Nanoscale origin of thermal anisotropy in monoclinic \texorpdfstring{$β$-Ga$_2$O$_3$}{beta-Ga2O3}

Kai Xu; Shuo Zhao; Luca Sung-Min Choi; Nils Bernhardt; Pouria Emtenani; Felix Nippert; Moritz Meißner; Hans Tornatzky; Oliver Bierwagen; Piero Mazzolini; Riccardo Mincigrucci; Laura Foglia; Danny Fainozzi; Filippo Bencivenga; Zbigniew Galazka; George Fytas; Bartlomiej Graczykowski; Riccardo Rurali; Matthias Scheffler; Christian Carbogno; Juan Sebastian Reparaz; Markus R. Wagner

arXiv · 2610.31976

Nanoscale origin of thermal anisotropy in monoclinic \texorpdfstring{$β$-Ga$_2$O$_3$}{beta-Ga2O3}

View original source ↗Read source document ↗Export metadata ↓

Abstract

Monoclinic $β$-Ga$_2$O$_3$ is a promising ultra-wide-bandgap semiconductor for power electronics, but its low and anisotropic thermal conductivity limits heat removal, making it a compelling model system for nanoscale thermal transport studies. Here, we demonstrate a pronounced nanoscale enhancement of thermal anisotropy and uncover the underlying phonon mechanism by combining complementary thermal and acoustic spectroscopy techniques with first-principles calculations. Anisotropic thermoreflectance thermometry determines the full thermal-conductivity tensor from angular measurements within the (100), (010), and (001) crystallographic planes. Angle-resolved Brillouin light scattering reveals that low-frequency acoustic phonons exhibit only weak velocity anisotropy, insufficient to account for the measured thermal anisotropy. Frequency-resolved ab initio Green--Kubo calculations show that the bulk anisotropy pattern emerges only when the accumulated conductivity includes phonon modes above 4 THz, whereas the sub 3 THz acoustic contributions are nearly isotropic. Extreme-ultraviolet transient thermal grating spectroscopy reveals that reducing the grating period to 28 nm strongly enhances the in-plane thermal anisotropy, most markedly in the (001) plane, where it reaches nearly twice its macroscopic value. Reconstructed and calculated mean-free-path (MFP) accumulation functions link this enhancement to the stronger directional contrast of short-MFP phonons. Together, these results identify high-frequency, short-MFP phonons as the dominant origin of thermal anisotropy in $β$-Ga$_2$O$_3$, while low-frequency phonons attenuate the directional contrast at macroscopic scales.

Explore related subjects

cond-mat.mtrl-sci

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Kai Xu, Shuo Zhao, Luca Sung-Min Choi, Nils Bernhardt, Pouria Emtenani, Felix Nippert, Moritz Meißner, Hans Tornatzky, Oliver Bierwagen, Piero Mazzolini, Riccardo Mincigrucci, Laura Foglia, Danny Fainozzi, Filippo Bencivenga, Zbigniew Galazka, George Fytas, Bartlomiej Graczykowski, Riccardo Rurali, Matthias Scheffler, Christian Carbogno, Juan Sebastian Reparaz, Markus R. Wagner. 2026-10-22. Nanoscale origin of thermal anisotropy in monoclinic \texorpdfstring{$β$-Ga$_2$O$_3$}{beta-Ga2O3}. https://arxiv.org/abs/2610.31976

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Impact of electron--spin coupling on exchange coupling parameters: a nonperturbative approach

Exchange coupling parameters $J_{ij}$ in the Heisenberg model are crucial for describing magnetic behavior at the atomic level. In magnetic materials, spin fluctuations can be accompanied by a self-consistent electronic response, i.e., electron--spin coupling in the sense of electronic feedback to finite spin rotations. However, the quantitative importance of this coupling in extracting reliable $J_{ij}$ has not been fully clarified. Here, using fully self-consistent, nonperturbative evaluations, we show that finite-angle spin rotations induce such electronic feedback and quantify how strongly it renormalizes the extracted $J_{ij}$. We examine systems of both fundamental and practical interest, including perovskite SrMnO$_3$, Nd-based permanent-magnet compounds (Nd$_2$Fe$_{14}$B and Nd$_2$Co$_{14}$B), and elemental 3$d$ transition metals. The nonperturbative approach yields exchange couplings that remain consistent over a wide range of rotation angles. Moreover, when the sampled configurations represent the magnetic disorder near the transition, spin models parameterized in this way give reasonable agreement with experimental magnetic phase-transition temperatures. Overall, our results demonstrate the quantitative impact of electron--spin coupling on the exchange coupling parameters $J_{ij}$ and provide a nonperturbative route to effective $J_{ij}$ for a specified regime of magnetic disorder.

cond-mat.mtrl-sci↗

arXiv2026

Benchmarking and advancing machine-learning interatomic potentials for 3C-SiC across equilibrium and extreme conditions

Several machine-learning interatomic potentials (MLIPs) have been developed for cubic silicon carbide (3C-SiC). Here, we benchmark seven existing MLIPs against a common set of structural, thermal, defect, radiation-damage, disordered-phase, and computational-performance tests. We also introduce two complementary MLIPs trained on DFT-labeled crystalline, liquid, amorphous, and defective configurations. TGAP, a Gaussian approximation potential based on the \verb|soap_turbo| descriptor, provides consistently high accuracy across the sampled configurational space. MTP, a custom moment tensor potential, retains good accuracy across these regimes while offering substantially lower computational cost, GPU acceleration, and access to multi-million-atom simulations. As an application-level test, both potentials remain stable in displacement cascades spanning short-range repulsion, transient disorder, and recrystallization. Overall, MTP emerges as a particularly strong accuracy--cost compromise for large-scale and strongly non-equilibrium simulations of 3C-SiC.

cond-mat.mtrl-sci↗

arXiv2026

Loss of altermagnetic order and smooth restoration of Kramers' spin degeneracy with increasing temperature in CrSb and MnTe

We describe how thermally induced spin fluctuations modify the electronic structures of two prototypical altermagnets, CrSb and MnTe, via application of the disordered local moment picture. For both materials, our self-consistent, ab initio calculations demonstrate that local magnetic moments persist on Cr and Mn atoms in their paramagnetic states, necessitating a spin-polarised description of the electronic structure even above the Néel temperature, $T_\mathrm{N}$. Moreover, Kramers' spin degeneracy, which is broken for both materials in their altermagnetic ground states, is shown to be smoothly restored - on the average - as the local moments thermally disorder. In metallic CrSb, this occurs at temperatures well below $T_\mathrm{N}$ and the signature effects of its altermagnetism are lost as the magnetic disorder induces heavy smearing of strongly dispersive electronic states around the Fermi energy. By contrast, in semiconducting MnTe, with its band gap largely unaffected by magnetic disorder, the spin degeneracy only returns at temperatures close to and above $T_\mathrm{N}$. We quantify the temperature dependence of the altermagnetic order parameter and the underlying electronic structures of both materials, with implications for their spin transport and spectroscopic properties.

cond-mat.mtrl-sci↗