Wydarzenia

Seminarium Międzynarodowego Laboratorium Silnych Pól Magnetycznych i Niskich Temperatur PAN

Experimental observation of Aharonov-Bohm conductance steps in bismuth nanowires

prof. Tito E. Huber

Howard University, Washington, USA

      Three dimensional topological insulators (3D-TIs) are a new class of materials with a wide range of potential applications, including spintronics and interconnect. From an interconnect perspective the salient feature of the material include: graphene-like 2D surface transport with high mobility and linear bands; spin-polarized carrier motion due to high spin-orbit coupling; immunity to backscattering, surface defects and even high level of alloy impurities. However, closer review of the theoretical and experi-mental results shows that the protection of the surface state exists only for elastic backscattering, and only as long as the charge carrier energy does not exceed the bulk band gap and the thickness of the bulk material is larger than ~5nm. Neither inelastic backscattering nor medium- angle elastic scattering are suppressed on the surface of 3D-TIs. However, the spin-polarized nature of electron motion on the surface TIs holds promise for spintronics applications. Bismuth is a trivial topological insulator which means that that the Rashba bands are not immune to backscattering but still has many interesting properties for spintronics. Surprisingly, we find that the Rashba bands of Bi exhibit extraordinarily high mobility. We present unambiguous experimental evidence of quantum mechanically enhanced transport by Rashba bands in the surface of Bi nanowires with an insulating bulk interior. With increasing magnetic fields, the nanowires exhibit stepwise increase of conductance with as many as 4 distinct plateaus at low magnetic fields and linear magnetoconductance at high magnetic fields. This is caused by the consecutive filling of spin-split subbands associated with Aharonov-Bohm quantum interference around the perimeter, demonstrating that surface band mobility is very high (>300,000 cm²V^-1s^-1 ), comparable to graphene.

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