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The interaction between distinct excitations in solids is of both fundamental interest and technological importance. One such interaction is the coupling between an exciton, a Coulomb bound electron-hole pair, and a magnon, a collective spin excitation. The recent emergence of van der Waals magnetic semiconductors

Semiconductors, featuring tunable electrical transport, and magnets, featuring tunable spin configurations, form the basis of many information technologies. A long-standing challenge has been to realize materials that integrate and connect these two distinct properties. Two-dimensional (2D) materials offer a platform to realize this concept, but known 2D magnetic semiconductors are electrically insulating in their magnetic phase. Here we demonstrate tunable electron transport within the magnetic phase of the 2D semiconductor CrSBr and reveal strong coupling between its magnetic order and charge transport. This provides an opportunity to characterize the layer-dependent magnetic order of CrSBr down to the monolayer via magnetotransport. Exploiting the sensitivity of magnetoresistance to magnetic order, we uncover a second regime characterized by coupling between charge carriers and magnetic defects. The magnetoresistance within this regime can be dynamically and reversibly tuned by varying the carrier concentration using an electrostatic gate, providing a mechanism for controlling charge transport in 2D magnets.

Metal chalcophosphates, M2P2Q6 (M = transition metals; Q = chalcogen), are notable among the van der Waals materials family for their potential magnetic ordering that can be tuned with an appropriate choice of the metal or chalcogen. However, there has not been a systematic investigation of the basic structural evolution in these systems with alloying of the crystal subunits due to the challenge in the diffusion process of mixing different metal cations in the octahedral sites of M2P2Q6 materials. In this work, the P2S5 flux method was used to enable the synthesis of a multilayered mixed metal thiophosphate Fe2-xCoxP2S6 (x = 0, 0.25, 1, 1.75, and 2) system. Here, we studied the structural, vibrational, and electronic fingerprints of this mixed M2P2Q6 system. Structural and elemental analyses indicate a homogeneous stoichiometry averaged through the sample over multiple layers of Fe2-xCoxP2S6 compounds. It was observed that there is a correlation between the intensity of specific phonon modes and the alloying concentration. The increasing Co alloying concentration shows direct relations to the in-plane [P2S6]4- and out-of-plane P-P dimer vibrations. Interestingly, an unusual nonlinear electronic structure dependence on the metal alloying ratio is found and confirmed by two distinct work functions within the Fe2-xCoxP2S6 system. We believe this work provides a fundamental structural framework for mixed metal thiophosphate systems, which may assist in future studies on electronic and magnetic applications of this emerging class of binary cation materials.

We report a reactive flux technique using the common reagent P2S5 and metal precursors developed to circumvent the synthetic bottleneck for producing high-quality single- and mixed-metal two-dimensional (2D) thiophosphate materials. For the monometallic compound, M2P2S6 (M = Ni, Fe, and Mn), phase-pure materials were quickly synthesized and annealed at 650 °C for 1 h. Crystals of dimensions of several millimeters were grown for some of the metal thiophosphates using optimized heating profiles. The homogeneity of the bimetallic thiophosphates MM'P2S6 (M, M' = Ni, Fe, and Mn) was elucidated using energy-dispersive X-ray spectroscopy and Rietveld refinement. The quality of the selected materials was characterized by transmission electron microscopy and atomic force microscopy measurements. We report two novel bimetallic thiophosphates, MnCoP2S6 and FeCoP2S6. The Ni2P2S6 and MnNiP2S6 flux reactions were monitored in situ using variable-temperature powder X-ray diffraction to understand the formation reaction pathways. The phases were directly formed in a single step at approximately 375 °C. The work functions of the semiconducting materials were determined and ranged from 5.28 to 5.72 eV.

We report the open framework semiconductor, Sn4B12Se12, synthesized using a Sn/Se flux method. The framework in this compound features the rare icosahedral [B12Se12]14– anion assembled into a 3D tu...

Halide perovskite semiconductors are poised to revitalize the field of ionizing radiation detection as they have done to solar photovoltaics. We show that all-inorganic perovskite CsPbBr3 devices resolve 137Cs 662-keV γ-rays with 1.4% energy resolution, as well as other X- and γ-rays with energies ranging from tens of keV to over 1 MeV in ambipolar sensing and unipolar hole-only sensing modes with crystal volumes of 6.65 mm3 and 297 mm3, respectively. We report the scale-up of CsPbBr3 ingots to up to 1.5 inches in diameter with an excellent hole mobility–lifetime product of 8 × 10−3 cm2 V−1 and a long hole lifetime of up to 296 μs. CsPbBr3 detectors demonstrate a wide temperature region from ~2 °C to ~70 °C for stable operation. Detectors protected with suitable encapsulants show a uniform response for over 18 months. Consequently, we identify perovskite CsPbBr3 semiconductor as an exceptional candidate for new-generation high-energy γ-ray detection. Energy resolution of high-energy photon detectors is desired for applications ranging from biomedical imaging to homeland security. In this work, perovskite-based γ-ray detection with 1.4% energy resolution is demonstrated.

Highly efficient neutron detectors are critical in many sectors, including national security1,2, medicine3, crystallography4 and astronomy5. The main neutron detection technologies currently used involve 3He-gas-filled proportional counters6 and light scintillators7 for thermalized neutrons. Semiconductors could provide the next generation of neutron detectors because their advantages could make them competitive with or superior to existing detectors. In particular, solids with a high concentration of high-neutron-capture nuclides (such as 6Li, 10B) could be used to develop smaller detectors with high intrinsic efficiencies. However, no promising materials have been reported so far for the construction of direct-conversion semiconductor detectors. Here we report on the semiconductor LiInP2Se6 and demonstrate its potential as a candidate material for the direct detection of thermal neutrons at room temperature. This compound has a good thermal-neutron-capture cross-section, a suitable bandgap (2.06 electronvolts) and a favourable electronic band structure for efficient electron charge transport. We used α particles from an 241Am source as a proxy for the neutron-capture reaction and determined that the compact two-dimensional (2D) LiInP2Se6 detectors resolved the full-energy peak with an energy resolution of 13.9 per cent. Direct neutron detection from a moderated Pu–Be source was achieved using 6Li-enriched (95 per cent) LiInP2Se6 detectors with full-peak resolution. We anticipate that these results will spark interest in this field and enable the replacement of 3He counters by semiconductor-based neutron detectors. The semiconductor 6LiInP2Se6 is used for the direct detection of thermal neutrons at room temperature, demonstrating good energy resolution.

Two-dimensional (2D) magnetic semiconductors feature both tightly-bound excitons with large oscillator strength and potentially long-lived coherent magnons due to the presence of bandgap and spatial confinement. While magnons and excitons are energetically mismatched by orders of magnitude, their coupling can lead to efficient optical access to spin information. Here we report strong magnon-exciton coupling in the 2D van der Waals (vdW) antiferromagnetic (AFM) semiconductor CrSBr. Coherent magnons launched by above-gap excitation modulate the interlayer hybridization, which leads to dynamic modulation of excitonic energies. Time-resolved exciton sensing reveals magnons that can coherently travel beyond 7 micrometer, with coherence time above 5 ns. We observe this exciton-coupled coherent magnons in both even and odd number of layers, with and without compensated magnetization, down to the bilayer limit. Given the versatility of vdW heterostructures, these coherent 2D magnons may be basis for optically accessible magnonics and quantum interconnects., 14 pages, 5 figures, 30 pages Supporting Info

Metal chalcophosphates, M

The search for new halide perovskites has recently expanded to the double perovskites A2M+M3+X6, which form in the 3D elpasolite structure with alternating M+ and M3+ octahedra. Here, we report the...

We studied the narrow band-gap (0.55 eV) semiconductor K2.5Bi8.5Se14 as a potential thermoelectric material for power generation. Samples of polycrystalline K2.5Bi8.5Se14 prepared by spark plasma sintering exhibit exceptionally low lattice thermal conductivities (κlat) of 0.57–0.33 W m–1 K–1 in the temperature range of 300–873 K. The physical origin of such low κlat in K2.5Bi8.5Se14 is related to the strong anharmonicity and low phonon velocity caused by its complex low symmetry, large unit cell crystal structure, and mixed occupancy of Bi and K atoms in the lattice. High-resolution scanning transmission electron microscopy studies and microanalysis indicate that the K2.5Bi8.5Se14 sample is a single phase without intergrowth of the structurally related K2Bi8Se13 phase. The undoped material exhibits an n-type character and a figure-of-merit (ZT) value of 0.67 at 873 K. Electronic band structure calculations indicate that K2.5Bi8.5Se14 is an indirect band-gap semiconductor with multiple conduction bands clo...

The new compound NaCu4Se4 forms by the reaction of CuO and Cu in a molten sodium polyselenide flux, with the existence of CuO being unexpectedly critical to its synthesis. It adopts a layered hexagonal structure (space group P63/ mmc with cell parameters a = 3.9931(6) A and c = 25.167(5) A), consisting of infinite two-dimensional [Cu4Se4]- slabs separated by Na+ cations. X-ray photoelectron spectroscopy suggests that NaCu4Se4 is mixed-valent with the formula (Na+)(Cu+)4(Se2-)(Se-)(Se2)2-. NaCu4Se4 is a p-type metal with a carrier density of ∼1021 cm-3 and a high hole mobility of ∼808 cm2 V-1 s-1 at 2 K based on electronic transport measurements. First-principles calculations suggest the density of states around the Fermi level are composed of Cu-d and Se-p orbitals. At 2 K, a very large transverse magnetoresistance of ∼1400% was observed, with a nonsaturating, linear dependence on field up to 9 T. Our results indicate that the use of metal oxide chemical precursors can open reaction paths to new low-dimensional compounds.

We report a reactive flux technique using the common reagent P

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Halide perovskites exhibit remarkably high-performance as semiconductors compared to conventional materials because of an unusually favorable combination of optoelectronic properties. We demonstrate here that solution-grown single-crystals of organic–inorganic hybrid perovskite CH3NH3PbI3 (MAPbI3), implemented in a Schottky-type device design, can produce outstanding hard radiation detectors with high spectral response and low dark current for the first time. Schottky-type MAPbI3 detector achieves an excellent energy resolution of 6.8% for 57Co 122 keV gamma ray. The high detector performance is achieved due to the balanced charge collection efficiency for both electrons and holes, reflected in the high mobility-lifetime (μτ) products of both carriers (∼0.8 × 10–3 cm2/V). MAPbI3 also demonstrates remarkably long electron and hole lifetimes (τe = 10 μs and τh = 17 μs) and impressive operational stability over time. Furthermore, dual-source detection of α particle (5.5 MeV) and γ-ray (59.5 keV) from the 241...

The polyoxometalate (POM), H3PW12O40, was postsynthetically incorporated into the metal–organic framework (MOF), NU-1000. The POM@MOF composite, PW12@NU-1000, was activated under mild conditions, resulting in a material whose diffraction pattern and spectroscopic properties differ from the same material heated at elevated temperatures. These discrepancies, corroborated by difference envelope density analyses, were attributed to the POM residing either in the mesoporous or microporous channels of NU-1000. As a testament to the importance of catalyst accessibility, the POM's locational change also induced a change in the composite's rate and selectivity toward oxidizing 2-chloroethyl ethyl sulfide.

The common approach to the synthesis of a new material involves reactions held at high temperatures under certain conditions such as heating in a robust vessel in the dark for a period until it is judged to have concluded. Analysis of the vessel contents afterward provides knowledge of the final products only. Intermediates that may form during the reaction process remain unknown. This lack of awareness of transient intermediates represents lost opportunities for discovering materials or understanding how the final products form. Here we present new results using an emerging in situ monitoring approach that shows high potential in discovering new compounds. In situ synchrotron X-ray diffraction studies were conducted in the Cs/Sn/P/Se system. Powder mixtures of Cs2Se2, Sn, and PSe2 were heated to 650 °C and then cooled to room temperature while acquiring consecutive in situ synchrotron diffraction patterns from the beginning to the end of the reaction process. The diffraction data was translated into the ...

Highly efficient neutron detectors are critical in many sectors, including national security

The new compound NaCu