Medium-entropy semiconductors represent a unique category of entropy-engineered materials. They possess a considerable level of randomness in atomic mixing, although this is not sufficient to conclusively achieve single-phase structure stabilization, in contrast to high-entropy materials. This introduces strong competition between the formation of different phases, which can potentially lead to structural heterogeneity. In this work, we uncover endotaxial nanoprecipitates in the microscopically identified homogeneous medium-entropy semiconductor AgMnSbPbTe4. These nanoprecipitates initially crystallize in a cubic phase (Fm3̅m) within kinetically stabilized AgMnSbPbTe4, subsequently evolving into a thermodynamically stable monoclinic phase (P21/c) during thermal annealing while maintaining an endotaxial relationship with the matrix lattice. This nanophase segregation and the resultant lattice mismatch at interfaces introduce strain fluctuations up to 5% at intervals of 20 nm across the entire microstructure. Within the matrix phase, atomic displacement of up to 23 pm was observed. This structural heterogeneity results in glass-like thermal transport behavior, achieving an ultralow lattice thermal conductivity κL = 0.312 Wm-1 K-1 at 800 K, which is in accordance with the amorphous limit predicted by the Cahill model. The synergy of band convergence effect and well-maintained carrier mobility leads to a maximum ZT of 1.72 at 800 K and an average ZTavg of 1.02 over the temperature range of 300-825 K. This study highlights that the underexplored structural heterogeneity in medium-entropy semiconductors can potentially yield beneficial phenomena, such as the phonon-glass electron-crystal transport behavior in this case, which holds promise for advancing thermoelectric applications.

Topological quantum materials have emerged as a frontier in condensed matter physics, with electronic states governed by symmetry and lattice geometry. Among the various lattices, kagome, chiral, and square-net lattices represent distinct structural motifs where topology is intrinsically encoded. These systems exhibit diverse quantum phenomena. This review highlights the roles of lattice geometry, symmetry, spin–orbit coupling, single crystal synthesis strategies, current challenges and future directions of such topological materials.

Topological kagome magnets offer a rich landscape for exploring the intricate interplay of quantum interactions among geometry, topology, spin, and correlation. GdTi 3 Bi 4 crystallizes in layered Ti-based kagome nets intertwined with zigzag Gd chains along the a axis and orders antiferromagnetically below ∼ 15 K . Here, we present the temperature- and field-dependent electrical transport of GdTi 3 Bi 4 in different directions. The material exhibits anomalous Hall conductivity (AHC) of 410 Ω − 1 c m − 1 at 2 K for μ 0 H ∥ c , and it is completely absent for μ 0 H ∥ a , despite the similar magnetizations observed in both orientations. This behavior is quite contradictory, as the anomalous Hall effect (AHE) typically scales with the magnetization. Through first-principles calculations, it is demonstrated that in the presence of time-reversal symmetry broken by the Gd 4 f sublattice and spin-orbit coupling, the magnetization direction controls the orbital mixing in the Ti t 2 g bands, relocating Berry-curvature hot spots and producing the observed orientation-selective AHC. The results establish GdTi 3 Bi 4 as a platform for investigating new avenues of the AHE, such as directional AHE, and thus shed light on the intricate coupling between magnetic and electronic structures, paving the way for exploring novel quantum phenomena.

Topological kagome magnets offer a rich landscape for exploring the intricate interplay of quantum interactions among geometry, topology, spin, and correlation. GdTi3Bi4 crystallizes in layered Ti-based kagome nets intertwined with zigzag Gd chains along the a axis and orders antiferromagnetically below '15 K. Here, we present the temperature-and field-dependent electrical transport of GdTi3Bi4 in different directions. The material exhibits anomalous Hall conductivity (AHC) of 410 ohm-1 cm-1 at 2 K for mu 0H H c, and it is completely absent for mu 0H H a, despite the similar magnetizations observed in both orientations. This behavior is quite contradictory, as the anomalous Hall effect (AHE) typically scales with the magnetization. Through first-principles calculations, it is demonstrated that in the presence of time-reversal symmetry broken by the Gd 4 f sublattice and spin-orbit coupling, the magnetization direction controls the orbital mixing in the Ti t2g bands, relocating Berry-curvature hot spots and producing the observed orientation-selective AHC. The results establish GdTi3Bi4 as a platform for investigating new avenues of the AHE, such as directional AHE, and thus shed light on the intricate coupling between magnetic and electronic structures, paving the way for exploring novel quantum phenomena.

The convergence of crystalline symmetry, spin-orbit coupling (SOC), and electron correlations provides a powerful route to realizing quantum states with nontrivial topology and exotic transport responses. Here, the discovery of a topological semimetallic state is reported in BiRe2O6, a newly identified 5d metallic oxide that combines low carrier density with high mobility and nonsymmorphic symmetry protection. Density functional theory (DFT) calculations and angle-resolved photoemission spectroscopy (ARPES) measurements reveal the presence of gapless Dirac cones located at high symmetry points of the Brillouin zone, stabilized by nonsymmorphic symmetry and robust against strong SOC. This results in a remarkably high mobility of 1.95 x 104 cm2 V-1 s-1 and large magnetoresistance (MR). Angle-dependent magnetotransport measurements further uncover a field-induced butterfly-like anisotropic magnetoresistance (AMR), reflecting the orbital motion of carriers on an anisotropic Fermi surface. Additionally, de Haas-van Alphen (dHvA) quantum oscillations demonstrate a quasi-2D Fermi surface with nontrivial band topology, consistent with both DFT and ARPES results. While the experimental and DFT band structures align at U = 0, the Kadowaki-Woods and Wilson ratios suggest moderate electronic correlations. These findings establish BiRe2O6 as a promising platform for investigating the interplay of topological protection, SOC, and electron correlations in low-density 5d oxides.

The transverse thermoelectric (Nernst) effect is a powerful probe for studying the electronic and structural properties of materials. In this study, we employ transverse thermoelectric measurements to investigate the ferroelectric distortion in the topological crystalline insulator (TCI) Pb0.60Sn0.40Te, a compound derived from PbTe and SnTe, known for their exceptional thermoelectric performance and distinct ferroelectric properties. By leveraging Nernst measurements, we provide direct evidence of ferroelectric distortion in this TCI, corroborated by Shubnikov-de Haas quantum oscillations that confirm the presence of two topologically nontrivial Fermi pockets. Density functional theory calculations show that these pockets originate from the L and T points in the Brillouin zone of the distorted structure within the TCI phase. Raman spectroscopy further identifies a structural phase transition below 50 K, consistent with the quantum oscillation observations. This observation is further substantiated by temperature-dependent synchrotron X-ray pair distribution function analysis and transmission electron microscopy, which confirm the local off-centering of cations at low temperature. These findings underscore the potential of transverse thermoelectric measurements in unveiling ferroelectric distortions and their role in modulating topological quantum states, opening new directions for research into the synergy between ferroelectricity and topological phases.

Given their rich chemical diversity and the interplay among the p-, d-, and f-orbitals of chalcogens, transition metals, and lanthanides, respectively, rare-earth transition-metal chalcogenides exhibit a wide variety of structural, magnetic, and transport phenomena. As a result, they form a particularly appealing platform for investigating structure-property relationships, emergent electronic and magnetic behaviors, and thermal transport. Here we investigate AgErTe2 as a model system to understand phonon-glass behavior in ordered crystalline solids, which establishes the design principles for thermal barrier coatings and next-generation thermoelectrics. The local bonding asymmetry and lattice softness suppress the inherently low lattice thermal conductivity, resembling the characteristics of amorphous materials. This suppression is significantly influenced by local off-centering of Ag atoms, which breaks lattice periodicity while maintaining global crystallinity. The presence of antibonding states just below the Fermi level, arising from Ag 4d and Te 5p orbital interactions, leads to lattice softening and destabilizes ideal tetrahedral coordination, resulting in a pseudo Jahn-Teller distortion. Furthermore, the coexistence of weaker, more polarizable Ag-Te bonds and stronger Er-Te bonds creates a complex vibrational landscape enriched with low-frequency modes and enhanced phonon scattering. A pronounced disparity in interatomic force constants gives rise to highly localized, low-energy optical phonons linked to Ag rattling. These flat vibrational modes exhibit strong coupling with transverse acoustic phonons, resulting in ultrashort phonon lifetimes and mean free paths approaching interatomic distances. These features collectively enhance phonon scattering across a broad range of length and energy scales. This work offers a framework for engineering suppressed thermal conductivity in crystalline systems without the introduction of alloying elements.

Spin-gapless semiconductors (SGSs) represent an intriguing class of quantum materials that bridge the gap between half-metallic ferromagnets and conventional semiconductors, offering promising avenues for spintronic applications. The discovery of intrinsic ferromagnetism in ultrathin two-dimensional van der Waals crystals has further fueled interest in exploring magnetism at the ultimate two-dimensional limit. Here, we demonstrate the growth of environmentally stable, atomically thin Co3Sn2S2 nanosheets via a simple hydrothermal method. These nanosheets exhibit robust ferromagnetism with a Curie temperature of ∼100 K and remarkably, host a spin-gapless semiconducting (SGS) state, distinct from the well-known half-metallic Weyl ferromagnetism observed in the bulk counterpart. Structural analysis reveals that enhanced lattice distortion and strain effects in the nanosheets, induced by reduced dimensionality and surface defects, play a critical role in stabilizing this phase. Williamson-Hall analysis confirms the presence of strain, while DFT calculations reveal that strain-induced lattice distortions annihilate the Weyl points and the emergence of SGS semiconductivity. Charge transport measurements indicate a Mott variable-range hopping mechanism, while temperature-dependent conductivity suggests a coexistence of semiconducting and weakly gapless features. These findings not only establish atomically thin Co3Sn2S2 nanosheets as a novel platform for SGS physics but also open up exciting possibilities for strain-engineered topological phases and next-generation spintronic and quantum technologies.

Berry curvature physics is responsible for the anomalous electromagnetic responses in solids. One such response is the circular photogalvanic effect (CPGE), typically observed in systems with pronounced Berry curvature─such as flat-band systems or topological semimetals featuring band crossings near the Fermi level, where Berry curvature exhibits sharp discontinuities. To maximize CPGE, one must develop the ability to tune their electronic band dispersion without introducing disorder, which is a challenging endeavor. Here, we demonstrate that it is possible to maximize the CPGE response in a topological material by a fundamentally different approach: controlling the proximity of a given system to a symmetry-breaking phase transition that induces a reconstruction of the electronic band structure. Through measurements of the longitudinal circular photogalvanic effect in the Weyl semimetal (TaSe4)2I, we show that the circular photogalvanic effect can be amplified by a dramatic factor of 2 by tuning the proximity of this compound to charge density wave order. The first-principles calculations we present here show that this enhancement arises from the development of the CDW order parameter and the divergence of the associated relaxation time near the critical temperature. Therefore, this work provides a paradigm for boosting CPGE responses in solids─not by engineering band structure alone but by exploiting critical fluctuations near phase transitions in topological materials.

The green phase compounds R2BaCuO5 (R = Rare earth) have recently emerged as promising candidates for magnetoelectric coupling arising from 4 f-3d exchange interactions. Here, we report the discovery of multiferroicity in a previously unexplored magnetic phase of Yb2BaCuO5. While earlier studies identified two antiferromagnetic (AFM) transitions below 15 K, our comprehensive investigation using magnetic, heat capacity, and neutron diffraction reveals three successive magnetic transitions occurring at TN1 = 15.9 K, TN2 = 5.2 K, and TN3 = 3.5 K. Neutron diffraction study evidences a sequence of magnetic phases: a transition from a paramagnetic state to (i) a first commensurate (CM) AFM phase with k1 = (0, 1/2, 0), below TN1, (ii) an incommensurate (ICM) AFM phase with k2 = (0, delta, 0), below TN2, and (iii) a second commensurate AFM phase with k3 = (0, 1/2, 1/2) below TN3. Notably, multiferroic behavior emerges exclusively in the incommensurate AFM region, consistent with the deduced polar magnetic symmetry 2mm. These results establish Yb2BaCuO5 as a new spin-driven multiferroic and underscore the critical role of 4 f-3d coupling in governing the magnetoelectric properties of the R2BaCuO5 family.

Compounds with kagome lattice structure are known to exhibit Dirac cones, flat bands, and van Hove singularities, which host numerous versatile quantum phenomena. Inspired by these intriguing properties, we investigate the temperature and magnetic field dependent electrical transports along with the theoretical calculations of ScV6Sn6, a nonmagnetic charge density wave (CDW) compound. At low temperatures, the compound exhibits Shubnikov-de Haas quantum oscillations, which help to design the Fermi surface (FS) topology. This analysis reveals the existence of several small FSs in the Brillouin zone, combined with a large FS. Among them, the FS possessing Dirac band is a non-trivial and generates a non-zero Berry phase. In addition, the compound also shows the anomalous Hall-like behaviour up to the CDW with the CDW phase, ScV6Sn6 presents a unique material example of the versatile HfFe6Ge6 family and provides various promising opportunities to explore the series further.

We report a comprehensive investigation into the magnetic and magnetoelectric characteristics of green phase compounds R2BaCuO5 (R = Er, Eu, Y, Tm, and Lu) through an array of experimental techniques, including dc magnetization, specific heat, dielectric, pyrocurrent, and neutron diffraction measurements. Our study reveals that all these compounds exhibit antiferromagnetic ordering of Cu2+ ions in the range T Cu Specifically, magnetic ordering of Er3+ ions is observed at T Er of Tm3+ ions is not observed. Furthermore, the isothermal magnetization curves for the Er compound confirm the metamagnetic transition at a critical magnetic field of Hc = 0.9 T, reaching a saturation magnetization value of 9 mu B/f.u. Notably, above Hc, this compound exhibits field-induced magnetoelectric states at TNEr ,underscoring a pronounced magnetoelectric coupling. Conversely, the compounds with R = Eu, Y, Tm, and Lu do not display magnetoelectric coupling. The presence or absence of such coupling aligns with the magnetic symmetry derived from neutron diffraction. Our findings conclusively establish that 4 f -3d exchange coupling is pivotal in enabling the magnetoelectric or multiferroic properties in these well-established green phase compounds. Consequently, our study underscores the rich and diverse magnetism and magnetoelectric properties exhibited by the green phase family, positioning them as equally intriguing as manganites in condensed matter physics.

A topological magnetic material showcases a multitude of intriguing properties resulting from the compelling interplay between topology and magnetism. These include notable phenomena such as a large anomalous Nernst effect (ANE), an anomalous Hall effect (AHE), and a topological Hall effect (THE). In most cases, topological transport phenomena are prevalent at temperatures considerably lower than room temperature, presenting a challenge for practical applications. However, the noncollinear ferromagnetic (FM) LaMn 2 Ge 2 , characterized by a Mn square-net lattice and a notably high Curie temperature ( T C ) of approximately 325 K, defies this trend as a topological semimetal. This work observes a giant topological Hall resistivity, ρ y x T $\rho _{yx}^T$ , of ≈4.5 µΩ cm at room temperature when the angle between the applied field and the c -axis is 75°, which is significantly higher than state-of-the-art materials with noncoplanar spin structures. The single crystal neutron diffraction measurements agree with an incommensurate conical magnetic structure as the ground state. This observation suggests the enhanced spin chirality resulting from the noncoplanar spin configuration when the applied field is away from the magnetic easy axis as the origin of a large contribution to the observed THE. The findings unequivocally demonstrate that the FM LaMn 2 Ge 2 holds great promise as a potential topological semimetal for spintronic applications even at room temperature.

Colossal magnetoresistance (CMR) is an exotic phenomenon that allows for the efficient magnetic control of electrical resistivity and has attracted significant attention in condensed matter due to its potential for memory and spintronic applications. Heusler alloys are the subject of considerable interest in this context due to the electronic properties that result from the nontrivial band topology. Here, the observation of CMR near room temperature is reported in the shape memory Heusler alloy Ni 2 Mn 1.4 In 0.6 , which is attributed to the combined effects of magnetic field-induced martensite twin variant reorientation (MFIR) and magnetic field-induced structural phase transformation (MFIPT). This compound undergoes a structural phase transition from a cubic (austenite-L2 1 ) ferromagnetic (FM) to a monoclinic (martensite) antiferromagnetic (AFM), which leads to an effective increase in the size of the Fermi surface and consequently in CMR. Additionally, it exhibits significant anomalous Hall conductivity in both antiferromagnetic and ferromagnetic phases. Furthermore, it demonstrates a giant topological Hall resistivity (THR) ρ yx T $\rho _{{\mathrm{yx}}}^{\mathrm{T}}$ ≈6 µΩ.cm in the vicinity of martensite transition due to the enhanced spin chirality resulting from the formation of magnetic domains with Bloch-type domain walls. The findings contribute to the understanding of the magnetotransport of Ni-Mn-In Heusler alloys, which are prospective candidates for room-temperature spintronic applications.

Cation-ordered polar (Pna21) materials RFeWO6 (R = rare earth) have gained significant attention due to their multiferroic properties. These materials are derived from the parent aeschynite-type material CaTa2O6 possessing a centrosymmetric orthorhombic structure (Pnma). The ordering of M3+ and W6+ ions in the octahedral sites with distinct Wyckoff positions breaks the inversion symmetry of the parent structure. Our investigation of TbFeWO6 using symmetry-adapted mode analysis, neutron powder diffraction, and density functional theory calculations (DFT) has revealed that the ordered polar (Pna21) structure can emerge from ordered centrosymmetric (Pnam or Pnan) structures through the relaxation of stress. Our low-temperature neutron diffraction experiments have provided evidence of a noncollinear commensurate magnetic structure exhibiting polar magnetic symmetry m (magnetic space group: Cac), consistent with the observed additional polarization below TN. Based on the spin structure, we propose that the mechanisms of exchange striction and/or inverse Dzyaloshinskii-Moriya may serve as origins of the multiferroic behavior exhibited by these materials.

We report a comprehensive investigation into the magnetic and magnetoelectric characteristics of green phase compounds ${R}_{2}\mathrm{BaCu}{\mathrm{O}}_{5}$ ($R=\mathrm{Er}$, Eu, Y, Tm, and Lu) through an array of experimental techniques, including dc magnetization, specific heat, dielectric, pyrocurrent, and neutron diffraction measurements. Our study reveals that all these compounds exhibit antiferromagnetic ordering of $\mathrm{C}{\mathrm{u}}^{2+}$ ions in the range ${T}_{\mathrm{N}}^{\mathrm{Cu}}$ = 15--20 K. Specifically, magnetic ordering of $\mathrm{E}{\mathrm{r}}^{3+}$ ions is observed at ${T}_{\mathrm{N}}^{\mathrm{Er}}$ = 5.1 K. Intriguingly, independent ordering of $\mathrm{T}{\mathrm{m}}^{3+}$ ions is not observed. Furthermore, the isothermal magnetization curves for the Er compound confirm the metamagnetic transition at a critical magnetic field of ${\mathrm{H}}_{\mathrm{c}}=0.9\phantom{\rule{0.16em}{0ex}}\mathrm{T}$, reaching a saturation magnetization value of $9\phantom{\rule{0.16em}{0ex}}{\textmu{}}_{\mathrm{B}}/\mathrm{f}.\mathrm{u}.$ Notably, above ${\mathrm{H}}_{\mathrm{c}}$, this compound exhibits field-induced magnetoelectric states at ${T}_{\mathrm{N}}^{\mathrm{Er}}$, underscoring a pronounced magnetoelectric coupling. Conversely, the compounds with $R=\mathrm{Eu}$, Y, Tm, and Lu do not display magnetoelectric coupling. The presence or absence of such coupling aligns with the magnetic symmetry derived from neutron diffraction. Our findings conclusively establish that $4f\text{\ensuremath{-}}3d$ exchange coupling is pivotal in enabling the magnetoelectric or multiferroic properties in these well-established green phase compounds. Consequently, our study underscores the rich and diverse magnetism and magnetoelectric properties exhibited by the green phase family, positioning them as equally intriguing as manganites in condensed matter physics.

The magnetic properties of disordered Nd0.5Ba0.5Mn0.5Fe0.5O3-delta/2 and ordered NdBaMnFeO6-delta perovskites were investigated through temperature- and field-dependent DC-magnetization measurements. The temperature dependence of magnetic susceptibilities revealed that antiferromagnetic ordering occurs at temperatures below 185 K for the disordered Nd0.5Ba0.5Mn0.5Fe0.5O3-delta/2 sample, whereas the ordered NdBaMnFeO6-delta perovskite exhibited a paramagnetic state throughout the entire temperature range examined. Notably, the disordered sample exhibited a glassy state, even at room temperature, which transformed into an antiferromagnetic state under higher applied magnetic fields. The magnetic ordering in the disordered Nd0.5Ba0.5Mn0.5Fe0.5O3-delta/2 perovskite and the magnetic-disordering state in the structurally ordered NdBaMnFeO6-delta perovskite could be attributed to the alteration of the oxidation state of Mn.

The combination of structural chirality and magnetism leads to the formation of spin chirality through noncoplanar magnetic structures, resulting in unusual electronic transport properties. The spin chirality generates nonzero Berry curvature in real space, acting as an emergent magnetic field and contributing to the unconventional anomalous Hall effect, known as the geometrical or topological Hall effect (THE). This study unveils the remarkable occurrence of THE in a chiral antiferromagnetic (AFM) semiconductor EuIr2P2 in the hopping regime. It exhibits a complex incommensurately spiral AFM ground state due to its chiral crystalline structure, providing fertile ground for the emergence of topologically nontrivial spin textures such as skyrmions. A substantial THE is observed under finite magnetic fields, making EuIr2P2 an exceptional case within the ultralow-conductivity hopping regime for investigating the interplay between topologically nontrivial magnetic structures and hopping carriers. Owing to its semiconducting nature, we have formulated a theoretical model based on Mott's variable range-hopping mechanism, effectively elucidating the temperature and magnetic fielddependent behavior of THE. EuIr2P2 thus serves as an ideal candidate for comprehending transport properties in the hopping regime and offers a unique opportunity for the implementation of AFM semiconductor-based spintronic devices.

The zeolitic imidazolate framework, ZIF-4, exhibits soft porosity and is known to show pore volume changes with temperatures, pressures, and guest adsorption. However, the mechanism and adsorption behavior of ZIF-4 are not completely understood. In this work, we report an open to narrow pore transition in ZIF-4 around T ∼ 253 K upon lowering the temperature under vacuum (10-6 Torr) conditions, facilitated by C-H···π interactions. In the gaseous environment of N2 and CO2 around the framework, characteristic Raman peaks of adsorbed gases were observed under ambient conditions of 293 K and 1 atm. A guest-induced transition at ∼153 K resulting in the opening of new adsorption sites was inferred from the Raman spectral changes in the C-H stretching modes and low-frequency modes (<200 cm-1). In contrast to a single vibrational mode generally reported for entrapped N2, we show three Raman modes of adsorbed N2 in ZIF-4. The adsorption is facilitated by dispersive and quadrupolar interactions. From our temperature-dependent Raman results and theoretical analysis based on the density functional tight-binding approach, we conclude that the C-Hs are the preferred adsorption sites on ZIF-4 in the following order: C4-H, C5-H > C2-H > center of the Im ring (interacting with C-H centers) > center of the cavity. We also show that with an increasing concentration of N2 adsorbed at low temperatures, the ZIF-4 structure undergoes shear distortion of the window formed by 4-imidazole rings and consequent volumetric expansion. Our results have immediate implications in the field of porous materials and could be vital in identifying subtle structural transformations that may favor or hinder guest adsorption.