Unveiling the valence band nature of GaMnAs anisotropic carriers by inter-band tunneling spectroscopy

R. GIRAUD; M. GRANADA; E. BRIONES; U. GENNSER; A. LEMAITRE; G. FAINI

Dresden, Alemania

Conferencia; DPG Spring Meeting 2011; 2011

The discovery of highly anisotropic properties of magnetic tunnel junctions based on GaMnAs [1] has led to new concepts for spintronics devices, such as magnetic memories based on anisotropy relaxation in nanostructures [2], or magnetic switches relying on electrical control of the magnetic anisotropy [3]. However, despite the success of mean-field theories of hole-induced ferromagnetism, a direct evidence of the existence of Bloch states is still missing, and the nature of carriers remains controversial (impurity-band vs. valence-band models). Here, based on inter-band tunneling spectroscopy of p-GaMnAs/n-GaAs Zener-Esaki diodes [4], we directly evidence the valence band nature of GaMnAs carriers and, importantly, reveal the spin-split valence bands dependence of their cubic and uniaxial anisotropies (which can be tuned under applied bias or magnetic field). In particular, the Fermi energy is found well below the top of the valence band, and the energy dependence of Bloch states anisotropies shows some specific features predicted by a k.p modelling of the spin-split valence bands. [1] C. Gould et al., Phys. Rev. Lett. 93, 117203 (2004) [2] K. Pappert et al., Nat Phys. 3, 573 (2007) [3] C. Bihler et al., Phys. Rev. B 78, 045203 (2008) [4] R. Giraud et al., Appl. Phys. Lett. 87, 242505 (2005)