RAlSi: Rare-Earth Aluminosilicides
- RAlSi is a rare-earth aluminosilicide family characterized by noncentrosymmetric tetragonal LaPtSi-type structures and rare-earth tunable magnetism.
- These compounds exhibit Weyl-semimetal behavior with measurable ARPES signals corrected through multi-zone reconstruction and distinct quantum oscillation signatures.
- Magnetic order and transport properties in RAlSi evolve with rare-earth substitution, offering insights into CEF effects, Berry phases, and topological conduction.
Searching arXiv for recent and foundational papers on RAlSi and closely related usages. RAlSi commonly denotes the rare-earth aluminosilicide family AlSi, where is a rare-earth element such as Ce, Nd, Sm, or Pr. In the recent arXiv literature, these compounds are treated primarily as noncentrosymmetric or closely related rare-earth intermetallics within the broader Al platform, notable for magnetic order, Weyl-semimetal candidacy, and strong coupling between itinerant topology and localized $4f$ degrees of freedom (Morita et al., 2024, Cao et al., 2021, Yang et al., 14 Aug 2025). The same letter sequence can appear in broader Al–Si materials contexts, but the exact designation “RAlSi” is used most concretely for this rare-earth intermetallic family; related Al–Si eutectics, Si–Al composites, and silica–alumina systems are relevant only by compositional analogy rather than exact nomenclature (Zhou et al., 2023, Takekoshi et al., 2022, Wang et al., 2016).
1. Chemical identity and crystallographic setting
In its principal usage, RAlSi denotes compounds of formula with a rare-earth element on the site. CeAlSi and NdAlSi are described as belonging to the Al family ( rare earth, 0 Si or Ge), which has attracted attention as a platform for magnetic Weyl semimetals (Morita et al., 2024). SmAlSi and CeAlSi were likewise investigated as members of the noncentrosymmetric rare-earth aluminum silicide family and placed within the broader 1 or 2Al3 context (Cao et al., 2021).
For CeAlSi and NdAlSi, the crystal structure is reported as noncentrosymmetric, with space group 4, and also nonsymmorphic (Morita et al., 2024). The same space group 5 (No. 109) is reported for SmAlSi and CeAlSi, where the structure is described as tetragonal LaPtSi-type and explicitly noncentrosymmetric (Cao et al., 2021). In the soft-x-ray ARPES study of CeAlSi and NdAlSi, the rare-earth ions form two interpenetrating body-centered tetragonal sublattices offset by 6, a structural feature central to the observed zone-selection effect (Morita et al., 2024).
Concrete lattice parameters are reported for several members. For the ARPES study, the experimental lattice constants were 7 and 8 for CeAlSi and NdAlSi (Morita et al., 2024). For single-crystal SmAlSi and CeAlSi, Rietveld refinement yielded 9, 0 for SmAlSi and 1, 2 for CeAlSi, with 3 in both cases (Cao et al., 2021). CeAlSi and NdAlSi are explicitly stated to crystallize in 4 with the rare-earth ion at Wyckoff 5, site symmetry 6, i.e. point symmetry 7, in the crystalline-electric-field analysis (Yang et al., 14 Aug 2025). PrAlSi is treated separately there as centrosymmetric, space group 8 (No. 141), with Pr9 in point symmetry 0 (Yang et al., 14 Aug 2025).
2. Electronic structure and Weyl-semimetal context
The modern interest in RAlSi is driven by its role as a magnetic Weyl-semimetal platform. Because inversion symmetry is broken, the paramagnetic phase can host Weyl nodes; in CeAlSi and NdAlSi, first-principles calculations predict three types of 32 Weyl nodes near the Fermi level, specifically 8 W1, 16 W2, and 8 W3 (Morita et al., 2024). These compounds are therefore treated not simply as magnetic intermetallics, but as systems in which rare-earth magnetism and Weyl electronic structure coexist on the same crystallographic backbone.
The soft-x-ray ARPES measurements establish that the observed states are bulk three-dimensional bands. In CeAlSi, a 1-2 constant-energy map at 3 shows elliptical contours around 4 points and clear 5 dispersion, with a band-folding periodicity 6, matching 7 (Morita et al., 2024). NdAlSi shows the same essential behavior at 8, again with 9 (Morita et al., 2024). This establishes that the ARPES spectra probe bulk 3D electronic structure rather than a surface-limited band manifold.
A central result is the “zone-selection effect,” defined operationally as the strong sensitivity of photoelectron intensity distributions to the covered Brillouin zone in the nonsymmorphic structure (Morita et al., 2024). The paper does not provide an explicit analytical selection rule, but attributes the effect conceptually to interference among photoelectron amplitudes from sublattice-related orbitals displaced by fractional lattice translations, analogous to graphite (Morita et al., 2024). As a consequence, the same intrinsic band can appear bright in one Brillouin zone and weak or nearly absent in another equivalent zone.
This effect has direct implications for Weyl-cone detection. By combining data from multiple equivalent zones and summing intensity maps with a weighting ratio of $4f$0, the reconstructed spectra agree well with DFT after an overall 80 meV energy shift (Morita et al., 2024). That reconstruction permits experimental tracing of W1 on $4f$1, W3 on $4f$2, and W2 on a plane at $4f$3 (Morita et al., 2024). A plausible implication is that single-zone ARPES can systematically under-represent topological features in nonsymmorphic RAlSi compounds.
3. Magnetic order and transport phenomenology
Magnetism in RAlSi depends strongly on the rare-earth ion. CeAlSi is reported as ferromagnetic below $4f$4 K in the ARPES study and below $4f$5 K in the transport study (Morita et al., 2024, Cao et al., 2021). NdAlSi is antiferromagnetic below $4f$6 K in the ARPES study, while the crystalline-electric-field work resolves a more specific sequence: incommensurate ferrimagnetic order below $4f$7 K and a commensurate ferrimagnetic phase below about $4f$8–$4f$9 K (Morita et al., 2024, Yang et al., 14 Aug 2025). SmAlSi is reported as antiferromagnetic with 0 K (Cao et al., 2021). PrAlSi is described as ferromagnetic with multiple transitions at 1 K, 2 K, and 3 K (Yang et al., 14 Aug 2025).
Transport measurements place SmAlSi and CeAlSi in the semimetallic regime with nonsaturating magnetoresistance. At 4 K and 5 T, SmAlSi exhibits magnetoresistance of about 6, whereas CeAlSi exhibits about 7 under the same conditions (Cao et al., 2021). In SmAlSi, the Hall resistivity is nonlinear and changes slope sign between low and high field at 2 K, indicating coexisting electrons and holes and motivating a two-band analysis (Cao et al., 2021). For CeAlSi, Hall resistivity is nearly linear below 100 K, with a small anomalous Hall effect in the ferromagnetic state, and fitting in the 8–9 T range gives 0, implying dominant electron-type carriers (Cao et al., 2021).
The two-band transport equations used for SmAlSi are reported explicitly as
1
and
2
with the magnetoresistance defined as
3
At 1.8 K, the fitted carrier densities for SmAlSi are 4 and 5 (Cao et al., 2021).
An important family-level feature is the sensitivity of carrier density to magnetic ordering. In SmAlSi, both 6 and 7 show a kink around 8, while in CeAlSi the electron carrier density shows a kink around 9 (Cao et al., 2021). This suggests direct coupling between rare-earth magnetic order and the low-energy electronic structure.
4. Quantum oscillations and topological transport signatures
Among the RAlSi compounds examined by transport, SmAlSi provides the clearest quantum-oscillation evidence for nontrivial topology. With 0, clear Shubnikov–de Haas oscillations are observed in 1 up to 14 T over the temperature range 2–3 K (Cao et al., 2021). The FFT spectra show two principal frequencies, 4 and 5, together with a harmonic near 6 (Cao et al., 2021).
Using the Onsager relation,
7
the extremal cross-sectional areas are reported as 8 and 9, with corresponding Fermi wavevectors 0 and 1 (Cao et al., 2021). These small frequencies and cross-sections indicate small Fermi pockets.
The oscillations are analyzed with the Lifshitz–Kosevich expression
2
with
3
4
and
5
The effective masses are 6 and 7 (Cao et al., 2021). Table II further gives 8, 9, 0, 1, 2, 3, 4, 5, 6, and 7 (Cao et al., 2021).
Berry phases extracted by LK phase fitting are 8 and 9, and Landau-fan analysis yields intercepts near 00 and 01 for the 02 and 03 pockets (Cao et al., 2021). The paper interprets these results as consistent with nontrivial Berry phase. For CeAlSi, by contrast, low-field MR shows no quantum oscillations in that study, so no comparable SdH analysis is reported there (Cao et al., 2021).
5. Crystalline electric fields and single-ion anisotropy
The crystalline-electric-field structure of RAlSi provides a quantitative account of how different rare-earth ions select different magnetic ground states. Polycrystalline CeAlSi, PrAlSi, and NdAlSi were studied by inelastic neutron scattering, heat capacity, and magnetic susceptibility, with LaAlSi serving as a nonmagnetic reference for phonon background and lattice heat capacity (Yang et al., 14 Aug 2025).
For CeAlSi and NdAlSi, the CEF Hamiltonian used at the 04 rare-earth site is
05
whereas PrAlSi in point symmetry 06 is modeled by
07
The neutron cross section is written as
08
and magnetic entropy is obtained from
09
These formulas structure the family-wide CEF analysis (Yang et al., 14 Aug 2025).
CeAlSi shows well-resolved CEF excitations at 19.2 and 24.9 meV, with a Kramers-doublet ground state dominated by 10 at 94.5% weight (Yang et al., 14 Aug 2025). The fitted CEF parameters are 11, 12, 13, 14, and 15, with 16 because Ce17 has 18 (Yang et al., 14 Aug 2025). The first excited doublet lies at 19 meV and the second at 20 meV, implying a well-isolated low-energy doublet (Yang et al., 14 Aug 2025).
PrAlSi shows a single clear INS excitation at 5.4 meV, but the fitted level scheme contains multiple nearby levels at 21, 22, 23, 24, 25, and 26 meV (Yang et al., 14 Aug 2025). Its ground-state doublet is almost pure 27, with 99.2% weight, making it the most anisotropic of the three magnetic members analyzed (Yang et al., 14 Aug 2025).
NdAlSi has much lower-lying CEF excitations, observed at 2.5 and 4.2 meV, with fitted levels at 28, 29, 30, and 31 meV (Yang et al., 14 Aug 2025). Its ground-state doublet is only 76.2% 32, with substantial admixture of other 33 states (Yang et al., 14 Aug 2025). The paper interprets this as weaker single-ion anisotropy than in CeAlSi or PrAlSi.
A key comparative conclusion follows. CeAlSi and PrAlSi are described as having robust CEF levels in the magnetic state, whereas NdAlSi exhibits broadening, shifting, and eventually splitting of CEF excitations below 15 K, especially in the commensurate ferrimagnetic phase (Yang et al., 14 Aug 2025). McPhase estimates molecular fields of about 1.5 T in-plane and 3.7 T out-of-plane for NdAlSi, and the authors connect the resulting CEF renormalization to competing magnetic couplings and possible Dzyaloshinskii–Moriya interactions (Yang et al., 14 Aug 2025). This suggests that RAlSi spans both rigid-doublet ferromagnets and exchange-competing ferrimagnets within the same broad chemical family.
6. Related usages, boundary cases, and nomenclature
The exact string “RAlSi” does not uniformly identify every Al–Si material discussed in adjacent literatures. One recurrent ambiguity concerns whether the term is being used as a chemical family name, a shorthand for rapidly solidified Al–Si, or a loose label for silicon–aluminum materials more generally. The available papers distinguish these usages sharply.
In materials processing, laser rapid solidification of a hyper-eutectic Al–20 wt% Si alloy produces an ultrafine, bicontinuous, highly connected, isotropically branched Si network with average equivalent radius 34, spacing 35, and specific surface density 36 (Zhou et al., 2023). That paper explicitly frames the subject as rapidly solidified Al–Si eutectics, not as the rare-earth intermetallic RAlSi family. Its “bottom line for rapidly solidified Al–Si / ‘RAlSi’” indicates broad relevance by abbreviation or context rather than exact stoichiometric naming (Zhou et al., 2023). This suggests a secondary usage in which “RAlSi” functions informally as a contraction for rapidly solidified Al–Si, but not as a crystallographic family label.
In cryogenic instrumentation, the silicon–aluminum composite Japan Fine Ceramics SA001 is a 75 vol% Si / 25 vol% Al material with 37, residual resistivity 38 at 1.5 K, and measured thermal contraction 39 from 293 K to 77 K (Takekoshi et al., 2022). That paper explicitly states that it does not identify SA001 as “RAlSi” and treats the match only as a closely related Si–Al composite material family match by composition, cryogenic function, and application (Takekoshi et al., 2022).
Likewise, amorphous silica–alumina nanoparticles containing homogeneously dispersed pentacoordinated Al(V) species on Si–O–Al surface motifs are highly relevant to Al–Si connectivity, but the system is chemically and structurally distinct from intermetallic 40AlSi (Wang et al., 2016). The ASA work concerns Al coordination in an amorphous oxide network, not rare-earth aluminosilicide intermetallics.
A practical nomenclature distinction therefore emerges. In the exact and best-established sense, RAlSi refers to the rare-earth aluminosilicides 41, especially CeAlSi, NdAlSi, SmAlSi, and PrAlSi (Morita et al., 2024, Cao et al., 2021, Yang et al., 14 Aug 2025). Other Al–Si materials may be compositionally related or occasionally associated with the same letter sequence, but they are separate materials classes.
7. Scientific significance and current picture
The current arXiv literature presents RAlSi as a rare-earth-tunable platform where topology, nonsymmorphic photoemission selection effects, magnetic order, and crystalline-electric-field anisotropy can all be studied within closely related compounds. CeAlSi and NdAlSi show that soft-x-ray ARPES can resolve bulk 3D bands and Weyl-cone dispersions, but only if zone-selection effects are handled through deliberate multi-zone reconstruction (Morita et al., 2024). SmAlSi shows that at least some members possess small Fermi pockets and transport signatures consistent with a nontrivial Berry phase (Cao et al., 2021). CeAlSi, PrAlSi, and NdAlSi further show that the local 42 physics is not incidental: the CEF level scheme and ground-state wavefunction purity govern whether the material behaves as a robust anisotropic ferromagnet or as a more weakly anisotropic system with competing ferrimagnetic orders and low-temperature CEF renormalization (Yang et al., 14 Aug 2025).
This body of work supports a compact comparative picture. CeAlSi combines noncentrosymmetric Weyl-semimetal band topology, ferromagnetism, a nearly pure 43 CEF doublet, and ARPES-visible Weyl cones after multi-zone reconstruction (Morita et al., 2024, Yang et al., 14 Aug 2025). PrAlSi exhibits an even purer anisotropic ground state, but with a denser manifold of low-lying excited levels that plausibly enrichs its magnetic phase behavior (Yang et al., 14 Aug 2025). NdAlSi retains the same broader family identity yet differs qualitatively through weaker single-ion anisotropy, incommensurate-to-commensurate ferrimagnetism, and exchange-driven CEF reshaping (Morita et al., 2024, Yang et al., 14 Aug 2025). SmAlSi broadens the family further by providing strong quantum-oscillation evidence for small pockets with 44-like Berry phases and by showing that magnetic order remains robust under pressure up to 46.2 GPa (Cao et al., 2021).
Taken together, the literature establishes RAlSi as a rare-earth intermetallic family in which fixed structural motifs coexist with sharply variable magnetic ground states and experimentally accessible topological electronic structure. A plausible implication is that rare-earth substitution in 45 offers an unusually direct route for tuning the balance among nonsymmorphic band interference, Weyl-node phenomenology, 46-derived anisotropy, and exchange-driven magnetic complexity.