Semimetal Compound Research Articles

Two-band superconductivity in Pt-intercalated ZrTe2, a Dirac semimetal

This study presents compelling evidence of superconductivity with 3.5 K onset and zero-resistance state at 2.25 K in the Dirac semimetal compound ZrTe2, upon intercalation with platinum in the van der Waals gap. The temperature dependence of the upper critical field and the normalized superfluid density can be modeled effectively using a two-gap model, consistent with the possibility of topological superconductivity.

Mechanical and Optical Properties of Topological Semimetal Compound YPtBi

We have reported the mechanical properties of topological semimetals half-Heusler compound YPtBi with LDA and GGA approximation which is implemented in density functional theory. We have calculated elastic parameters which ensure good machinability, covalent bonding, brittleness, low value of Kleinman parameter and high Vickers hardness. Our results reveal the hardness or large resistance of these topological semimetals. Moreover, Born mechanical stability conditions are well fulfilled by the topological semimetal YPtBi. Present study reveals that the low value of bulk modulus and shear modulus wheras high value of Youngs modulus of this topological semimetals which deforms easily with applied external force. We have also calculated optical properties of topological semi-metal YPtBi with both LDA and GGA. Optical properties are calculated in terms of dielectric function and we have calculated dielectric constant, optical reflectivity, absorption co-efficient, optical conductivity, refractive index and electron energy loss in the energy range 0 – 14 eV. We have found higher dielectric constants with GGA in comparison to LDA that imply YPtBi is excellent materials in solar cell applications. Also, YPtBi possess high refractive index in the visible range and it is optically isotropic.

Arsenite Impairs BRCA1-Dependent DNA Double-Strand Break Repair, a Mechanism Potentially Contributing to Genomic Instability.

BRCA1 is a key player in maintaining genomic integrity with multiple functions in DNA damage response (DDR) mechanisms. Due to its thiol-rich zinc-complexing domain, the protein may also be a potential target for redox-active and/or thiol-reactive (semi)metal compounds. The latter includes trivalent inorganic arsenic, which is indirectly genotoxic via induction of oxidative stress and inhibition of DNA repair pathways. In the present study, we investigated the effect of NaAsO2 on the transcriptional and functional DDR. Particular attention was paid to the potential impairment of BRCA1-mediated DDR mechanisms by arsenite by comparing BRCA1-deficient and -proficient cells. At the transcriptional level, arsenite itself activated several DDR mechanisms, including a pronounced oxidative stress and DNA damage response, mostly independent of BRCA1 status. However, at the functional level, a clear BRCA1 dependency was observed in both cell cycle regulation and cell death mechanisms after arsenite exposure. Furthermore, in the absence of arsenite, the lack of functional BRCA1 impaired the largely error-free homologous recombination (HR), leading to a shift towards the error-prone non-homologous end-joining (NHEJ). Arsenic treatment also induced this shift in BRCA1-proficient cells, indicating BRCA1 inactivation. Although BRCA1 bound to DNA DSBs induced via ionizing radiation, its dissociation was impaired, similarly to the downstream proteins RAD51 and RAD54. A shift from HR to NHEJ by arsenite was further supported by corresponding reporter gene assays. Taken together, arsenite appears to negatively affect HR via functional inactivation of BRCA1, possibly by interacting with its RING finger structure, which may compromise genomic stability.

Crystal structure and magnetic properties of Gd8Mn3Sb19

In this study, a novel magnetic semimetal compound, Gd8Mn3Sb19, was synthesized successfully via high-temperature solid-state reaction. The crystal structure of Gd8Mn3Sb19 was determined using both single crystal and powder X-ray diffraction techniques, revealing a non-centrosymmetric orthorhombic space group, Pmn21 (No. 31). The Sb atoms in Gd8Mn3Sb19 form five-atom-wide Sb57− ribbons, narrower three-atom-wide Sb35− ribbons, and single Sb3− anions. On the other hand, both Gd3+ and Mn2+ ions form the distorted Gd3 and Mn3 triangular lattices, respectively. The magnetic measurements suggest the complex magnetic interactions contributed by both Gd3+ and Mn2+ ions. A sharp peak observed in the magnetic susceptibility plot at approximately 25 K corresponds to the antiferromagnetic-type transition in Gd8Mn3Sb19. Furthermore, the magnetic measurements along different directions indicate the strong magnetic anisotropy present in Gd8Mn3Sb19, which is likely due to the complex magnetic interactions arising from the existence of Gd and Mn ions. Finally, the electrical resistivity measurements of Gd8Mn3Sb19 indicate semimetallic behavior with a positive magnetoresistance.

First-principles calculations for the effect of energetic point defect formation on electronic properties of the Weyl MX family (M = Nb, Ta; X = P, As)

• The unfolding technique was used for the first time to highlight the impact of point defects on the electronic band structure. • The transition metal Nb and Ta vacancies are energetically nearer to stability in the cases of NbAs and TaAs. • The pnictide P vacancy is energetically favorable among four possible point defects in both NbP and TaP. • For TaAs, the Ta vacancy concentration is significantly higher than all other types of defect concentrations. • All four of these compounds are thermodynamically, dynamically, and mechanically stable. By the first-principles of the density functional theory (DFT) approach, the structural parameters, elastic, vibrational, electronic properties, and enthalpies of formation of four stoichiometric Weyl semimetal compounds were evaluated. Besides, we calculated point defect formation energies and electronic band structures of defect-containing supercells by using an unfolding technique to highlight the effects of point defects (vacancies and anti-sites) on Weyl points in the electronic structure of these compounds. The transition metal Nb and Ta vacancies are energetically nearer to stability in the cases of NbAs and TaAs, but the pnictide P vacancy is energetically favorable among four possible point defects in both NbP and TaP. The band structure results, obtained from the unfold method, agree with defect formation energies at the ground state. Moreover, a true and accurate description of defects is based on the well-ordered compounds (NbAs, TaAs, NbP, and TaP). A relationship between temperature (K based on defect formation energies) and defect concentrations for these Weyl compounds was derived. In particular, for TaAs, the Ta vacancy concentration is significantly higher than all other types of defect concentrations.

First-principles calculations for structural, elastic, electronic, and phonon properties of topological WC-type TMO (TM = Ti, Zr and Hf; O) family

Through first-principles calculation, we have explored the first three (TiO, ZrO, and HfO) WC-type topological semimetal compounds in transition metal oxides and studied their structural, thermodynamic, elastic, electronic, and dynamical properties systematically. Among these three compounds, only TiO has been experimentally reported as a WC-type, and the other two, ZrO and HfO, are supposed to be WC-type materials. Our density functional theory derived results confirmed that these three compounds are structurally, thermodynamically, mechanically, and dynamically stable, which means they can be easily synthesized. The R. Hill approximation is used to calculate the actual bulk and shear modulus of the single crystal phase with the help of resultant elastic constants and the bulk and shear modulus of the W. Voigt and A. Reuss schemes. Among these compounds, TiO has a high bulk, shear modulus, and low passion ratio, which are directly linked to the high hardness of this compound. Furthermore, TiO is quite an unusual candidate due to the co-existence of 3-fold fundamental particles (3-fold fermions and 3-fold bosons) in the electronic band structure and phonon dispersion along the same Γ-A direction in the Brillouin zone, respectively, providing a perfect platform to explore the probable multi-functional quantum-mechanical properties of these two fundamental particles in a single crystal at the atomistic level. The spin-orbital coupling effect is ignored in TiO due to the light atomic masses of Ti and O elements, and their electronic and topological properties have been more studied.

The “Snow Line” on Venus’s Maxwell Montes: Varying Elevation Implies a Dynamic Atmosphere

Radar images of Venus’s tallest mountain range, Maxwell Montes, show a sharp increase in radar reflectivity, a “snow line,” at high elevation. This snow line has been inferred to represent a single common elevation (and thus temperature and pressure) above which metallic or semimetal compounds are present on the surface, either as direct precipitates from the atmosphere or from atmosphere–rock chemical reactions. Here, we show that Maxwell’s snow line is not at a constant elevation—it is ∼3.5 km higher in the NW than the SE. The best explanation is that atmospheric composition is not constant across Maxwell. The higher snow line elevation to the NW can be interpreted as a snow shadow, produced as winds from the SE cross Maxwell and becomes progressively depleted in its snow-producing component.

Degradable mesoporous semimetal antimony nanospheres for near-infrared II multimodal theranostics

Metallic and semimetallic mesoporous frameworks are of great importance owing to their unique properties and broad applications. However, semimetallic mesoporous structures cannot be obtained by the traditional template-mediated strategies due to the inevitable hydrolytic reaction of semimetal compounds. Therefore, it is yet challenging to fabricate mesoporous semimetal nanostructures, not even mention controlling their pore sizes. Here we develop a facile and robust selective etching route to synthesize monodispersed mesoporous antimony nanospheres (MSbNSs). The pore sizes of MSbNSs are tunable by carefully controlling the partial oxidation of Sb nuclei and the selective etching of the as-formed Sb2O3. MSbNSs show a wide absorption from visible to second near-infrared (NIR-II) region. Moreover, PEGylated MSbNSs are degradable and the degradation mechanism is further explained. The NIR-II photothermal performance of MSbNSs is promising with a high photothermal conversion efficiency of ~44% and intensive NIR-II photoacoustic signal. MSbNSs show potential as multifunctional nanomedicines for NIR-II photoacoustic imaging guided synergistic photothermal/chemo therapy in vivo. Our selective etching process would contribute to the development of various semimetallic mesoporous structures and efficient multimodal nanoplatforms for theranostics.

Transport in the non-Fermi liquid phase of isotropic Luttinger semimetals

Luttinger semimetals have quadratic band crossings at the Brillouin zone-center in three spatial dimensions. Coulomb interactions in a model that describes these systems stabilize a non-trivial fixed point associated with a non-Fermi liquid state, also known as the Luttinger-Abrikosov-Beneslavskii phase. We calculate the optical conductivity $\sigma (\omega) $ and the dc conductivity $\sigma_{dc} (T) $ of this phase, by means of the Kubo formula and the Mori-Zwanzig memory matrix method, respectively. Interestingly, we find that $\sigma (\omega) $, as a function of the frequency $\omega$ of an applied ac electric field, is characterized by a small violation of the hyperscaling property in the clean limit, which is in marked contrast to the low-energy effective theories that possess Dirac quasiparticles in the excitation spectrum and obey hyperscaling. Furthermore, the effects of weak short-ranged disorder on the temperature-dependence of $\sigma_{dc} (T)$ give rise to a much stronger power-law suppression at low temperatures compared to the clean limit. Our findings demonstrate that these disordered systems are actually power-law insulators. Our theoretical results agree qualitatively with the data from recent experiments performed on Luttinger semimetal compounds like the pyrochlore iridates [ (Y$_{1-x}$Pr$_x$)$_2$Ir$_2$O$_7$ ].

Patterning of type-II Dirac semimetal PtTe2 for optimized interface of tellurene optoelectronic device

The controllable transformation between the semiconductor and metal plays a key role for the electronic and optoelectronic applications of atomically thin two-dimensional (2D) layered materials. Herein, we report laser-driven synthesis of PtTe 2 from Pt-deposited 2D tellurium (Te) for optimized interface of 2D Te optoelectronic device. The size and shape of the synthesized area of the PtTe 2 can be designable in the laser irradiation process. The electrical properties of 2D Te change from p-type semiconducting to metallic due to the formation of semimetallic PtTe 2 after laser irradiation, increasing the conductivity by factors of 500. In addition, by using PtTe 2 contact, the carrier mobility and photoresponsivity of the 2D Te devices could be greatly enhanced. Our photodetector shows high responsivity and detectivity up to 5.8 × 10 4 A W −1 and 5.31 × 10 11 Jones, respectively. Ideal interfaces for highly performing optoelectronics devices could be realized by an original way of depositing Pt nanoparticles and patterning a semimetal compound based on the Pt at the junction. • A controllable process to synthesize and pattern a semimetallic PtTe 2 from 2D Te by laser irradiation is reported. • The electrical properties of p-type 2D Te were transformed to metallic (PtTe 2 ) with an increase of conductivity up to 500 times. • By using PtTe 2 contact, the 2D Te devices show effective enhancements of mobility and responsivity. • Ideal interfaces for highly performing optoelectronics devices could be realized by patterning a semimetal at the junction.

Medical management of Rhodococcus equi infections: A clinical epidemiology perspective

SummaryRhodococcus equi infections cause severe pulmonary disease in foals, affecting animal welfare and increasing production costs in horse‐breeding farms. Extra‐pulmonary disorders (EPD) are relatively common and can occur independently of pulmonary disease; foals with EPD have a more guarded prognosis. The accompanying paper by Shaw et al. (2021) reports the successful diagnosis and medical treatment of a large abdominal abscess caused by R. equi infection. The authors report on the benefits of using gallium maltolate, a semimetal compound with antimicrobial activity, in combination with traditional R. equi infection antimicrobial treatment (combination of a macrolide and rifampicin). Experimental studies are needed to understand further the benefits of this combined therapy, to evaluate the synergistic effects and if it improves the concentration of antimicrobial drugs into infected tissues. The publication of this case report in Equine Veterinary Education is of clinical importance to equine practitioners when diagnosing and treating R. equi infected foals with or without EPD.

Morphology and Optical Properties of Thin Cd3As2 Films of a Dirac Semimetal Compound

Using atomic-force microscopy (AFM) and wide-band (0.02–8.5 eV) spectroscopic ellipsometry techniques, we investigated the morphology and optical properties of Cd3As2 films grown by non-reactive RF magnetron sputtering on two types of oriented crystalline substrates (100)p-Si and (001) α-Al2O3. The AFM study revealed the grainy morphology of the films due to island incorporation during the film growth. The complex dielectric function spectra of the annealed Cd3As2/Al2O3 films manifest pronounced interband optical transitions at 1.2 and 3.0 eV, in excellent agreement with the theoretical calculations for the body centered tetragonal Cd3As2 crystal structure. We discovered that due to electronic excitations to the Cd(s) conical bands, the low-energy absorption edge of the annealed Cd3As2 films reveals a linear dependence. We found that for the annealed Cd3As2 films, the Cd(s) conical node may be shifted in energy by about 0.08–0.18 eV above the heavy-flat As(p) valence band, determining the optical gap value. The as-grown Cd3As2 films exhibit the pronounced changes of the electronic band structure due to the doping effect associated with Cd non-stoichiometry, where fine-tuning of the Cd concentration may result in the gapless electronic band structure of Dirac semimetals.

Electronic correlations in nodal-line semimetals

Dirac fermions with highly dispersive linear bands1–3 are usually considered weakly correlated due to the relatively large bandwidths (W) compared to Coulomb interactions (U). With the discovery of nodal-line semimetals, the notion of the Dirac point has been extended to lines and loops in momentum space. The anisotropy associated with nodal-line structure gives rise to greatly reduced kinetic energy along the line. However, experimental evidence for the anticipated enhanced correlations in nodal-line semimetals is sparse. Here, we report on prominent correlation effects in a nodal-line semimetal compound, ZrSiSe, through a combination of optical spectroscopy and density functional theory calculations. We observed two fundamental spectroscopic hallmarks of electronic correlations: strong reduction (1/3) of the free-carrier Drude weight and also the Fermi velocity compared to predictions of density functional band theory. The renormalization of Fermi velocity can be further controlled with an external magnetic field. ZrSiSe therefore offers the rare opportunity to investigate correlation-driven physics in a Dirac system. What happens to topological materials when their electrons are strongly interacting is an open question. Shao and others demonstrate that ZrSiSe is a material that can address this as it has a topological band structure and non-trivial correlations.

Nonsaturating large magnetoresistance in semimetals

The rapidly expanding class of quantum materials known as topological semimetals (TSMs) displays unique transport properties, including a striking dependence of resistivity on applied magnetic field, that are of great interest for both scientific and technological reasons. So far, many possible sources of extraordinarily large nonsaturating magnetoresistance have been proposed. However, experimental signatures that can identify or discern the dominant mechanism and connect to available theories are scarce. Here we present the magnetic susceptibility (χ), the tangent of the Hall angle ([Formula: see text]), along with magnetoresistance in four different nonmagnetic semimetals with high mobilities, NbP, TaP, NbSb2, and TaSb2, all of which exhibit nonsaturating large magnetoresistance (MR). We find that the distinctly different temperature dependences, [Formula: see text], and the values of [Formula: see text] in phosphides and antimonates serve as empirical criteria to sort the MR from different origins: NbP and TaP are uncompensated semimetals with linear dispersion, in which the nonsaturating magnetoresistance arises due to guiding center motion, while NbSb2 and TaSb2 are compensated semimetals, with a magnetoresistance emerging from nearly perfect charge compensation of two quadratic bands. Our results illustrate how a combination of magnetotransport and susceptibility measurements may be used to categorize the increasingly ubiquitous nonsaturating large magnetoresistance in TSMs.

Anomalous Hall effect in Weyl semimetal half-Heusler compounds RPtBi (R = Gd and Nd)

Topological materials ranging from topological insulators to Weyl and Dirac semimetals form one of the most exciting current fields in condensed-matter research. Many half-Heusler compounds, RPtBi (R = rare earth), have been theoretically predicted to be topological semimetals. Among various topological attributes envisaged in RPtBi, topological surface states, chiral anomaly, and planar Hall effect have been observed experimentally. Here, we report an unusual intrinsic anomalous Hall effect (AHE) in the antiferromagnetic Heusler Weyl semimetal compounds GdPtBi and NdPtBi that is observed over a wide temperature range. In particular, GdPtBi exhibits an anomalous Hall conductivity of up to 60 Ω-1⋅cm-1 and an anomalous Hall angle as large as 23%. Muon spin-resonance (μSR) studies of GdPtBi indicate a sharp antiferromagnetic transition (TN) at 9 K without any noticeable magnetic correlations above TN Our studies indicate that Weyl points in these half-Heuslers are induced by a magnetic field via exchange splitting of the electronic bands at or near the Fermi energy, which is the source of the chiral anomaly and the AHE.

Large magnetoresistance and superconductivity in \u03b1-gallium single crystals

Topological metals, including Dirac and Weyl semimetals, represent a wide class of quantum materials with non-trivial electronic band structures. The essential properties of Dirac or Weyl fermions, including light effective mass and high mobility, have been observed in a number of semimetal compounds, which in turn exhibit large positive magnetoresistances. Here, we report an unexpected observation of all these properties in α-gallium (α-Ga) single crystals, a pure metal that is in the liquid phase at room temperature and ambient pressure. Based on systematical transport measurements, α-Ga single crystal is found to exhibit large magnetoresistance, reaching about 1.66 × 106 per cent at 2 K in a magnetic field of 9 T. At low temperatures the de Haas–van Alphen and Shubinikov de Hass quantum oscillations show ultrahigh mobility and very small cyclotron effective mass for charge carriers, together with a non-trivial Berry phase. Combined with first-principle band structure calculations, these properties demonstrate α-Ga as a rare topological pure metal. Furthermore, superconductivity with Tc of ~0.9 K is confirmed by both specific heat and resistivity measurements. These findings suggest that α-Ga is a unique pure metal displaying both non-trivial topological and superconducting properties.

Unconventional Superconductivity in Topological Semimetal Half-Heusler Compounds

Unconventional Superconductivity in Topological Semimetal Half-Heusler Compounds

NO2 sensing properties of a borazine doped nanographene: A DFT study

Nanographenes are definite segments of graphene whose end atoms are saturated with hydrogens and their properties are different from those of the graphene because of size confinement. Herein, we investigated the structural properties, reactivity and electronic sensitivity of a newly synthesized borazine-like ring doped nanographene (BNG) to NO2 gas by means of density functional theory. We found that the central and peripheral rings of BNG are aromatic, while the middle ones are non-aromatic, revealing that this pattern follows the Clar’s sextet rule of aromaticity. Different thermodynamically stable NO2/BNG complexes are predicted, but most of them cannot be formed at room temperature because of the high transition barrier energies. The most favorable complex is that in which one oxygen atom of NO2 molecule is located above the center of B3N3 doped ring with adsorption energy of about −5.1kcal/mol. It was found that the electronic properties of BNG are highly sensitive to the presence of NO2 molecules so that after the NO2 adsorption, the BNG is converted from a semiconductor to a semimetal compound. Thus, it was concluded that the BNG may be used in the NO2 sensor devices. Also, a short recovery time is predicted for the NO2 desorption process.

A computational study on the SO2 adsorption by the pristine, Al, and Si doped BN nanosheets

It has been previously indicated that SO2 gas cannot be detected by graphene and a carbon nanotubes. Herein, the reactivity and electronic sensitivity of a boron nitride (BN) nanosheet and its Al- and Si-doped forms to the SO2 gas was investigated, using density functional theory. It was mainly found that, 1) the BN sheet has a good sensitivity to SO2 gas, but it suffers from a weak interaction energy, 2) replacing a B atom of the BN sheet by an Si atom significantly increases its reactivity but does not change the sensitivity, 3) the Al-doping moderately increases the reactivity and significantly improves the sensitivity. The adsorption energy is about −7.3, −24.3, and −51.3 kcal/mol on the pristine, Al-doped and Si-doped BN sheets. After the adsorption of SO2 gas on the Al-doped BN sheet, it is converted from a semiconductor to a semimetal compound, indicating that it may be used in the SO2 sensor devices. A recovery time of about 23.8 min at 298 K and 27.6 s at 335 K is predicted for Al-doped BN sheet. Also, the effect of density functional on the results are investigated.

Signatures of Fermi Arcs in the Quasiparticle Interferences of the Weyl Semimetals TaAs and NbP.

The recent discovery of the first Weyl semimetal in TaAs provides the first observation of a Weyl fermion in nature. Such a topological semimetal features a novel type of anomalous surface state, the Fermi arc, which connects a pair of Weyl nodes through the boundary of the crystal. Here, we present theoretical calculations of the quasiparticle interference (QPI) patterns that arise from the surface states including the topological Fermi arcs in the Weyl semimetals TaAs and NbP. Most importantly, we discover that the QPI exhibits termination points that are fingerprints of the Weyl nodes in the interference pattern. Our results, for the first time, propose a universal interference signature of the topological Fermi arcs in TaAs, which is fundamental for scanning tunneling microscope (STM) measurements on this prototypical Weyl semimetal compound. More generally, our work provides critical guideline and methodology for STM studies on new Weyl semimetals. Further, the scattering channels revealed by our QPIs are broadly relevant to surface transport and device applications based on Weyl semimetals.