Experimental and theoretical study of the CISS magnetoresistance
In his thesis, Sytze Tirion explores the connection between two fundamental symmetries, chirality and magnetism, using both theoretical and experimental approaches. He studies how these symmetries influence the transport of electrons and electron spin in chiral materials connected to ferromagnets. In particular, Tirion studies the change of electrical resistance due to chirality and magnetism, which is known as the CISS magnetoresistance, after the chirality-induced spin selectivity effect. Currently, the origin of the CISS magnetoresistance is commonly assumed to originate from spin-dependent transport in the chiral system. However, there are serious discrepancies between this explanation and the experimental results.
Tirion proposes an alternative mechanism to generate the CISS magnetoresistance, based on the electrostatic modification of the transport barrier by reversing either the chirality or magnetization. As part of the ongoing discussions about the electrostatically generated CISS magnetoresistance, Tirion discusses a bias-induced modification of the charge accumulation, which can alter the electrostatics of the transport barrier and generate magnetoresistance, but changes sign as the bias is reversed.
Experimentally, Tirion developed a new approach to detect electrostatic modifications by reversing either the chirality or magnetization with high experimental sensitivity. Furthermore, he studied the effects of chirality and magnetism in several atomic force microscopy experiments.
Lastly, Tirion provides a theoretical description of the injection and detection of electron spins in a semiconductor in Hanle spin precession experiments.
The results in this thesis pave the way for future experimental and theoretical directions to study the role of chirality in electron and spin transport experiments.