To take full advantage of twisted bilayers of graphene or other two-dimensional materials, it is essential to precisely control the twist angle between the stacked layers, as this parameter determines the properties of the heterostructure. In this context, a growth routine using borazine as a surfactant molecule on SiC(0001) surfaces has been reported, leading to the formation of high-quality epitaxial graphene layers that are unconventionally oriented, i.e., aligned with the substrate lattice $\left(\mathrm{G}\text{−}R{0}^{\circ }\right)$ [Bocquet et al. Phys. Rev. Lett. 125, 106102 (2020)]. Since the $\mathrm{G}\text{−}R{0}^{\circ }$ layer sits on a buffer layer, also known as zeroth-layer graphene (ZLG), which is rotated ${30}^{\circ }$ with respect to the SiC substrate and still covalently bonded to it, decoupling the $\mathrm{ZLG}\text{−}R{30}^{\circ }$ from the substrate can lead to high-quality twisted bilayer graphene (tBLG). Here, we report the decoupling of $\mathrm{ZLG}\text{−}R{30}^{\circ }$ by increasing the temperature during annealing in a borazine atmosphere. While this converts $\mathrm{ZLG}\text{−}R{30}^{\circ }$ to $\mathrm{G}\text{−}R{30}^{\circ }$ and thus produces tBLG, the growth process at elevated temperature is no longer self-limiting, so that the surface is covered by a patchwork of graphene multilayers of different thicknesses. We find a 20% coverage of tBLG on ZLG, while on the rest of the surface tBLG sits on one or more additional graphene layers. In order to achieve complete coverage with tBLG only, alternative ways of decoupling the ZLG, e.g., by intercalation with suitable atoms, may be advantageous.

Quantum transport in graphene nanoribbons (GNRs) is essential for advancing electronic and quantum device applications. In particular, the Coulomb blockade effect in GNR-based devices holds promise for quantum computing, single-electron transistors, and highly sensitive charge detectors. To investigate electron transport characteristics at the nanoscale, we synthesized and tailored suspended CVD graphene nanoribbons with widths ranging from 705 nm to 50 nm and lengths of approximately 150 nm. While bottom-up synthesis offers precise control over edge structure, tailoring graphene into narrower strips significantly enhances edge disorder and quantum confinement effects. Our study focuses on fabricated GNRs with sub-100 nm widths to explore quantum interference-induced localization and Coulomb blockade phenomena. We observe a transition in transport behavior from magnetoresistance fluctuations associated with quantum interference effects—such as weak localization and universal conductance fluctuations (UCF)—to single-electron transport, characterized by Coulomb blockade effects. Notably, Coulomb blockade behavior is particularly evident in narrow nanoribbons (50 nm width), as seen in diamondlike structures in source-drain voltage versus back-gate voltage characteristics. The phase coherence length, extracted using weak localization theory, varies from 60 nm to 220 nm as the ribbon width is reduced from 700 nm to 50 nm at 2 K. Importantly, our findings indicate that nanoscale GNRs exhibit Coulomb blockade behavior due to enhanced ribbon disorder and edge roughness. These results provide valuable insights into quantum transport mechanisms in graphene nanoribbons and offer significant advantages for the design and application of graphene-based electronic and quantum devices.

Optoelectronic devices operate under continuous thermal stress that may influence both long-term stability and optical properties of the active material. It is therefore useful to know the elastic properties of the active materials. In general, the elastic constants of a material may be deduced by the measurement of the speed of sound in that material. In this work, we report on the measurements of the speed of sound in three lead-free halide perovskites, namely, the inorganic ${\mathrm{Cs}}_3{\mathrm{Bi}}_2{\mathrm{I}}_9$ and the hybrid ${\mathrm{MA}}_3{\mathrm{Bi}}_2{\mathrm{I}}_9$ and ${\mathrm{MA}}_3{\mathrm{Sb}}_2{\mathrm{I}}_9$, by means of femtosecond transient optical reflectivity that shows oscillations of the signal intensity that are related to the strain field caused by the photoexcitation of electron-hole pairs. The values of the speed of sound thus obtained have allowed us to extract the elastic constant, $c_{11}$ , along the propagation direction of the light. The $c_{11}$ values indicate a lower stiffness of the hybrid materials, an important aspect when designing optoelectronic devices.

We present a ferromagnetic material with full spin-polarization, but with zero net moment (a magnetic moment compensation point). The compensation of the magnetic moment stems from the combination of spin-dominated and orbital-dominated lanthanide ions in solid-solutions of the rare-earth mononitrides and is robust over a range of temperatures but limited to a critical composition.

The interplay between half-metallic ferromagnetism and spin-orbit coupling within the inversion-symmetry-broken structure of half-Heuslers provides an ideal platform for various spintronics functionalities. Taking advantage of good lattice matching, it is highly desired to epitaxially integrate promising Heuslers into III-V semiconductor-based devices. PtMnSb is one of the first half-Heuslers predicted to be an above-room-temperature half-metal with large spin orbit coupling, however, its half-metallicity and potential as a spintronics material has remained elusive due to lack of high quality samples. Here we demonstrate epitaxial growth of single crystal PtMnSb(001) film on GaSb(001) substrates using molecular beam epitaxy. Direct observation of the band structure via angle-resolved photoemission spectroscopy and many-body perturbation theory within the quasi-particle self-consistent GW approximation (QPGW) reveals that PtMnSb hosts rather a near-half-metallic state with both spin bands crossing the Fermi level and with high spin polarization over 90%. Temperature dependence of magnetization also shows an anomalous enhancement below 60 K, which can be associated with the development of such a near-half-metallic state at low temperatures. Epitaxial growth of high-crystalline PtMnSb on a III-V paves the way for systematic clarification of its spin transport properties with fine-tuning of strain in heterostructure devices.

Using spin-orbit torque to realize field-free switching of magnetic moments in spintronic devices has attracted extensive attention. Here, we observed, in $\mathrm{SrIr}{\mathrm{O}}_3$/$\mathrm{Sr}{\mathrm{Mn}}_{0.35}{\mathrm{Ir}}_{0.65}{\mathrm{O}}_3$ heterostructures, that the spin-Hall effect in the $\mathrm{SrIr}{\mathrm{O}}_3$ layer produced a spin-orbit torque strong enough to switch the magnetization in the adjacent $\mathrm{Sr}{\mathrm{Mn}}_{0.35}{\mathrm{Ir}}_{0.65}{\mathrm{O}}_3$ layer with perpendicular magnetic anisotropy. The magnetic easy axis tilting helps to realize a field-free magnetization switching in the heterostructure with a critical current density as low as $1.20\times {10}^6\mathrm{A}\mathrm{c}{\mathrm{m}}^{-2}$. There is a dampinglike torque in this all-oxide heterostructure with a high efficiency about $82.9\times {10}^{-6}\mathrm{Oe}{\mathrm{A}}^{-1}\mathrm{c}{\mathrm{m}}^2$. These findings may help to explore the potential applications of perovskite material in highly efficient spintronic devices.

$\mathrm{Ba}{\mathrm{Ni}}_2{\mathrm{As}}_2$, a structural analog to the iron-based parent compound ${\mathrm{BaFe}}_2{\mathrm{As}}_2$, offers a unique platform to study the interplay between superconductivity, charge density waves, and, possibly, electronic nematicity. Here, we report on the growth and characterization of ${\mathrm{Ba}}_{1-x}{\mathrm{Ca}}_x{\mathrm{Ni}}_2{\mathrm{As}}_2$ single crystals with $0\le x\le 0.1$, using a combination of x-ray diffraction, diffuse x-ray scattering, heat capacity, and electronic transport measurements. Our results demonstrate that calcium substitution affects the structural, electronic, and thermodynamic properties of $\mathrm{Ba}{\mathrm{Ni}}_2{\mathrm{As}}_2$ in a way that is strongly reminiscent of moderate hydrostatic pressures albeit with marked differences. In particular, Ca substitution efficiently suppresses both the triclinic structural transition and the associated commensurate charge density wave formation, while increasing the superconducting transition temperature. We found that the substitution range in which the crystals remain homogeneous is limited with concentrations $x\ge 0.04$ exhibiting intense diffuse x-ray scattering indicative of stacking fault formation, which, despite the preserved integrity of the NiAs layers, prevents investigation up to concentrations where chemical pressure is expected to completely suppress the structural instability.

We demonstrate the possibility of growing textured $\mathrm{L}{\mathrm{a}}_{2/3}\mathrm{S}{\mathrm{r}}_{1/3}\mathrm{Mn}{\mathrm{O}}_3$ (LSMO) thin films on silicon substrates with magneto-optical and optical properties comparable to high-quality epitaxial layers grown on bulk $\mathrm{SrTi}{\mathrm{O}}_3$ (STO). The pulsed laser deposition growth of LSMO is achieved by a two-dimensional nanosheet (NS) seed layer of $\mathrm{C}{\mathrm{a}}_2\mathrm{N}{\mathrm{b}}_3{\mathrm{O}}_{10}^{-}$ (CNO) inducing epitaxial stabilization of LSMO films. The resulting 40 nm thick layer possesses a higher Curie temperature and a lower overall magnetization than an LSMO layer with a similar thickness on STO. Spectra of the full permittivity tensor were calculated from optical and magneto-optical measurements. Spectral dependencies of both the diagonal and off-diagonal elements share many similarities between the LSMO/NS/Si and LSMO/STO samples. These similarities indicate comparable electronic structures of the layers and demonstrate comparable optical quality of textured LSMO on NS/Si and epitaxial LSMO on STO.

The capability of an Ir spacer to modulate interlayer exchange coupling (IEC) and perpendicular magnetic anisotropy in a synthetic antiferromagnetic (SAF) is critical for practical applications. Here, we present a comprehensive analysis on the dual roles of Ir for the modulation of IEC and the generation of spin current in SAF structures with symmetric and asymmetric perpendicular ferromagnetic layers. The results reveal that the Ir thickness and symmetry of the ferromagnetic layer are pivotal in tuning the IEC strength. Strikingly, a critical Ir thickness of 1.4 nm is identified: Beyond this threshold, full magnetization switching is achieved, whereas a thinner Ir layer results in partial or nonswitching due to insufficient spin current. This switching behavior is mapped using a phase diagram correlating Ir thickness with IEC states, which is further corroborated by polar magneto-optical Kerr effect microscopy. The dampinglike spin-orbit torque efficiency $[1.16-1.36\text{Oe}/({10}^6\mathrm{A}/{\text{cm}}^2)]$ and the spin Hall angle $(\sim 0.03)$ are quantitatively characterized, which is close to the spin Hall angle of Ir. Notably, the symmetric SAF structure exhibits superior switching performance compared to the asymmetric structure, a result attributed to the elimination of spin current cancellation between Pt and Ir layers. This paper significantly advances our understanding of SAF systems and provides essential guidelines for developing high-efficiency spintronic devices.

Originating from the coupling of excess charge with the ionic vibrations, polaron formation is a pervasive phenomenon that has been observed in different types of materials. Depending on their spatial extensions, these quasiparticles have conventionally been categorized into small or large polarons typically for polarizable materials with major implications on their physical properties such as charge mobilities. However, a lack of comprehensive and mechanistic understanding of polarons has limited the ability to systematically control the sizes of these quasiparticles. Herein, we employ density functional theory-based calculations to show that hydrostatic pressure can be used as a tool to control the size of polaron wave functions in some lithium halides. More specifically, we show that a transition from a small to a large hole polaron is achievable in lithium bromide through the application of pressure, which can drastically improve their charge mobilities. We attribute the increase in the size of hole polarons to the systematically increasing contributions from states at the top of the valence band (and their increased localization near the Brillouin zone center) with rising pressures. Moreover, our spectral analysis shows that contrary to the traditional theories that predict the coupling of the excess charge primarily with optical phonons, contributions from low-wave vector acoustic modes dominate the large hole polarons at higher pressures in lithium bromide. Our study provides critical insights into the intrinsic mechanisms controlling the size of polarons in pressurized lithium halides, thus opening up an enticing platform for manipulating the material functionalities dictated by polarons in polar semiconductors and insulators.

Transition metal dichalcogenides exhibit many unexpected properties including two-dimensional (2D) superconductivity as the interlayer coupling being weakened upon either layer-number reduction or chemical intercalation. Here, we report the realization of 2D superconductivity in the newly synthesized niobium dichalcogenides-based bulk superlattices ${\mathrm{Ba}}_{0.75}{\mathrm{ClNbS}}_2$ and ${\mathrm{Ba}}_{0.75}{\mathrm{ClNbSe}}_2$, which consist of the alternating stacking of monolayer $H\text{−}{\mathrm{NbS}}_2$ (or $H\text{−}{\mathrm{NbSe}}_2$) and monolayer inorganic insulator spacer ${\mathrm{Ba}}_{0.75}\mathrm{Cl}$. Magnetic susceptibility and resistivity measurements show that both superlattices belong to type-II superconductor with $T_c$ of 1 K and 1.25 K, respectively. Intrinsic 2D superconductivity is confirmed for both compounds below a Berezinskii-Kosterlitz-Thouless transition and a large anisotropy of the upper critical field. Furthermore, the upper critical field along $ab$ plane $\left(H_{c2}^{\parallel ab}\right)$ exceeds the Pauli limit $\left({\mu }_0{H}_p\right)$ in ${\mathrm{Ba}}_{0.75}{\mathrm{ClNbSe}}_2$, highlighting the influence of spin-orbit interactions. Our results establish a generic method for realizing the 2D superconducting properties in bulk superlattice materials.

In valley electronic applications, transition metal dichalcogenides such as ${\mathrm{MoS}}_2$ are the most attractive candidates. Therefore, controlling their valley properties by doping, surface modification, and interface construction would be of great significance. However, these chemical or physical methods often destroy the valley degree of freedom, rendering it meaningless. In this theoretical paper, we suggest that oxygen modification not only modulates the band structures of monolayer ${\mathrm{MoS}}_2$ without destroying its valley properties but also imparts valley-contrasting properties to bilayer ${\mathrm{MoS}}_2$. The effects of oxygen coverage on valleys are also investigated. These results are helpful in the design of valley devices.

${\mathrm{As}}_2{\mathrm{Te}}_3$ is a layered chalcogenide that has garnered increasing recent interest; in particular, its metastable $\beta \text{−}{\mathrm{As}}_2{\mathrm{Te}}_3$ allotropic phase due to its relationship to other tetradymite (space group $R\overline{3}m$) chalcogenides which act as good thermoelectrics. Upon cooling below room temperature, $\beta \text{−}{\mathrm{As}}_2{\mathrm{Te}}_3$ transitions to ${\beta }^{\prime }\text{−}{\mathrm{As}}_2{\mathrm{Te}}_3$ and exhibits a notable increase in the resistivity which has been attributed to a transition to a charge density wave state. In this work we explore how Cu and Ge doping influences the electronic properties of $\beta \text{−}{\mathrm{As}}_2{\mathrm{Te}}_3$ and ${\beta }^{\prime }\text{−}{\mathrm{As}}_2{\mathrm{Te}}_3$. Samples with doping values $\mathrm{x}\lesssim 0.3$ for ${\mathrm{Ge}}_x{\mathrm{As}}_2{\mathrm{Te}}_3$ and $\mathrm{x}\lesssim 0.2$ for ${\mathrm{Cu}}_x{\mathrm{As}}_2{\mathrm{Te}}_3$ were synthesized and investigated by microwave plasma atomic emission spectroscopy, powder x-ray diffraction, differential scanning calorimetry, heat capacity, resistivity, and room temperature optical reflectance measurements. We use our results to create a temperature-doping phase diagram and show that doping with Ge can stabilize the $\beta$ phase and eliminate the low temperature ${\beta }^{\prime }\text{−}{\mathrm{As}}_2{\mathrm{Te}}_3$ phase. The optical reflectance is analyzed to extract information on the effectiveness of introducing charge carriers from which we conclude that while Ge adds carriers monotonically with doping for $\mathrm{x}\lesssim 0.2$, the effect of Cu doping is more complicated, exhibiting two regimes.

Crystal symmetries can enforce all bands of a material to be topological, a property that is commonly referred to as “supertopology.” Here, we determine the symmetry-enforced ${\mathbb{Z}}_2$ supertopologies of nonmagnetic centrosymmetric materials with weak and strong spin-orbit coupling (SOC). For weak (i.e., negligible) SOC, crystal symmetries can enforce Dirac nodal lines protected by a $\pi$-Berry phase, while for strong SOC, crystal symmetries can give rise to nontrivial weak ${\mathbb{Z}}_2$ topologies in two-dimensional subplanes of the three-dimensional Brillouin zone. We catalog all centrosymmetric space groups whose symmetries enforce these ${\mathbb{Z}}_2$ supertopologies. Suitable material realizations are identified and experimental signatures of the supertopologies, such as quantum spin Hall states, are discussed.

Noncontacting and nondestructive control of geometric phase in conventional semiconductors plays a pivotal role in various applications. In the current work, we present a theoretical and computational investigation of terahertz (THz) light-induced phase transformation of conventional binary semiconducting compounds among different structures such as rock salt, zinc-blende, wurtzite, and hexagonal phases. Using MgS and MgSe as prototypical examples, we perform anharmonic phonon-mediated calculations and reveal large contrasting lattice-contributed dielectric susceptibility in the THz regime. We then construct a THz-induced phase diagram under intermediate temperature and reveal rock salt to hexagonal and then wurtzite structure transformations with increasing light intensity. This does not require a high-temperature environment as observed in traditional experiments. The low energy barrier suggests that the phase transition kinetics can be fast, and the stable room temperature phonon dispersions guarantee their nonvolatile nature. Furthermore, we disclose the phononic hyperbolicity with strong anisotropic THz susceptibility components, which serves as a natural hyperbolic material with a negative refractive index. Our work suggests the potential to realize metastable hidden phases using noninvasive THz irradiation, which expands the conventional pressure-temperature ($P$–$T$) phase diagram by adding light as an additional control factor.

Using a first-principles study, we investigate the systematic of $n$-type and $p$-type ${\mathrm{LaBO}}_3/{\mathrm{SrIrO}}_3$ superlattices with B = Mn, Fe, Co, Ni moving from left to right of the 3d transition metal row of the periodic table. Our study unravels a clear trend in terms of interfacial charge transfer, and electronic, magnetic, and topological properties. For $p$-type superlattices, the charge is transferred to the ${\mathrm{SrIrO}}_3$ block for all four systems with the charge transfer strength dictated by B-Ir covalency. However, a marked distinction occurs for superlattices of type $n$, with interfacial charge transfer to the ${\mathrm{LaBO}}_3$ block for B = Co, Ni, having a nominal occupancy $d$ greater than ${\mathrm{Ir}}^{4+}$, and to the ${\mathrm{SrIrO}}_3$ block for B = Fe, Mn, having a nominal occupancy $d$ smaller than or equal to that of ${\mathrm{Ir}}^{4+}$. This makes the ${\mathrm{SrIrO}}_3$ essentially nonmagnetic for $n$-type ${\mathrm{LaFeO}}_3/{\mathrm{SrIrO}}_3$ and ${\mathrm{LaMnO}}_3/{\mathrm{SrIrO}}_3$. The band structure of magnetic ${\mathrm{SrIrO}}_3$ block with ferromagnetic Ir-Ir exchange and spin-orbit coupling effect supports the $C=2$ double Weyl points, giving rise to appreciable values of intrinsic anomalous Hall conductivity for the $n$-type as well as $p$-type ${\mathrm{LaCoO}}_3/{\mathrm{SrIrO}}_3$ and ${\mathrm{LaNiO}}_3/{\mathrm{SrIrO}}_3$. Our calculations further predict only $p$-type ${\mathrm{LaMnO}}_3/{\mathrm{SrIrO}}_3$ and ${\mathrm{LaFeO}}_3/{\mathrm{SrIrO}}_3$ to exhibit anomalous Hall conductivity, which is expected to be heavily suppressed for ${\mathrm{LaFeO}}_3/{\mathrm{SrIrO}}_3$ due to the weakening of Ir-Ir ferromagnetic exchange arising from the proximity to antiferromagnetic ${\mathrm{LaFeO}}_3$ block. Our comprehensive study should provide a microscopic understanding of some of the recent experimental observations and will serve as a guide to future experiments.

The present work addresses the simulation of pore emptying during the drying of battery electrodes. For this purpose, a model based on the multiphase-field (MPF) method is used, since it is an established approach for modeling and simulating multiphysical problems. A model based on phase fields is introduced that takes into account fluid flow, capillary effects, and wetting behavior, all of which play an important role in drying. In addition, the MPF method makes it possible to track the movement of the liquid-air interface without computationally expensive adaptive mesh generation. The presented model is used to investigate pore emptying in real hard carbon microstructures. For this purpose, the microstructures of real dried electrodes are used as input for the simulations. The simulations performed here demonstrate the importance of considering the resolved microstructural information compared to models that rely only on statistical geometry parameters such as pore size distributions. The influence of various parameters such as different microstructures, fluid viscosity, and the contact angle on pore emptying are investigated. In addition, this work establishes a correlation between the capillary number and the breakthrough time of the solvent as well as the height difference of the solvent front at the time of breakthrough. The results indicate that the drying process can be optimized by doping the particle surface, which changes the contact angle between the fluids and the particles.