Graduate Program in Spintronics Seminar

Control of Spin Relaxation in Disordered
Quantum Wells and Nanowires

1:00-2:00 pm
Thursday,October 3 2019102

Room, Education and Research Building [B01]
School of Engineering,
Aobayama East Campus, Tohoku University

Dr. Michael Kammermeier(School of Chemical and Physical Sciences,
Victoria University of Wellington)[School of Engineering, Aobayama East Campus]

1st floor, 102

Inquiries: GP-Spin Office
spin.all[at]grp.tohoku.ac.jp
Phone: 022-795-3657 / 5716

Control of Spin Relaxation in Disordered
Quantum Wells and Nanowires
Michael Kammermeier
School of Chemical and Physical Sciences andMacDiarmid Institute for Advanced Materials and Nanotechnology,
Victoria University of Wellington, Wellington 6140, New ZealandIn this lecture, we address the topic of Dyakonov-Perel spin relaxation for two
important types of semiconductor nanostructures: disordered 2D quantum wells andnanowires. Theoretically, we investigate possibilities to control the spin relaxation
process by adjusting spin-orbit coupling (SOC) parameters, crystal orientation, orgeometrical confinement. We pay close attention to the experimental signatures of thespin relaxation, with the focus on the optical orientation and weak (anti)localization
measurement.
As a generalization of earlier findings,1,2 we identify general conditions for therealization of spin-preserving symmetries for 2D electron gases with Rashba andDresselhaus SOC.3 It is shown that a persistent spin helix can be realized if and only if
at least two growth-direction Miller indices agree in modulus. We determine theappropriate requirements on the axial symmetric Rashba and Dresselhaus contributions
and discuss the impact of cubic Dresselhaus terms which usually break this symmetry.
A general closed-form expression for the weak (anti)localization is provided to support asubsequent experimental investigation. Aside from this, we demonstrate that also in[001]-oriented 2D hole gases spin-conserving symmetries can be found if, in addition,
uniaxial shear strain is present.4
Semiconductor nanowires can have very distinct spin relaxation properties due totheir mesoscopic nature and the huge degree of freedom in device preparation. Most
prominent is the boundary-induced motional narrowing effect which strongly alters thespin lifetime as well as the structure of the long-lived spin texture. We developed
theoretical models to describe the spin relaxation mechanism and the weak(anti)localization correction in different types of nanowires.5-8 These models are fitted toexperimental data and transport parameters extracted. We demonstrate that theexperimental results for the spin lifetime can differ dramatically between optical andtransport measurements.8
References:
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J. Schliemann, et al., Phys. Rev. Lett. 90, 146801 (2003).
B. A. Bernevig, et al., Phys. Rev. Lett. 97, 236601 (2006).
M. Kammermeier, et al., Phys. Rev. Lett. 117, 236801 (2016).
P. Wenk, et al., Phys. Rev. B 93, 115312 (2016).
P. Wenk, et al., Phys. Rev. B 83, 115301 (2011).
M. Kammermeier, et al., Phys. Rev B 93, 205306 (2016).
M. Kammermeier, et al., Phys. Rev B 96, 235302 (2017).
M. Kammermeier, et al., Phys. Rev B 98, 035407 (2018).