gray and red arrows in the TI layer represent the directions of electron propagation and its spin, respectively. JFMI is the exchange-coupling constant between Mn moments in (Ga,Mn)As while JTI−FMI is the weaker exchange-coupling constant between electrons in the TI bottom surface and Mn moments in (Ga,Mn)As
