Hydrogen is a ubiquitous impurity that deteriorates the metal/oxide interface, causing challenges such as current leakage and blistering. Here, we uncover the mechanisms behind hydrogen-induced damage at the prototypical $\mathrm{Al}/\mathrm{A}{\mathrm{l}}_2{\mathrm{O}}_3$ interface. The precursor that we identify is charge trapping at the interface, which facilitates hydrogen segregation to the interface plane as ${\mathrm{H}}^{-}$. Presence of hydrogen increases aluminum vacancy concentration at the interfacial metal and oxide planes. Each Al vacancy can trap multiple hydrogen atoms. As a result, the interfacial aluminum vacancy and hydrogen concentrations increase by orders of magnitude. Additionally, hydrogen behaves as an $n$-type dopant and increases electronic conductivity at the oxide layer adjacent to the interface by forming ${\mathrm{H}}^{+}$, and the $\left[{\mathrm{V}}_{\mathrm{Al}}\text{−}\mathrm{H}\right]$ complex is the predominant defect at this layer. These findings provide the precursor mechanisms of hydrogen-induced damage at the metal-oxide interfaces and have implications for advancing $\mathrm{Al}/\mathrm{A}{\mathrm{l}}_2{\mathrm{O}}_3\text{−}\mathrm{based}$ coatings and electronic devices.

A coarse-grained spring network model is proposed for the prediction of the mechanical response of metallic glasses as a function of the microstructure prior to loading. This model describes the mechanical response of metallic glasses using a network of parallel springs that can break and reform, mimicking atomic rearrangements during deformation. We compare predictions of the spring network model for stress versus strain to results from numerical simulations of athermal quasistatic, uniaxial tensile deformation of ${\mathrm{Cu}}_{50}{\mathrm{Zr}}_{50}$ metallic glasses using Lennard-Jones (LJ) and embedded atom method (EAM) atomic interactions. We show that both the LJ and EAM models possess qualitatively similar stress $\sigma$ versus strain $\gamma$ curves. By specifying five parameters [ultimate strength, strain at ultimate strength, slopes of $\sigma \left(\gamma \right)$ at $\gamma =0$ and at large strain, and strain at fracture where $\sigma =0]$, we demonstrate that the spring network model can accurately describe the form of the stress-strain curves during uniaxial tension for the computational studies of ${\mathrm{Cu}}_{50}{\mathrm{Zr}}_{50}$, as well as recent experimental studies of several Zr-based metallic glasses.

Transition metal oxides are known to have a strong interplay of many degrees of freedom giving rise to their rich phase diagrams with competing ground states. The Mott material ${\mathrm{V}}_2{\mathrm{O}}_3$ hosting a room- and low-temperature metal-insulator transition is a great example where electronic, structural and magnetic ordering are the directors at play. By combining first-principle calculations and Raman spectroscopy, we study the phonon dynamics of ${\mathrm{V}}_2{\mathrm{O}}_3$ to gain further understanding in the interplay of these ordering mechanisms driving the transitions. First-principle calculations show that the Raman active vibrations correspond to the structural distortions occurring in the phase diagram. Additionally, Raman spectroscopy is performed on a unique series of epitaxial strained $1.5\%$ Cr-doped ${\mathrm{V}}_2{\mathrm{O}}_3$ thin films, where both paramagnetic insulating, metallic, as well as intermediate electronic states are stabilized. This has led to identifying the importance of the local V-V dimer elongation that drives both the room- and low-temperature MIT in ${\mathrm{V}}_2{\mathrm{O}}_3$ compounds.

We present Nb thin films deposited in situ on GaAs by combining molecular beam epitaxy and magnetron sputtering within an ultrahigh vacuum cluster. Nb films deposited at varying power, and a reference film from a commercial system, are compared. The results show clear variation between the in situ and ex situ deposition which we relate to differences in magnetron sputtering conditions and chamber geometry. The Nb films have critical temperatures of around $9\mathrm{K}$ and critical perpendicular magnetic fields of up to $B_{c2}=1.4\mathrm{T}$ at $4.2\mathrm{K}$. From STEM images of the GaAs-Nb interface we find the formation of an amorphous interlayer between the GaAs and the Nb for both the ex situ and in situ deposited material.

Single crystals of HoPtSn and its nonmagnetic analog LuPtSn are grown by flux method. They crystallize in the ${\mathrm{Fe}}_2\mathrm{P}$-type hexagonal structure with a distorted kagome lattice of rare-earth ions. Magnetic susceptibility measurements confirm that HoPtSn exhibits two antiferromagnetic transitions at 7.3 and 2.4 K, consistent with previous neutron-diffraction studies. Our detailed magnetic and electrical studies indicate that the transition at 2.4 K is a first-order magnetic transition, which is supported by the hysteresis loops observed in the temperature-dependent magnetic susceptibility and resistivity curves. In the case of $H\left|\right|c$, the magnetic states of HoPtSn are sensitive to applied magnetic fields. The first-order magnetic transition can also be induced by magnetic fields, which is evidenced by the hysteresis loops observed from the isothermal magnetization and magnetoresistance curves. The magnetic phase diagram is depicted for the case of $H\left|\right|c$. In the case of $H\perp c$, the antiferromagnetic transitions are relatively robust against magnetic fields up to 9 T.

Metal $d$-electron oxides having an odd number of electrons per cell should exhibit band degeneracy at the Fermi energy, making them, in band theory, formally metallic. In many cases, however, these are false metals, as evidenced by the observation that many $\mathrm{AB}{\mathrm{O}}_3$ oxide perovskites with a magnetic $3d$ B atom are observed to be insulators both below and above the Néel temperature. These inconsistencies between experimental observation and expectation have historically been resolved by invoking degeneracy-breaking physics, based largely on pure electron effects, such as strong interelectronic correlation for $d$-electron compounds (the Mott mechanism). Such explanations generally consider the microscopic lattice or magnetic degrees of freedom (m-DOFs) as largely passive spectators, not causes of the formal metal being an insulator. However, it has long been known that $\mathrm{AB}{\mathrm{O}}_3$ perovskites can manifest an arrangement of m-DOFs in the form of octahedral tilting, bond dimerization, Jahn-Teller distortions, and ordering of local magnetic moments. It appears reasonable that such structural and magnetic local degrees of freedom need to be allowed to compete with purely electronic strong correlation. To answer this question, we explored a range of $d$-electron oxide perovskites exemplified by the archetypes $\mathrm{LaTi}{\mathrm{O}}_3$, $\mathrm{LaV}{\mathrm{O}}_3$, $\mathrm{SrMn}{\mathrm{O}}_3$, and $\mathrm{LaMn}{\mathrm{O}}_3$ with 1, 2, 3, or 4 $d$ electrons, respectively. Using a mean-field-like electronic structure method (here, density functional theory), we find that a combination of magnetic symmetry breaking (SB) with structural distortions can account for insulating band gaps in this series while correctly predicting for the control case, an intrinsic paramagnetic metal in $\mathrm{SrV}{\mathrm{O}}_3$, as SB is insufficiently strong to remove the degeneracy. This indicates that calculating quantitatively local magnetic and positional SB motifs in unit cells that avoid averaging at the outset over the low-symmetry motifs can provide consistent trends in a Mott transition without Mott U.

Ferromagnetic (FM) systems have attracted interest because a variety of novel phases can arise near a quantum critical point (QCP) where the FM order is suppressed to zero temperature. The Kondo lattice compound $\mathrm{CePt}{\mathrm{Al}}_4{\mathrm{Si}}_2$ is a candidate FM quantum critical material that becomes the FM state below $T_{\mathrm{c}}=3.7$ K, but the possibility of the quantum criticality has yet to be studied. Here, we report a comprehensive temperature-pressure phase diagram of $\mathrm{CePt}{\mathrm{Al}}_4{\mathrm{Si}}_2$ using a systematic transport investigation. The FM compound $\mathrm{CePt}{\mathrm{Al}}_4{\mathrm{Si}}_2$ goes through three distinct ground states under pressure. In the low-pressure FM state, $T_{\mathrm{c}}$ is gradually suppressed by pressure and a smooth extrapolation of $T_{\mathrm{c}}\left(P\right)$ reaches zero temperature at a critical pressure of 7.0 GPa. However, the suppression of $T_{\mathrm{c}}$ is interrupted by the appearance of another crossover temperature $T^{*}$ in the intermediate pressure range of 5.4–11.7 GPa, which shows a nonmonotonic pressure dependence. A fully coherent Kondo screened state is observed in the high-pressure regime. These results suggest that a FM QCP is avoided under pressure in the disordered Kondo system $\mathrm{CePt}{\mathrm{Al}}_4{\mathrm{Si}}_2$.

Thermoelectric properties were determined in self-substituted ${\mathrm{Fe}}_2\mathrm{VAl}$ Heusler alloys $({\mathrm{Fe}}_2{\mathrm{V}}_{1+x}{\mathrm{Al}}_{1-x}$, $-0.1<x<0.1)$, pursuing the goal of their optimization. A parabolic band model fitted to experimental plots of Seebeck coefficient versus charge carrier concentration at 220 K yielded values of the density of states (DOS) effective mass, $m_v^{*}=3.2m_e$ and $m_c^{*}=13.7m_e$ for the holes and electrons, respectively ($m_e$ is the bare electron mass). The measured Sommerfeld coefficient of the electronic specific heat is consistently smaller in $p$-type ${\mathrm{Fe}}_2{\mathrm{V}}_{0.92}{\mathrm{Al}}_{1.08}$ $({\gamma }_p=7.8\mathrm{mJ}\mathrm{mo}{\mathrm{l}}^{-1}{\mathrm{K}}^{-2})$ than in $n$-type ${\mathrm{Fe}}_2{\mathrm{V}}_{1.07}{\mathrm{Al}}_{0.93}$ $({\gamma }_n=11.5\mathrm{mJ}\mathrm{mo}{\mathrm{l}}^{-1}{\mathrm{K}}^{-2})$. First-principles calculations of the DOS lead to the theoretical values $m_v^{*}=2.4m_e$, $m_c^{*}=13.0m_e$, and $\frac{{\gamma }_n}{{\gamma }_p}=1.9$, in good agreement with the experimental values. These direct comparisons of calculations with experiments unambiguously show that the heavy electrons arise from flat Fe $e_g$ conduction bands. Calculations of the optimum thermoelectric power factor $\left(PF\right)$ show that it is nearly reached experimentally in $n$-type ${\mathrm{Fe}}_2{\mathrm{V}}_{1.03}{\mathrm{Al}}_{0.97}$ ($PF=6.6\mathrm{mW}{\mathrm{m}}^{-1}{\mathrm{K}}^{-2}$ for $n=1.4\times {10}^{21}\mathrm{c}{\mathrm{m}}^{-3}$) whereas $p$-type ${\mathrm{Fe}}_2{\mathrm{V}}_{0.985}{\mathrm{Al}}_{1.015}$ ($PF=2.7\mathrm{mW}{\mathrm{m}}^{-1}{\mathrm{K}}^{-2}$ at $p=6.7\times {10}^{20}\mathrm{c}{\mathrm{m}}^{-3}$) is not yet optimum. The easier optimization of the thermoelectric properties in $n$-type self-substituted ${\mathrm{Fe}}_2\mathrm{VAl}$ can be traced back to the larger effective DOS mass of its electrons.

Strontium niobate has triggered a lot of interest as a transparent conductor and as a possible realization of a correlated Dirac semimetal. Using the lattice parameters as a tunable knob, the energy landscape of octahedral tilting was mapped using density functional theory calculations. We find that biaxial compressive strain induces tilting around the out-of-plane axis, while tensile strain induces tilting around the two in-plane axes. The two competing distorted structures for compressive strain show semi-Dirac dispersions above the Fermi level in their electronic structure. Our density functional theory calculations combined with dynamical mean field theory reveal that dynamical correlations downshift these semi-Dirac-like cones towards the Fermi energy. More generally, our study reveals that the competition between the in-phase and out-of-phase tilting in ${\mathrm{SrNbO}}_3$ provides a new degree of freedom that allows for tuning the thermoelectric and optical properties. We show how the tilt angle and mode are reflected in the behavior of the Seebeck coefficient and the plasma frequency due to changes in the band structure.

Quantum tunneling rotors in a zeolitic imidazolate framework ZIF-8 can provide insights into local gas adsorption sites and local dynamics of porous structure, which are inaccessible to standard physisorption or x-ray diffraction sensitive primarily to long-range order. Using in situ high-resolution inelastic neutron scattering at 3 K, we follow the evolution of methyl tunneling with respect to the number of dosed gas molecules. While nitrogen adsorption decreases the energy of the tunneling peak, and ultimately hinders it completely (0.33 meV to zero), argon substantially increases the energy to 0.42 meV. Ab initio calculations of the rotational barrier of ZIF-8 show an exception to the reported adsorption sites hierarchy, resulting in anomalous adsorption behavior and linker dynamics at subatmospheric pressure. The findings reveal quantum tunneling rotors in metal-organic frameworks as a sensitive atomistic probe of local physicochemical phenomena.

Magnetic Dirac electron systems have attracted intense research interest for their unique magnetoelectric properties. Here, we report the magnetic and transport properties of the antiperovskite ${\mathrm{Eu}}_3\mathrm{SnO}$, which was identified as a topological semimetal characteristic by first-principles theoretical calculations [A. Pertsova et al., Phys. Rev. B 99, 205126 (2019)]. A metastable canted antiferromagnetic state between the paramagnetic and the ferromagnetic phases was observed in ${\mathrm{Eu}}_3\mathrm{SnO}$. Further, the magnetoresistance and Hall resistance show the anomalies below the Néel temperature. On the corresponding magnetic phase transition point, the transport properties undergo sharp drops which verify the characteristics of magnetic properties. Meanwhile, we found the coexistence of ${\mathrm{Eu}}^{2+}$ and ${\mathrm{Eu}}^{3+}$ in ${\mathrm{Eu}}_3\mathrm{SnO}$ by analyzing experimental and theoretical data, which indicate the localized-itinerant dual properties of the $f$-orbital electrons. Finally, we plot the phase diagram for ${\mathrm{Eu}}_3\mathrm{SnO}$ by collecting the inflection/maximum points of the magnetization, heat capacity, and magnetoresistance/Hall-resistance curves. The phase diagram shows four magnetic-ordered regions including antiferromagnetic phase I, ferrimagnetic phases II and III, and ferromagnetic-like phase IV. This study opens up possibilities for the investigation of fascinating properties in such theoretically predicted antiferromagnetic topological semimetals.

The Weyl semimetal CeAlGe is a promising material to study nontrivial topologies in real and momentum space due to the presence of a topological magnetic phase. Our results at ambient pressure show that the electronic properties of CeAlGe are extremely sensitive to small stoichiometric variations. In particular, the topological Hall effect (THE) present in CeAlGe is absent in some samples of almost identical chemical composition. The application of external pressure favors the antiferromagnetic ground state. It also induces a THE where it was not visible at ambient pressure. Furthermore, a small pressure is sufficient to drive the single region of the THE in magnetic fields into two different ones. Our results reveal an extreme sensitivity of the electronic properties of CeAlGe to tiny changes in its chemical composition, leading to a high tunability by external stimuli. We can relate this sensitivity to a shift in the Fermi level and to domain walls.

A recent experiment of polycrystalline ${\mathrm{WB}}_2$ with hP3 (space-group 191, prototype ${\mathrm{MgB}}_2$) and hP12 (space-group 194, prototype ${\mathrm{WB}}_2$) structures was reported to realize 17-K superconductivity (SC) at 90 GPa, and the hP3 structure is believed to be responsible for this emergent SC. However, a microscopic understanding of what makes the hP3 structure so different from the hP12 structure and why the hP3 can feature such strong electron-phonon coupling (EPC) SC is still missing. Here, based on first-principles calculations, we found that in the hP3 structure, W $d$ orbitals contribute most to electronic occupation near the $E_{\mathrm{F}}$, and $d_{z^2}$ orbitals of two neighboring W atoms have some hybridization to form weak $\sigma$ bonds. The further EPC analysis indicates that the dominant $d_{z^2}$ states are strongly coupled with the out-of-plane phonon modes by stretching the $\mathrm{W}\text{−}\mathrm{W}\sigma$ bond, thereby yielding a large superconducting gap and high $T_{\mathrm{c}}$ of $\sim 35$ K. By contrast, for the hP12 structure, two neighboring W atoms are isolated without charge hybridization to form the covalent bonds, and, accordingly, their phonon modes become very stiffened, which cannot effectively couple to W $d$ orbital states associated with a lower $T_{\mathrm{c}}$ of $\sim 4$ K. Therefore, our findings not only provide an explanation for the emergent strong EPC SC in the hP3 structure, but also have important implications for the design of high-$T_{\mathrm{c}}$ superconductors among transition metal borides.

Despite recent advances of layered square-net topological material models that possess ideal semimetallic electronic structures and promising potential in material applications, the identification of experimentally accessible two-dimensional square-net materials with related topological properties has proven challenging. Due to the highly tunable physical and topological properties of III-V semiconductors, we revisit the class of III-V materials and observe that the litharge-phase InBi is a layered square-net material and can be exfoliated into the InBi monolayer. We present a comprehensive first-principles study of the energy landscape of the InBi monolayer. We identify a paraelastic phase and three ferroelastic phases and study their topological properties. Specifically, we show that the paraelastic InBi monolayer is a trivial insulator due to the orbital-ordering-induced band inversion occurring between states with the same parity. Substituting one Bi atom per cell with another V-group element (N, P, As) or applying an electric field that breaks the inversion symmetry and changes the orbital onsite energy, the paraelastic InBi monolayer can be driven into the topological insulator phase. Furthermore, one of the ferroelastic phases of pure InBi, which can be obtained by gently straining the paraelastic phase, also possesses such topological insulating properties. These results provide several experimentally accessible routes to tune the nontrivial topology in the InBi monolayer, including creating heterostructures with piezoelectric or ferroelectric substrates and applying mechanical strain, making the InBi monolayer an ideal platform to study the interplay of reduced dimensionality, square-net chemical bonding networks, and band topology.

We report on the geometrically frustrated two-dimensional triangular-lattice magnets $A_2{\mathrm{La}}_2{\mathrm{NiW}}_2{\mathrm{O}}_{12}$ ($A=\mathrm{Sr},\mathrm{Ba}$) studied mostly by means of neutron powder diffraction (NPD) and muon-spin rotation and relaxation ($\mu \mathrm{SR}$) techniques. The chemical pressure induced by the Ba-for-Sr substitution suppresses the ferromagnetic (FM) transition from 6.3 K in the Ba compound to 4.8 K in the Sr compound. We find that the $R\overline{3}$ space group reproduces the NPD patterns better than the previously reported $R\overline{3}m$ space group. Both compounds adopt the same magnetic structure with a propagation vector $\mathit{k}=(0,0,0)$, in which the ${\mathrm{Ni}}^{2+}$ magnetic moments are aligned ferromagnetically along the $c$ axis. The zero-field $\mu \mathrm{SR}$ results reveal two distinct internal fields (0.31 and 0.10 T), caused by the long-range FM order. The small transverse muon-spin relaxation rates reflect the homogeneous internal field distribution in the ordered phase and, thus, further support the simple FM arrangement of the ${\mathrm{Ni}}^{2+}$ moments. The small longitudinal muon-spin relaxation rates, in both the ferromagnetic and paramagnetic states of $A_2{\mathrm{La}}_2{\mathrm{NiW}}_2{\mathrm{O}}_{12}$, indicate that spin fluctuations are rather weak. Our results demonstrate that chemical pressure indeed changes the superexchange interactions in $A_2{\mathrm{La}}_2{\mathrm{NiW}}_2{\mathrm{O}}_{12}$ compounds, with the FM interactions being dominant.

GeSn is a promising group-IV semiconductor material for on-chip Si photonics devices and high-mobility transistors. These devices require the use of doped GeSn regions, achieved preferably in situ during epitaxy. From the electronic valence point of view, $p$-type dopants of group-IV materials include B, Al, Ga, and In. The latter element has never been investigated as $p$-type dopant in GeSn. In this work, we explore in situ In $p$-type doping of GeSn grown by molecular beam epitaxy. We demonstrate that In acts as a surfactant during epitaxial growth of GeSn:In, accumulating on surface and inducing Sn segregation in the form of mobile Sn-In liquid droplets, strongly affecting the local composition of the material. In nondefective GeSn, we measure a maximal In incorporation of $2.8\times {10}^{18}$ ${\mathrm{cm}}^{-3}$, which is two orders of magnitude lower than the values reported in the literature for in situ p-type doping of GeSn. We further show that In induces the nucleation of defects at low growth temperatures, hindering out-of-equilibrium growth processes for maximization of dopant incorporation. This work provides insights on the limitations associated with in situ In doping of GeSn and discourages its utilization in GeSn-based optoelectronic devices.

Ionic liquid gating (ILG) induced proton doping has appeared as an efficient tuning knob to manipulate novel ground states and realize rich applications in complex spinel oxides. We report insights into the influences of cation distribution on local atomic and electronic structure of ${\mathrm{NiCo}}_2{\mathrm{O}}_4$ (NCO) epitaxial films as well as its correlation with proton insertion dynamics. For NCO films deposited at lower oxygen partial pressure (${\mathrm{P}}_{O_2}$), we verify the dominant structural variation as cation distribution rather than oxygen vacancies through electric and magnetic transport analyses. The x-ray absorption spectra at the O K-edge further suggests two couples of cation inversion at octahedral (${\mathrm{O}}_h$)-${\mathrm{Ni}}^{2+}$ and tetrahedral (${\mathrm{T}}_d$)-${\mathrm{Co}}^{2+}$ sites, resulting in ${\mathrm{Ni}}^{3+}$ at ${\mathrm{T}}_d$ and more ${\mathrm{Co}}^{3+}$ at ${\mathrm{O}}_h$ sites. Through systematic investigations of the structural and valence states of NCO films with different ILG treatment conditions, our results display the robust ionic reduction procedure, i.e., the Ni ions near the Fermi level exhibit a prior ${\mathrm{Ni}}^{3+}$ to ${\mathrm{Ni}}^{2+}$ reduction whereas the Co ions at different coordinated sites show the gradual ${\mathrm{Co}}^{3+}$ $\to {\mathrm{Co}}^{2+}$ reduction procedure. However, more stringent conditions are necessary for fully protonating NCO films deposited at low ${\mathrm{P}}_{O_2}$, which can be ascribed to the short relaxation time and poor diffusion coefficient accompanying with the increased cation disorders.

The elucidation of the residual and intentional doping processes in ZnO nanowires (NWs) grown by chemical bath deposition (CBD) is a major but still largely unexplored issue despite its primary importance for many nanoscale engineering devices. Here, we investigate the local structural environment around Ga dopants in ZnO NWs by combining synchrotron radiation-based x-ray linear dichroism with density functional theory calculations. We show that the family of ${\mathrm{V}}_{\mathrm{Zn}}\text{−}{\mathrm{Ga}}_{\mathrm{Zn}}\text{−}n\mathrm{H}$ defect complexes is predominantly formed and hence that hydrogen acts as an efficient passivating species even for intentional dopants like Ga. The residual and intentional doping processes are found to be highly correlated through significant interplay effects. These findings revisit the nature of intentional dopant-induced defects and defect complexes in ZnO NWs. They further reveal that hydrogen should be considered in unintentionally doped ZnO NWs grown by CBD as major defects but also in intentionally doped ZnO NWs through its efficient passivating effect, opening perspectives to more finely control their optical and electrical properties.

Understanding and controlling the composition of III-V ternary nanomaterials is essential for band-gap tunability and fabrication of functional nanoheterostructures. The kinetic approach developed so far is based on the assumption of $C$-rich growth of a ternary $A_x{B}_{1-x}C$ material based on intermix of $A$ and $B$ atoms. This holds for epilayers based on group III intermix, but is not true for epilayers based on group V intermix or vapor-liquid-solid nanowires based on group III intermix. Herein, we develop a general growth theory and obtain a vapor-solid distribution which described the ternary composition under arbitrary material fluxes and for any III-V material. This vapor-solid distribution is a combination of the kinetic and equilibrium distributions, whose weights depend on the ratio $\varepsilon$ of the total flux of $A$ and $B$ atoms over the flux of $C$ atoms. At $\varepsilon \ll 1$, the composition is kinetically controlled, while at $\varepsilon \gg 1$ it becomes thermodynamically limited even at infinitely high binary supersaturations for $\mathit{AC}$ and $\mathit{BC}$ pairs. The model fits very well the compositional data on the $\mathrm{In}{\mathrm{Sb}}_x{\mathrm{As}}_{1-x}$ epilayers, $\mathrm{Al}{\mathrm{Sb}}_x{\mathrm{As}}_{1-x}$ epilayers, and $\mathrm{In}{\mathrm{Sb}}_x{\mathrm{As}}_{1-x}$ nanowires under different total V/III flux ratios. It reveals some fundamental properties of the vapor-solid distribution beyond the assumption of decoupled binary fluxes. In particular, the vapor-solid distribution becomes purely thermodynamic and presents the miscibility gap below the critical temperature under $\mathit{AB}$-rich conditions for an $A_x{B}_{1-x}C$ ternary regardless of the vapor supersaturation. The miscibility gap can be fully circumvented in the $C$-rich regime, where the solid composition is driven by the kinetic factors.

We have used temperature-dependent photoconductivity (PC) with different excitation wavelengths and intensities to study the photoexcited charge-carrier transport within GeSn/Ge/Si heterostructures. The evolution of the PC spectra with temperature was analyzed between 10 and 200 K. These strained GeSn films were grown with high enough Sn content such that the band gaps were direct. As such, the relationships between the band gaps and the temperature were determined using photoconductivity spectroscopy. As a result, an anomalous, linear blueshift of the PC spectral edge was found with increasing temperature. This was attributed to the variation of the GeSn band gap within the film, due to variations in strain and the increased contribution to PC from the region of highest Sn content. The change in photocurrent with excitation intensity and temperature demonstrates that conduction occurs predominantly through the GeSn and Ge layers under low optical pumping and through the Si substrate under high optical pumping. A phenomenological model of photoconductivity in GeSn as it depends on strain was proposed. This detailed understanding of the transport of photoexcited carriers along the GeSn layers is critical for developing GeSn/Ge-based optoelectronic devices.