[Paper Review] Band dependent emergence of heavy quasiparticles in CeCoIn5

A. Koitzsch, T. K. Kim+8 more|arXiv (Cornell University)|Jul 23, 2013

Rare-earth and actinide compounds3 citations

TL;DR

This study uses angle-resolved photoemission spectroscopy (ARPES) at T = 1.4 K to directly measure band-dependent f-electron hybridization in the heavy fermion superconductor CeCoIn5. It finds that the most two-dimensional band (band 133) exhibits the weakest hybridization with conduction electrons, challenging assumptions about 2D bands being most strongly hybridized, and provides semi-quantitative agreement with de-Haas-van-Alphen measurements of mass enhancement.

ABSTRACT

We investigate the low temperature (T $

Motivation & Objective

• To clarify the band-dependent nature of f-electron hybridization in CeCoIn5, a prototypical heavy fermion superconductor near a quantum critical point.
• To resolve the long-standing ambiguity on whether hybridization is strongest on two-dimensional (2D) bands or uniformly distributed across bands near the Fermi level.
• To quantitatively link ARPES-measured electronic structure with bulk properties such as effective mass enhancement and Fermi surface topology.
• To test the validity of simplified multiband Periodic Anderson Model (PAM) descriptions against high-resolution, low-temperature ARPES data.
• To investigate the implications of band-dependent hybridization for unconventional superconductivity and magnetic fluctuations in 115-type heavy fermion systems.

Proposed method

• Angle-resolved photoemission spectroscopy (ARPES) was performed at the BESSY II beamline using a photon energy of 121 eV to achieve resonant enhancement of Ce 4f states.
• Measurements were conducted on high-quality CeCoIn5 single crystals cleaved in situ at temperatures as low as 1.4 K to access the coherent, heavy quasiparticle regime.
• Energy resolution was maintained at ΔE = 22 meV, enabling precise determination of band dispersions and hybridization gaps.
• A simplified multiband Periodic Anderson Model (PAM) was used to simulate the observed spectral features and extract hybridization parameters (Vcf) for individual bands.
• Fermi velocity renormalization was calculated by comparing simulated band dispersions with unrenormalized LDA bands, allowing extraction of effective mass enhancements (m*/m_b).
• Results were cross-validated with de-Haas-van-Alphen (dHvA) measurements to confirm bulk nature of Fermi surface and consistency of mass enhancement factors.

Experimental results

Research questions

• RQ1 Is the hybridization between f-electrons and conduction electrons in CeCoIn5 strongest on the two-dimensional bands, as often assumed in models of unconventional superconductivity?
• RQ2 How does the degree of f-electron hybridization vary across different electronic bands in CeCoIn5, and what is its momentum (k) and temperature dependence?
• RQ3 To what extent do ARPES-measured band dispersions and hybridization gaps agree with bulk-sensitive dHvA measurements of effective mass and Fermi surface topology?
• RQ4 Can a simplified multiband PAM description quantitatively reproduce the observed low-energy electronic structure and mass enhancement in CeCoIn5?
• RQ5 What is the role of band-dependent hybridization in determining the interplay between superconductivity, magnetism, and quantum criticality in 115-type heavy fermion materials?

Key findings

• The most two-dimensional band (band 133) in CeCoIn5 exhibits the weakest f-electron hybridization, with a hybridization matrix element Vcf ≈ 12.5 meV, contrary to expectations of enhanced 2D hybridization.
• Band 135 shows a significantly larger mass enhancement (m*/m_b ≈ 16.5 at ΓM) than band 133, indicating stronger hybridization despite its 3D character, though its hybridization gap is below the detection limit of ARPES.
• The ARPES-derived Fermi surface areas for bands 133 and 135 agree quantitatively with de-Haas-van-Alphen (dHvA) measurements, confirming the bulk nature of the ARPES data.
• Effective mass enhancements derived from ARPES simulations (e.g., m*/m_b ≈ 14.7 for band 133 at MX) are in semi-quantitative agreement with dHvA results, validating the model-based extraction of m*.
• The hybridization gap opening at low temperatures is confirmed via ARPES, with band 133 showing a clear gap structure, while band 135 may have a sub-22 meV gap undetected due to resolution limits.
• The results suggest that weaker hybridization on the 2D band may enhance two-dimensional magnetic fluctuations, potentially favoring unconventional superconductivity, and highlight the need for k_z-dependent hybridization models.