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Here, based on first-principles calculations and topological analysis, we show that the spin-polarized topological phase is present in a van der Waals (vdW) heterostructure WSe2/CrI3. We reveal that magnetism induced by proximity effects in the heterostructure breaks the time-reversal symmetry (TRS) and thus induces gapped topological edge states, exhibiting the TRS-breaking quantum spin Hall (QSH) effect. By applying a stress field, the WSe2/CrI3 heterostructure manifests enhanced spin polarization, Rashba splitting, and tunable bandgap. The TRS-breaking QSH effect observed in the WSe2/CrI3 heterostructure exhibits remarkable robustness against interlayer shearing. The distinct anisotropy associated with in-plane strain provides precise manipulation strategies for bandgap engineering. Notably, in-plane tensile strain can significantly increase the nontrivial bandgap by up to 98 meV, suggesting the magnetic WSe2/CrI3 heterostructure represents an outstanding platform for achieving the TRS-breaking QSH effect at room temperature. Our findings provide a theoretical foundation for the development of low-dissipation spintronic nanodevices. [ABSTRACT FROM AUTHOR]

In response to the pressing energy crisis, thermoelectric materials have emerged as promising solutions for converting waste heat into electrical energy. Meanwhile, low-dimensional thermoelectric materials with micro/nanoscale dimensions are playing an increasingly important role in chip thermal management and self-powered wearable electronic devices. This work investigates the thermoelectric properties of three SixGey monolayers, predicted through the approach that combines the advantages of silicene and germanene. Utilizing density functional theory and semiclassical Boltzmann transport theory, we systematically analyze crystal structures, stabilities, electrical and thermal transport, and thermoelectric properties of three stable SixGey monolayers. Compared to traditional two-dimensional materials such as silicene and germanene, the SixGey monolayers exhibit significantly enhanced Seebeck coefficients (∼100 μV/K) and reduced lattice thermal conductivity, ranging from 1.15 to 1.43 W m–1 K–1 at 300 K. These results demonstrate a significant improvement in the thermoelectric figure of merit (zT) compared to silicon (0.02) and germanium (0.05) monolayers, reaching values of 0.15 (GeSi), 0.13 (GeSi2), and 0.11 (Ge2Si) at 700 K, respectively. Our findings not only underscore the potential of SixGey monolayers as promising candidates for thermoelectric generators and thermoelectric coolers but also shed light on the utilization of silicon–germanium-based materials in thermoelectric generation and semiconductor cooling micro/nanoscale electronic devices. [ABSTRACT FROM AUTHOR]

Investigations into topological materials typically emphasize either electronic or phononic properties in isolation, often disregarding their coexistence, which could restrict the full realization of their practical applications. Here, we investigate HOD-graphene, an emergent macroporous carbon material featuring a unique configuration of hexagonal, octagonal, and dodecagonal carbon rings. This distinctive structure imparts exceptional mechanical properties to the material. Using a combination of first-principles calculations and symmetry analysis, we demonstrate that HOD-graphene hosts multiple nodal lines within both its electronic and phononic spectra. For the electronic bands, three nodal lines and several Dirac points manifest near the Fermi energy, generating unconventional electronic properties and distinct topological characteristics. Likewise, the phonon spectrum displays pronounced nodal lines, intricately associated with the material's vibrational modes. Our findings provide a promising platform for exploring the coexistence of electronic and phononic multiple nodal lines in two-dimensional materials, opening avenues for realizing exotic quantum phenomena. [ABSTRACT FROM AUTHOR]

Recently, two-dimensional (2D) ternary monolayer MSi2N4 (M = Mo, W) was synthesized by chemical vapor deposition. However, monolayer MSi2N4 (M = Mo, W) has an indirect bandgap, which seriously hinders its application in optoelectronic devices. Herein, we propose two MSi2N4/InS (M = Mo, W) van der Waals heterojunctions (vdWHs) possessing type-II band alignments by first-principles. Our results indicate that these vdWHs achieve an indirect-to-direct bandgap transition and exhibit fascinating optical absorption spectra in the range of visible light. Moreover, the light absorption efficiencies of both vdWHs are significantly strengthened, and the intrinsic electric field of vdWHs can effectively promote the separation of photogenerated electron–hole pairs. In particular, the most significant electron mobility of MSi2N4/InS (M = Mo, W) vdWHs is up to 6.6 × 103 cm2 V−1 s−1, demonstrating their considerable potential for optoelectronic device applications. Notably, MSi2N4/InS (M = Mo, W) vdWHs can facilitate water splitting due to their suitable band edges. Therefore, our findings demonstrate two 2D MSi2N4/InS (M = Mo, W) type-II vdWHs with fascinating potentials for photocatalysis. [ABSTRACT FROM AUTHOR]

Recently, centimeter-scale monolayer MoSi2N4 (α1-phase) was successfully synthesized in experiments with excellent ambient stability. However, it is an indirect band gap semiconductor, which hinders its wide application. Here, we systematically studied the stability of the structure and optoelectronic properties of two new α1-phase monolayers (MoSi2Sb4 and WSi2Sb4) and a new family of α2-phase monolayer MSi2Z4 (M = Mo, W; Z = P, As, Sb) using first-principles calculations. Our results indicated that all of these monolayer structures showed high structural stability, and the α2-phase structures are more stable than the α1-phase structures. Moreover, all of them have direct band gaps with fascinating optical absorption efficiencies ranging from infrared to visible light. Importantly, the high hole mobility (up to 105 cm2 V−1 s−1) reveals that these monolayer MSi2Z4 will have potential applications in photoelectric devices. In addition, α2-MoSi2P4 possesses a desirable power conversion efficiency of 20.3%. Interestingly, spin–orbit coupling plays a key role in exploring the optoelectronic properties of MSi2Z4 ternary compounds. These new ternary monolayer structures can effectively broaden the 2D materials family and provide promising potential candidates for optoelectronic applications. [ABSTRACT FROM AUTHOR]

The synthesis of graphene-like structure [Fan et al., Science 372 (2021) 8527] with periodically embedded one-dimensional grain boundaries [Liu et al., Nat. Commun. 8 (2017)14924] is a strong incentive for exploration of carbon allotropes. In this work, a series of stable carbon allotropes with Dirac cones, (DSF)n-graphene, consisting of graphene nanoribbons and one-dimensional grain boundaries are proposed. The grain boundary composed of tetragonal and octagonal rings is constructed by a double stacking fault (DSF), where n refers to the width of the nanoribbon between the two grain boundaries. Interestingly, the Dirac cone of (DSF)n-graphene is mainly contributed by the atoms of grain boundaries, thus forming a one-dimensional conductive channel. Specifically, with the increase of n, the position of the Dirac points changes periodically on the two high symmetry lines, and the DSF ensures the robustness of the Dirac cones. Both (DSF)3-graphene and (DSF)4-graphene, as two prototypes, have Fermi velocities comparable to graphene, although the Dirac cones of the two are distributed on different high symmetry lines. Importantly, the calculation of surface states proves that (DSF)3-graphene and DSF4-graphene have nontrivial topological features. Furthermore, the massless Dirac fermions in the one-dimensional conductive channel bring many promising applications for future electronic devices. [ABSTRACT FROM AUTHOR]

Nodal line semimetal (NLSM) has become a captivating medium for studying varieties of novel quantum phenomena. Here, based on first-principles calculations, we identify a square compound lattice (SCL) structure, namely C-Me-graphene, featuring a NLSM, wherein the nodal line of this configuration resides precisely at the Fermi energy without any extraneous bands in the vicinity, manifesting the quintessential characteristics of an ideal NLSM. As a corollary, utilizing symmetry analysis, we propose that nodal lines can be generated by exploiting the two-dimensional (2D) SCL of carbon. This is because the SCL not only satisfies time-reversal symmetry and inversion symmetry but also conforms to glide mirror symmetry. Additionally, this structure reveals remarkable mechanical attributes, exemplifying the highest Young's modulus within the realm of 2D materials, second only to graphene. Our work not only identifies an ideal carbon-based NLSM but also advances a scheme for crafting NLSMs, which would greatly enrich topological materials with exotic properties.

Competing Interests: No conflicts of interest. Table S1Demographic characteristics of 4 local cases and 39 imported cases, and specimen testing information.CaseGenderAge (years)Date of first positive detectionof COVID-19 virusCt value (ORF1ab/N) of specimen used for sequencingDaanBojieNote: There were 43 subjects in total, and the male/female ratio and mean age of subjects was 2.58∶1 and 40.9 years, respectively. Abbreviations: Undet=Undetected; Ct=Cycle threshold; COVID-19=Coronavirus disease 2019. Case AMale30June 14, 202114/1816/18Case BFemale21June 17, 202123/2122/22Case CMale35June 18, 202124/2222/24Case DFemale64June 20, 202130/3035/28Case 1Male36June 11, 202131/3130/31Case 2Male35June 11, 202131/3126/28Case 3Female42June 11, 202133/3434/34Case 4Female58June 11, 202130/2727/28Case 5Male53June 13, 202117/1616/17Case 6Male32June 14, 202124/2324/23Case 7Male52June 14, 202117/1716/17Case 8Male33June 15, 202117/1515/17Case 9Male47June 15, 202116/1615/16Case 10Male64June 15, 202121/2020/21Case 11Male40June 15, 202115/1414/15Case 12Male50June 15, 202118/1716/18Case 13Male33June 15, 202128/2627/28Case 14Female31June 15, 202119/1718/17Case 15Male61June 15, 202114/1415/15Case 16Female38June 15, 202135/3436/33Case 17Male39June 15, 202137/40Undet/35Case 18Female50June 15,202114/1514/14Case 19Male35June 15, 202117/1616/17Case 20Male58June 15, 202116/1515/16Case 21Female47June 15, 202129/2526/26Case 22Male29June 15, 202135/3538/UndetCase 23Male32June 15, 202138/36Undet/35Case 24Male63June 15, 202135/3435/32Case 25Female63June 15, 202135/3333/33Case 26Male45June 15, 202138/35Undet/UndetCase 27Male44June 15, 2021Undet/38Undet/35Case 28Male61June 15, 2021Undet/3737/UndetCase 29Male58June 15, 202137/UndetUndet/36Case 30Male9June 15, 202121/2122/22Case 31Female45June 15, 202128/2827/28Case 32Male42June 15, 202115/1514/15Case 33Male35June 16, 202126/2423/26Case 34Male1June 16, 202130/2727/29Case 35Female24June 17, 202134/3032/30Case 36Male25June 17, 202119/1819/18Case 37Female32June 19, 202122/1919/20Case 38Male38June 19, 202131/2928/30Case 39Female28June 25, 202118/1617/18Table S2Genome sequence information for 30 SARS-CoV-2 strains of lineage B.1.617.2 from this study.CaseVirus nameLength in nt(% GC content)Closest strain by an audacity instantsearch in GISAIDAbbreviation: nt=Nucleotide.Case AhCoV-19/Shenzhen/IVDC-06-14/202129,813nt (37.97)hCoV-19/England/MILK-155F811/2021Case BhCoV-19/Shenzhen/IVDC-06-17/202129,562nt (37.98)hCoV-19/England/MILK-155F811/2021Case ChCoV-19/Shenzhen/IVDC-06-18/202129,428nt (37.98)hCoV-19/England/MILK-155F811/2021Case DhCoV-19/Shenzhen/IVDC-06-20/202129,612nt (37.98)hCoV-19/England/MILK-155F811/2021Case 1hCoV-19/Shenzhen/IVDC-0610-01/202129,702nt (37.96)hCoV-19/India/GJ-NCDC-NIV-INSACOG-24095/2021Case 2hCoV-19/Shenzhen/IVDC-0610-02/202129,813nt (37.97)hCoV-19/England/MILK-155F811/2021Case 4hCoV-19/Shenzhen/IVDC-0610-04/202129,836nt (37.96)hCoV-19/England/MILK-155F811/2021Case 5hCoV-19/Shenzhen/IVDC-0610-05/202129,555nt (37.99)hCoV-19/England/MILK-155F811/2021Case 6hCoV-19/Shenzhen/IVDC-0610-06/202129,657nt (38.00)hCoV-19/England/MILK-155F811/2021Case 7hCoV-19/Shenzhen/IVDC-0610-07/202129,814nt (37.97)hCoV-19/England/MILK-155F811/2021Case 8hCoV-19/Shenzhen/IVDC-0610-08/202129,824nt (37.97)hCoV-19/England/MILK-155F811/2021Case 9hCoV-19/Shenzhen/IVDC-0610-09/202129,831nt (37.96)hCoV-19/England/MILK-155F811/2021Case 10hCoV-19/Shenzhen/IVDC-0610-10/202129,833nt (37.95)hCoV-19/England/MILK-155F811/2021Case 11hCoV-19/Shenzhen/IVDC-0610-11/202129,830nt (37.96)hCoV-19/England/MILK-155F811/2021Case 12hCoV-19/Shenzhen/IVDC-0610-12/202129,830nt (37.96)hCoV-19/England/MILK-155F811/2021Case 13hCoV-19/Shenzhen/IVDC-0610-13/202129,710nt (37.99)hCoV-19/England/MILK-155F811/2021Case 14hCoV-19/Shenzhen/IVDC-0610-14/202129,551nt (37.98)hCoV-19/England/MILK-155F811/2021Case 15hCoV-19/Shenzhen/IVDC-0610-15/202129,834nt (37.96)hCoV-19/England/MILK-155F811/2021Case 18hCoV-19/Shenzhen/IVDC-0610-18/202129,820nt (37.96)hCoV-19/England/MILK-155F811/2021Case 19hCoV-19/Shenzhen/IVDC-0610-19/202129,828nt (37.96)hCoV-19/England/MILK-155F811/2021Case 20hCoV-19/Shenzhen/IVDC-0610-20/202129,820nt (37.96)hCoV-19/England/MILK-155F811/2021Case 21hCoV-19/Shenzhen/IVDC-0610-21/202129,574nt (37.99)hCoV-19/England/MILK-155F811/2021Case 30hCoV-19/Shenzhen/IVDC-0610-30/202129,827nt (37.97)hCoV-19/England/MILK-155F811/2021Case 31hCoV-19/Shenzhen/IVDC-0610-31/202129,829nt (37.96)hCoV-19/England/MILK-155F811/2021Case 32hCoV-19/Shenzhen/IVDC-0610-32/202129,849nt (37.96)hCoV-19/England/MILK-155F811/2021Case 34hCoV-19/Shenzhen/IVDC-0610-34/202129,809nt (37.97)hCoV-19/England/MILK-155F811/2021Case 36hCoV-19/Shenzhen/IVDC-0610-36/202129,819nt (37.96)hCoV-19/England/MILK-155F811/2021Case 37hCoV-19/Shenzhen/IVDC-0610-37/202129,827nt (37.97)hCoV-19/England/MILK-155F811/2021Case 38hCoV-19/Shenzhen/IVDC-0610-38/202129,553nt (37.99)hCoV-19/England/MILK-155F811/2021Case 39hCoV-19/Shenzhen/IVDC-0610-39/202129,797nt (37.94)hCoV-19/England/MILK-155F811/2021

Competing Interests: Conflicts of interest: No conflicts of interest.

Bioconversion of elemental mercury (Hg 0 ) into immobile, nontoxic, and less bioavailable species is of vital environmental significance. Here, we investigated bioconversion of Hg 0 in a sulfate-reducing membrane biofilm reactor (MBfR). The MBfR achieved effective Hg 0 removal by sulfate bioreduction. 16 S rDNA sequencing and metagenomic sequencing revealed that diverse groups of mercury-oxidizing/sulfate-reducing bacteria ( Desulfobulbus , Desulfuromonas , Desulfomicrobium, etc.) utilized Hg 0 as the initial electron donor and sulfate as the terminal electron acceptor to form the overall redox. These microorganisms coupled Hg 0 bio-oxidation to sulfate bioreduction. Analysis on mercury speciation in biofilm by sequential extraction processes (SEPs) and inductively coupled mass spectrometry (ICP-MS) and by mercury temperature programmed desorption (Hg-TPD) showed that mercury sulfide (HgS) and humic acid-bound mercury (HA-Hg) were two major products of Hg 0 bio-oxidation. With HgS and HA-Hg comprehensively characterized by X-ray diffraction (XRD), excitation-emission matrix spectra (EEM), scanning electron microscopy-energy disperse spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR), it was proposed that biologically oxidized mercury (Hg 2+ ) further reacted with biogenic sulfides to form cubically crystallized metacinnabar (β-HgS) extracellular particles. Hg 2+ was also complexed with functional groups -SH, -OH, -NH - , and -COO - in humic acids from extracellular polymeric substances (EPS) to form HA-Hg. HA-Hg may further react with biogenic sulfides to form HgS. Bioconversion of Hg 0 into HgS was therefore achieved and can be a feasible biotechnique for flue gas demercuration.