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arxiv: 1907.10084 · v1 · pith:M5OBSSOYnew · submitted 2019-07-23 · ❄️ cond-mat.str-el

CeAu₂Bi: a new nonsymmorphic antiferromagnetic compound

M. M. Piva , W. Zhu , F. Ronning , J. D. Thompson , P. G. Pagliuso , P. F. S. Rosa This is my paper

Pith reviewed 2026-05-24 16:53 UTC · model grok-4.3

classification ❄️ cond-mat.str-el
keywords CeAu2Biheavy fermionantiferromagnetismnonsymmorphic structuresymmetry-protected crossingstriangular latticeband structure
0
0 comments X

The pith

CeAu₂Bi hosts symmetry-protected crossings at kz=π in its paramagnetic state according to band calculations.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper presents CeAu₂Bi as a new heavy-fermion material that crystallizes in a nonsymmorphic hexagonal structure and orders antiferromagnetically at 3.1 K. Thermodynamic data establish a large Sommerfeld coefficient and a specific crystal-field ground state, while pressure increases the ordering temperature. The central result is that electronic band calculations combined with symmetry analysis identify protected crossings at kz=π when the system remains paramagnetic.

Core claim

Electronic band structure calculations and symmetry analysis in k-space reveal that CeAu₂Bi hosts symmetry-protected crossings at kz=π in the paramagnetic state.

What carries the argument

Symmetry analysis in k-space that identifies protected crossings at kz=π arising from the nonsymmorphic hexagonal structure.

Load-bearing premise

The DFT band-structure calculation plus symmetry analysis correctly identifies protected crossings without experimental band mapping or consideration of magnetic order effects on the bands.

What would settle it

Angle-resolved photoemission spectroscopy above 3.1 K that either detects or fails to detect the symmetry-protected crossings at kz=π.

Figures

Figures reproduced from arXiv: 1907.10084 by F. Ronning, J. D. Thompson, M. M. Piva, P. F. S. Rosa, P. G. Pagliuso, W. Zhu.

Figure 1
Figure 1. Figure 1: FIG. 1: (a) Hexagonal structure of CeAu [PITH_FULL_IMAGE:figures/full_fig_p001_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: (a) shows the magnetic susceptibility (χ) as a function of temperature at µ0H = 0.1 T applied paral￾lel and perpendicular to the c-axis of CeAu2Bi. These measurements find that the c-axis is the hard axis and that Ce3+ moments order antiferromagnetically at TN = 3.1 K, as we can clearly see in the top inset of [PITH_FULL_IMAGE:figures/full_fig_p002_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3: (a) Specific heat measurements for CeAu [PITH_FULL_IMAGE:figures/full_fig_p002_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4: (a) [PITH_FULL_IMAGE:figures/full_fig_p003_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5: (a) Electronic band structure of CeAu [PITH_FULL_IMAGE:figures/full_fig_p004_5.png] view at source ↗
Figure 1
Figure 1. Figure 1: presents the detailed EDX spectra for CeAu2Bi. 0 2 4 6 8 10 12 14 0 3 6 9 12 15 I (10 3counts) Energy (keV) CeM CeL AuM AuL BiM BiL 0.0 0.3 0.6 0.9 1.2 1.5 0.0 0.5 1.0 C N O FIG. 1: EDX spectra for CeAu2Bi [PITH_FULL_IMAGE:figures/full_fig_p009_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: presents the electrical resistivity (ρ) for CeAu2Bi and LaAu2Bi at low temperatures (T < 10 K). Both samples present a downturn close to 2 K, which may be associated to an Au2Bi impurity phase [4]. CeAu2Bi also displays a kink at TN = 3.1 K, due to the loss of spin-scattering. 2 4 6 8 10 5 10 15 20 25 30 35 40 ( cm) T (K) CeAu2Bi LaAu2Bi FIG. 2: Electrical resistivity for CeAu2Bi and LaAu2Bi at low tempera… view at source ↗
read the original abstract

Here we report the structural and electronic properties of CeAu$_{2}$Bi, a new heavy-fermion compound crystallizing in a nonsymmorphic hexagonal structure ($P63/mmc$). The Ce$^{3+}$ ions form a triangular lattice which orders antiferromagnetically below $T_{N} = 3.1$~K with a magnetic hard axis along the c-axis. Under applied pressure, $T_{N}$ increases linearly at a rate of $0.07$~K/kbar, indicating that the Ce $f$-electrons are fairly localized. In fact, heat capacity measurements provide an estimate of 150(10) mJ/mol.K$^{2}$ for the Sommerfeld coefficient. The crystal-field scheme obtained from our thermodynamic data points to a ground state with dominantly $|j_{z}=\pm1/2\rangle$ character, which commonly occurs in systems with a hard c-axis. Finally, electronic band structure calculations and symmetry analysis in $k$-space reveal that CeAu$_{2}$Bi hosts symmetry-protected crossings at $k_{z} = \pi$ in the paramagnetic state

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 0 minor

Summary. The manuscript reports the synthesis and basic characterization of CeAu₂Bi, a new nonsymmorphic hexagonal (P6₃/mmc) antiferromagnet in which Ce³⁺ ions form a triangular lattice. It gives TN = 3.1 K with c-axis hard axis, a linear pressure coefficient dTN/dp = 0.07 K/kbar, a Sommerfeld coefficient γ = 150(10) mJ mol⁻¹ K⁻², a crystal-field ground state of dominant |jz = ±1/2⟩ character, and DFT plus symmetry analysis claiming symmetry-protected band crossings at kz = π in the paramagnetic state.

Significance. If the claimed symmetry-protected crossings survive a proper treatment of the localized f-electrons, the material would furnish a concrete example of nonsymmorphic topology in a heavy-fermion antiferromagnet. The thermodynamic data (pressure dependence and large γ) are internally consistent with fairly localized f-electrons, which is a useful baseline for future work.

major comments (1)
  1. [Abstract, final sentence] Abstract, final sentence: the assertion that 'electronic band structure calculations and symmetry analysis in k-space reveal that CeAu₂Bi hosts symmetry-protected crossings at kz = π' is load-bearing for the paper’s most distinctive claim. The same abstract reports γ = 150(10) mJ mol⁻¹ K⁻², indicating strong correlations and localized Ce f-electrons. No information is supplied on the DFT setup (open-core vs. itinerant f-treatment, Hubbard U, spin-orbit coupling details, or paramagnetic vs. antiferromagnetic supercell), nor is any comparison made to experimental probes of the bands. Standard DFT is known to misplace f-derived states near EF in such systems; without this justification the crossings cannot be taken as established for the low-energy physics.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their careful reading of the manuscript and for highlighting the need for greater clarity on the electronic structure calculations. We address this point below and will revise the manuscript to supply the requested methodological details while preserving the symmetry-based claim.

read point-by-point responses

  1. Referee: [Abstract, final sentence] Abstract, final sentence: the assertion that 'electronic band structure calculations and symmetry analysis in k-space reveal that CeAu₂Bi hosts symmetry-protected crossings at kz = π' is load-bearing for the paper’s most distinctive claim. The same abstract reports γ = 150(10) mJ mol⁻¹ K⁻², indicating strong correlations and localized Ce f-electrons. No information is supplied on the DFT setup (open-core vs. itinerant f-treatment, Hubbard U, spin-orbit coupling details, or paramagnetic vs. antiferromagnetic supercell), nor is any comparison made to experimental probes of the bands. Standard DFT is known to misplace f-derived states near EF in such systems; without this justification the crossings cannot be taken as established for the low-energy physics.

    Authors: We agree that the original manuscript omitted essential details on the DFT methodology. In the revised version we will insert a methods paragraph stating that an open-core treatment was used for the Ce 4f electrons (consistent with the large experimental γ), with no additional Hubbard U, full spin-orbit coupling included self-consistently, and all calculations performed in the paramagnetic state on the primitive cell. The symmetry analysis demonstrates that the crossings at kz = π are enforced by the nonsymmorphic glide and screw operations of P6₃/mmc and arise primarily from Au/Bi p-derived bands; the f-states lie well below EF and do not participate. We acknowledge that no ARPES or other direct band-structure data are available for comparison and will explicitly note this as a limitation. These additions should satisfy the referee’s request for justification without altering the central claim. revision: partial

Circularity Check

0 steps flagged

Symmetry-protected crossings identified via standard DFT and group theory on reported space group; no reduction to inputs by construction

full rationale

The paper's derivation chain for the central claim consists of reporting the space group P63/mmc from structural data, performing standard electronic band structure calculations, and applying symmetry analysis in k-space to identify protected crossings at kz=π. This is an external application of group theory and DFT to the measured structure, with no equations or steps that define the crossings in terms of themselves or rename fitted parameters as predictions. Thermodynamic data (TN, Sommerfeld coefficient) are independent measurements and not used to force the band result. No self-citations are invoked as load-bearing uniqueness theorems. The analysis is self-contained against external benchmarks of standard solid-state methods and receives a low circularity score.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The central claims rest on standard crystallographic identification of space group P63/mmc, conventional interpretation of thermodynamic data for crystal-field levels, and DFT plus symmetry analysis for band crossings; no free parameters, ad-hoc axioms, or new entities are introduced beyond the new material itself.

axioms (2)
  • domain assumption Standard space-group assignment from diffraction data correctly identifies P63/mmc
    Invoked when stating the nonsymmorphic hexagonal structure
  • domain assumption DFT band-structure calculation plus point-group analysis suffices to identify symmetry-protected crossings
    Invoked in the final sentence of the abstract

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