Status  Confirmed 
Seminar Series  SOUTENTH 
Subjects  physics 
Date  Friday 15 September 2017 
Time  14:00 
Institute  IPHT 
Seminar Room  Amphi Claude Bloch, Bât. 774 
Speaker's Last Name  Vardan Kaladzhyan 
Speaker's First Name  
Speaker's Email Address  
Speaker's Institution  IPhT 
Title  Spin polarisation and topological properties of YuShibaRusinov states 
Abstract  In this manuscript we first revisit the physics of YuShibaRusinov subgap states, focusing on their spin polarisation. We start by showing theoretically that we can extract a considerable amount of information about the host superconductor, by analysing spinpolarised local density of states related to the presence of magnetic impurities. First, we demonstrate that the spinorbit coupling in twodimensional and onedimensional systems, both superconducting and metallic, can be readoff directly and unambiguously via spinresolved STM. We analyse the impurityinduced oscillations in the local density of states. In particular, we focus on the Fourier transform (FT) of the Friedel oscillations and we note that highintensity FT features appear at a wave vector given by twice the inverse spinorbit length. Second, in unconventional superconductors with both swave and pwave pairing, by analysing the spinresolved spectral structure of the YuShibaRusinov states it is possible to determine the dominating pairing mechanism. Most strikingly, we demonstrate that a careful analysis of spinpolarised density of states allows not only to unambiguously characterise the degree of triplet pairing, but also to define the orientation of the triplet pairing vector, also known as the dvector. Finally, we discuss two different ways of engineering and controlling topological phases with both scalar and magnetic impurities. We start with providing a microscopic theory of scalar impurity structures on chiral superconductors. We show that given a nontrivial chiral superconductor, the scalar impurities give rise to a complex hierarchy of distinct nontrivial phases with high Chern numbers. Second, we propose and study theoretically a new promising platform that we call 'dynamical Shiba chain', i.e. a chain of classical magnetic impurities in an swave superconductor with precessing spins. We have shown that it can be employed not only for engineering a topological superconducting phase, but most remarkably for controlling topological phase transitions by means of magnetisation texture dynamics. This manuscript is organised as follows. In the first part, the essential introductory information on superconductivity, Friedel oscillations and YuShibaRusinov states is provided. The second part is dedicated to spin polarisation of YuShibaRusinov states and the properties that could be extracted by means of spinresolved STM measurements. In the last part, two setups proposed for topological phase engineering based on impurityinduced states are presented, followed by conclusions with a brief summary of the thesis achievements and further directions to pursue. 
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