Direct probing of band structure Berry phase in diluted magnetic semiconductors

M. GRANADA; D. LUCOT; R. GIRAUD; A. LEMAÎTRE; C. ULYSSE; X. WAINTAL; G. FAINI

Buenos Aires

Workshop; X Latin American Workshop on Magnetism, Magnetic Materials and their Applications; 2013

A quantum system undergoing an adiabatic evolution accumulates a geometrical phase, which adds to the standard dynamical phase. This phase, introduced by Berry in his 1984 seminal paper, has become a central concept in our understanding of quantum mechanics. In condensed matter, the Berry phase is intimately related to band theory. It provides a deep understanding of, say, the topological nature of quantum Hall effect or some peculiar features of graphene. Despite its fundamental nature, no direct experimental signatures have been reported, except through reinterpretation of anomalous Hall-related effects. Here, we report on experimental evidences of a Berry phase accumulated by the quasi-particle (hole) wave function in a mesoscopic device made from a ferromagnetic semiconductor (Ga,Mn)(As,P) layer. Its signature is revealed as unusual patterns in the universal conductance fluctuations (UCF), which arise from quantum interferences between different electronic trajectories in disordered materials. Such patterns had been observed previously [1,2], and the presence of domain walls was thought to be their cause. More recently, a theoretical work proposed that a Berry phase, rather than domain walls, is at the origin of this effect [3]. Magnetotransport experiments were carried at low temperatures (T