WFU Physics Colloquium

TITLE: Amazing spin transport effects at the nanoscale

SPEAKER: Dr. Ewelina Hankiewicz ,

TIME: Tuesday Jan. 22, 2008 at 4:00 PM

PLACE: Room 101 in Olin Physical Laboratory

The exponential increase of computational speed through miniaturization, known as Moore's law, seems increasingly difficult to achieve. Based on current power consumption trends, we could possibly face the so-called problem 2020 where the temperature of a miniaturized computer would be equal to the sun's temperature. Something generally considered hazardous to the health of the consumer.

Manipulation of electron spins through electric fields (so-called spintronics) is an avenue to produce a new generation of devices that would consume less power and circumvent problem 2020. I will discuss my recent research concerning a novel phenomenon under this umbrella: the spin-Hall effect. The spin-Hall effect is the generation of a steady spin-current perpendicular to an externally imposed dc electric field. This effect can typically be caused by band structure and/or impurities in semiconductors. Thus far, the spin-Hall effect has been measured in semiconductors by optical pump-probe experiments [1] and the mechanism of the effect was not clear. In this talk, I will address theoretically how to determine different factors contributing to the spin-Hall phenomenon as well as explain the exciting physics of non-additive behavior of impurity and band structure mechanisms [2]. Later, I will discuss my theoretical proposal to generate and detect the spin-Hall effect in transport by using purely electrical means (the so-called H-bar device) [3]. In addition, I will talk about current work, performed in close collaboration with the experimentalists, concerning the realization and optimization of this device in HgTe/HgCdTe nanosize samples.

1. Y. K. Kato et al., Science 306, 1910 (2004); V. Sih et al., Nature Physics 1, 31 (2005).
2. E. M. Hankiewicz, G. Vignale and M. Flatté, Phys. Rev. Lett. 97, 266601 (2006); Phys. Rev. Lett. in press (2008).
3. E. M. Hankiewicz et al., Phys. Rev. B 70, 241301(R) (2004).