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[Sang J. Park](https://orcid.org/0000-0003-1684-4876), Tsuneyoshi Kan, [Takamasa Hirai](https://orcid.org/0000-0002-5577-8018), [Ken-ichi Uchida](https://orcid.org/0000-0001-7680-3051)

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[Observation of orbital-angular-momentum-driven temperature modulation via the spin Peltier effect](https://mdr.nims.go.jp/datasets/ca56fb01-b755-4f74-a940-15c430ee6bdd)

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Park et al., Sci. Adv. 12, eaej1838 (2026)     2 October 2026S c i e n c e  A d v a n c e s  |  R e s e ar  c h  A r t i c l e1 of 8C O N D E N S E D  M AT T E R  P H Y S I C SObservation of orbital-angular-momentum-driven temperature modulation via the spin Peltier effectSang J. Park1*, Tsuneyoshi Kan2, Takamasa Hirai1,2, Ken-ichi Uchida1,2*Angular-momentum transport provides a pathway for controlling energy flow in solids beyond conventional charge-based mechanisms. Although spin currents are known to mediate spin-caloritronic phenomena such as the spin Peltier effect (SPE), the role of orbital angular momentum (OAM) in heat transport remains largely unexplored. Here, we demonstrate OAM-driven temperature modulation via the SPE in yttrium-iron-garnet/Pt/CuOx heterostructures. Using wedge-shaped CuOx layers combined with spatially resolved active thermal measurement techniques, we map the continuous thickness dependence and quantitatively disentangle the spin- and orbital-current-mediated contri-butions within a single device. The orbital-mediated component exhibits a pronounced maximum at an intermediate thickness, revealing a characteristic length scale for interfacial OAM generation and propagation at the Cu/CuOx in-terface. These results provide direct experimental evidence that charge-current-driven OAM can drive SPE-induced temperature modulation, establishing interfacial orbital processes as an additional channel for heat transport and providing a pathway toward spin-orbit caloritronics.INTRODUCTIONControlling the flow of energy in solids is central to next-generation information and energy technologies (1, 2). Beyond conventional charge and phonon transport, angular momentum has emerged as a fundamental degree of freedom governing nonequilibrium dynam-ics in condensed matter systems. In spintronics, the generation and manipulation of spin currents, or fluxes of spin angular momentum, enable electrical control of magnetism through spin-orbit coupling (SOC) (3, 4), thereby establishing angular momentum as an active channel for controlling material functionality.When coupled with heat, angular-momentum dynamics give rise to spin-caloritronic phenomena (5–7). Representative examples in-clude the spin Seebeck effect (SSE) (8, 9) and the spin Peltier effect (SPE) (10, 11), which are related through Onsager reciprocity and enable interconversion between heat and spin currents at magnetic interfaces. These discoveries have established spin angular momen-tum as a key mediator of temperature modulation in magnetic het-erostructures. To date, most experimental realizations rely on heavy metals (HMs) with strong SOC such as Pt (12, 13), reflecting a spin-centric framework in which spin currents are assumed to be the pri-mary carriers of thermo-spin conversion.Recent advances in orbitronics challenge this spin-centric para-digm by identifying orbital angular momentum (OAM) as a distinct transport channel in solids (14–23). The orbital Hall effect (OHE) (16–18) and orbital Rashba-Edelstein effect (OREE) (19–21) dem-onstrate that charge currents can generate orbital transport in bulk materials and orbital accumulation at inversion-symmetry-broken interfaces, respectively. Theoretically, such orbital responses origi-nate from momentum-space orbital textures and are predicted to be widespread in solids, often exceeding their spin counterparts in magni-tude (14, 24). In materials with finite SOC, these orbital responses can be partially converted into spin currents through bulk or interfacial spin-orbit interactions (16, 18), providing a pathway for orbital-to-spin angular-momentum conversion.Although orbital transport has been studied mainly in the con-text of magnetic switching and torque generation (15, 25, 26), recent studies have begun to explore its role in thermally driven transport. Theoretical studies have predicted thermally driven orbital trans-port phenomena in magnetic systems (27, 28). Experimentally, the orbital Seebeck effect, an orbital counterpart of the SSE, has been demonstrated in ferrimagnetic insulators through thermal magnons (29) and in nonmagnetic insulators through chiral phonons (30). However, whether charge-current-driven OAM can induce temper-ature modulation via the SPE remains unexplored.Here, we report the observation of OAM-driven temperature mod-ulation via the SPE in ferromagnetic or ferrimagnetic insulator (FMI)/HM/orbital-active material (OM) heterostructures (Fig. 1). Using yttrium-iron-garnet (YIG; FMI)/Pt (HM)/naturally oxidized Cu (CuOx; OM) trilayers, we observe a pronounced temperature modula-tion associated with the introduction of the CuOx layer. By continu-ously tuning the CuOx thickness (tCuOx = 0 to 16 nm) in wedge-shaped structures and spatially resolving the resulting temperature modula-tion using lock-in thermography (LIT), we identify a well-defined thickness at which the temperature modulation is maximized. At this optimal thickness, the orbital-current-mediated contribution reaches up to ∼3 times the conventional spin-Hall-driven SPE response in Pt, demonstrating efficient charge-to-heat conversion mediated by OAM. The decrease in modulation efficiency with increasing tCuOx indicates that interfacial coupling involving the CuOx layer plays a key role in the observed behavior, supporting an interfacial origin as-sociated with the OREE. These findings provide direct evidence that interfacial OAM generation and transport contribute to SPE-induced temperature modulation, thereby extending the framework of spin-orbit caloritronics beyond conventional spin-dominated paradigms.RESULTSExperimental systemFigure 1 illustrates the conceptual framework of the present study. In a conventional FMI/HM bilayer, a charge current JC flowing in 1National Institute for Materials Science, Tsukuba 305-0047, Japan. 2Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa 277-8561, Japan.*Corresponding author. Email: sangjunpark94@​gmail.​com (S.J.P.); UCHIDA.​Kenichi@​nims.​go.​jp (K.-i.U.)Copyright © 2026 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution License 4.0 (CC BY). Downloaded from https://www.science.org at National Institute for Materials Science on October 29, 2026mailto:sangjunpark94@​gmail.​commailto:UCHIDA.​Kenichi@​nims.​go.​jpmailto:UCHIDA.​Kenichi@​nims.​go.​jphttp://crossmark.crossref.org/dialog/?doi=10.1126%2Fsciadv.aej1838&domain=pdf&date_stamp=2026-10-02Park et al., Sci. Adv. 12, eaej1838 (2026)     2 October 2026S c i e n c e  A d v a n c e s  |  R e s e ar  c h  A r t i c l e2 of 8the HM generates a transverse spin current JSHES via the spin Hall effect (SHE) (Fig. 1A) (3). Subsequently, the injected spin current exchanges angular momentum with magnons at the FMI/HM inter-face, producing interfacial heat absorption or release through the SPE (Fig. 1C) (10, 11).To examine whether orbital currents can similarly drive angular-momentum transfer responsible for temperature modulation, we introduced an OM layer on top of the HM, forming FMI/HM/OM trilayers (Fig. 1D). At interfaces involving this layer, inversion sym-metry breaking enables the generation of nonequilibrium OAM via the OREE (Fig. 1B), an orbital analog of the Rashba-Edelstein effect (31, 32). The generated OAM can propagate toward the HM as an orbital current JOREEL , where it is subsequently converted into a spin current JOREES through SOC, thereby providing an additional contri-bution to interfacial angular-momentum injection and the resulting SPE alongside the conventional JSHES.To experimentally implement this concept, we used YIG, Pt, and CuOx as the FMI, HM, and OM layers, respectively. To systemati-cally examine the orbital contribution, we fabricated a wedge-shaped CuOx layer with continuously varying thickness (tCuOx) on a uni-form YIG/Pt bilayer (Fig. 2 and Materials and Methods), covering a tCuOx range of 0 to 16 nm. This geometry enables tCuOx-dependent evaluation without batch-to-batch variations in thin-film growth and measurement conditions. Because the CuOx layer is formed through natural oxidation of deposited Cu, the layer consists of coexisting metallic and oxidized Cu regions with a tCuOx-dependent distribution, which is expected to promote OAM generation at the Cu/CuOx in-terface (15, 20, 33–35). All uncapped samples were exposed to ambi-ent air for 2 days, after which electrical contacts were formed using silver epoxy, which was cured at 80°C for 30 min before the LIT measurements. A time-dependent resistance measurement using the same processing sequence showed a rapid initial resistance in-crease during ambient exposure and a further change following the 80°C curing treatment (fig. S1). Throughout this manuscript, we re-fer to this mixed Cu/CuOx structure as an effective OM layer and denote it as CuOx. Accordingly, tCuOx represents the total thickness of the layers containing both metallic and oxidized Cu regions.We used a 72-μm-thick YIG grown by liquid-phase epitaxy on a gadolinium-gallium-garnet (GGG) substrate (Materials and Meth-ods). This thickness is much larger than both the magnon energy relaxation length (∼250 nm) (36, 37) and the magnon diffusion length (∼10 μm) (38) in YIG at room temperature, enabling bulk-like magnetic behavior without boundary or diffusion limitations. Accordingly, the GGG substrate is not explicitly discussed through-out the manuscript. The Pt thickness was fixed at 2.5 nm, which pro-vides robust SOC-mediated angular-momentum conversion within the layer (18).Thickness-dependent SPE-induced temperature modulationThe SPE-induced temperature modulation was detected using LIT under a square-wave-modulated ac charge current with zero dc off-set and a steady magnetic field H (Fig. 2A) (39, 40). The infrared camera measured the amplitude A and phase ϕ of the temperature oscillation relative to the applied current JC. To ensure sufficiently high and spatially uniform infrared emissivity, the surfaces of all sam-ples were coated with black ink having an emissivity greater than 0.94 (fig. S2). The patterned line was oriented along the tCuOx-gradient direction (y), enabling continuous tCuOx-dependent evaluation of the SPE-induced temperature modulation under a constant current den-sity jC. The measurements were performed at a modulation frequency of f = 5 Hz and opposite saturating magnetic fields of μ0H = ±0.3 T, where μ0 is the vacuum permeability.Figure 2 (B and C) shows the A and ϕ images measured at μ0H = +0.3 and −0.3 T, respectively. Upon reversal of the magnetic field, the lock-in amplitude remained similar, whereas the phase in the current-carrying region changed by ∼180°, indicating reversal of the complex temperature-modulation signal with the YIG magnetiza-tion. To extract the magnetization-dependent, field-odd component associated with spin and/or OAM transfer, the complex LIT signals were antisymmetrized according to Zodd = [Z(+H)−Z(−H)]∕2 (see Materials and Methods). Because Joule heating ( ∝ JC2) yields a con-stant background without a first-harmonic response and the con-ventional Peltier effect ( ∝ JC) is field independent, this procedure isolates the SPE-induced temperature modulation that is linear in JC and odd with respect to magnetization (11, 41).Figure 2E shows the resulting spatial maps of the field-odd lock-in amplitude Aodd and phase ϕodd, obtained from the raw signals shown in Fig. 2 (B and C). The LIT images had a pixel size of 15 × 15 μm2, corresponding to an effective tCuOx sampling interval of 0.04154 nm per pixel along the wedge gradient. The corresponding tCuOx-dependent profiles shown in Fig. 2D were obtained by averaging the spatial maps along the constant-tCuOx direction (x direction). The field-even compo-nents were negligibly small, as shown in fig. S3.Figure 2D shows that Aodd remains nearly constant up to tCuOx ∼ 4 nm, followed by a gradual and monotonic decrease with increasing A BC DFig. 1. Conceptual illustration of spin- and orbital-angular-momentum-driven temperature modulation via the SPE. (A) Generation of a spin current JSHES via the SHE in an HM with large SOC. (B) Generation of interfacial OAM, followed by orbital-current propagation JOREEL , at the HM/OM interface with broken inversion symmetry via the OREE. (C) Temperature modulation through the conventional SPE ( ΔTSPE ) in a FMI/HM bilayer, driven solely by the spin current JSHES (i.e., ΔTSPE = ΔTSHESPE∝ JSHES ). (D) Orbital-angular-momentum-driven SPE in an FMI/HM/OM trilayer, driven by both JSHES and the orbital current JOREEL . The JOREEL is converted into a spin current JOREES in the HM via SOC. The resulting temperature modulation is given by ΔTSPE= ΔTSHESPE+ ΔTOREESPE , with ΔTOREESPE∝ JOREES∝ JOREEL.Downloaded from https://www.science.org at National Institute for Materials Science on October 29, 2026Park et al., Sci. Adv. 12, eaej1838 (2026)     2 October 2026S c i e n c e  A d v a n c e s  |  R e s e ar  c h  A r t i c l e3 of 8tCuOx. The corresponding ϕodd remains stable within the finite-signal regime and becomes noisy only when Aodd approaches the sub-millikelvin regime at larger tCuOx. No systematic phase shift or sign reversal is observed over the entire finite-signal regime. The constant ϕodd suggests that the SPE contributions associated with Pt and CuOx share the same sign and symmetry with respect to magnetization and charge-current direction, consistent with previous observations in TmIG/Pt/CuOx systems (15). The systematic suppression of Aodd at larger tCuOx suggests a reduction of the effective angular-momentum injection at the YIG/Pt interface, potentially associated with (i) cur-rent redistribution within the multilayer and/or (ii) modification of interfaces involving the CuOx layer responsible for OAM generation.To further characterize the magnetic-field and current dependences of the temperature modulation, we performed additional LIT mea-surements using an isolated YIG/Pt(2.5 nm)/CuOx(5.6 nm) device. A and ϕ were measured at magnetic-field magnitudes ranging from 0.08 to 0.30 T under both field polarities. Within the saturated-field re-gime, the amplitude remained nearly constant within the experimental uncertainty, whereas the phase reversed with the magnetic-field po-larity (fig. S4). These results show that the temperature-modulation signal follows the YIG magnetization orientation. In addition, current-dependent measurements showed that Aodd increased linearly with JC (R2 > 0.9999) (fig. S5). The field-odd symmetry and linear current dependence support the assignment of the observed field-odd tem-perature modulation to the SPE and distinguish it from the field-independent conventional Peltier effect and JC2-dependent Joule heating contribution. Because the observed temperature modula-tion contains contributions from both the conventional SHE in Pt and the orbital-mediated component associated with CuOx, quanti-tative separation of these contributions is required to clarify the role of OAM in SPE-induced temperature modulation.Quantitative separation of spin- and orbital-current contributionsTo clarify the orbital contribution, we quantitatively separated the individual components associated with the SHE and orbital-current AD EBCFig. 2. Observation of angular-momentum-driven temperature modulation via the SPE using LIT. (A) Observation of SPE-induced temperature modulation using LIT in a CuOx wedge layer fabricated on a YIG/Pt bilayer. The CuOx thickness (tCuOx) was continuously varied from 0 to 16 nm in a single sample, and the signal was spa-tially resolved using an infrared camera with high spatial resolution and temperature sensitivity. A square-wave-modulated current with zero offset was applied to isolate the SPE-induced temperature modulation (see Materials and Methods). An external magnetic field H was applied along the x axis to satisfy the symmetry condition for detecting the SPE-induced temperature modulation along the z direction using LIT. (B and C) Measured lock-in amplitude and phase under magnetic fields of (B) μ0H = +0.3 T and (C) μ0H = −0.3 T, respectively, at a frequency of f = 5 Hz and a current amplitude of JC = 8.0 mA. The corresponding quantities are denoted by A+H and ϕ+H in (B) and by A−H and ϕ−H in (C). The LIT images were acquired using a 1 × infrared lens, corresponding to a pixel size of 15 × 15 μm2. deg., degrees. (D) Line profiles of the field-odd lock-in amplitude Aodd and phase ϕodd as functions of tCuOx. The Aodd and ϕodd values represent spatial averages along the x direction over the region be-tween the dashed lines in (E). The error bars indicate the SD. (E) Spatial maps of the field-odd lock-in amplitude Aodd and phase ϕodd, obtained from complex antisym-metrization of the LIT signals measured in (B) and (C), as defined in Materials and Methods.Downloaded from https://www.science.org at National Institute for Materials Science on October 29, 2026Park et al., Sci. Adv. 12, eaej1838 (2026)     2 October 2026S c i e n c e  A d v a n c e s  |  R e s e ar  c h  A r t i c l e4 of 8mechanisms based on the thickness-dependent current distribution within the multilayer. We first evaluated the effective electrical resis-tivity ρ of the CuOx films as a function of tCuOx using a standard four-probe method (Materials and Methods and Fig. 3A, inset). As mentioned above, tCuOx represents the effective thickness of the Cu/CuOx layers. The electrical resistivity exhibits strong thickness de-pendence in the ultrathin regime; ρ increases when tCuOx decreases because of enhanced interface scattering and reduced metallic con-duction thickness. At tCuOx = 2 nm, ρ increases sharply by ∼1 order of magnitude to ∼1.1 × 103 μΩ·cm, indicating the percolation limit and suggesting an effective oxidation layer thickness of ∼2 to 3 nm.To estimate the current distribution in the multilayers continu-ously as a function of tCuOx, we described the resistivity for tCuOx in the range of 3 to 15 nm using a phenomenological power-law formwhere ρ∞ is the bulk resistivity limit of Cu (1.68 μΩ·cm), and C and n are fitting parameters (Fig. 3B). This fitting allows estimation of the resistivity values for continuous current-distribution analysis in the wedged sample. The fitting parameters are C = 88.2 ± 7.9 and n = 0.513 ± 0.051. The resistivity of 2.5-nm-thick Pt (ρPt) was mea-sured independently as 71 μΩ·cm.Using the extracted resistivity values and layer thickness, we de-termined the sheet conductance of Pt (GPt) and CuOx (GCuOx) layers and calculated the thickness-dependent conductance ratio. Assum-ing parallel current flow within the metallic layers, the fractions of the applied current flowing through Pt and CuOx were determined from their relative conductances as GPt/Gtot and GCuOx/Gtot, where Gtot = GPt + GCuOx. Figure 3C shows the conductance ratio, which represents the current distribution within the multilayer. At tCuOx = 3 nm, ∼63% of the applied current flows through the CuOx layer, and this fraction increases with increasing tCuOx. It is noted that the current flowing through a 2-nm-thick CuOx layer is merely 5% of the total applied current, suggesting that the SPE signal observed below 2 nm is primarily governed by conventional charge-to-spin conversion processes rather than by orbital transport through the ultrathin CuOx layer.On the basis of this conductance model, we separated the SPE-induced temperature modulation attributed to the CuOx layer by subtracting the Pt-only contribution expected from the convention-al SHE. As experimentally observed in Fig. 2, ϕodd remains constant; therefore, the complex lock-in signals add constructively without additional phase lag, allowing direct subtraction of the amplitudes. Accordingly, the CuOx-associated component is obtained aswhere ⟨APt∕CuOxodd(tCuOx)⟩ and ⟨APt−onlyodd⟩ represent the spatial averages in the constant tCuOx region (along the x direction) and the YIG/Pt reference region, respectively. The Pt contribution (second term on ρ(tCuOx)= ρ∞ + CtCuOx−n (1)ΔACuOxodd(tCuOx)=⟨APt∕CuOxodd(tCuOx)⟩−⟨APt−onlyodd⟩[JPtC(tCuOx)JPt−onlyC](2)A B CD E FFig. 3. Quantitative separation of SPE contributions from Pt and CuOx based on bilayer electrical conductance. (A) Electrical resistivity ρ of uniform CuOx films as a function of CuOx thickness (tCuOx), measured using the standard four-probe method (inset). The dashed line indicates the percolation limit. (B) Selected view of ρ for 3- to 15-nm-thick films. The data are fitted using a phenomenological power-law function, ρ(tCuOx)= ρ∞ + CtCuOx−n , where ρ∞ is the bulk resistivity limit of Cu, and C and n are fitting parameters. The ρ of 2.5-nm-thick Pt was measured to be 71 μΩ·cm. The error bars for (A) and (B) are smaller than the symbols. (C) Electrical conductance ratio of CuOx(tCuOx) and Pt(2.5 nm) as a function of tCuOx, used to determine the current distribution within the multilayer. (D and E) Separated components of the measured SPE-induced temperature modulation signal Aodd as a function of tCuOx: (D) the Pt contribution and (E) the orbital contribution associated with CuOx (see Eq. 2 for details). (F) Charge-to-heat conversion efficiency ηCuOx associated with the CuOx orbital contribution, defined as SPE-induced temperature modulation per the current density flowing through the CuOx layer (see Eq. 3). The decay in the tCuOx ≥ 7 nm region is fitted using an exponential function exp(−tCuOxλCuOxeff) . The values in (F) are replotted in Fig. 4 and fig. S5C for comparison.Downloaded from https://www.science.org at National Institute for Materials Science on October 29, 2026Park et al., Sci. Adv. 12, eaej1838 (2026)     2 October 2026S c i e n c e  A d v a n c e s  |  R e s e ar  c h  A r t i c l e5 of 8the right-hand side of Eq. 2) is shown in Fig. 3D, whereas the CuOx-associated component (left-hand side) is presented in Fig. 3E. JPtC(tCuOx) is the thickness-dependent current flowing through the Pt layer, es-timated from the conductance model as JPtC(tCuOx)=(GPt∕Gtot)JC (Fig. 3C). The resulting CuOx-associated SPE contribution was then normalized by the corresponding current density jCuOxC(tCuOx) flow-ing through the CuOx layer asthereby defining a temperature-modulation efficiency associated with the orbital contribution.Notably, ηCuOx exhibits a peak at tCuOx ∼ 6 to 7 nm (Fig. 3F), in-dicating an optimal thickness scale for the orbital-mediated response. If the signal originated from bulk orbital transport (e.g., the OHE), it would be expected to increase with thickness and eventually satu-rate over a scale determined by the propagation length (17, 42). The pronounced peak instead suggests an interfacial origin of OAM gener-ation, consistent with an OREE-driven SPE heat-modulation mech-anism. Considering an estimated oxide-layer thickness of ∼2 to 3 nm (Fig. 3A), OAM generation is likely most effective when oxidized and metallic Cu regions coexist, a configuration reported to favor the OREE (15, 29, 34, 35, 43–46). First-principles calculations have shown that hybridization between O 2p and Cu 3d orbitals induces a pronounced orbital Rashba effect in surface-oxidized Cu (35). More recently, combined x-ray photoelectron spectroscopy (XPS), transmis-sion electron microscopy (TEM), electron energy-loss spectroscopy (EELS), and first-principles analyses identified orbital hybridization at the Cu4O3/Cu interface as a key factor in enhancing orbital-current generation in naturally oxidized CuOx heterostructures (46). These findings support our interpretation that the coexistence of oxidized and metallic Cu regions promotes interfacial OAM generation.At this optimal thickness, the peak value (177 × 10−14 K·m2/A) exceeds the conventional spin-driven SPE value measured in the same device (58 × 10−14 K·m2/A) and the representative value re-ported for YIG/Pt (47 × 10−14 K·m2/A) (41), highlighting efficient charge-to-heat conversion mediated by the OAM. This wedge-based approach minimizes uncertainties arising from batch-to-batch vari-ations and interfacial differences, enabling direct evaluation of the intrinsic thickness dependence. At larger tCuOx, the signal mono-tonically decreases and becomes comparable to the experimental uncertainties. The orbital contribution persists into the thickness regime where a direct Pt/CuOx interface is effectively suppressed, further suggesting that the signal is associated with the Cu/CuOx interface. To further quantify this behavior, we fitted the decreasing data for tCuOx ≥ 7 nm using an exponential function exp(−tCuOxλCuOxeff) , where λCuOxeff represents an effective characteristic length. The decay is well described by the exponential function within the experimen-tal uncertainty (R2 > 0.996), yielding λCuOxeff = 11.0 ± 0.5 nm. This exponential decay indicates a diffusion-like attenuation of the inter-facial orbital contribution. The extracted length scale λCuOxeff = 11.0 ± 0.5 nm is comparable to the orbital transport length scale reported in a previous study on metallic Cu, where a characteristic length of ∼9 nm was obtained from time-resolved measurements (47). The observed behavior strongly supports OAM generation at the Cu/CuOx interface, whereas a direct Pt/CuOx contribution is unlikely, with the signal attenuating through the metallic Cu layer between Pt and CuOx. As an independent check, a finite ηCuOx was also obtained for a fixed-thickness isolated-line device, indicating that the orbital contribu-tion persists without the continuous wedge geometry (fig. S5C).Origin of the orbital-current-induced temperature modulationTo further investigate the origin of OAM generation, we fabricated additional Al-capped and Al-inserted samples using the same pro-cedures (see Materials and Methods), as shown in Fig. 4 (A to C). The Al-capped sample [YIG/Pt(2.5)/Cu(tCuOx)/Al(2), where all thick-nesses are in nanometers] was fabricated to suppress oxidation of Cu and thereby inhibit the formation of CuOx. The Al-inserted sam-ples [YIG/Pt(2.5)/Al(1 or 2)/CuOx(tCuOx)] were fabricated to probe the origin of the signals by suppressing the Pt/CuOx interface while preserving the Cu/CuOx interface. Ultrathin Al layers (with a thickness ηCuOx = ΔACuOxodd(tCuOx)∕ jCuOxC(tCuOx)(3)A DB CFig. 4. Separated orbital-angular-momentum-induced temperature modulation efficiency in samples patterned along the x direction, perpendicular to the CuOx thickness gradient. (A to C) Schematic illustrations of sample structures with (A) YIG/Pt(2.5 nm)/Cu(tCuOx) capped with a 2-nm-thick Al layer to suppress surface oxidation, (B) YIG/Pt(2.5 nm)/Al(1 nm)/CuOx(tCuOx), and (C) YIG/Pt(2.5 nm)/Al(2 nm)/CuOx(tCuOx), where a thin Al layer is inserted between the Pt and CuOx layers. (D) Or-bital temperature modulation efficiency ηCuOx for the samples in (A) to (C) and the main data in Fig. 3F for reference. The corresponding LIT images and analysis regions are provided in fig. S6.Downloaded from https://www.science.org at National Institute for Materials Science on October 29, 2026Park et al., Sci. Adv. 12, eaej1838 (2026)     2 October 2026S c i e n c e  A d v a n c e s  |  R e s e ar  c h  A r t i c l e6 of 8of ∼0.8 nm) have been reported to provide appreciable interfacial orbital transparency (48). Therefore, if the OAM is generated at the Cu/CuOx interface via the OREE and propagates toward Pt as an orbital current through the metallic Cu layer, as suggested by the results in Fig. 3, this Al-inserted structure is expected to exhibit a finite orbital-driven temperature modulation. The patterned lines were oriented along the x direction, perpendicular to the tCuOx-gradient direction, enabling discrete evaluation at selected thicknesses. Four patterned lines, L1 to L4, were fabricated corresponding to tCuOx = 0, 0.8, 2.9, and 5.6 nm, respectively. The variation in tCuOx across the width of each patterned line was estimated to be ∼0.3 nm and is represented by the horizontal error bars in Fig. 4D. L1 was used as a reference, and L2 (tCuOx = 0.8 nm) exhibited nearly identical signals. All LIT measurements were conducted sequentially by attaching electrodes to each patterned line. Using the LIT measurements and quantitative signal separation described above, we extracted the or-bital contribution ηCuOx (Fig. 4D). The detailed LIT data are pro-vided in fig. S6.The Al-capped sample [YIG/Pt(2.5)/Cu(tCuOx)/Al(2); Fig. 4A] showed negligible orbital contribution (∼2 × 10−14 K·m2/A) for both L3 and L4, well below the experimental uncertainty (4 × 10−14 to 6 × 10−14 K·m2/A). In these samples, the observed signal is dominated by the conventional SHE in Pt. This result indicates that, in the YIG/Pt/CuOx samples used for the experiments in Figs. 2 and 3, CuOx plays a critical role in OAM generation through the OREE, consistent with previous theoretical and experimental studies (15, 29, 34, 35, 43–45). Although bulk orbital currents generated in Cu have been reported (49), the disappearance of the signal upon Al capping indi-cates that bulk contributions are not the dominant origin of the tem-perature modulation observed in our system. It is worth noting that both YIG/Cu(5)/Pt(5) and YIG/Al2O3(1)/Pt(5) produce negligibly small SPE signals (41), further indicating that pure Cu or oxidized Al layers alone do not produce a measurable SPE response in the present configuration.We then investigated structures with an Al layer inserted between Pt and CuOx (Fig. 4, B and C), designed to disrupt the Pt/CuOx in-terface while preserving the Cu/CuOx side of the stack. With a 1-nm- thick Al layer, which is reported to provide appreciable interfacial orbital transparency (48), we observed a finite orbital contribution with a maximum ηCuOx of 144 × 10−14 K·m2/A at L4. However, no orbital-driven signal was observed when the Al thickness was 2 nm. The persistence of the signal with the 1-nm-thick Al insertion, de-spite disruption of the direct Pt/CuOx interface, supports OAM gen-eration at the Cu/CuOx interface (46, 50). Its disappearance with the 2-nm-thick Al insertion is consistent with reduced orbital-current transmission through the thicker Al layer. Together with the expo-nential decay trend observed in Fig. 3, these results strongly support the conclusion that OAM generation predominantly occurs at the Cu/CuOx interface, whereas contributions from a direct Pt/CuOx in-terface are unlikely in the present configuration.DISCUSSIONWe demonstrate that orbital currents can contribute to temperature modulation in magnetic heterostructures via the SPE. Using YIG/Pt/CuOx trilayers with continuously tuned CuOx thickness, we identify an orbital-current-mediated contribution that becomes pronounced under optimized conditions. The thickness-dependent behavior, char-acterized by a distinct maximum followed by exponential decay, together with control experiments using Al-capped and Al-inserted structures, indicates that the observed temperature modulation is primarily associated with interfacial OAM generation at the Cu/CuOx interface. The suppression of the orbital contribution in the Al-capped structure and the persistence of a finite signal with a 1-nm- thick Al insertion highlight the essential role of interfacial coupling, ruling out bulk orbital transport as the dominant mechanism. These results establish a direct link between charge-current-driven OAM transport and SPE-induced temperature modulation, extending the scope of spin caloritronics beyond spin-dominated frameworks. In addition, the interplay between orbital and spin currents suggests a potential driving principle for transverse thermoelectric conversion, where angular-momentum transport can be used for heat-to-charge energy conversion. In this context, orbital contributions may provide an additional degree of freedom to complement established spin-based mechanisms (51, 52). Future observation of the orbital Peltier effect, the Onsager reciprocal counterpart of the orbital Seebeck effect, would further broaden the framework of orbital-mediated heat transport. The ability to engineer interfacial OAM generation and transport provides a design principle for heat control in solids, thereby open-ing a pathway toward spin-orbit caloritronics and highlighting the potential for further performance improvement in solid-state ther-mal management and energy conversion technologies.MATERIALS AND METHODSSample preparationThe heterostructure samples were fabricated by depositing thin metallic layers using a magnetron sputtering system (Comet Inc., CMS-A6250X2) on (111)-oriented single-crystalline YIG grown on (111)-oriented GGG substrates by liquid-phase epitaxy. The GGG/YIG substrates were mirror-polished before deposition using a slurry containing 50-nm-diameter alumina particles (Baikowski Interna-tional Corporation) and cleaned by sonication in acetone and de-ionized water to remove residues. dc power sources were used for the Pt, Cu, and Al targets with a power of 30 W, and the deposition rates were 0.0349, 0.0339, and 0.0123 nm/s, respectively. The deposi-tion was conducted at room temperature under vacuum conditions with a base pressure below 6.0 × 10−6 Pa and at an Ar process gas pressure of 0.5 Pa. Uniform films of Pt and Al were deposited while rotating the substrates, whereas the wedged Cu layer was fabricated using a linearly moving shutter over a length of ∼6 mm at a fixed substrate angle. The layers were deposited without breaking vacuum. All samples were exposed to ambient air for 2 days before further pro-cessing. In samples without a capping layer, this exposure resulted in the formation of naturally oxidized CuOx layers from the deposited Cu films, whereas the Al-capped sample was protected from oxidation. For the LIT samples, electrical contacts were formed at the edges of the patterned lines using silver epoxy, which was cured at 80°C for 30 min. The samples used for electrical resistivity measurements were subjected to the same thermal treatment before measurement.LIT measurement and field antisymmetrizationThe spatial distribution of temperature modulation associated with the SPE was measured using a LIT system (DCG Systems Inc., ELITE). Before the LIT measurements, all sample surfaces were uniformly coated with black ink having an emissivity greater than 0.94. For the continuous wedge sample shown in Fig. 2, a 1 × infrared lens with an f-number of 1.5 and a working distance of 40 mm was used, Downloaded from https://www.science.org at National Institute for Materials Science on October 29, 2026Park et al., Sci. Adv. 12, eaej1838 (2026)     2 October 2026S c i e n c e  A d v a n c e s  |  R e s e ar  c h  A r t i c l e7 of 8corresponding to a pixel size of 15 × 15 μm2. The total image dimen-sions were 329 × 486 pixels, and the quantitative analysis was per-formed over a region of 17 × 486 pixels. For the measurements corresponding to Fig. 4 and shown in fig. S6, a 5 × infrared lens with an f-number of 4.0 and a working distance of 14 mm was used, cor-responding to a pixel size of 3 × 3 μm2. The total image dimensions were 446 × 304 pixels, and the quantitative analysis was performed over a region of 91 × 304 pixels.To isolate the magnetization-dependent SPE component, the sig-nals were antisymmetrized with respect to the magnetic field (±H). The complex LIT signal measured under each magnetic-field direc-tion was defined aswhere A±H and ϕ±H denote the lock-in amplitude and phase mea-sured under positive or negative H, respectively. The field-odd com-plex LIT signal was obtained by complex antisymmetrization as follows (11, 39, 40)The corresponding field-odd amplitude and phase, Aodd and ϕodd, were determined fromSimilarly, the field-even complex LIT signal was obtained by com-plex symmetrizationThe corresponding field-even amplitude and phase, Aeven and ϕeven, were determined fromBecause the conventional Peltier effect is independent of H and the magneto-Peltier effect is symmetric with respect to H, their con-tributions do not appear in the field-odd amplitude and phase, Aodd  and ϕodd.Electrical transport measurementsThe resistivity was calculated from the measured resistance using the geometrical dimensions of the channel at room temperature. The distance between the voltage electrodes was 4.4 mm, and the chan-nel width was 0.3 mm. The samples for electrical resistivity estima-tion were fabricated using the same procedure as the main samples (described above). A standard four-probe method was used with a digital multimeter (Keithley, DMM6500) and a probe system equipped with four needle probes. The measured voltage fluctuation was less than 0.1% for all samples.For the time-dependent electrical characterization, the resistance of a YIG/Pt(2.5 nm)/Cu(6 nm) reference sample was measured in a four-probe configuration using the same digital multimeter. The mea-surement was initiated within 20 min after the sample was removed from the sputtering chamber and was performed at 10-min intervals. The sample was maintained under ambient conditions for 48 hours and subsequently heated on a hot plate at 80°C for 30 min to repro-duce the silver-epoxy curing treatment used for the LIT samples. 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Competing interests: The authors declare that they have no competing interests. Data, code, and materials availability: All data and code needed to evaluate and reproduce the results in the paper are present in the paper and Supplementary Materials. No new code was generated in this study. New materials generated in this study are available from the corresponding author by contacting S.J.P. at sangjunpark94@​gmail.​com.Submitted 26 May 2026 Accepted 28 August 2026 Published 2 October 2026 10.1126/sciadv.aej1838Downloaded from https://www.science.org at National Institute for Materials Science on October 29, 2026mailto:sangjunpark94@​gmail.​comObservation of orbital-angular-momentum-driven temperature modulation via thespin Peltier effectSang J. Park, Tsuneyoshi Kan, Takamasa Hirai, and Ken-ichi UchidaSci. Adv. 12 (40), eaej1838.  DOI: 10.1126/sciadv.aej1838View the article onlinehttps://www.science.org/doi/10.1126/sciadv.aej1838Permissionshttps://www.science.org/help/reprints-and-permissionsUse of this article is subject to the Terms of serviceScience Advances (ISSN 2375-2548) is published by the American Association for the Advancement of Science. 1200 New York AvenueNW, Washington, DC 20005. The title Science Advances is a registered trademark of AAAS. Copyright © 2026 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claimto original U.S. Government Works. Distributed under a Creative Commons Attribution License 4.0 (CC BY).Downloaded from https://www.science.org at National Institute for Materials Science on October 29, 2026https://www.science.org/content/page/terms-service Observation of orbital-angular-momentum-driven temperature modulation via the spin Peltier effect INTRODUCTION RESULTS Experimental system Thickness-dependent SPE-induced temperature modulation Quantitative separation of spin- and orbital-current contributions Origin of the orbital-current-induced temperature modulation DISCUSSION MATERIALS AND METHODS Sample preparation LIT measurement and field antisymmetrization Electrical transport measurements Supplementary Materials This PDF file includes: REFERENCES Acknowledgments