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Observation of Majorana quantum critical behaviour in a resonant level coupled to a dissipative environment

Abstract

A quantum phase transition is an abrupt change between two distinct ground states of a many-body system, driven by an external parameter. In the vicinity of the quantum critical point (QCP) where the transition occurs, a new phase may emerge that is determined by quantum fluctuations and is very different from either phase. In particular, a conducting system may exhibit non-Fermi-liquid behaviour. Although this scenario is well established theoretically, controllable experimental realizations are rare. Here, we experimentally investigate the nature of the QCP in a simple nanoscale system—a spin-polarized resonant level coupled to dissipative contacts. We fine-tune the system to the QCP, realized exactly on-resonance and when the coupling between the level and the two contacts is symmetric. Several anomalous transport scaling laws are demonstrated, including a striking non-Fermi-liquid scattering rate at the QCP, indicating fractionalization of the resonant level into two Majorana quasiparticles.

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Figure 1: Sample and schematic.
Figure 2: Differential conductance maps close to the QCP.
Figure 3: Critical flow.
Figure 4: Runaway flow.

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Acknowledgements

We appreciate valuable discussions with I. Affleck, C. H. Chung, P. Coleman, K. Ingersent, K. Le Hur and P. A. Lee. We thank J. Liu for providing the nanotube growth facilities and W. Zhou for helping to optimize the nanotube synthesis. H.Z., S.F. and H.U.B. thank the Fondation Nanosciences de Grenoble for facilitating the exchange between Grenoble and Duke. The work in the US was supported by US DOE awards DE-SC0002765, DE-SC0005237 and DE-FG02-02ER15354.

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Contributions

H.T.M., I.V.B. and G.F. designed the experiment. H.T.M. fabricated the samples. H.T.M., I.V.B., Y.V.B., A.I.S. and G.F. conducted the experiment. H.T.M., H.Z., S.F., H.U.B. and G.F. analysed and interpreted the data. H.Z., S.F. and H.U.B. developed the theory.

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Correspondence to G. Finkelstein.

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The authors declare no competing financial interests.

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Mebrahtu, H., Borzenets, I., Zheng, H. et al. Observation of Majorana quantum critical behaviour in a resonant level coupled to a dissipative environment. Nature Phys 9, 732–737 (2013). https://doi.org/10.1038/nphys2735

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