Alternating spin splitting of electronic and magnon bands in two-dimensional altermagnetic materials

Unconventional antiferromagnetism dubbed as altermagnetism was first discovered in rutile structured magnets,which is featured by spin splitting even without the spin–orbital coupling effect.This interesting phenomenon has been discovered in more altermagnetic materials.In this work,we explore two-dimensional altermagnetic materials by studying two series of two-dimensional magnets,including MF4 with M covering all 3d and 4d transition metal elements,as well as TS2 with T=V,Cr,Mn,Fe.Through the magnetic symmetry operation of RuF4 and MnS2,it is verified that breaking the time inversion is a necessary condition for spin splitting.Based on symmetry analysis and first-principles calculations,we find that the electronic bands and magnon dispersion experience alternating spin splitting along the same path.This work paves the way for exploring altermagnetism in two-dimensional materials.

Electronic and Thermoelectric Properties in SnS-Nanoribbon-Based Heterojunctions

As an earth-abundant and environmentally friendly material,tin sulfide(SnS)is not only a high-performance photovoltaic material,but also a new promising thermoelectric material.Despite extensive research on the thermoelectric properties of this material in recent years,the room-temperature thermoelectric figure of merit(ZT)of SnS has not been broke through 2[2022 Sci.China Mater.651143].In this work,based on a combination of density functional theory and non-equilibrium Green’s function method,the electronic and thermoelectric properties in SnS-nanoribbon-based heterojunctions are studied.The results show that although SnS nanoribbons(SNSNRs)with zigzag edges(ZSNSNRs)and armchair edges(ASNSNRs)both have semiconductor properties,the bandgaps of ASNSNRs are much wider than those of ZSNSNRs,which induces much wider conductance gaps of𝑁N-ASNSNR(N is the number of tin-sulfide lines across the ribbon width)).In the positive energy region,the ZT peaks of𝐿L-SNS-Au are much larger than those of𝐿L-SNS-GNR(L represents the number of longitudinal repeating units of SNSNR in the scattering region).While in the positive energy region,the ZT peaks of L-SNSGNR are larger than those of L-SNS-Au.Further calculations reveal that the figure of merit will be over 3.7 in L-SNS-Au and 2.2 in L-SNS-GNR at room temperature,and over 4 in L-SNS-Au and 2.6 in L-SNS-GNR at 500 K.

Optical Properties of C-rich(12C,SiC and FeC)Dust Layered Structure of Massive Stars

The composition and structure of interstellar dust are important and complex for the study of the evolution of stars and the interstellar medium(ISM).However,there is a lack of corresponding experimental data and model theories.By theoretical calculations based on ab-initio method,we have predicted and geometry optimized the structures of Carbon-rich(C-rich)dusts,carbon(^(12)C),iron carbide(Fe C),silicon carbide(Si C),even silicon(^(28)Si),iron(^(56)Fe),and investigated the optical absorption coefficients and emission coefficients of these materials in 0D(zero-dimensional),1D,and 2D nanostructures.Comparing the nebular spectra of the supernovae(SN)with the coefficient of dust,we find that the optical absorption coefficient of the 2D^(12)C,^(28)Si,^(56)Fe,Si C and Fe C structure corresponds to the absorption peak displayed in the infrared band(5–8)μm of the spectrum at 7554 days after the SN1987A explosion.It also corresponds to the spectrum of 535 days after the explosion of SN2018bsz,when the wavelength was in the range of(0.2–0.8)and(3–10)μm.Nevertheless,2D Si C and Fe C correspond to the spectrum of 844 days after the explosion of SN2010jl,when the wavelength is within(0.08–10)μm.Therefore,Fe C and Si C may be the second type of dust in SN1987A corresponding to infrared band(5–8)μm of dust and may be in the ejecta of SN2010jl and SN2018bsz.The nano-scale C-rich dust size is~0.1 nm in SN2018bsz,which is 3 orders of magnitude lower than the value of 0.1μm.In addition,due to the ionization reaction in the supernova remnant(SNR),we also calculated the Infrared Radiation(IR)spectrum of dust cations.We find that the cation of the 2D layered(Si C)^(2+)has a higher IR spectrum than those of the cation(Si C)^(1+)and neutral(Si C)^(0+).

Covalent coupling of DNA bases with graphene nanoribbon electrodes: Negative differential resistance, rectifying, and thermoelectric performance

By applying nonequilibrium Green's functions in combination with the density-functional theory, we investigate the electronic, thermal, and thermoelectric properties of four kinds of bases in DNA perpendicularly coupling between two ZGNR electrodes. The results show that the electron transport is highly sensitive to different base-ZGNR coupling geometries, and the system can present large rectifying and negative differential resistance effects. Moreover, the fluctuations of electronic transmission and super-low thermal conductance result in significant enhancement of the thermoelectric figure of merit (ZT): the ZT will be over 1.4 at room temperature, and over 1.6 at 200 K. The results show that the base-ZGNR coupling devices can present large rectifying, negative differential resistance, and enhanced thermoelectric effects.

Modulated thermal transport for flexural and in-plane phonons in double-stub graphene nanoribbons

Thermal transport properties are investigated for out-of-plane phonon modes （FPMs） and it-plane phonon modes （IPMs） in double-stub graphene nanoribbons （GNRs）. The results show that the quantized thermal conductance plateau of FPMs is narrower and more easily broken by the double-stub structure. In the straight GNRs, the thermal conductance of FPMs is higher in the low temperature region due to there being less cut-off frequency and more low-frequency excited modes. In contrast, the thermal conductance of IPMs is higher in the high temperature region becau~,＇.e of the wider phonon energy spectrum. Furthermore, the thermal transport of two types of phonon modes can be modulated by the double-stub GNRs, the thermal conductance of FPMs is less than that of IPMs in the low temperatures, but it dominates the contribution to the total thermal conductance in the high temperatures. The modulated thermal conclu~＇tanc：e can provide a guideline for designing high-performance thermal or thermoelectric nanodevices based on graphene.

Effects of edge hydrogenation and Si doping on spin-dependent electronic transport properties of armchair boron–phosphorous nanoribbons

In this article, the spin-dependent electronic and transport properties of the armchair boron–phosphorous nanoribbons（ABPNRs） are mainly studied by using the non-equilibrium Green function method combined with the spin-polarized density function theory. Our calculated electronic structures indicate that the edge hydrogenated ABPNRs exhibit a ferromagnetic bipolar magnetic semiconductor property, and that the Si atom doping can make ABPNRs convert into up-spin dominated half metal. The spin-resolved transport property results show that the doped devices can realize 100% spinfiltering function, and that the interesting negative differential resistance phenomenon can be observed. Our calculations suggest that the ABPNRs can be constructed as a spin heterojunction by introducing Si doping partially, and it would be used as a spin-diode for nano-spintronics in future.

Fano Resonance Effect in CO-Adsorbed Zigzag Graphene Nanoribbons

Quantum interference plays an important role in tuning the transport property of nano-devices. Using the non- equilibrium Green＇s Function method in combination with density functional theory, we investigate the influence to the transport property of a CO molecule adsorbed on one edge of a zigzag graphene nanoribbon device. Our results show that the CO molecule-adsorbed zigzag graphene nanoribbon devices can exhibit the Fano resonance phenomenon. Moreover, the distance between CO molecules and zigzag graphene nanoribbons is closely related to the energy sites of the Fano resonance. Our theoretical analyses indicate that the Fano resonance would be attributed to the interaction between CO molecules and the edge of the zigzag graphene nanoribbon device, which results in the localization of electrons and significantly changes the transmission spectrum.