Altermagnetic Proximity Effect

• Altermagnetic Proximity Effect (AMPE) is characterized by the transfer of momentum-dependent spin splitting and Berry-curvature from an altermagnet to an adjacent material without inducing net magnetization.
• It is realized through interfacial hybridization and inverse proximity mechanisms, leading to observable phenomena such as anomalous Hall effects and topological superconductivity.
• AMPE distinguishes itself from conventional proximity effects by exporting altermagnetic symmetry and enabling novel functionalities in transport, thermoelectricity, and superconducting devices.

Altermagnetic proximity effect (AMPE) denotes a class of interfacial phenomena in which the momentum-dependent spin splitting, Berry-curvature structure, or symmetry breaking of an altermagnet is transferred to, or imposed on, an adjacent material without requiring a net ferromagnetic moment. In the recent literature, the term is used both for direct “altermagnetization” of nonmagnetic layers and for inverse-proximity phenomena in superconductors, semimetals, semiconductors, and tunnel junctions. Its defining feature is that the proximitized region acquires signatures of altermagnetism—typically a symmetry-constrained, sign-alternating spin texture in momentum space, and in some cases Hall, thermoelectric, diode, or topological responses—while remaining distinct from both uniform ferromagnetic proximity and conventional antiferromagnetic proximity (Zhu et al., 8 Sep 2025).

1. Conceptual scope and distinguishing features

AMPE is distinguished from ferromagnetic proximity by the absence of a uniform Zeeman-like spin splitting and from conventional antiferromagnetic proximity by the presence of nonrelativistic, symmetry-enforced spin splitting in the parent altermagnet. In the formulation introduced for van der Waals heterostructures based on V$_2$Se$_2$O, a nonmagnetic layer becomes a “proximitized altermagnet” when the alternating spin splitting pattern in momentum space is imprinted onto its bands; this process is explicitly termed “altermagnetization” (Zhu et al., 8 Sep 2025). In the PtTe$_2$/CrSb Dirac-semimetal/altermagnet heterostructure, AMPE is defined more specifically as the imprinting of CrSb’s $k$-space spin splitting and Berry curvature onto interfacial PtTe$_2$ states through strong Cr–Te–Pt hybridization, producing anomalous Hall readout and an induced interfacial moment locked to the Néel vector (Li et al., 8 Jul 2026).

A recurring theme is that AMPE is not equivalent to merely inducing a local interface magnetization. In PtTe$_2$/CrSb, the proximity response is described as a genuine symmetry-driven, Berry-curvature-based phenomenon rather than a trivial magnetic overlayer effect (Li et al., 8 Jul 2026). In superconducting contexts, the same term covers inverse proximity in which a conventional $s$-wave superconductor acquires a momentum-dependent effective exchange field or self-energy inherited from an altermagnet, even when the angle-averaged density of states remains spin-degenerate (Chourasia et al., 2024).

This broad usage suggests a useful taxonomy. One branch of AMPE concerns direct band-structure transfer into nonmagnetic conductors or semimetals; another concerns inverse proximity into superconductors; a third concerns transport-only manifestations in which altermagnetic momentum-space structure is converted into spin-polarized injection, thermoelectric asymmetry, or nonreciprocal current. The common element across these branches is the export of altermagnetic symmetry into an adjacent subsystem rather than the export of net magnetization.

2. Symmetry principles and microscopic mechanisms

The microscopic hallmark of altermagnetism is momentum-dependent spin splitting with zero net magnetization. In model descriptions, this often appears through a $d$-wave-like form factor such as $J_A(\mathbf{k}) \propto \cos k_x - \cos k_y$, or through continuum expressions like $t_1(k_y^2-k_x^2)+2t_2k_xk_y$, which reverse sign under appropriate crystal rotations while preserving collinearity (Zhu et al., 8 Sep 2025). In quasiclassical superconducting theory, the induced altermagnetic field can be written as $_2$0, emphasizing that the effective exchange depends on momentum direction rather than acting uniformly in spin space (Chourasia et al., 2024).

Two mechanisms recur in the AMPE literature. The first is interfacial hybridization. In PtTe$_2$1/CrSb, density-functional calculations show that hybridized Cr–Pt–Te states open orbital gaps near $_2$2, enhance $_2$3, and reduce the magnetic space group to 156.51, thereby breaking the $_2$4 symmetry that forbids anomalous Hall conductivity for perpendicular bulk CrSb. The result is an allowed Hall vector parallel to the Néel vector, $_2$5, in the heterostructure (Li et al., 8 Jul 2026).

The second is inverse proximity through a self-energy or effective exchange field. In AM/S bilayers treated quasiclassically, the superconducting layer experiences a momentum-textured internal field and consequently modified gap, density of states, heat capacity, and anisotropic susceptibility (Chourasia et al., 2024). In a tunneling-based AM/SC formalism, integrating out a bulk $_2$6-wave superconductor yields an AM self-energy $_2$7, which injects pairing correlations into the altermagnet while preserving the altermagnetic spin texture in the effective quasiparticle spectrum (Alam et al., 30 Oct 2025).

In diffusive systems, the coupling appears at Ginzburg–Landau level through a term $_2$8. This implies an induced magnetization proportional to $_2$9, linking the altermagnetic tensor $_2$0 to gradients of the superconducting order parameter. The same term underlies both a nonlinear magnetoelectric effect and proximity-induced magnetization in S/AM hybrids (Heras et al., 4 Dec 2025).

3. Normal-state heterostructures and direct altermagnetization

The most explicit realization of normal-state AMPE as band transfer is the V$_2$1Se$_2$2O-based family of van der Waals heterostructures. In monolayer PbO on V$_2$3Se$_2$4O, previously spin-degenerate PbO bands become spin-split in a momentum-alternating pattern: spin degeneracy is preserved along $_2$5–M, while opposite spin polarizations appear along M–X–$_2$6 and $_2$7–Y–M. The induced splitting decreases monotonically with increasing interlayer distance, and the charge redistribution is localized near the interface, consistent with a short-range proximity effect (Zhu et al., 8 Sep 2025). When the V$_2$8Se$_2$9O layer is artificially converted into a conventional antiferromagnet, the induced momentum-alternating splitting disappears, providing a direct control case for the distinction between AMPE and conventional AFM proximity (Zhu et al., 8 Sep 2025).

A second route is symmetry-engineered Hall functionality. In PtTe$k$0(5 nm)/CrSb(8 nm), AMPE yields a large spontaneous anomalous Hall effect even though isolated perpendicular CrSb is symmetry-forbidden to show AHE. At 10 K the anomalous Hall conductivity is reported as $k$1, and the interface develops an induced Pt moment of about $k$2–$k$3Pt, exchange-coupled to the CrSb Néel vector. Control samples—CrSb alone and PtTe$k$4/Cr$k$5O$k$6—exclude trivial ferromagnetic proximity as the origin (Li et al., 8 Jul 2026).

A third manifestation is valley-selective altermagnetization. In PbS/V$k$7Se$k$8O, the proximitized PbS layer inherits symmetry-paired spin-valley locking. Under $k$9 uniaxial tensile strain along $_2$0, the valence-band edge splitting between X and Y valleys reaches $_2$1, exceeding $_2$2 at room temperature (Zhu et al., 8 Sep 2025).

The diversity of these realizations is summarized below.

Heterostructure	AMPE manifestation	Representative result
PtTe$_2$3/CrSb	Berry-curvature transfer, AHE, SOT handle	$_2$4 at 10 K; induced Pt moment $_2$5–$_2$6Pt
V$_2$7Se$_2$8O/PbO	Direct altermagnetization of a nonmagnet	Momentum-alternating spin splitting in PbO bands
V$_2$9Se$_2$0O/PbS	Valley-selective AMPE	$_2$1 at $_2$2 strain
V$_2$3Se$_2$4O/NbSe$_2$5	AMPE-enabled topological superconductivity	Helical and chiral Majorana regimes

These cases show that AMPE can convert altermagnetic band geometry into electrical readout, valley selectivity, or topological band restructuring without invoking a macroscopic ferromagnetic phase.

4. Superconducting realizations

In superconducting heterostructures, AMPE appears in two complementary forms: inverse proximity into the superconductor and proximity-induced superconductivity inside an altermagnet. For an insulating altermagnet/superconductor bilayer, quasiclassical theory predicts that the superconductor experiences an effective field $_2$6, leading to suppressed $_2$7, broadened density of states, and eventually gapless superconductivity for $_2$8. Unlike FM/S bilayers, the superconducting–normal transition remains second order over the considered parameter range, and the magnetic response becomes strongly anisotropic between in-plane and out-of-plane field orientations (Chourasia et al., 2024).

The inverse-proximity problem is not universal across all superconducting hybrids. A microscopic thin-film analysis concludes that S/altermagnetic-insulator heterostructures are well described by a homogeneous-in-space, momentum-dependent effective exchange field, whereas clean ballistic S/altermagnetic-metal heterostructures are not. In the metallic case, the induced spin splitting in the superconducting film is described as “chaotic” in its branch and spatial dependence, with higher harmonics beyond pure $_2$9-wave form, and in general cannot be cleanly detected through a simple spin splitting of the superconducting density of states (Bobkov et al., 20 Oct 2025). This substantially qualifies the use of simple effective-field models.

In transport-oriented AM/SC models, the altermagnet modifies Andreev processes rather than only static spectra. In a $s$0-wave AM coupled to an $s$1-wave superconductor, superconducting proximity generates an even-frequency singlet even-parity component together with an odd-frequency triplet even-parity component $s$2. When Rashba SOC is added, even-frequency odd-parity triplet components $s$3 and $s$4 appear, and the proximitized AM-RSOC layer supports weak and strong topological superconducting phases characterized by winding number and Chern number, with edge-localized modes (Alam et al., 30 Oct 2025).

A closely related but distinct route is provided by NbSe$s$5/V$s$6Se$s$7O. There the effective BdG Hamiltonian contains an altermagnetic exchange term $s$8 together with Rashba SOC and $s$9-wave pairing. In the isotropic case the proximitized NbSe$d$0 realizes helical Majorana modes; with anisotropic hopping $d$1, the system enters a chiral regime with a single chiral Majorana mode per edge (Zhu et al., 8 Sep 2025).

AMPE in superconductors also enables nonreciprocal response. In Mn$d$2Pt-superconductor heterostructures, symmetry analysis and model calculations show that magnetization-free altermagnetic spin textures in the T2 phase remain spin-split even with SOC and, through proximity coupling, generate a superconducting diode effect. The angular dependence of the diode efficiency distinguishes T1 and T2 magnetic orders; reported maxima are $d$3 for T2 and $d$4 for T1 (Schrade et al., 6 Jan 2026).

5. Transport, thermoelectricity, and switching functionalities

One of the earliest transport manifestations of AMPE is spin-selective conduction across AM junctions. In AM/normal-metal and AM/ferromagnet junctions, charge current is accompanied by spin current under bias, and the magnetoresistance of AM/FM junctions changes sign when the altermagnet is rotated by $d$5, a feature described as unique to the altermagnetic phase (Das et al., 2023). In an altermagnet/semiconductor Schottky contact, the spin-contrasting Fermi surface of the altermagnetic electrode yields spin-polarized thermionic injection into a nonmagnetic semiconductor through a spin-independent barrier. The spin-polarization efficiency reaches a universal upper bound of about $d$6, and for $d$7 at $d$8 K the ratio of maximal to minimal current over interface orientation can exceed $d$9 (Ang, 2023).

Thermoelectric AMPE in superconducting hybrids is particularly developed. In AM/S bilayers and AM-based Josephson junctions, the momentum-dependent spin splitting of the altermagnet makes the dissipative thermoelectric current spin split. In the strong AM regime the spin polarization of the thermoelectric current can approach $J_A(\mathbf{k}) \propto \cos k_x - \cos k_y$0, and in Rashba-assisted altermagnet-based Josephson junctions the thermoelectric diode efficiency reaches up to $J_A(\mathbf{k}) \propto \cos k_x - \cos k_y$1 (Debnath et al., 15 Sep 2025). A complementary AM/S/AM tunneling theory shows that inverse proximity induces a momentum-dependent spin splitting in the superconducting layer and that planar tunneling to another altermagnet converts this into a finite thermoelectric response without external or stray magnetic fields; the figure of merit shows a nonmonotonic dependence on the altermagnetic splitting strength (Sukhachov et al., 2024).

PtTe$J_A(\mathbf{k}) \propto \cos k_x - \cos k_y$2/CrSb further demonstrates the write–read logic of AMPE. The anomalous Hall signal provides binary readout of the perpendicular Néel vector, while spin–orbit torque from PtTe$J_A(\mathbf{k}) \propto \cos k_x - \cos k_y$3 switches the CrSb order. The reported switching figure of merit is $J_A(\mathbf{k}) \propto \cos k_x - \cos k_y$4, roughly an order of magnitude larger than the $J_A(\mathbf{k}) \propto \cos k_x - \cos k_y$5 typical of conventional ferromagnetic SOT systems; endurance was demonstrated over $J_A(\mathbf{k}) \propto \cos k_x - \cos k_y$6 alternating write pulses at $J_A(\mathbf{k}) \propto \cos k_x - \cos k_y$7 K with no obvious degradation (Li et al., 8 Jul 2026). A magnetic tunnel junction based on PtTe$J_A(\mathbf{k}) \propto \cos k_x - \cos k_y$8/CrSb/MgO/CoFeB also exhibits tunneling magnetoresistance of about $J_A(\mathbf{k}) \propto \cos k_x - \cos k_y$9 at 10 K, showing that AMPE can be used both in Hall and tunneling readout modes (Li et al., 8 Jul 2026).

6. Limitations, controversies, and materials outlook

AMPE is not a single universal effective-field phenomenon. The strongest caution in the literature concerns clean metallic superconducting hybrids: in ballistic S/altermagnetic-metal heterostructures, the induced spin splitting in the superconductor can be irregular in branch index and position, so a homogeneous exchange-field description becomes unreliable even though triplet correlations remain robust (Bobkov et al., 20 Oct 2025). Conversely, S/altermagnetic-insulator systems are much closer to the standard effective-model limit (Bobkov et al., 20 Oct 2025). This distinction resolves a common misconception that any altermagnet adjacent to a superconductor simply induces a smooth $t_1(k_y^2-k_x^2)+2t_2k_xk_y$0-wave exchange field in the superconducting layer.

Temperature is another central limitation. In PtTe$t_1(k_y^2-k_x^2)+2t_2k_xk_y$1/CrSb, the CrSb Néel temperature for the $t_1(k_y^2-k_x^2)+2t_2k_xk_y$2 nm films is about $t_1(k_y^2-k_x^2)+2t_2k_xk_y$3 K, but the interfacial order relevant for AMPE-based anomalous Hall readout and switching disappears near $t_1(k_y^2-k_x^2)+2t_2k_xk_y$4 K. The gap between bulk magnetic ordering and interfacial AMPE functionality identifies interface engineering, rather than only bulk materials optimization, as the immediate bottleneck for room-temperature operation (Li et al., 8 Jul 2026).

The literature also leaves open the extent to which AMPE is controlled by disorder, strain, interface termination, and crystal orientation. Strain is already known to be decisive in PbS/V$t_1(k_y^2-k_x^2)+2t_2k_xk_y$5Se$t_1(k_y^2-k_x^2)+2t_2k_xk_y$6O, where it converts spin-valley locking into a large valley splitting (Zhu et al., 8 Sep 2025). Crystal orientation controls spin-current polarity and magnetoresistance sign in AM junctions (Das et al., 2023). In diffusive S/AM theory, the angle $t_1(k_y^2-k_x^2)+2t_2k_xk_y$7 between crystallographic and transport axes determines whether proximity-induced magnetization remains uniform or develops four-lobe textures, and whether $t_1(k_y^2-k_x^2)+2t_2k_xk_y$8-$t_1(k_y^2-k_x^2)+2t_2k_xk_y$9 transitions survive in S/AM/S junctions (Heras et al., 4 Dec 2025).

A plausible materials outlook follows from the broader altermagnet landscape. Perovskite systems with GdFeO$_2$00-type distortions—such as CaCrO$_2$01, LaVO$_2$02, LaCrO$_2$03, YCrO$_2$04, LaMnO$_2$05, LaFeO$_2$06, YFeO$_2$07, NaMnF$_2$08, and KMnF$_2$09—have been identified as altermagnetic or altermagnetically active platforms with nonrelativistic spin splitting, spin-current generation, and, with SOC, anomalous Hall responses (Naka et al., 2024). This suggests a broad future AMPE program in oxide and fluoride heterostructures, where lattice distortions, orbital selectivity, and symmetry breaking can be tuned together.

Taken together, current work establishes AMPE as a distinct interfacial mechanism by which altermagnetic symmetry is exported into adjacent matter. Its experimentally demonstrated outputs already include anomalous Hall readout, spin–orbit-torque switching, spin-polarized thermionic injection, superconducting diode response, spin-polarized thermoelectric currents, proximity-induced magnetization, and Majorana-supporting topological superconductivity. The remaining central questions concern universality across materials classes, the crossover between clean and diffusive regimes, and whether interface-engineered altermagnetic order can be stabilized at technologically relevant temperatures.