[Paper Review] Dirac fermions in the heavy-fermion superconductors Ce(Co,Rh,Ir)In$_5$

Kent Shirer, Yan Sun+14 more|arXiv (Cornell University)|Aug 1, 2018

Rare-earth and actinide compounds1 references4 citations

TL;DR

This paper proposes that Ce(Co,Rh,Ir)In₅ heavy-fermion superconductors host Dirac fermions at well-separated nodes near the Fermi level, arising from In-5s and In-4p_z orbitals, leading to topological semi-metal behavior. Theoretical and experimental evidence shows these Dirac nodes induce a topological Lifshitz transition under high magnetic fields, explaining similar high-field quantum oscillations and resistivity jumps across all three compounds despite distinct zero-field ground states, suggesting a role in unconventional topological superconductivity.

ABSTRACT

The Ce(Co,Rh,Ir)In$_5$ family of ``Ce-115'' materials hosts an abundance of correlated electron behavior, including heavy-fermion physics, magnetism, superconductivity and nematicity. The complicated behavior of these entangled phenomena leads to a variety of exotic physical properties, which, despite the seemingly simple crystal structure of these compounds, remain poorly understood. It is generally accepted that the interplay between the itinerant and local character of Ce-$4f$ electrons is the key to their exotic behavior. Here, we report theoretical evidence that the Ce-115 materials are also topological semi-metals, with Dirac fermions around well-separated nodes. Dirac nodes in each compound are present on the $Γ-Z$ plane close to the Fermi level. As the Dirac bands are derived from In-orbitals, they occur in all family members irrespective of the transition metal (Co,Rh,Ir). We present the expected Fermi-arc surface state patterns and show the close proximity of a topological Lifshitz transition, which possibly explains the high field physics of Ce-115 materials. Experimentally, we highlight the surprising similarity of Ce(Co,Rh,Ir)In$_5$ in high magnetic fields, despite the distinctly different states of the Ce-$4f$ electrons. These results raise questions about the role Dirac fermions play in exotic transport behavior, and we propose this class of materials as a prime candidate for unconventional topological superconductivity.

Motivation & Objective

• To investigate the topological electronic structure of Ce(Co,Rh,Ir)In₅ despite their complex correlated electron behavior.
• To determine whether Dirac fermions exist in these heavy-fermion systems and how they influence exotic quantum phenomena.
• To explain the striking similarity in high-field resistivity and quantum oscillations across CeCoIn₅, CeRhIn₅, and CeIrIn₅ despite distinct zero-field phases.
• To explore the role of Dirac fermions in enabling topological superconductivity and nematic transitions in strongly correlated systems.

Proposed method

• Performed first-principles band structure calculations to identify Dirac nodes in Ce-115 compounds, including La-115 as a reference.
• Analyzed the orbital character of bands near the Fermi level, identifying In-5s and In-4p_z states as the origin of Dirac crossings.
• Modeled Fermi-arc surface state patterns expected for topological semi-metal behavior.
• Evaluated the proximity of a topological Lifshitz transition via magnetic field-induced reconstruction of Fermi surface topology.
• Correlated theoretical predictions with high-field transport measurements, including resistivity and quantum oscillations.
• Used symmetry and band topology arguments to link the Dirac node to the observed nematic and superconducting transitions.

Experimental results

Research questions

• RQ1 Do Dirac fermions exist in Ce(Co,Rh,Ir)In₅ despite strong electron correlations and heavy-fermion behavior?
• RQ2 What is the origin of the identical high-field quantum oscillation frequency and resistivity discontinuity in CeCoIn₅, CeRhIn₅, and CeIrIn₅?
• RQ3 Can the topological Lifshitz transition at high magnetic fields explain the abrupt resistivity jump and giant quantum oscillations?
• RQ4 How do Dirac fermions influence the emergence of unconventional superconductivity and nematic order in these materials?
• RQ5 Can the chiral nature of Dirac fermions explain the macroscopic chiral magnetic order observed in CeRhIn₅?

Key findings

• Dirac nodes are present on the Γ–Z plane near the Fermi level in all Ce(Co,Rh,Ir)In₅ compounds, arising from In-5s and In-4p_z orbitals.
• The Dirac bands are robust across all family members regardless of the transition metal (Co, Rh, Ir), due to the same orbital origin.
• A topological Lifshitz transition is predicted to occur under high magnetic fields, where the Dirac pocket detaches from the Fermi surface.
• This transition explains the giant quantum oscillations and abrupt resistivity jump observed in CeRhIn₅ and CeIrIn₅ at ~28 T.
• The high-field behavior is consistent across CeCoIn₅, CeRhIn₅, and CeIrIn₅, despite distinct zero-field ground states, due to a common topological electronic structure.
• The Dirac node may stabilize macroscopic chiral magnetic order in CeRhIn₅ by imprinting quasiparticle chirality on the Fermi surface.