Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session E23: Majorana States in Topological SuperconductorsInvited
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Sponsoring Units: DCMP Chair: Andrei Bernevig, Princeton University Room: New Orleans Theater B |
Tuesday, March 14, 2017 8:00AM - 8:36AM |
E23.00001: Transport signatures of chiral Majorana edge modes Invited Speaker: Stephan Rachel Majorana states in condensed matter physics hold unprecedented potential as a novel platform for quantum computing. Recent groundbreaking experiments have demonstrated that Majorana bound states can be realized at the end of chains of iron atoms located on a lead s-wave superconductor. A recent proposal focuses on the possibility to generalize from ``Shiba chains'' to ``Shiba islands''. The topological phases are expected to possess propagating Majorana edge states.\\ \phantom{xxx}In this talk, I will demonstrate that the topological nature of such propagating Majorana edge states can be identified through transport measurement using a scanning tunneling microscope (STM). I will show that the differential conductance of Majorana edge states can be quantized, and in certain situations equal to the quantum of conductance times the magnitude of the Chern number. Implications of these results for future experiments are discussed. [Preview Abstract] |
Tuesday, March 14, 2017 8:36AM - 9:12AM |
E23.00002: Design of Majorana Edge States in Topological Superconductors Invited Speaker: Dirk Morr The experimental observation of Majorana bound states in topological superconductors represents a major breakthrough in realizing their applications in quantum computation. Recent proposals focusing on the creation of Majorana states on the edges of 2D magnetic islands have raised the question of whether Majorana states can also emerge in more complex spatial structures of magnetic islands or layers and s-wave superconductors. In this talk, I discuss the design of Majorana edge states in magnetic-superconducting hybrid structures and their stability with regards to the spatial form of the magnetic order and spatial variations in the superconducting order parameter. I show that by investigating the relation between local transport properties – as reflected in the spatial flow of charge – and global transport properties of topological states [1], one can identify transport characteristics of Majorana states, such as a quantized conductance, that distinguish them from conventional Shiba states [2]. We demonstrate the existence and unconventional spatial structure of superconducting triplet correlations which can be both time reversal (TR) breaking and TR preserving within the same system [2]. While these correlations exists both in the topologically trivial as well as non-trivial phases, low-energy edge modes that carry a supercurrent exist only in the topologically non-trivial phases. Implications for the existence or lack of chiral edge modes in triplet superconductors will be discussed. References: [1] J. Van Dyke and D. K. Morr , Controlling the Flow of Spin and Charge in Nanoscopic Topological Insulators,Phys. Rev. B 93, 081401(R) (2016), Rapid Communication. [2] S. Rachel and D.K.Morr, Design of Majorana Edge States in Topological Superconductors, unpublished. [Preview Abstract] |
Tuesday, March 14, 2017 9:12AM - 9:48AM |
E23.00003: Majorana bound states in atomic structures Invited Speaker: Stevan Nadj-Perge Majorana bound states are zero-energy excitations predicted to localize at the edge of a one-dimensional (1D) topological superconductor. Such excitations are reported in several 1D experimental systems based on semiconductor nanowires and ferromagnetic atomic chains coupled to s-wave superconductors. The next set of experiments is therefore expected to go beyond simple spectroscopy measurements and aim at establishing the necessary control over these excitations. In this talk, I will discuss potential ways of achieving such control of Majorana states in atomic size structures. [Preview Abstract] |
Tuesday, March 14, 2017 9:48AM - 10:24AM |
E23.00004: From single magnetic adatoms on superconductors to coupled spin chains Invited Speaker: Katharina J. Franke Magnetic adsorbates on conventional s-wave superconductors lead to exchange interactions that induce Yu-Shiba-Rusinov (YSR) states inside the superconducting energy gap. Here, we employ tunneling spectroscopy at 1.1 K to investigate magnetic atoms and chains on superconducting Pb surfaces. We show that individual Manganese (Mn) atoms give rise to a distinct number of YSR-states. The single-atom junctions are stable over several orders of magnitude in conductance. We identify single-electron tunneling as well as Andreev processes [1]. When the atoms are brought into sufficiently close distance, the Shiba states hybridize, thus giving rise to states with bonding and anti-bonding character. It has been shown that the Pb(110) surface supports the self-assembly of Fe chains, which exhibit fingerprints of Majorana bound states [2]. Using superconducting tips, we resolve a rich subgap structure including peaks at zero energy and low-energy resonances, which overlap with the putative Majorana states [3].\\[4pt] References:\\[0pt] [1] M. Ruby, et al., Phys. Rev. Lett. 115, 087001 (2015).\\[0pt] [2] S. Nadj-Perge, et al., Science 346, 602 (2014).\\[0pt] [3] M. Ruby, et al., Phys. Rev. Lett. 115, 197204 (2015). [Preview Abstract] |
Tuesday, March 14, 2017 10:24AM - 11:00AM |
E23.00005: Shiba lattices as novel platforms for topological superconductivity Invited Speaker: Titus Neupert I will discuss forms of topological superconductivity that can arise when the surface of a bulk superconductor is decorated with a one- or two-dimensional lattice of magnetic or nonmagnetic impurities. For example, if magnetic impurities order ferromagnetically and the superconducting surface supports a sufficiently strong Rashba-type spin-orbit coupling, Shiba sub-gap states at impurity locations can hybridize into Bogoliubov bands with non-vanishing, sometimes large, Chern number C. This topological superconductor supports C chiral Majorana edge modes. I will discuss phase diagrams for model two-dimensional superconductors, both in the limit of dilute and dense magnetic impurity lattices. To address potential experimental systems, stable configurations of ferromagnetic iron atoms on the Pb (111) surface are identified and it is proposed that ferromagnetic adatoms on Pb surfaces can provide a versatile platform for two-dimensional topological superconductivity. In the one-dimensional case, I will cover both the physics of magnetic and nonmagnetic impurity chains on the surface of conventional and unconventional superconductors. [Preview Abstract] |
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