Seminarium Oddziału Badań Magnetyków
Microsoft Teams
Realization of the nontrivial topological phase in low dimensional structures
dr hab. Andrzej Ptok, prof. IFJ PAN
Instytut Fizyki Jądrowej Polskiej Akademii Nauk w Krakowie
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Streszczenie:
Interplay between superconductivity, spin orbit coupling and magnetic field can lead to realization of the topological phase shift [1]. Existence of this non-trivial topological phase allows for emergence of the bound states, which a most famous example is the Majorana bound state. The signatures of Majorana bound states at the ends of magnetic chains deposited on a superconducting substrate were reported experimentally [2,3], and recent experimental works suggest a possibility of realization of the topological superconducting domain in magnetic nanostructure coupled with bulk superconductor [4,5]. During seminar, results obtained in context of both experimental systems will be presented.
In the case of a magnetic monoatomic chains, we employ first principles (DFT) calculations to directly investigate the topological properties of 3d transition metal nanochains (i.e., Mn, Cr, Fe and Co) [6]. In contrast to the previous studies, we found the exact tight-binding models in the Wannier orbital basis for the isolated chains as well as for the surface-deposited wires. Based on these models, we calculate the topological invariant for all systems. Firstly, for the isolated chains we demonstrate the existence of the topological phase only in Mn and Co systems. Secondly, we showed that a coupling between the chain and substrate leads to strong modification of the band structure. Moreover, the analysis of the topological invariant indicates the possibility of emergence of the topological phase in all studied nanochains deposited on the Pb surface. Therefore, our results demonstrate an important role of the coupling between deposited atoms and a substrate for topological properties of nanosystems, that should be implemented in future studies. In the second case, we study a realization of the nonotrivial topological phase in a nanoflake [7]. The boundary between trivial and topological phase are "marked" by nearly-zero in-gap bound state. The analysis of the topological phase diagram of such a system shows that a similar phase separation occurs by tuning the chemical potential of the nanoflake. We study such a possibility in detail, analyzing the spatial extent of the edge modes circulating around the nanoflake and discussing some practical implementations. We also show how the chirality of Majorana edge states can be probed using scanning tunneling spectroscopy with a double tip setup.
[1] Superconducting monolayer deposited on substrate: Effects of the spin-orbit coupling induced by proximity effects, A. Ptok, K. Rodrìguez, and K.J. Kapcia, Phys. Rev. Materials 2, 024801 (2018)
[2] Observation of Majorana fermions in ferromagnetic atomic chains on a superconductor, S. Nadj-Perge, I. K. Drozdov, J. Li, H. Chen, S. Jeon, J. Seo, A. H. MacDonald, B. A. Bernevig, and A. Yazdani, Science 346, 602 (2014)
[3] Exploring a Proximity-Coupled Co Chain on Pb(110) as a Possible Majorana Platform, M. Ruby, B. W. Heinrich, Y. Peng, F. von Oppen, and K. J. Franke, Nano Lett. 17, 4473 (2017)
[4] Two-dimensional topological superconductivity in Pb/Co/Si(111), G. C. Ménard, S. Guissart, Ch.Brun, R.T. Leriche, M. Trif, F. Debontridder, D. Demaille, D. Roditchev, P. Simon, and T. Cren, Nat. Commun. 8, 2040 (2017)
[5] Atomic-Scale Interface Engineering of Majorana Edge Modes in a 2D Magnet- Superconductor Hybrid System, A. Palacio-Morales, E. Mascot, S. Cocklin, H. Kim, S. Rachel, D. K. Morr, and R. Wiesendanger, Sci. Adv. 5, eaav6600 (2019)
[6] First-principles study of the nontrivial topological phase in chains of 3d transition metals, A. Kobiałka, P. Piekarz, A. M. Oleś, and A. Ptok, Phys. Rev. B 101, 205143 (2020)
[7] Probing the chirality of one-dimensional Majorana edge states around a two-dimensional nanoflake in a superconductor, A. Ptok, D. J. Alspaugh, Sz. Glodzik, A. Kobiałka, A. M. Oleś, P. Simon, and P. Piekarz, Phys. Rev. B accepted, arXiv:2008.11807
