a test for Majorana character of the vortex zero modes*

Majorana zero modes are intriguing, exotic quasiparticles in condensed matter physics and are predicted to enable fault-tolerant quantum computation. Recently, quite a few experimental platforms, including nanowires, atom chains, and superconducting vortices, have shown promising signatures of Majorana zero modes, but the evidence generally remains phenomenological: a peak in differential conductance exactly at the zero-bias voltage. In the putative Majorana platform, the iron-based superconductor FeTe_0.55Se_0.45, additional evidence^[1] stems from the saturation of differential conductance but remains controversial. Theoretical work^[2] has shown that an unambiguous experimental test for the Majorana character is possible using local noise spectroscopy. In this talk, I will present scanning tunneling noise spectroscopy experiments^[3] in the vortex cores of FeTe_0.55Se_0.45 and answer the question of whether the zero-energy modes have the Majorana character. 

[1] S. Zhu, et al., Science, 367, 189 (2020).

[2] C. J. Bolech and E. Demler, PRL 98, 237002 (2007); J. Nilsson, A. R. Akhmerov, and C. W. J. Beenakker, PRL 101, 120403 (2008); A. Golub and B. Horovitz, PRB 83, 153415 (2011).

[3] K. M. Bastiaans, et al., RSI 89, 093709 (2018); K. M. Bastiaans, et al., PRB 100, 104506 (2019).