High-Temperature Anomalous Hall Effect in a Transition Metal Dichalcogenide Ferromagnetic Insulator Heterostructure

Excited State Band Mapping and Ultrafast Nonequilibrium Dynamics in Topological Dirac Semimetal 1T-ZrTe2

We performed time- and polarization-resolved extreme ultraviolet momentum microscopy on the topological Dirac semimetal candidate 1T-ZrTe2. Excited state band mapping uncovers the previously inaccessible linear dispersion of the Dirac cone above the Fermi level. We study the orbital texture of bands using linear dichroism in photoelectron angular distributions. These observations provide hints about the topological character of 1T-ZrTe2. Time-, energy-, and momentum-resolved nonequilibrium carrier dynamics reveal that intra- and interband scattering processes play a major role in the relaxation mechanism, leading to multivalley electron-hole accumulation near the Fermi level. We also show that electrons' inverse lifetime has a linear dependence as a function of their excess energy. Our time- and polarization-resolved XUV photoemission results shed light on the excited state electronic structure of 1T-ZrTe2 and provide valuable insights into the relatively unexplored field of quantum-state-resolved ultrafast dynamics in 3D topological Dirac semimetals.

Synthesis of Two-Dimensional MoO2 Nanoplates with Large Linear Magnetoresistance and Nonlinear Hall Effect

Two-dimensional (2D) materials with large linear magnetoresistance (LMR) are very interesting owing to their potential application in magnetic storage or sensor devices. Here, we report the synthesis of 2D MoO₂ nanoplates grown by a chemical vapor deposition (CVD) method and observe large LMR and nonlinear Hall behavior in MoO₂ nanoplates. As-obtained MoO₂ nanoplates exhibit rhombic shapes and high crystallinity. Electrical studies indicate that MoO₂ nanoplates feature a metallic nature with an excellent conductivity of up to 3.7 × 10⁷ S m^-1 at 2.5 K. MoO₂ nanoplates display a large LMR of up to 455% at 3 K and -9 T. A thickness-dependent LMR analysis suggests that LMR values increase upon increasing the thickness of nanoplates. Besides, nonlinearity has been found in the magnetic-field-dependent Hall resistance, which decreases with increasing temperatures. Our studies highlight that MoO₂ nanoplates are promising materials for fundamental studies and potential applications in magnetic storage devices.

Superconductivity in Te-Deficient ZrTe2

We present structural, electrical, and thermoelectric potential measurements on high-quality single crystals of ZrTe_1.8 grown from isothermal chemical vapor transport. These measurements show that the Te-deficient ZrTe_1.8, which forms the same structure as the nonsuperconducting ZrTe₂, is superconducting below 3.2 K. The temperature dependence of the upper critical field (H _c2) deviates from the behavior expected in conventional single-band superconductors, being best described by an electron-phonon two-gap superconducting model with strong intraband coupling. For the ZrTe_1.8 single crystals, the Seebeck potential measurements suggest that the charge carriers are predominantly negative, in agreement with the ab initio calculations. Through first-principles calculations within DFT, we show that the slight reduction of Te occupancy in ZrTe₂ unexpectedly gives origin to density of states peaks at the Fermi level due to the formation of localized Zr-d bands, possibly promoting electronic instabilities at the Fermi level and an increase at the critical temperature according to the standard BCS theory. These findings highlight that the Te deficiency promotes the electronic conditions for the stability of the superconducting ground state, suggesting that defects can fine-tune the electronic structure to support superconductivity.

Ultrafast photothermoelectric effect in Dirac semimetallic Cd3As2 revealed by terahertz emission

The thermoelectric effects of topological semimetals have attracted tremendous research interest because many topological semimetals are excellent thermoelectric materials and thermoelectricity serves as one of their most important potential applications. In this work, we reveal the transient photothermoelectric response of Dirac semimetallic Cd₃As₂, namely the photo-Seebeck effect and photo-Nernst effect, by studying the terahertz (THz) emission from the transient photocurrent induced by these effects. Our excitation polarization and power dependence confirm that the observed THz emission is due to photothermoelectric effect instead of other nonlinear optical effect. Furthermore, when a weak magnetic field (~0.4 T) is applied, the response clearly indicates an order of magnitude enhancement on transient photothermoelectric current generation compared to the photo-Seebeck effect. Such enhancement supports an ambipolar transport nature of the photo-Nernst current generation in Cd₃As₂. These results highlight the enhancement of thermoelectric performance can be achieved in topological Dirac semimetals based on the Nernst effect, and our transient studies pave the way for thermoelectric devices applicable for high field circumstance when nonequilibrium state matters. The large THz emission due to highly efficient photothermoelectric conversion is comparable to conventional semiconductors through optical rectification and photo-Dember effect.

Many topological semimetals are excellent thermoelectric materials, but previous studies were limited to steady-state properties. Here, the authors observe a transient thermoelectric response in Cd₃As₂ by detecting the resulting THz emission, with an enhanced response when a small magnetic field is applied.

2D Magnetic Heterostructures and Their Interface Modulated Magnetism

In recent years, two-dimensional (2D) magnetic heterostructures have captured widespread interest as they provide a fertile ground for exploring the novel properties induced by interfacial magnetic coupling, modulating the intrinsic magnetism of the 2D magnet, and exploiting new spintronic device applications. In this Spotlight on Applications, dominating synthetic strategies employed to fabricate 2D magnetic heterostructures are introduced first. Notably, we then concentrate on two different kinds of magnetic interfaces, namely, the magnetic-nonmagnetic interface and the magnetic-magnetic interface. Specifically, various interface modulated magnetisms such as valley splitting and the anomalous Hall effect as well as their related device applications such as magnetic tunnel junctions have been further reviewed and discussed. Finally, we briefly summarize the recent progress of 2D magnetic heterostructures and outline the future development direction of this booming field.

Role of Ferromagnetic Monolayer WSe2 Flakes in the Pt/Y3Fe5O12 Bilayer Structure in the Longitudinal Spin Seebeck Effect

The spin Seebeck effect (SSE) has attracted renewed interest as a promising phenomenon for energy harvesting systems. A noteworthy effort has been devoted to improving the SSE voltage by inserting ultrathin magnetic layers including Fe₇₀Cu₃₀ interlayers in Pt/Y₃Fe₅O₁₂ (Pt/YIG) systems with increased spin-mixing conductance at the interfaces. Nevertheless, the responsible underlying physics associated with the role of the interlayer in Pt/YIG systems in the SSE is still unknown. In this paper, we demonstrate that with a monolayer tungsten diselenide (ML WSe₂) interlayer in the Pt/YIG bilayer system, the longitudinal SSE (LSSE) voltage is significantly increased by the increased spin accumulation in the Pt layer; the spin fluctuation in ML WSe₂ amplifies the spin current transmission because the in-plane-aligned WSe₂ spins are coupled to thermally pumped spins under nonequilibrium magnetization conditions in the LSSE configuration at room temperature. The thermopower (V_LSSE/ΔT) improves by 323% with respect to the value of the reference Pt/YIG bilayer sample in the LSSE at room temperature. In addition, the induced ferromagnetic properties of the ML WSe₂ flakes on YIG increase the LSSE voltage (V_LSSE) of the sample; the ferromagnetic properties are a result of the improved magnetic moment density in the ML WSe₂ flakes and their two-dimensional (2D) ML nature in the LSSE under nonequilibrium magnetization conditions. The results can extend the application range of the materials in energy harvesting and provide important information on the physics of the LSSE with a transition metal dichalcogenide intermediate layer in spin transport.