The copper substituted lead oxyapatite, ${\mathrm{Pb}}_{10-x}{\mathrm{Cu}}_x{\left({\mathrm{PO}}_{3.92\left(4\right)}\right)}_6{\mathrm{O}}_{0.96\left(3\right)} [x$ = 0.94(6)] was studied using neutron and x-ray diffraction and neutron spectroscopy techniques. The crystal structure of the main phase of our sample, which has come to be colloquially known as LK-99, is verified to possess a hexagonal structure with space group $P{6}_3/m$, alongside the presence of impurity phases Cu and ${\mathrm{Cu}}_2\mathrm{S}$. We determine the primary substitution location of the Cu as the Pb1 $\left(6h\right)$ site, with a small substitution at the Pb2 $\left(4f\right)$ site. Consequently, no clear Cu-doping-induced structural distortion was observed in the investigated temperature region between 10 K and 300 K. Specially, we did not observe a reduction of coordinate number at the Pb2 site or a clear tilting of ${\mathrm{PO}}_4$ tetrahedron. Magnetic characterization reveals a diamagnetic signal in the specimen, accompanied by a very weak ferromagnetic component at 2 K. No long-range magnetic order down to 10 K was detected by the neutron diffraction. Inelastic neutron scattering measurements did not show magnetic excitations for energies up to 350 meV. There is no sign of a superconducting resonance in the excitation spectrum of this material. The measured phonon density of states compares well with density functional theory calculations performed for the main LK-99 phase and its impurity phases. Our study may shed some insight into the role of the favored substitution site of copper in the absence of structural distortion and superconductivity in LK-99.

${\mathrm{Mn}}_{3}X$ ($X=\text{Sn}$, Ge, Ga) kagome Weyl semimetals have attracted significant research interest due to their large anomalous Hall, thermal, and optical effects originating from their nontrivial band topology. These large topological effects together with the antichiral antiferromagnetic order that can be manipulated through various experimental means provide unique platforms for developing high-speed spintronics. ${\mathrm{Mn}}_3\mathrm{Ga}$ is known to have the largest Néel temperature ($T_{\mathrm{N}}\approx 480$ K), which is useful for developing antiferromagnetic spintronics. Here, we establish the epitaxial growth of antiferromagnetic ${\mathrm{Mn}}_3\mathrm{Ga}$ films by magnetron sputtering and present their structure, magnetotransport, terahertz properties, and exchange bias effect in ${\mathrm{Mn}}_3\mathrm{Ga}$/NiFe bilayers, establishing their remarkable properties essential for future investigations towards device applications.

Dislocation-mediated deformation mechanisms in body-centered-cubic solid solutions are expected to be influenced by spatial fluctuations in screw dislocation core energies. In refractory high-entropy alloys, the formation of chemical short-range order has been demonstrated to decrease the heterogeneity of this energy landscape, narrowing the distribution of dislocation core energies. It is, however, unclear if multicomponent compositionally complex systems display any unique effects or if these results are more generally applicable. To answer this question, this study computationally investigates how system chemistry, compositional complexity, and the presence of various degrees of chemical short-range order affect the distribution of screw dislocation energies in binary and ternary subsystems of the NbMoTaW alloy. We report the calculated averages and variances for the diffuse antiphase boundary energy and the dislocation core energy with various degrees of chemical short-range order. While short-range order negligibly affects the average core energies, their distributions are notably narrowed in some, but not all, systems, primarily depending on chemistry rather than the number of components.

A uniform 1-unit-cell-high step on the $\mathrm{SrTi}{\mathrm{O}}_3$ (STO) substrate is a prerequisite for growing high-quality epitaxial oxide heterostructures. However, it is inevitable that defects induced by mixed substrate-surface termination exist at the interface, significantly impacting the properties of ultrathin films. In this study, we microscopically identify the origin for the lateral inhomogeneity in the growth of ultrathin $\mathrm{SrRu}{\mathrm{O}}_3$ films due to the step effects of $\mathrm{SrTi}{\mathrm{O}}_3$ (001). By using atomic-resolved scanning transmission electron microscopy, we observe two distinct types of step propagation along the [011] and $\left[0\overline{1}1\right]$ crystallographic direction in $\mathrm{SrTi}{\mathrm{O}}_3-\mathrm{SrRu}{\mathrm{O}}_3$ heterostructures, respectively. In particular, the type-II $\left[0\overline{1}1\right]$ step results in lateral discontinuity of monolayer $\mathrm{SrRu}{\mathrm{O}}_3$ and originates from the SrO-terminated regions along the $\mathrm{Ti}{\mathrm{O}}_2-\mathrm{terminated}$ step edge. Such an induced lateral discontinuity should be responsible for the distinct electronic and magnetic properties of monolayer $\mathrm{SrRu}{\mathrm{O}}_3$. Our findings underscore the critical importance of using single-termination STO substrate to achieve high-quality termination-selective films and to unveil the intrinsic properties of epitaxial films in the atomic limit.

Crystalline sheets (e.g., graphene and transition metal dichalcogenides) liberated from a substrate are a paradigm for materials at criticality, because flexural phonons can fluctuate into the third dimension. Although studies of static critical behaviors (e.g., the scale-dependent elastic constants) are plentiful, investigations of dynamics remain limited. Here, we use molecular dynamics to study the time dependence of the midpoint (the height center of mass) of doubly clamped nanoribbons, as prototypical graphene resonators, under a wide range of temperature and strain conditions. By treating the ribbon midpoint as a Brownian particle confined to a nonlinear potential (which assumes a double-well shape beyond the buckling transition), we formulate an effective theory describing the ribbon's transition rate across the two wells and its oscillations inside a given well. We find that, for nanoribbbons compressed above the Euler buckling point and thermalized above a temperature at which the nonlinear effects due to thermal fluctuations become significant, the exponential term (the ratio between energy barrier and temperature) depends only on the geometry but not the temperature, unlike the usual Arrhenius behavior. Moreover, we find that the natural oscillation time for small strain shows a nontrivial scaling ${\tau }_{\mathrm{o}}\sim L_0^z{T}^{-\eta /4}$, with $L_0$ being the ribbon length, $z=2-\eta /2$ being the dynamic critical exponent, $\eta =0.8$ being the scaling exponent describing scale-dependent elastic constants, and $T$ being the temperature. These unusual scale- and temperature-dependent dynamics thus exhibit dynamic criticality and could be exploited in the development of graphene-based nanoactuators.

We study the optical generation and control of coherent phonons in elemental bismuth (Bi) and antimony (Sb) using a classical equation of motion informed by first-principles calculations of the potential energy surface and the frequency-dependent macroscopic dielectric function along the zone-centered optical phonon coordinates. Using this approach, we demonstrate that phonons with the largest optomechanical couplings also have the strongest degree of anharmonicity among the zone-centered modes, a result of the broken-symmetry structural ground state of Bi and Sb. We show how this anharmonicity, explaining the light-induced phonon softening observed in experiments, prevents the application of standard phonon-amplification and annihilation protocols. We introduce a simple linearization protocol that extends the use of such protocols to the case of anharmonic phonons in broken-symmetry materials, and demonstrate its efficiency at high displacement amplitudes. Our formalism and results provide a path for improving optical control in nonlinear phononics.

For the past few years, two-dimensional (2D) ferroelectric materials have attracted strong interest for their potential in future nanoelectronics devices. The recent discovery of 2D ferroelectricity in twisted layers of insulating hexagonal boron nitride, one of the most used 2D materials, has opened the route to its integration into complex van der Waals heterostructures combining hybrid properties. Here we show that opposite polarizations in ferroelectric domains of a folded $h\mathrm{BN}$ layer can imprint local $n$ and $p$ doping in a semiconducting transition metal dichalcogenide ${\mathrm{WSe}}_2$ monolayer. We demonstrate that ${\mathrm{WSe}}_2$ can be used as an optical probe of ferroelectricity in $h\mathrm{BN}$ and show that the doping density and type can be controlled with the position of the semiconductor with respect to the ferroelectric interface. Our results establish the ferroelectric $h\mathrm{BN}$/${\mathrm{WSe}}_2$ van der Waals stacking as a promising optoelectronic structure.

Nested sampling is a promising method for calculating phase diagrams of materials. However, if accuracy at the level of ab initio calculations is required, the computational cost limits its applicability. In the present work, we report on the efficient use of a neural-network force field in conjunction with the nested-sampling algorithm. We train our force fields on a recently reported database of silicon structures evaluated at the level of density functional theory and demonstrate our approach on the low-pressure region of the silicon pressure-temperature phase diagram between 0 and $16\mathrm{GPa}$. The simulated phase diagram shows good agreement with experimental results, closely reproducing the melting line. Furthermore, all of the experimentally stable structures within the investigated pressure range are also observed in our simulations. We point out the importance of the choice of exchange-correlation functional for the training data and show how the r2SCAN meta-generalized gradient approximation plays a pivotal role in achieving accurate thermodynamic behavior. We furthermore perform a detailed analysis of the potential energy surface exploration and highlight the critical role of a diverse and representative training data set.

The layered ${\mathit{AMP}}_2$ ($A$ = alkali-earth or rare-earth atom, $M$ = transition metal, $P$ = Sb, Bi) compounds are widely studied for their rich magnetism and electronic structure topology. We provide a detailed characterization of the magnetic and transport properties of ${\mathrm{LaMn}}_x{\mathrm{Sb}}_2$, an understudied member of the ${\mathit{AMP}}_2$ family. ${\mathrm{LaMn}}_x{\mathrm{Sb}}_2$ forms with intrinsic Mn vacancies, and we demonstrate that by varying the starting ratio of La, Mn, and Sb, we can synthetically control the Mn occupancy and produce single crystals with $x=0.74–0.97$. Magnetization and transport measurements indicate ${\mathrm{LaMn}}_x{\mathrm{Sb}}_2$ has a rich temperature-composition ($T\text{–}x$) magnetic phase diagram with physical properties strongly influenced by the Mn occupancy. ${\mathrm{LaMn}}_x{\mathrm{Sb}}_2$ orders antiferromagnetically at $T_1=130–180$ K, where $T_1$ increases with $x$. Below $T_1$, the $T\text{–}x$ phase diagram is complicated. At high $x$, there is a second transition $T_2$ that decreases in temperature as $x$ is lowered, vanishing below $x \le 0.85$. A third, first-order, transition $T_3$ is detected at $x \approx 0.92$, and the transition temperature increases as $x$ is lowered, crossing above $T_2$ near $x \approx 0.9$. On moving below $x <0.79$, we find the crystal structure changes from the $P$4/nmm arrangement to an $I\overline{4}2m$ structure with partially ordered Mn vacancies. The change in crystal structure results in the sudden appearance of two new low-temperature phases and a crossover between regimes of negative and positive magnetoresistance when $x \le 0.78$. Finally, we provide powder neutron diffraction for $x=0.93$, and find that the high-$x$ compositions first adopt a $G$-type antiferromagnetic structure with the Mn moments aligned within the $\mathit{ab}$ plane, which is followed upon further cooling by a second transition to a different, noncollinear structure where the moments are rotated within the basal plane. Our results demonstrate that ${\mathrm{LaMn}}_x{\mathrm{Sb}}_2$ is a highly tunable material with six unique magnetically ordered phases, depending on $T$ and $x$.

Dealloyed nanoporous metals with a hierarchical structure provide model systems for low-density structural and functional nanomaterials. It has been suggested that these materials are distinguished by particularly stringent design principles, with precisely defined characteristic length scales, and with geometrically similar structures on each hierarchy level, and that the length scales can be independently tuned on each level. Studying nanoporous gold made by two-step dealloying, we here demonstrate the tunability of the microstructure, independently for the upper and the lower hierarchy level. Small-angle (SAXS) and ultrasmall-angle x-ray scattering (USAXS) revealed sharp interference peaks corresponding to each of the two levels, confirming the stringent structural definition. Exploiting USAXS, we resolve and study upper-hierarchy-level ligament spacings of up to 600 nm. The length scales inferred from the peak positions correlate excellently with structure sizes determined by analysis of electron micrographs. This suggests a scaling factor that allows for size conversion between the two approaches. Furthermore, the analysis of the small-angle scattering enables a characterization of the volume-specific surface area, in good agreement with the estimate based on the ligament size and the leveled-wave model as an approximate description of the material's microstructure.

Heterostructures of two-dimensional (2D) van der Waals (vdW) magnets and topological insulators (TI) are of substantial interest as candidate materials for efficient spin-torque switching, quantum anomalous Hall effect, and chiral spin textures. However, since many of the vdW magnets have Curie temperatures below room temperature, we want to understand how materials can be modified to stabilize their magnetic ordering to higher temperatures. In this work, we utilize molecular beam epitaxy to systematically tune the Curie temperature ($T_C$) in thin film ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2/{\mathrm{Bi}}_2{\mathrm{Te}}_3$ from bulklike values ($\sim 220$ K) to above room temperature by increasing the growth temperature from 300 ${}^{\circ }\mathrm{C}$ to 375 ${}^{\circ }\mathrm{C}$. For samples grown at 375 ${}^{\circ }\mathrm{C}$, cross-sectional scanning transmission electron microscopy (STEM) reveals the spontaneous formation of different ${\mathrm{Fe}}_m{\mathrm{Ge}}_n{\mathrm{Te}}_2$ compositions (e.g., ${\mathrm{Fe}}_5{\mathrm{Ge}}_2{\mathrm{Te}}_2$ and ${\mathrm{Fe}}_7{\mathrm{Ge}}_6{\mathrm{Te}}_2$) as well as intercalation in the vdW gaps, which are possible origins of the enhanced Curie temperature. This observation paves the way for developing various ${\mathrm{Fe}}_m{\mathrm{Ge}}_n{\mathrm{Te}}_2$/TI heterostructures with novel properties.

${\mathrm{MnSiN}}_2$ is a transition-metal nitride with Mn and Si ions displaying an ordered distribution on the cation sites of a distorted wurtzite-derived structure. The ${\mathrm{Mn}}^{2+}$ ions reside on a three-dimensional (3D) diamondlike covalent network with strong superexchange pathways. We simulate its electronic structure and find that the N anions in ${\mathrm{MnSiN}}_2$ act as $\sigma$- and $\pi$-donors, which serve to enhance the N-mediated superexchange, leading to the high Néel ordering temperature of $T_N$ = 443 K. Polycrystalline samples of ${\mathrm{MnSiN}}_2$ were prepared to reexamine the magnetic structure and resolve previously reported discrepancies. An additional magnetic canting transition is observed at $T_{\mathrm{cant}}$ = 433 K and the precise canted ground-state magnetic structure has been resolved using a combination of density functional theory (DFT) calculations and powder neutron diffraction. The calculations favor a $G$-type antiferromagnetic spin order with lowering to $P{c}^{\prime }$. Irreducible representation analysis of the magnetic Bragg peaks supports the lowering of the magnetic symmetry. The computed model includes a ${10}^{\circ }$ rotation of the magnetic spins away from the crystallographic $c$ axis consistent with measured powder neutron diffraction data modeling and a small canting of $0.6{}^{\circ }$.

Topological insulators are promising materials in condensed-matter physics on the grounds that they host a peculiar spin texture that can generate very high spin-to-charge current interconversion, significantly relevant for up-and-coming low-energy-consumption spintronics devices. The goal of this study is to explore a promising family of topological materials showing distinctive properties such as high tunability—the half-Heuslers. We focus on the epitaxial growth of PdYBi and PtYBi thin films, which were grown and characterized on a series of interconnected UHV setups, allowing us to get a full set of in situ surface characterizations, such as electron diffraction, scanning tunneling microscopy, and angle-resoled photoemission spectroscopy. Ex situ structural characterization using standard x-ray diffraction and scanning transmission electron microscopy were used to control the crystalline quality and chemical ordering in the thin films. Angle-resolved photoemission spectroscopy was performed and reveals the presence of linear states around the $\mathrm{\Gamma }$ point of the Brillouin zone. Furthermore, we carry out thermospin transport measurements using on-chip devices with a designed geometry for a controlled heat propagation to test the potential interconversion efficiency of our compounds, finding a larger value of the spin Seebeck coefficient than that of platinum for different thicknesses for both PdYBi and PtYBi. This observation opens a pathway to develop efficient spin interconversion materials using half-Heuslers.

For layered materials, the interlayer stacking is a critical degree of freedom tuning electronic properties, while its microscopic characterization faces great challenges. The transition-metal dichalcogenide $1T\text{−}\mathrm{Ta}{\mathrm{S}}_2$ represents a novel example, in which the stacking pattern is not only enriched by the spontaneous occurrence of the intralayer charge density wave, but also recognized as a key to understand the nature of the low-temperature insulating phase. We exploit the ${}^{33}\mathrm{S}$ nuclei in a $1T\text{−}\mathrm{Ta}{\mathrm{S}}_2$ single crystal as sensitive probes of the local stacking pattern via quadrupolar coupling to the electron density distribution nearby, by combining nuclear magnetic resonance (NMR) measurements with the state-of-the-art first-principles electric-field gradient calculations. The applicability of our proposal is analyzed through temperature, magnetic-field, and angle-dependent NMR spectra. Systematic simulations of a single $1T\text{−}\mathrm{Ta}{\mathrm{S}}_2$ layer, bilayers with different stacking patterns, and typical stacking orders in three-dimensional (3D) structures unravel distinct NMR characteristics. Particularly, one 3D structure achieves a quantitative agreement with the experimental spectrum, which clearly rationalizes the coexistence of two types of interfacial environments. Our method may find general applications in the studies of layered materials.

Electron-electron ($e\text{−}e$) and electron-phonon ($e$-ph) interactions are challenging to describe in correlated materials, where their joint effects govern unconventional transport, phase transitions, and superconductivity. Here we combine first-principles $e$-ph calculations with dynamical mean-field theory (DMFT) as a step toward a unified description of $e\text{−}e$ and $e$-ph interactions in correlated materials. We compute the $e$-ph self-energy using the DMFT electron Green's function and combine it with the $e\text{−}e$ self-energy from DMFT to obtain a Green's function including both interactions. This approach captures the renormalization of quasiparticle dispersion and spectral weight on equal footing. Using our method, we study the $e$-ph and $e\text{−}e$ contributions to the resistivity and spectral functions in the correlated metal ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$. In this material, our results show that $e\text{−}e$ interactions dominate transport and spectral broadening in the temperature range we study ($50–310$ K), while $e$-ph interactions are relatively weak and account for only $\sim 10\%$ of the experimental resistivity. We also compute effective scattering rates and find that the $e\text{−}e$ interactions result in scattering several times greater than the Planckian value $k_{B}T$, whereas $e$-ph interactions are associated with scattering rates lower than $k_{B}T$. Our work demonstrates a first-principles approach to combine electron dynamical correlations from DMFT with $e$-ph interactions in a consistent way, advancing quantitative studies of correlated materials.

We examine the effects of Pt vacancies on the magnetotransport properties of Weyl semimetal candidate GdPtSb films, grown by molecular beam epitaxy on $c$-plane sapphire. Rutherford backscattering spectrometry and x-ray diffraction measurements suggest that phase-pure ${\mathrm{GdPt}}_x\mathrm{Sb}$ films can accommodate up to $15\%$ of Pt vacancies ($x=0.85$), which act as acceptors, as measured by the Hall effect. Two classes of electrical transport behavior are observed. Pt-deficient films display metallic temperature-dependent resistivity ($d\rho /dT>0$). The longitudinal magnetoresistance (LMR, magnetic field $\mathbf{B}$ parallel to electric field $\mathbf{E}$) is more negative than transverse magnetoresistance (TMR, $\mathbf{B}\perp \mathbf{E}$), consistent with the expected chiral anomaly for a Weyl semimetal. The combination of Pt-vacancy disorder and doping away from the expected Weyl nodes, however, suggests that conductivity fluctuations may explain the negative LMR rather than chiral anomaly. Samples closer to stoichiometry display the opposite behavior: semiconductorlike resistivity ($d\rho /dT>0$) and more negative TMR than LMR. Hysteresis and other nonlinearities in the low-field Hall effect and magnetoresistance suggest that spin-disorder scattering and possible topological Hall effect may dominate the near-stoichiometric samples. Our findings highlight the complications of transport-based identification of Weyl nodes but point to possible topological spin textures in GdPtSb.

Nitride perovskites are an emerging class of materials that have been predicted to display a range of interesting physics and functional properties, but they are highly underexplored due to the difficulty of synthesizing oxygen-free nitrides. ${\mathrm{LaWN}}_3$, recently reported as the first oxygen-free nitride perovskite, exhibited polar symmetry and a large piezoelectric coefficient. However, the predicted ferroelectric switching was hindered by a large leakage current, which motivates better understanding of the electronic structure and optical properties of this material. In this article, we study the structure and optoelectronic properties of thin film ${\mathrm{LaWN}}_3$ in greater detail, employing combinatorial techniques to correlate these properties with cation stoichiometry. We report a two-step synthesis method that utilizes a more common radio frequency substrate bias instead of a nitrogen plasma source, yielding nanocrystalline films that are subsequently crystallized by ex situ annealing. We investigate the crystal structure and composition of the combinatorial films produced by this method, finding polycrystalline La-rich films and highly textured W-rich films. The measured optical absorption onset (2.5–3.5 eV) and temperature- and magnetic field-dependent resistivity (0.0055–2 $\mathrm{\Omega }$ cm for W-rich and La-rich ${\mathrm{LaWN}}_3$, respectively) are consistent with semiconducting behavior and are highly sensitive to cation stoichiometry, which may be related to amorphous impurities: metallic W or ${\mathrm{WN}}_x$ in W-rich samples and insulating ${\mathrm{La}}_2{\mathrm{O}}_3$ in La-rich samples. The fractional magnetoresistance is linear and small, consistent with defect scattering, and a W-rich sample has n-type carriers with high densities and low mobilities. We demonstrate a photoresponse in ${\mathrm{LaWN}}_3$: The resistivity of a La-rich sample is enhanced by $\sim 28$% under illumination and at low temperature, likely due to a defect trapping mechanism. The physical properties of ${\mathrm{LaWN}}_3$ are highly sensitive to cation stoichiometry, like many oxide perovskites, which therefore calls for precise composition control to utilize the interesting properties observed in this nitride perovskite.

Halide pervoskites are an important class of semiconducting materials that hold great promise for optoelectronic applications. In this work we investigate the relationship between vibrational anharmonicity and dynamic disorder in this class of solids. Via a multiscale model parametrized from first-principles calculations, we demonstrate that the non-Gaussian lattice motion in halide perovskites is microscopically connected to the dynamic disorder of overlap fluctuations among electronic states. This connection allows us to rationalize the emergent differences in temperature-dependent mobilities of prototypical ${\mathrm{MAPbI}}_3$ and ${\mathrm{MAPbBr}}_3$ compounds across structural phase transitions, in agreement with experimental findings. Our analysis suggests that the details of vibrational anharmonicity and dynamic disorder can complement known predictors of electronic conductivity and can provide structure-property guidelines for the tuning of carrier transport characteristics in anharmonic semiconductors.

Ammonium sulphate ${\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4$ (AS) has recently been shown to display giant barocaloric and electrocaloric effects when its paraelectric-ferrielectric transition at $\sim 225$ K is driven by hydrostatic pressure or an electric field, respectively. Important aspects of the structural evolution in this context are coupling of strain to molecular librational modes, distortions, and rotations of ${{\mathrm{NH}}_4}^{+}$ and ${{\mathrm{SO}}_4}^{2-}$ groups, and to changes in hydrogen bonding. Resonant ultrasound spectroscopy (RUS) has been used to reveal subtle elastic and anelastic relaxation processes of single crystals of AS through the temperature interval 5–300 K that are indicative of (i) coupling of strain to the driving order parameter, modified by a transformation microstructure, and (ii) of hysteretic effects that are attributed to different dynamics of displacive and order/disorder components of the phase transition. At high temperatures, partial chemical decomposition results in the formation of triammonium hydrogen disulphate ${\left({\mathrm{NH}}_4\right)}_3\mathrm{H}{\left({\mathrm{SO}}_4\right)}_2$ (AHS) which displays elastic and anelastic anomalies associated with phase transitions at $\sim 265$, 139, 132, and 72 K. Freezing of defects coupled with strain occurs at temperatures below $\sim 35$ K in both AS and AHS.

In situ synthesized semiconductor/superconductor hybrid structures became an important material platform in condensed matter physics. Their development enabled a plethora of novel quantum transport experiments with focus on Andreev and Majorana physics. The combination of InAs and Al has become the workhorse material and has been successfully implemented in the form of one-dimensional structures and two-dimensional electron gases. In contrast to the well-developed semiconductor parts of the hybrid materials, the direct effect of the crystal nanotexture of Al films on the electron transport still remains unclear. This is mainly due to the complex epitaxial relation between Al and the semiconductor. Here, we present characterization of Al thin films grown on shallow InAs two-dimensional electron gas systems by molecular beam epitaxy. Using a growth approach based on an intentional roughening of the epitaxial interface, we demonstrate growth of grain-boundary-free Al. We show that the implemented roughening does not negatively impact either the electron mobility of the two-dimensional electron gas or the basic superconducting properties of the proximitized system. This is an important step in understanding the role of properties of the InAs/Al interface in hybrid devices. Ultimately, our results provide a growth approach to achieve a high-degree of epitaxy in lattice-mismatched materials.