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Condensed Matter Seminar: "Quantum anomalous vortex and Majorana zero mode in Fe-based superconductor Fe(Te,Se)"

Event Type
Physics - Condensed Matter
190 ESB
Apr 12, 2019   1:00 pm  
Ziqiang Wang, Boston College
Originating Calendar
Physics - Condensed Matter Seminar

In conventional s-wave superconductors, a magnetic impurity is known to create a vortex-free defect where only the amplitude of the superconducting order parameter deforms. An external magnetic field is required to generate topological defect excitations such as vortices. In this talk, we show that this folklore changes in a fundamental way in s-wave superconductors with strong spin-orbit coupling. In this case, topological defect excitations can nucleate around an interstitial magnetic ion with nonzero spin-orbital angular momentum by spontaneously developing a quantized phase winding in the pairing order parameter in the absence of an external magnetic field [1]. The role of the magnetic field is played by the exchange field as in the anomalous Hall effect. We find that such vortices, dubbed quantum anomalous vortices, are capable of clearing out the vortex core states and support uncontaminated Majorana zero mode when superconductivity is induced in the topological surface states [1]. We argue that the robust zero-energy bound states observed in Fe(Te,Se) superconductors without applying an external magnetic field [2] are realizations of the Majorana zero modes in the quantum anomalous vortices nucleated at the interstitial magnetic Fe sites. The quantum anomalous vortex matter may provide a new and advantageous platform for studying Majorana zero modes in connection to fault tolerant topological quantum computing.

[1] Kun Jiang, Xi Dai, and Ziqiang Wang, Phys. Rev. X 9, 011033 (2019).

[2] J.-X. Yin, et. al., Nat. Phys.  11, 543 (2015).

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