Quenched disorder can profoundly modify phase transitions. In low-dimensional systems, theory predicts that even weak quenched disorder can round the thermodynamic discontinuities associated with a first-order phase transition. Here, we employ time-domain terahertz spectroscopy to investigate the quasi-two-dimensional trimerized kagome van der Waals magnet family Nb_3Cl_8-xBr_x (x=0, 1 and 8). We observe the emergence of an additional phonon branch upon Br substitution, whose spectral weight increases and frequency softens with increasing Br concentration. The temperature evolution of the phonon frequencies reveals a clean first-order transition in Nb_3Cl_8 characterized by macroscopic phase coexistence and thermal hysteresis. In contrast, the transition in the substitutionally disordered compound Nb_3Cl_7Br retains its hysteresis while exhibiting a substantially broadened transition with no resolvable macroscopic phase coexistence. These observations reveal disorder-induced fragmentation of the transition into locally favored domains instead of well-defined bulk phases separated by stable phase boundaries. The behavior is consistent with the Imry-Wortis and the Aizenman-Wehr scenarios for the effect of quenched disorder in low-dimensional systems, which destabilizes macroscopic phase coexistence and rounds the thermodynamic discontinuities associated with first-order transitions. Thermal hysteresis persists in the disordered compound despite the lack of resolvable coexistence, indicating that the two features often treated as a single hallmark of first-order character arise distinctly and can be separated by disorder. Moreover, our results establish Nb_3Cl_8-xBr_x as a promising platform for investigating the effects of disorder on first-order transitions in low-dimensional systems.

Although Large Language Models (LLM) and Artificial Intelligence (AI) tools have enabled a rapid increase in the generation rate of predicted materials, the rate of new materials discovery has lagged behind. This is due to the challenges associated with designing a sequence of chemical reactions to predictably produce new materials, especially in new structure types. Here, we report a study of human and LLM generated recipes for the synthesis of known and new materials. The success of the recipes is determined through in-lab experimentation, and the results are passed back to the humans and LLMs in a closed-loop process to study the effects of their collaboration. The Ruddlesden-Popper homologous series was selected for all material candidates to provide a materials phase space that is simultaneously well studied and likely to host undiscovered materials. We find that humans (H) and LLM (L) have similar success rates: 83(8)

Abstract Incorporation of AlyGa1–yN semiconductors into high-power electronics offers efficiency improvements in power transmission, generation, and use, if approaches to eliminate the defects arising from film-lattice mismatch can be established. Here, we report the optical floating zone crystal growth of Ta1–xHfxC0.5 (x = 0.2), a new metallic substrate material family lattice matched to the ultrawide-band gap, Al-rich side (y = 0.91) of the AlyGa1–yN solid solution. Laue diffraction demonstrates large single-crystal domains in the as-grown boule. Single-crystal X-ray diffraction at T = 213 K in conjunction with first-principles calculations shows that the material adopts a layered crystal structure with AA-type stacking of (Ta/Hf)-C-(Ta/Hf) trilayers described in the trigonal space group P3̅m1 (#164), with a = 3. 1168(4) Å, c = 4.9644(4) Å, and β = 120.0°. X-ray photoelectron spectroscopy (XPS) measurements show the Hf:Ta ratio to be close to the nominal value of 0.8:0.2 in the grown crystal. Density Functional Theory calculations reveal that this structure is stabilized by the low energy of carbon-vacancy formation of a hypothetical (Ta/Hf)1C1 anti-NiAs structure type, and imply flexibility in interface structure with an overlayer nitride film. A surface preparation/polishing procedure is developed that reduces root-mean-square (RMS) surface roughness from as-cut 130 to 7 nm as measured by atomic force microscopy. Scanning electron microscopy shows the presence of a native surface oxide, removed by polishing, along with carbon-rich pits. Time-domain thermoreflectance measurements show a room temperature thermal conductivity of κ = 18.1(4) W m–1 K–1. These results provide key first steps for utilizing metallic, lattice-matched substrates for the growth of Al-rich AlyGa1–yN semiconductors.

In recent years, magnetically-frustrated triangular and honeycomb lattice cobaltates have seen extensive study in the pursuit of a quantum spin liquid (QSL) state in a real material. In this work, we describe the hydroflux synthesis of K_2Co_2(TeO_3)_3 · 2.5 H_2O (KCoTOH), a novel zemannite-type antiferromagnet (AFM) possessing structural elements of both triangular dimer and honeycomb structural motifs. Bulk magnetometry and specific heat data support the onset of long-range AFM order below T_N = 7.6(1) K, with neutron diffraction and muon spin relaxation (μSR) measurements placing the majority of the ordered moment within the pseudo-honeycomb plane. We resolve three unique oscillation frequencies from the zero-field μSR spectra, additionally suggesting a remarkably low level of structural disorder in as-grown KCoTOH crystals. Whereas interactions between dimerized chains of Co^2+ cations are typically observed to be negligible or ferromagnetic in nature, the largely planar ordering motif observed in KCoTOH is instead stabilized by net antiferromagnetic interactions through bridging tellurite groups. This work highlights the potential of hydroflux synthesis methods in the stabilization of magnetic materials possessing novel and potentially more frustrated lattice geometries.

Incorporation of Al_yGa_1-yN (AGN) semiconductors into high power electronics offers efficiency improvements in power transmission, generation, and use, if approaches to eliminate the defects arising from film-lattice mismatch can be established. Here, we report the optical floating zone crystal growth of Ta_1-xHf_xC_0.5 (x = 0.2), a new metallic substrate material family lattice matched to the ultra-wide-band-gap, Al-rich side (y = 0.91) of the AGN solid solution. Laue diffraction demonstrates large single crystal domains in the as-grown boule. Single crystal x-ray diffraction at T = 213 K in conjunction with first principles calculations shows that the material adopts a layered crystal structure with AA-type stacking of (Ta/Hf)-C-(Ta/Hf) trilayers described in the trigonal space group P-3m1 (#164), with a = 3.1168(4) Å, c = 4.9644(4) Å, and β = 120.0°. X-ray photoelectron spectroscopy (XPS) measurements show the Hf:Ta ratio to be close to the nominal value of 0.8:0.2 in the grown crystal. Density Functional Theory calculations reveal that this structure is stabilized by the low energy of carbon-vacancy formation of a hypothetical (Ta/Hf)_1C_1 anti-NiAs structure type, and imply flexibility in interface structure with an overlayer nitride film. A surface preparation/polishing procedure is developed that reduces root mean square (RMS) surface roughness from as-cut 130 nm to 7 nm as measured by atomic force microscopy. Scanning electron microscopy shows the presence of a native surface oxide, removed by polishing, along with carbon-rich pits. Time-domain thermoreflectance measurements show a room temperature thermal conductivity of κ = 18.1(4) W m-1 K-1. These results provide key first steps for utilizing metallic, lattice matched, substrates for the growth of Al-rich AGN semiconductors.

Polar metals and noncentrosymmetric superconductors are exceptionally rare, yet their broken inversion symmetry can give rise to emergent electronic phenomena including mixed singlet-triplet superconducting pairing. As only a few such materials have been found among known compounds, accessing new examples requires synthetic strategies that go beyond conventional crystal growth. Here, we use electrochemical topotactic deintercalation to remove Pb from the centrosymmetric parent compound Au_2PbP_2, producing the polar metal Au_2Pb_0.914P_2. Unlike conventional chemical doping, this transformation actively drives structural symmetry-breaking: the partial removal of Pb triggers a cooperative electronic and geometric rearrangement, mediated by a second-order Jahn-Teller effect and stereochemically active lone pairs, that locks the product into a polar, noncentrosymmetric superspace group Ama2(01g)ss0. We solve the complete (3+1)D modulated structure by synchrotron single-crystal X-ray diffraction and confirm the polar assignment through nonlinear electronic transport. Below T_c = 1.52 K, Au_2Pb_0.914P_2 becomes a type-II superconductor whose heat capacity and AC susceptibility both exhibit power-law behavior, suggestive of a gap structure governed by the broken inversion symmetry of the host lattice. This work establishes electrochemical oxidation as a rational route to metastable noncentrosymmetric superconductors through chemically directed symmetry-breaking.

There are a few examples of alloys with two or more passivating components where the specific role of each component in forming the passive film is understood. We examined the electrochemical passivation behavior of Fe1-xCrxVy alloys in 0.1 M H2SO4 in terms of the Cr + V content. Our results showed that for y $$\le$$ 0.04 we obtained an excellent fit to the percolation passivation theory, but for y > 0.04, the theory underestimated the number of monolayers dissolved in order for passivation to occur by about a factor of two. The chemical short-range order parameters for the alloys were characterized using neutron scattering; however, the differences among the alloys for y $$\le$$ 0.04 and y > 0.04 were minimal. Energy and wavelength dispersive spectroscopy revealed that all the alloys contained nanometer-scale V-oxygen clusters that served as sites for the initiation of pitting. Pit densities, pit diameters and pit depths were characterized using focused ion-beam machining, scanning electron microscopy and digital image analysis. These results allowed us to develop an analysis based on Faraday’s law for the difference in the number of monolayers dissolved for y = 0.04 and y > 0.04, and we found excellent agreement between our experimental results and the analysis. Our results provide a path forward for evaluating passivation behaviors of alloys that exhibit pitting.

We use a concerted theory-experiment effort to investigate the formation of chiral real space spin texture when the archetypal Dirac semimetal Cd3As2 is interfaced with In1-xMnxAs, a ferromagnetic semiconductor with perpendicular magnetic anisotropy. We combine density functional theory calculations, linear response theory for spin susceptibility and micromagnetic simulations to explore the possibility of chiral spin texture in this heterostructure. While a nonzero off-diagonal spin susceptibility in the Cd3As2 layer due to inversion symmetry breaking suggests the presence of Dzyaloshinskii-Moriya interaction (DMI) between local moments in the InMnAs layers, the amplitude may not be strong enough to give a "full" skyrmion texture. Instead, the interface states at the junction may promote a "partial" skyrmion texture. Using electrical magnetoresistance measurements at low temperature, we observe an emergent excess contribution to the transverse magnetoresistance whose behavior is consistent with a topological Hall effect arising from the formation of an interfacial chiral spin texture. This excess Hall voltage varies with gate voltage, indicating a promising electrostatically tunable platform for understanding the interplay between the helical momentum space states of a Dirac semimetal and chiral real-space spin textures in a ferromagnet.

ABSTRACT Magnetic skyrmions are topologically protected spin states that hold promise for shaping the future of electronics. Despite impressive progress in skyrmion research, the microscopic mechanisms underlying skyrmion phase transitions at specific temperatures and magnetic fields remain elusive. In this work, we systematically study the isostructural centrosymmetric magnets GdRu 2 X 2 (X = Si and Ge) and the role of X‐ p orbitals in modifying magnetic exchange interactions. Electronic structure and exchange interaction evaluations reveal that the more extended Ge‐4 p versus Si‐3 p orbitals enhance competing exchange interactions in GdRu 2 Ge 2 , thereby manifesting the evolution condition of skyrmions in GdRu 2 X 2 . GdRu 2 Ge 2 single crystals exhibit two high‐entropy regions associated with skyrmion phases at 0.9 T ≤ µ 0 H ≤ 1.2 T and 1.3 T ≤ µ 0 H ≤ 1.7 T, 2 K ≤ T ≤ 30 K—lower field and higher temperature conditions than those in the Si counterpart. Transport measurements reveal the topological Hall effect, validating the topologically nontrivial spin textures and Berry curvature. Our work bridges the gap between skyrmion discovery and material design by demonstrating, for the first time, how atomic‐scale control of exchange interactions enables tunable skyrmion phase transitions, making a significant step toward stabilizing skyrmions at desired temperatures and magnetic fields.

PSO-guided MD and explainable Al reveal that lower Mn/Cr and higher Co/Ni strengthen FeNiCoCrMn MPEA and provide molecular-level insights. Synthesized MPEAs showed qualitative agreement with predicted trends.

The superconducting diode effect occurs in superconducting materials in which both time-reversal and inversion symmetry are broken. The recently observed chirality-induced spin selectivity effect demonstrates that chiral materials break both symmetries. Thus, a Josephson junction interface with the left-handed structure on one side of the junction and the right-handed structure on the other should exhibit a diode effect. Here, we report the electrical transport properties of right-handed/left-handed and right-handed/right-handed devices fabricated from single crystals of the structurally chiral superconductor Mo3Al2C. Fraunhofer-like magnetic diffraction patterns confirm the presence of the Josephson effect in all but one of our devices. A magnetic-field-induced superconducting diode effect is demonstrated in the right-handed/left-handed devices by a statistically significant difference in Ic+ and divided by Ic-divided by, with a maximum asymmetry of 5%. The intrinsic superconducting diode effect is not observed in the right-handed/right-handed devices. We provide an explanation for the presence of the superconducting diode effect in the right-handed/left-handed devices.

Magnetic skyrmions are topologically protected spin states enabling high-density, low-power spin electronics. Despite growing efforts to find new skyrmion host systems, the microscopic mechanisms leading to skyrmion phase transitions at specific temperatures and magnetic fields remain elusive. Here, we systematically study the isostructural centrosymmetric magnets- GdRu2X2 (X = Si and Ge), and the role of X-p orbitals in modifying magnetic exchange interactions. GdRu2Ge2 single crystals, synthesized by arc melting, exhibit two high-entropy pockets associated with skyrmion phases at 0.9 T < H < 1.2 T and 1.3 T < H < 1.7 T, 2 K < T < 30 K-more accessible condition at lower fields and higher temperatures than that in the Si counterpart. Entropy estimations from heat capacity measurements align with magnetization data, and transport studies confirm a topological Hall effect, highlighting the system's nontrivial spin textures and Berry curvature. Compared to GdRu2Si2, electronic structure and exchange interaction evaluations reveal the more extended Ge-4p orbitals enhance competing exchange interactions in GdRu2Ge2, thereby manifesting the rich skyrmion behavior. This work demonstrates how modifying exchange interactions at the atomic level enables the tunability of topologically nontrivial electronic states while advancing our understanding of skyrmion formation mechanisms for future spintronics.

The appearance of spontaneous charge order in chemical systems is often associated with the emergence of novel, and useful, properties. Here we show through single crystal diffraction that the Eu ions in the mixed valent metal EuPd$_3$S$_4$ undergo long-range charge ordering at $T_{\mathrm{CO}} = 340 \mathrm{~K}$ resulting in simple cubic lattices of Eu$^{2+}$ ($J = 7/2$) and Eu$^{3+}$ ($J = 0$) ions. As only one of the two sublattices has a non-magnetic ground state, the charge order results in the emergence of remarkably simple G-type antiferromagnetic order at $T_{\mathrm{N}} = 2.85(6) \mathrm{~K}$, observed in magnetization, specific heat, and neutron diffraction. Application of a $0.3 \mathrm{~T}$ field is sufficient to induce a spin flop transition to a magnetically polarized, but still charge ordered, state. Density functional theory calculations show that this charge order also modifies the electronic degeneracies present in the material: without charge order, EuPd$_3$S$_4$ is an example of a double Dirac material containing 8-fold degenerate electronic states, greater than the maximum degeneracy of six possible in molecular systems. The symmetry reduction from charge order transmutes 8-fold double Dirac states into 4-fold Dirac states, a degeneracy that can be preserved even in the presence of the magnetic order. Our results show not only how charge order can be used to produce interesting magnetic lattices, but also how it can be used to engineer controlled degeneracies in electronic states.

Common belief is that the large band shifts observed in incommensurate misfit compounds, e.g., (LaSe)1.14(NbSe2)2, are due to interlayer charge transfer. By contrast, our analysis, based on both angle-resolved photoemission spectroscopy (ARPES) measurements and a specialized ab initio framework employing only quantities well defined in incommensurate materials, demonstrates that the large band shifts instead reflect changes in valence band hybridization and interlayer bonding. The strong alignment of our ab initio predictions and ARPES measurements confirms our understanding of the incommensurate electronic structure and charge transfer.

Large, high-purity single-crystals of hexagonal BN (h-BN) are essential for exploiting its many desirable and interesting properties. Here, we demonstrate via X-ray tomography, X-ray diffraction and scanning electron microscopy that h-BN crystals can be grown by traveling-solvent floating-zone (TSFZ). The diameters of grown boules range from 3-5 mm with lengths from 2-10 mm. Tomography indicates variable grain sizes within the boules, with the largest having areas of approximate to 1 mm x 2 mm and thickness approximate to 0.5 mm. Although the boules contain macroscale flux inclusions, the h-BN lattice itself is of high quality for samples grown under optimized conditions. The currently optimized growth procedure employs an Fe flux, moderate N2 pressure (PN2 approximate to 6 bar), and a growth rate of 0.1 mm/h. Raman spectroscopy for an optimized sample gives an average linewidth of 7.7(2) cm-1 for the E2g intralayer mode at 1365.46(4) cm-1 and 1.0(1) cm-1 for the E2g interlayer shear mode at 51.78(9) cm-1. The corresponding photoluminescence spectrum shows sharp phonon-assisted free exciton peaks and minimal signal in the energy range corresponding to carbon-related defects (E = 3.9-4.1 eV). Our work demonstrates the viability of growing h-BN by the TSFZ technique, thereby opening a new route towards larger, high-quality crystals and advancing the state of h-BN related research.

Elucidating the factors limiting quantum coherence in real materials is essential to the development of quantum technologies. Here we report a strategic approach to determine the effect of lattice dynamics on spin coherence lifetimes using oxygen deficient double perovskites as host materials. In addition to obtaining millisecond T_1 spin-lattice lifetimes at T 10 K, measurable quantum superpositions were observed up to room temperature. We determine that T_2 enhancement in Sr_2CaWO_6-δ over previously studied Ba_2CaWO_6-δ is caused by a dynamically-driven increase in effective site symmetry around the dominant paramagnetic site, assigned as W^5+ via electron paramagnetic resonance spectroscopy. Further, a combination of experimental and computational techniques enabled quantification of the relative strength of spin-phonon coupling of each phonon mode. This analysis demonstrates the effect of thermodynamics and site symmetry on the spin lifetimes of W^5+ paramagnetic defects, an important step in the process of reducing decoherence to produce longer-lived qubits.

The superconducting diode effect occurs in superconducting materials in which both spin and inversion symmetry are broken. The recently observed chirality-induced spin selectivity effect demonstrates that chiral materials break both symmetries. Thus a Josephson junction interface with the left-handed structure on one side of the junction and the right-handed structure on the other should exhibit a diode effect. Here, we report the electrical transport properties of right-handed/left-handed and right-handed/right-handed devices fabricated from single crystals of the structurally chiral superconductor Mo_3Al_2C. Fraunhofer-like magnetic diffraction patterns confirm the presence of Josephson effect in all but one of our devices. A magnetic field-induced superconducting diode effect is demonstrated in the right-handed/left-handed devices by a statistically significant difference in I_c+ and I_c-, with a maximum asymmetry of 5%. The intrinsic superconducting diode effect is not observed in the right-handed/right-handed devices. We provide an explanation for the presence of the superconducting diode effect in the right-handed/left-handed devices.

The hydrothermal synthesis of novel materials typically relies on both knowledge of the redox activities of all cations present in the reaction solution and a small toolset of so-called mineralizers to tune the solution's overall chemical potential. Upon the use of a less conventional mineralizer species, SiO2, we show the stabilization of spiroffite-type Co2Te3O8 under less forceful hydrothermal conditions than those in previous reports. When synthesized in the presence of both SiO2 and each respective alkali carbonate as a secondary mineralizer, silicon substitution in place of tellurium in the host structure becomes apparent, and the corresponding disorder introduced gives rise to enhanced low-temperature ferromagnetism. Our results highlight the complexities of underutilized and combined mineralizer species in the stabilization and tuning of complex magnetic ground states via hydrothermal synthesis techniques.

Machine learning (ML) approaches to materials discovery are limited by data curation, availability, and bias. These issues can be addressed through the generation of new data points representing novel material compositions and/or structures. We demonstrate the implementation of this process to produce and subsequently determine the stability of novel materials using a generative ML model. Furthermore, we successfully synthesize two predicted materials, LiZn2Pt and NiPt2Ga, and use these predictions to extrapolate to other unreported ternary compounds in the Heusler family. Our work demonstrates and expands the use of generative ML models to successfully discover and synthesize novel materials. This has broad implications for material exploration by design, as previous ML approaches to materials discovery were biased by the limits of known phase spaces and experimentalist bias, and has the potential to enable inverse-design of materials with targeted properties.