Intercalation of two-dimensional (2D) iron chalcogenides with molecular species requires disentangling electronic and structural contributions to understand the puzzling limit to superconducting transition temperature ($T_{\mathrm{c}}$) at the frontier of long interlayer separations. Here, synchrotron x-ray absorption spectroscopy at the Se $K$ edge sheds light on the impact of carrier doping on the local structure of the high-$T_{\mathrm{c}}$ ($\sim 39\mathrm{K}$) $\mathrm{L}{\mathrm{i}}_{1.0}{\left({\mathrm{C}}_5{\mathrm{H}}_5\mathrm{N}\right)}_y\mathrm{F}{\mathrm{e}}_{2-z}\mathrm{S}{\mathrm{e}}_2$ phase. This material is derived by annealing the structurally related as-made derivative ($T_{\mathrm{c}}\sim 44\mathrm{K}$), with layers being primed apart by (alkali-molecule) guests. Metrics, such as a reduced filling of Se $4p$ orbitals and shorter Fe-Se bonds in the annealed phase, corroborate to a lower electron doping level with respect to the as-made one. Analysis of the metal-ligand thermal motion, based on the correlated Debye model, further relates the higher-$T_{\mathrm{c}}$ intercalates with the softening of the local Fe-Se bond. Beyond electronic effects, intercalation brings forth host-guest interactions that mediate the dynamics of the bulk crystal structure. For this, neutron time-of-flight spectroscopy on the annealed derivative corroborates the Se-Fe-Se layer being sensitive to chemical pressure effects imposed by the confined organic guests. This reflects in the phonon density of states, where harder low-energy transverse acoustic matrix phonons and molecular vibrations are witnessed, with respect to the pristine inorganic ($\beta$-FeSe) and organic (${\mathrm{C}}_5{\mathrm{D}}_5\mathrm{N}$) counterparts. On cooling through $T_{\mathrm{c}}$, these excitations arrive without a collective magnetic-resonance mode—essential in unconventional, spin-mediated mechanisms—enquiring about deviations from optimal doping. The work highlights that when the Fe square planes are tuned far apart, carrier doping leveraged by intercalation plays a key role in the $T_{\mathrm{c}}$ parametrization.

In this study we investigate the degree to which the design methods of solid-state band diagrams might be extended and applied to realize high-performance electrochemical luminescence (ECL) heterostructures. Taking quantum dots (QDs) as a model system, we first build up a description of their ECL properties in the single-particle picture utilizing the Gerischer-Hopfield framework of electron transfer. This is then applied to the construction of single- and two-probe electrode designs, where it is shown that the internal quantum efficiencies of individual QDs can theoretically reach performance metrics competitive with solid-state devices. These near-ballistic designs, characterized by single-step carrier transfer events at each electrode, are demonstrated to only attain such high efficiencies through the use of band-gap (heterostructure) engineering in the electrodes. Subsequently, we propose a further diffusive operating design composed of an electrolyte-infused network of QDs, forming a functional material whereby carriers hop between QD sites. The operation of this diffusive ECL heterostructure is further analyzed to possess maximum theoretical light emission intensities and efficiencies rivaling solid-state devices. Ultimately, this work underscores the potential utility of applying band-diagram-based design methods and electrochemical approaches when seeking to enhance the efficiency of QD emitters for a wide range of processable electronics applications.

Two-dimensional (2D) oxides stand out as one of the most promising host materials for solid-state quantum defects, combining the advantages of easier fabrication from 2D systems and long coherence time from oxide materials. Here, we systematically screen the single-point defect families for promising quantum defects in two-dimensional (2D) silica bilayer $\left({\mathrm{SiO}}_2\right)$ by analyzing the electronic, magnetic, and optical properties from theoretical simulations. The zero-phonon transition energies $\left(E_{\mathrm{ZPL}}\right)$ range from 0.22 eV to 6.35 eV, offering wide application potential. The X substitution for Si $(X_{\mathrm{Si}}, \mathrm{X}=\mathrm{Cr}, \mathrm{Mo}, \mathrm{W})$ defect family with a tetrahedral crystal field provides 1.77 to 2.91 eV $E_{\mathrm{ZPL}}$ due to the large energy gap between $e_g$ and $t_{2g}$ orbitals, while the $E_{\mathrm{ZPL}}$ of X substitution for O $(X_O, \mathrm{X}=\mathrm{C}, \mathrm{N}, \mathrm{O}, \mathrm{Ti}, \mathrm{Zr}, \mathrm{Hf})$ defect family highly depends on the substitution element. We have identified the ${\mathrm{Ti}}_{\mathrm{O}}$ defect as a single photon emitter operating in the telecom band and spin-defect qubits $({\mathrm{Cr}}_{\mathrm{Si}} \text{and} {\mathrm{Mo}}_{\mathrm{Si}})$ with desirable spin-triplet ground state, $E_{\mathrm{ZPL}}$ (2.08 eV for ${\mathrm{Cr}}_{\mathrm{Si}}$; 1.77 eV for ${\mathrm{Mo}}_{\mathrm{Si}}$), moderate zero-field splitting, and fast intersystem crossing. The 2D ${\mathrm{SiO}}_2$ bilayer host would benefit the integration of quantum networks and conventional silicon-based semiconductor electronic devices.

The intersection between nonsymmorphic symmetry and electronic correlations has emerged as a platform for topological Kondo semimetallic states and unconventional spin textures. Here, we report the synthesis of nonsymmorphic ${\mathrm{UPd}}_{0.65}{\mathrm{Bi}}_2$ single crystals and their structural, electronic, magnetic, and thermodynamic properties. ${\mathrm{UPd}}_{0.65}{\mathrm{Bi}}_2$ orders antiferromagnetically (AFM) below $T_N\simeq 161\mathrm{K}$ as evidenced by a sharp cusp in magnetic susceptibility, a second-order phase transition in specific heat, and an upturn in electrical resistivity, which suggests an incommensurate AFM structure that deviates from the A-type magnetism typically observed in this class of materials. Across $T_N$, Hall effect measurements reveal a change from electron-dominated to hole-dominated transport, which points to a sharp reconstruction in the electronic structure at $T_N$. Upon further cooling, a first-order transition is observed at $T_1\simeq 30\mathrm{K}$ in magnetic susceptibility and heat capacity but not in electrical resistivity or Hall measurements, which indicates a small change in the AFM structure that does not affect the electronic structure. Our specific heat data reveal a small Sommerfeld coefficient ($\gamma \simeq 13{\mathrm{mJmol}}^{-1}{\mathrm{K}}^{-2}$), consistent with localized $5f$ electrons. Our results indicate that ${\mathrm{UPd}}_{0.65}{\mathrm{Bi}}_2$ hosts weak electronic correlations and is likely away from a Kondo semimetallic state. Low-temperature magnetization measurements show that the AFM structure is remarkably stable to 160 kOe and does not undergo any field-induced transitions. Neutron diffraction and magnetization experiments at higher fields would be valuable to probe the presence of unconventional spin textures.

Polymer networks invariably possess topological inhomogeneities in the form of loops and dangling ends. The macroscopic properties of such materials are directly dependent on the local cyclic topology around nodes and chains. Here, a formalism to model polymer network topology is presented based on the concept of three-dimensional (3D) nets that enables computation of these local cyclic topologies. A cycle-counting algorithm is developed which characterizes the relevant local topological cycles around every node, enabling comparison of networks with ideal nets based on local cycle distributions. Comparison of networks formed by different simulation algorithms, using a topology-based distance metric, reveals that polymer networks possess a fundamental cycle size which depends on the topological proximity of crosslinkers during bond formation. This parameter identifies distinct topological classes of networks and provides an effective method to simulate a wide array of networks starting from suitable 3D nets. This approach can be readily generalized beyond polymer networks, enabling quantification of the cyclic topology and facilitating study of topology-property correlations.

Following the discovery of superconductivity in hole-doped ${\mathrm{NdNiO}}_2$ infinite-layer thin films, extensive research has been conducted particularly to compare these materials with cuprates. Superconductivity has also been observed in nickelate thin films with other rare-earth elements such as Pr and La, but not in their bulk forms, suggesting a critical role for substrate-induced strain/interface or dimensionality effects. In this study, we used water-soluble (Ca,${\mathrm{Sr})}_3{\mathrm{Al}}_2{\mathrm{O}}_6$ sacrificial layers to fabricate freestanding perovskite nickelate membranes and explore the phase transformation to infinite layers of the membranes via topotactic reduction in the absence of any template effect from the substrate. Highly metallic ${\mathrm{NdNiO}}_3$ membranes with bulk-like hysteretic metal-to-insulator transitions could be obtained when transferred from a ${\mathrm{LaAlO}}_3$ substrate. The topotactic reduction of these membranes with ${\mathrm{CaH}}_2$ was shown to be successful as characterized by the expected decrease of the out-of-plane cell parameter and absence of apical oxygens. The reduced membranes, however, displayed insulating characteristics similar to those of bulk infinite-layer nickelates. Our findings strongly indicate that a template is necessary to stabilize a coherent and robust infinite-layer phase with optimal transport properties.

Recent experiments reveal spontaneous formation of core-shell heterostructures in different nanowires including ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}, {\mathrm{Ga}}_x{\mathrm{Al}}_{1-x}\mathrm{As}$, and ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$. Here, we develop a general growth theory for III-V ternary nanostructures that are fed from a confined reservoir of atoms, and discuss different effects leading to the compositional inhomogeneity and core-shell elemental distributions. In quasi-instantaneous growth of single ternary monolayers $A_x{B}_{1-x}C$, the material separation can be due to (i) different transport rates of atoms $A$ and $B$ from a mother phase into the solid, (ii) changing the growth environment in favor of $C$-poor conditions, and (iii) decrease of total supersaturation in the course of monolayer growth. It is shown that scenario (ii) yields abrupt heterointerfaces separating the In-rich or Ga-rich cores from the barrier-type shells in ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}, {\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{P}, {\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$, and ${\mathrm{Ga}}_x{\mathrm{Al}}_{1-x}\mathrm{As}$ nanowires. The obtained interfacial profiles are primarily determined by the periodically changing V/III ratio of atomic fluxes entering partial monolayer, and are very close for systems with very different pseudobinary interaction parameters. The model fits quite well the interfacial profiles in spontaneous core-shell ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ and ${\mathrm{In}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ nanowires, and provides the basis for the future advancements in understanding and controlling these complex effects in different material systems, epitaxy techniques, and nanostructure geometries.

In two-dimensional (2D) spin systems, the augmentation of spin fluctuations gives rise to quasi-long-range order; however, how they manifest in spin transport remains unclear. Here, we investigate the spin Seebeck effect (SSE) in a quasi-2D antiferromagnet, ${\mathrm{BaNi}}_2{\mathrm{V}}_2{\mathrm{O}}_8$, which has been reported to exhibit the Berezinskii-Kosterlitz-Thouless (BKT) transition owing to its very weak interlayer interaction. We found that the SSE in $\mathrm{Pt}/{\mathrm{BaNi}}_2{\mathrm{V}}_2{\mathrm{O}}_8$ persists well above the Néel temperature, significantly different from the behavior of 3D-ordered magnets. Our numerical analysis for a 2D microscopic spin model confirms that the observed SSE is linked to the gapless magnon excitations and strong magnetic correlations characteristic of BKT magnets.

Antiferromagnets (AFs) are characterized by spin structures that are resistant to external magnetic fields, rendering them ideal for persistent information storage but challenging to control. This study demonstrates that a thin ferromagnetic adlayer can serve as a magnetic ‘lever’ to provide a strong handle on the spin texture of an adjacent antiferromagnet. In bilayers composed of NiO(001) and Co, the expected exchange bias effect—a unidirectional shift in the Co hysteresis due to coupling with NiO—is notably absent. Instead, a strong interfacial coupling is observed, causing the NiO to partially follow the magnetization of Co under an applied magnetic field. Using x-ray magnetic linear dichroism, we detect an inversion of dichroism, indicating a reorientation of the Néel vector in NiO. X-ray spectromicroscopy imaging further reveals a direct correlation between ferromagnetic and antiferromagnetic domain structures. These findings are explained using a toy model that distinguishes between stable and unstable AF domains, highlighting the dynamic interplay between NiO and the Co adlayer in the presence of a magnetic field.

$\mathrm{Mn}{\left(\mathrm{Sb}/\mathrm{Bi}\right)}_{2n}\mathrm{T}{\mathrm{e}}_{3n+1}$, a well-known family of intrinsic magnetic topological insulator, possesses nontrivial topological electronic structures, making this family an excellent platform to investigate exotic quantum phenomena. These materials are closely related to the well-known thermoelectric material $\mathrm{B}{\mathrm{i}}_2\mathrm{T}{\mathrm{e}}_3$. Particularly, with the introduction of intrinsic magnetism, energy conversion based on the magnetothermoelectric effect has also attracted researcher's attentions. Here, we study the magnetic, electrical, and thermoelectric transport properties of a 39% Sb-doped ferromagnetic $\mathrm{MnB}{\mathrm{i}}_6\mathrm{T}{\mathrm{e}}_{10}$ single crystal. Upon Sb doping, the carrier density is suppressed, the electrical resistivity exhibits a semiconducting behavior, and the power factor $\mathit{PF}$ and the figure of merit $\mathit{ZT}$ are estimated to be $5.07\mu \mathrm{W}\mathrm{c}{\mathrm{m}}^{-1}{\mathrm{K}}^{-2}$ and 0.14, respectively, at 300 K. At low temperatures, the sample displays the characteristics of two-carriers transport as indicated by the nonlinear Hall effect. The spontaneous anomalous Hall effect and anomalous Nernst effect are observed below the Curie temperature $T_C\sim 13\mathrm{K}$. The Nernst thermopower versus magnetization, $|S_{yx}|/M$, exceeds the scaling law of conventional magnets, highlighting the enhanced anomalous Nernst effect arising from the intrinsic contribution of the net Berry curvature. Our results provide experimental evidence of nontrivial electronic structures in the ferromagnetic $\mathrm{Mn}{\left(\mathrm{Sb}/\mathrm{Bi}\right)}_6\mathrm{T}{\mathrm{e}}_{10}$ and highlight its potential for thermoelectric applications.

The influence of copolymer topology on the phase behavior of binary blends containing AB-type block copolymers and A homopolymers is studied by examining the instability modes of the system using the random-phase approximation. Depending on the concentration of the homopolymers, the blends could undergo microscopic or macroscopic phase separation, forming one ordered phase or two coexisting phases. The transition between these two distinct behaviors occurs at the Lifshitz point (LP), at which the wavelength of the most unstable mode diverges. We demonstrate that AB-type copolymers with identical block compositions but distinct chain topologies have different abilities to solubilize homopolymers, and their LPs exhibit two distinct, continuous (second-order) or discontinuous (first-order), features connected by a tricritical point. A more complex behavior featuring the coexistence of two instability modes with different finite length scales is also observed in multiblock copolymer/homopolymer blends. These behaviors are shown to be independent of specific chain models.

Cold metals, characterized by their distinctive band structures, hold promise for innovative electronic devices such as tunnel diodes with negative differential resistance (NDR) effect and field-effect transistors (FETs) with sub-60 mV/dec subthreshold swing (SS). In this study, we employ the $GW$ approximation and HSE06 hybrid functional to investigate the correlation effects on the electronic band structure of two-dimensional cold metallic materials, specifically focusing on $M{X}_2$ and $M{A}_2{Z}_4$ ($M=\mathrm{Nb}$, $\mathrm{Ta}$; $X=\mathrm{S}$, $\mathrm{Se}$, $\mathrm{Te}$; $A=\mathrm{Si}$, $\mathrm{Ge}$; $Z=\mathrm{N}$, $\mathrm{P}$) compounds in 1H structure. These materials exhibit a unique band structure with an isolated metallic band around the Fermi energy, denoted as $W_{\mathrm{m}}$, as well as two energy gaps: the internal gap $E_{\mathrm{g}}^{\mathrm{I}}$ below the Fermi level and the external gap $E_{\mathrm{g}}^{\mathrm{E}}$ above the Fermi level. These three electronic structure parameters play a decisive role in determining the current-voltage ($I\text{−}V$) characteristics of tunnel diodes, the nature of the NDR effect, and the transfer characteristics and SS value of FETs. Our calculations reveal that both $GW$ and HSE06 methods yield consistent electronic structure properties for all studied compounds. We observed a consistent increase in both internal and external band gaps, as well as metallic bandwidths, across all pn-type cold metal systems. Notably, the internal band gap $E_{\mathrm{g}}^{\mathrm{I}}$ exhibits the most substantial enhancement, highlighting the sensitivity of these materials to correlation effects. In contrast, the changes in the metallic bandwidth $W_{\mathrm{m}}$ and external band gap $E_{\mathrm{g}}^{\mathrm{E}}$ are relatively modest. These findings offer valuable insights for designing and optimizing cold metal-based devices. Materials like ${\mathrm{NbSi}}_2{\mathrm{N}}_4, {\mathrm{NbGe}}_2{\mathrm{N}}_4$, and ${\mathrm{TaSi}}_2{\mathrm{N}}_4$ show particular promise for high-performance NDR tunnel diodes and sub-60 mV/dec SS FETs.

The phenomenon of second harmonic generation (SHG) was found for phonons in anharmonic NaBr by inelastic neutron scattering. The temperature dependence of this phonon SHG was measured from 300 K to 650 K. At 300 K the second harmonic (SH) is seen as a high-energy branch around 33 meV, nearly independent of $\vec{Q}$. The temperature effective potential (TDEP) method and classical molecular dynamics (MD) simulation with machine learning interatomic potential were able to reproduce the SH, and showed that SHG occurs with the flat transverse optical (TO) phonon branch. A classical model of a nonlinear medium explains the intensity and lifetime of the SH, compared to those of the TO modes. Also successful was a quantum model based on the Heisenberg-Langevin equation for interacting phonons coupled to a thermal bath, which also predicts a spectral distribution of the SH. The measured temperature dependence of the intensity of the second harmonic showed that it follows the Planck distribution of a one-phonon quasiparticle, and not two TO phonons.

Determining the strength of electronic correlations of correlated electrons plays important roles in accurately describing the electronic structures and physical properties of transition-metal (TM) perovskite oxides. Here, we study the evolution of electronic interaction parameters as a function of $d$-electron occupancy in an extended class of TM perovskite oxides $AB{\mathrm{O}}_3$ ($A=\mathrm{Sr}$, Ca, and $B=3d\text{−}5d$ TM elements) using the constrained random-phase-approximation method adopting two distinct models: $t_{2g}\text{−}{t}_{2g}$ and $d\text{−}dp$. For $\mathrm{Sr}B{\mathrm{O}}_3$ with $B=\mathrm{Fe}$, Ru, and Ir, the $t_{2g}\text{−}{t}_{2g}$ model faces critical challenges, as the low-energy Hamiltonian spanning $t_{2g}$ manifolds is ill-defined. The $t_{2g}\text{−}{t}_{2g}$ model suggests that, for the early $AB{\mathrm{O}}_3$ series ($B=d^1–d^3$), the bare Coulomb interaction parameters $V$ remain nearly constant due to the competition between extended $t_{2g}$ Wannier orbitals and bandwidth reduction. As the $d$-electron filling increases, both partially screened Coulomb interaction parameters $U$ and fully screened Coulomb interaction parameters $W$ decrease, which are attributed to enhanced $e_g\text{−}{t}_{2g}$ and $e_g\text{−}p$ screenings. In contrast to the $t_{2g}\text{−}{t}_{2g}$ model, the $d\text{−}dp$ model effectively handles both early and late $AB{\mathrm{O}}_3$ perovskites and reveals different trends. Specifically, $V$ varies inversely with the spreads of $d$ orbitals. $W$ reaches its minimum at the $d^3$ occupancy due to an interplay between increasing $d$-orbital localization and increasing screening effects. An unusual trend is observed for $U$, with local maxima at both $d^1$ and $d^4$ occupations. This can be understood from two aspects: (1) the increasing full screening effects from $d^1$ to $d^3$ and (2) the strongest $d\text{−}d$ and the weakest $d\text{−}p$ screening effects near $d^4$ for $\mathrm{Sr}B{\mathrm{O}}_3$. Our results underscore that the Coulomb interaction parameters not only depend on the choice of model frameworks, but also the interplay between the localization of $d$ orbitals and screening strength, which are affected by $d$-orbital fillings and details of the band dispersion.

The ground state of monolayer $1T^{\prime }\text{−}{\mathrm{WTe}}_2$ has been a target of intensive debate on whether or not it is a two-dimensional topological insulator (2D TI) associated with exciton formation. We investigated the band structure of an epitaxial monolayer $1T^{\prime }\text{−}{\mathrm{WTe}}_2$ film grown on graphene/SiC(0001) in a wide temperature range of $T=40-400\mathrm{K}$ by angle-resolved photoemission spectroscopy (ARPES). We observed an electron band above the Fermi level ($E_{\mathrm{F}}$) slightly away from the $\mathrm{\Gamma }$ point, together with four hole bands below $E_{\mathrm{F}}$ just at the $\mathrm{\Gamma }$ point. This signifies an indirect band gap exceeding 0.1 eV in support of the 2D-TI phase with the inverted band structure. We uncovered an unexpectedly large downward shift of valence bands upon cooling, accompanied with an upward shift of the conduction band. Comparison of the ARPES-derived band structure with first-principles band calculations suggests that the observed band shift is ascribed to the systematic local atomic distortion of tungsten atoms, which should be incorporated into the interpretation of unusual transport properties of $1T^{\prime }\text{−}{\mathrm{WTe}}_2$.

Kagome-lattice materials offer novel playgrounds of exploring topologically nontrivial states of electrons under influence of many-body interactions. A noncollinear kagome antiferromagnet $\mathrm{M}{\mathrm{n}}_3\mathrm{Sn}$ has attracted particular interest for application in spintronics owing to the large anomalous Hall effect related to the Weyl dispersion near the Fermi energy. In addition, strong electronic correlation suggesting the Kondo physics has also been implied. However, the effect of correlation on the band topology and their interplay remains elusive. Here, we investigate nonequilibrium Hall transport in a photoexcited $\mathrm{M}{\mathrm{n}}_3\mathrm{Sn}$ using time-resolved terahertz Faraday rotation spectroscopy. In equilibrium, $\mathrm{M}{\mathrm{n}}_3\mathrm{Sn}$ is a bad metal close to the Mott-Ioffe-Regal limit with low carrier mobility, and thus only the anomalous Hall effect is discerned. By contrast, intense photoexcitation beyond an approximate threshold gives rise to a clear cyclotron resonance, namely the normal Hall effect, indicating the emergence of unusual carriers with 50 times lighter effective mass and 40 times less scattering. The lifetime of high-mobility carriers as long as a few tens of picoseconds and a thresholdlike behavior for the pump fluence are hardly explained by contribution of photoexcited hot carriers. Instead, the emergence of unusual carriers may be accounted for by dielectric screening of the on-site Coulomb interaction by high-density delocalized photocarriers. A possible role of electronic correlation in equilibrium transport in $\mathrm{M}{\mathrm{n}}_3\mathrm{Sn}$ beyond the single-particle picture is discussed.

Magnetic excitations in the noncentrosymmetric magnet ${\mathrm{Sr}}_2{\mathrm{MnSi}}_2{\mathrm{O}}_7$ were investigated through inelastic neutron scattering measurements. Major magnetic excitations are limited up to the energy transfer of 0.5 meV, and two magnon branches under zero magnetic field were well explained in the framework of linear spin-wave theory. The magnitudes of the square-lattice in-plane and interplane nearest-neighbor interactions, spin anisotropy term, and the Dzyaloshinskii-Moriya interaction are, respectively, estimated to be $J_1=45.54\left(5\right)\mu \mathrm{eV}, J_2=0.52\left(1\right)\mu \mathrm{eV}, \mathrm{\Lambda }=4.98\left(11\right)\mu \mathrm{eV}, D_{xy}=0.02\left(9\right)\mu \mathrm{eV}$, and $D_z=4.10\left(1\right)\mu \mathrm{eV}$, and calculations using these parameters reproduce experimental data quite well. ${\mathrm{Sr}}_2{\mathrm{MnSi}}_2{\mathrm{O}}_7$ appears to have the smallest energy scale among the melilite-type compounds, and the small $J_2/J_1=0.0114\left(2\right)$ indicates the strong two dimensionality.

High-shear methods have long been used in experiments to refine grain structures in metals, yet the underlying mechanisms remain elusive. We demonstrate a refinement process using molecular dynamic simulations of iron wherein nanocrystalline structures are generated from initially perfect lattices under high-shear strain. The simulation cells undergo a highly disordered state, followed by an atomic reordering and grain coarsening, resulting in nanograins. We explore the dependence on parameters such as temperature, heat dissipation rate, shear strain rate, and carbon impurity concentration. Higher temperatures lead to the formation of larger and longer grains. The faster heat dissipation sample initially yields more small grains, but their number subsequently reduces and is lower than the slower heat dissipation sample at approximately $\gamma =1.5$. Slower strain rates do not promote nanograin formation. The presence of carbon impurities appears to have little effect on grain formation. This detailed analysis affords insight into the mechanisms that control the formation of nanograins under high-shear conditions.