Majoranas in mixed-valence insulators

A physical model for a mixed-valence impurity in metal must satisfy the Friedel screening theorem for both valences. Such a model is shown, following earlier work which showed low-energy singularities in it, to be supersymmetric, leading to a free Majorana and a phase-shifted Majorana excitation. Th...

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Bibliographic Details
Published in:Physical review. B 2020-10, Vol.102 (15), p.1, Article 155145
Main Author: Varma, C. M.
Format: Article
Language:English
Subjects:
Anomalies
Chemical potential
De Haas-Van Alphen effect
Fermions
Insulators
Oscillations
Zeeman effect
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Summary:A physical model for a mixed-valence impurity in metal must satisfy the Friedel screening theorem for both valences. Such a model is shown, following earlier work which showed low-energy singularities in it, to be supersymmetric, leading to a free Majorana and a phase-shifted Majorana excitation. The theory extended approximately to a lattice of mixed-valence ions at appropriate filling gives, without fine-tuning the parameters, a protected gapless Majorana fermion band across the chemical potential, besides the mixed-valence particle and hole bands separated by gaps. In this situation, the system is electrically neutral in linear response but has de Haas-van Alphen oscillations. This is used to explain the recently observed magneto-oscillations in mixed-valence insulators as well as their accompanying low-energy thermodynamic and relaxation rate anomalies. Some predictions to test the validity of the theoretical results are provided, the most striking of which are that there should be extensive ground-state entropy in such compounds and no Zeeman splitting of the magneto-oscillation frequencies.
ISSN:2469-9950
2469-9969
DOI:10.1103/PhysRevB.102.155145