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Graphical abstract, The perovskite oxide interface has attracted extensive attention as a platform for achieving strong coupling between ferroelectricity and magnetism. In this work, robust control of magnetoelectric (ME) coupling in the BiFeO3/BaTiO3 (BFO/BTO) heterostructure (HS) was revealed by using the first-principles calculation. Switching of the ferroelectric polarization of BTO induce large ME effect with significant changes on the magnetic ordering and easy magnetization axis, making up for the weak ME coupling effect of single-phase multiferroic BFO. In addition, the Dzyaloshinskii-Moriya interaction (DMI) and the exchange coupling constants J for the BFO part of the HSs are simultaneously manipulated by the ferroelectric polarization, especially the DMI at the interface is significantly enhanced, which is three or four times larger than that of the individual BFO bulk. This work paves the way for designing new nanomagnetic devices based on the substantial interfacial ME effect.

Low-dimensional ferroelectricity and Dirac materials with protected band crossings are fascinating research subjects. Based on first-principles calculations, we predict the coexistence of spontaneous in-plane polarization and novel 2D emergent fermions in dynamically stable quadruple-layer (QL) XSbO

Distinguishing from traditional working environments, we propose the harsh gamma radiation method to study the stability and reliability of the emerging two-dimensional (2D) quantum material tungsten diselenide (WSe

Perovskite oxide interfaces have become a platform for the realization of many unexpected physical properties in recent years, while effective electric control of magnetism is promising for future spintronic devices. In this work, external electric field is applied to control the physical properties of LaFeO3/SrTiO3 perovskite oxide heterostructures investigated by first-principles calculations based on density functional theory (DFT). We find that external electric field can effectively modulate the band dispersion around the Fermi level of both the n-type and the p-type interfaces. Negative electric field can weaken the band shift, even leading to a two-dimensional electron gas, which is accompanied by a reversible insulator-to-metal/half-metal transition at the n-type interface. Moreover, the n-type interface perfectly realizes a transformation from G-type antiferromagnetic to ferrimagnetic at −0.3 V/A. Meanwhile, the electric field also regulates the electronic structure of the p-type interface of the heterostructure. Our work mainly focus on using electric field to tune the interfacial electronic structure and magnetic properties of perovskite oxides heterostructures, and further pave the way to the experimental design of novel magnetoelectric interface materials.

We investigate the transport properties of bulk Ca

The previous experimental work showed that n-type low-temperature (LT) SnSe doped with BiCl3 simultaneously exhibited larger Seebeck coefficient (S), higher electrical conductivity (σ), and lower thermal conductivity (κ) compared with polycrystalline LT SnSe. Here, the first-principles method was used to explore how the independent adjustment to the tangled thermoelectric (TE) transport coefficients of n-type LT SnSe was achieved and whether there exist the similar adjustment mechanisms in n-type high-temperature (HT) SnSe. Cl doping increases the electron-pockets and the total density of states (TDOS) near the Fermi level (EF). This results in a high σ and an obvious decrease in S. Whereas, Bi doping introduces two half-filled bands into the band gap. The two bands originate from the 6s “lone-pairs” of Bi atoms and the sigma bonds formed by Bi atoms and their nearest Se atoms. This contributes to maintaining a relative large S and a low κ, but this cannot effectively enhance σ. Fortunately, the coexistence of Cl ions and Bi ions can make Bi/Cl codoped LT (or HT) SnSe set a high σ and a relatively large S in one through independent controlling the electronic structures and charge distribution near the EF. Further, we predict that Bi/Cl co-doping is also an effective strategy to improve the TE performance of HT SnSe.

Perovskite oxide interfaces have been used recently as platforms for demonstrating rich physical properties that are not possessed by their bulk constituents. In this work, we will not only demonstrate rich physical properties at polar perovskite oxide interfaces, but also the tuning of such properties by switching the polarization in PbTiO3/tetragonal BiFeO3 (BFO) two-dimensional ferroelectric heterostructures (HSs). Our first-principles calculations reveal that both magnetism and conductivity can be induced by the discontinuity of the ferroelectric (FE) polarization and the valence states at the interface, and they can also be robustly manipulated by reversing polarization. These properties include the coupling between an interfacial two-dimensional electron gas and magnetism, a transition from half-metal to band insulator or Mott insulator, and the conversion from G-type antiferromagnetic order to local ferromagnetic (FM) ordering, and finally, to the local C-type antiferromagnetic order (C-AFM). Furthermore, by setting different terminations, we can artificially control the local FM ordering that occurs arbitrarily in any one of the polarization directions, and we can even control whether the local FM ordering appears at the interface or at the surface. This novel control can be applied in the fabrication of memory devices for information storage where bits can be written by an electric field (to switch ferroelectric polarization) while reading magnetically. Such a device will drastically reduce energy consumption.

The magneto-Seebeck effect has recently attracted considerable attention because of its novel fundamental physics and future potential application in spintronics. Herein, employing first-principles calculations and the spin-resolved Boltzmann transport theory, we have systematically investigated the electronic structures and spin-related transport properties of Co2FeAl/MgO/Co2FeAl multilayers with parallel (P) and anti-parallel (AP) magnetic alignment. Our results indicate that the sign of tunneling magneto-Seebeck (TMS) value with Co2/O termination is consistent with that of the measured experimental result although its value (-221%) at room temperature is smaller than the experimental one (-95%). The calculated spin-Seebeck coefficients of the Co2/O termination with P and AP states and the FeAl/O termination with the AP state are all larger than other typical Co2MnSi/MgO/Co2MnSi heterostructures. By analyzing the geometries, electronic structures, and magnetic behaviors of two different terminations (Co2/O and FeAl/O terminations), we find that the two terminations in the interface region form anti-bonding and bonding states, reconstructing the energy gap, changing the magnetic moment of O atoms, and improving the spin-polarization (-82%). This phenomenon can be ascribed to the charge transfer and hybridization between Co/Fe 3d and O 2p states, which also results in a bowknot orbital shape of Co atoms with Co2/O termination and an ankle shape of Co atoms with FeAl/O termination far away from the interface. Moreover, there are spin-splitting transmission gaps with the Co2/O-termination around the Fermi level, while the transmission gaps with the FeAl/O-termination are closed and thus show a typical metallic character. Our findings will guide the experimental design of magneto-Seebeck devices for future spintronic applications.

Magnetism in two-dimensional (2D) materials, that is, a 2D version of the magnetism of three-dimensional bulk materials, and the associated novel physics have recently been the focus of many spintronics researchers. Here we investigate the manipulation of 2D magnetism at the interfaces of ferromagnetic/ferroelectric hematene/BaTiO3(001) heterostructures (HSs) fabricated via a precisely chosen sequence. By introducing four types of interfaces of 2D hematene and three-dimensional BaTiO3 that induce different oxygen environments, the control of magnetism is directly demonstrated from first-principles. An obvious 2D electron gas originates from the Fe-3d and O-2p hybridization; the electron gas is sensitive to the interfacial atomic displacements. Robust control of both the direction and magnitude of the net magnetization has been realized for an Fe/TiO2 terminated bilayer HS. The electron occupancies of the dxy and dxz orbitals and changes to the Fe-O bond play a key role in determining the magnetism of our systems. Our work not only demonstrates the technique's potential for manipulating magnetism in 2D hematene, but also sheds light on the underlying mechanism and the fundamental properties of hematene HSs.

SrTiO3-based transition-metal oxide heterostructures with superconducting, ferromagnetic, ferroelectric, and ferroelastic properties exhibit high application potential in the fields of energy storage, energy conversion, and spintronic devices. Meanwhile, high effective (charge)-Seebeck coefficient materials composed of a ferromagnetic layer and SrTiO3 insulator layer have been achieved but we still have blocks to pursuing high spin-Seebeck coefficient materials. Here, we use first-principles calculations combined with spin-resolved Boltzmann transport theory to investigate the spin- and effective-Seebeck coefficients in the LaX(X = Mn and Co)O3/SrTiO3 superlattice. Compared with the LaMnO3/SrTiO3 superlattice, LaCoO3/SrTiO3 with ferromagnetic ordering has high spin polarization, relatively low valence valley degeneracy but high effective mass. Utilizing these characteristics, the maximum spin-Seebeck coefficient of LaMnO3/SrTiO3 is -152 μV K-1 at 450 K along the cross-plane direction, while LaCoO3/SrTiO3 reaches -247 μV K-1 under the same conditions. Interestingly, the spin- and effective-Seebeck coefficients are amazingly consistent with each other below 200 K, which indicates that one spin channel (spin-up or spin-down) dominates the carrier transport, and the other one (spin-down or spin-up) is filtered out. These characteristics are mainly associated with the magnetic MnO2/CoO2 layers with distinct dxy and dz2 orbitals near the Fermi level. Our results clarify the relationship of spin- and effective-Seebeck coefficients and indicate that SrTiO3-based transition metal oxide heterointerfaces are a key candidate for spin caloritronics.

The highest thermoelectric figure of merit (ZT) value of 2.6 has been experimentally determined in p-type single crystalline SnSe. In this work, we propose possible method to further enhance the thermoelectric performance of SnSe by comparing different thermoelectric performances of p- and n-type SnSe using the first-principles method and the semiclassical Boltzmann theory. There are relatively stronger intra-layer interactions between Sn and Se atoms for the layered single crystalline SnSe. The Sn p and s electrons near the Fermi level are pushed away along the a-direction because of the anti-bonding interaction between Sn and Se atoms. The pushed away electrons would hinder holes transport in the a-direction. This leads to the lowest electrical conductivity and ZT value along the a-direction for the p-type single crystalline SnSe. For n-type SnSe, the Sn p and Se p electrons are primarily distributed along the a-direction near the Fermi level. This would lead to high electrical conductivity and large Seebeck coefficient simultaneously in the a-direction. Combined with its ultralow thermal conductivity in the a-direction, the ZT value (∼3.1 at 770 K by a rough estimation) of n-type SnSe along the a-direction is probably much higher than that of p-type one. The peak values of S 2 σ τ of the p-type SnSe correspond to different carrier concentrations along the a- and b-directions. This is one reason for the low experimental peak ZT value of 0.6 for the p-type polycrystalline SnSe at 750 K. For the n-type SnSe, the S 2 σ τ can attain their peak values almost at the same carrier concentration along the a-, b-, and c-directions. This suggests that the power factor value of n-type polycrystalline SnSe would be much higher than that of p-type one at 770 K.

We have investigated the structural, electronic, and magnetic properties of A-site-ordered double-perovskite-structured oxides, AA'3B4O12 (A = Na, Ca, and La) with Mn and V at A' and B sites, respectively, using first-principle calculations based on the density functional theory. Our calculation results show that the antiferromagnetic phase is the ground state for all the compounds. By changing the A-site ions from Na(+) to Ca(2+) and then to La(3+), the transfer of charge between Mn and O ions was changed from 1.56 to 1.55 and then to 1.50, and that between the V and O ions changed from 2.01 to 1.95 and then to 1.93, revealing the cause for the unusual site-selective doping effect. Mn 3d electrons dominate the magnetic moment and are localized, with an intense hybridization with O 2p orbitals, which indicates that the magnetic exchange interaction between Mn ions is mediated through O and that the super exchange mechanism will take effect. These materials have a large one-electron bandwidth W, and the ratio of the on-site Coulomb repulsion U to W is less than the critical value (U/W)c, which leads to metallic behavior of AMn3V4O12. This is further evidenced by the large number of free electrons contributed by V at the Fermi surface. These calculations, in combination with the reported experimental data, prove that these double perovskites belong to the rare antiferromagnetic metallic oxides.

The electronic structure and transport properties of A 5 M 2 Pn 6 (A = Ca, Sr, Ba; M = Ga, Al, In; Pn = As, Sb) are investigated by using the first-principles calculations and Boltzmann transport theory, respectively. The results show that the order of the width of these band gaps is Ca 5 Ga 2 As 6 (0.37 eV) > Ca 5 Al 2 Sb 6 (0.35 eV) > Ca 5 In 2 Sb 6 (0.32 eV) > Sr 5 In 2 Sb 6 (0.29 eV) > Ba 5 In 2 Sb 6 (0.27 eV) > Ca 5 Ga 2 Sb 6 (0.088 eV). For intrinsic A 5 M 2 Pn 6 , increasing the band gap is better for improving their thermoelectric properties. For doped A 5 M 2 Pn 6 , increasing the band gap is helpful to improve the high-temperature thermoelectric properties of A 5 M 2 Pn 6 . However, at 300 K, when the band gap is small enough, regardless of n -type or p -type doping, A 5 M 2 Pn 6 exhibits good thermoelectric properties. Our analysis shows that the band gaps can be roughly adjusted by changing the electronegativity difference between Pn and A, and subtly adjusted by changing the electronegativity difference between Pn and M atoms. So the electronegativity difference among the constituent element is a very important factor affecting the thermoelectric properties.

Spin-dependent thermoelectric effects in Aharonov–Bohm (AB) interferometer with four Rashba quantum dots (QDs) coupled to external two one-dimensional semi-infinite metallic leads are investigated theoretically. The basic thermoelectric transport characteristics, like charge (spin) Seebeck coefficient, and the charge (spin) figure of merits, have been calculated in terms of Green's function formalism. It is found that a pure spin-up (spin-down) Seebeck coefficient can be generated by the coaction of the magnetic flux and the Rashba spin-orbit interaction (RSOI) at room temperature.

The high-pressure structures of molybdenum (Mo) at zero temperature have been extensively explored through the newly developed particle swarm optimization (PSO) algorithm on crystal structural prediction. All the experimental and earlier theoretical structures were successfully reproduced in certain pressure ranges, validating our methodology in application to Mo. A double-hexagonal close-packed (dhcp) structure found by Mikhaylushkin et al. (2008) [12] is confirmed by the present PSO calculations. The lattice parameters and physical properties of the dhcp phase were investigated based on first principles calculations. The phase transition occurs only from bcc phase to dhcp phase at 660 GPa and at zero temperature. The calculated acoustic velocities also indicate a transition from the bcc to dhcp phases for Mo. More intriguingly, the calculated density of states (DOS) shows that the dhcp structure remains metallic. The calculated electron density difference (EDD) reveals that its valence electrons are localized in the interstitial regions.

The effects of doping on the transport properties of Ca5Al2Sb6 are investigated using first-principles electronic structure methods and Boltzmann transport theory. The calculated results show that a maximum ZT value of 1.45 is achieved with an optimum carrier concentration at 1000 K. However, experimental studies have shown that the maximum ZT value is no more than 1 at 1000 K. By comparing the calculated Seebeck coefficient with experimental values, we find that the low dopant solubility in this material is not conductive to achieve the optimum carrier concentration, leading a smaller experimental value of the maximum ZT. Interestingly, the calculated dopant formation energies suggest that optimum carrier concentrations can be achieved when the dopants and Sb atoms have similar electronic configurations. Therefore, it might be possible to achieve a maximum ZT value of 1.45 at 1000 K with suitable dopants. These results provide a valuable theoretical guidance for the synthesis of high-performance bulk thermoelectric materials through dopants optimization.

BiCuSeO is an attractive material for its high temperature stability, high Seebeck coefficient, and low lattice thermal conductivity. However, its electrical conductivity is low. To enhance the thermoelectric properties of BiCuSeO further, we investigated the material's electronic structure and transport property using first-principles calculations. We determine that the low electrical conductivity may originate from strong ionic bonding and without a Cu–Se conductive pathway forming near the Fermi level. Moreover, although p-type BiCuSeO has a high thermopower due to the high density of states near the Fermi level, its electrical conductivity is relatively low because no conductive pathway for carrier transport exists along the c axis. In contrast, a conductive pathway is formed between Bi and Cu atoms at the conduction-band minimum along the c axis. This feature would lead to high electrical conductivity for n-type BiCuSeO. With relatively high electrical conductivity and slightly decreased thermopower, n-type BiCuSeO exhibits a higher power factor than that of p-type BiCuSeO. The maximum ZT value could be improved by 32% for n-type BiCuSeO compared with the prevailing p-type doping approach at 920 K.

We theoretically investigate the optical properties of a hybrid nanostructure consisting of one triangle and one nanorod. A plasmon-induced transparency (PIT) resonance appears in the transmission spectrum, which is ascribed to the induced multipole plasmon mode of the nanorod. Multispectral PIT resonances are observed, when two or more nanorods are put in proximity to the triangle. It is proved that the combined effects of the induced multipole plasmon mode of nanorods and the cavity resonant mode contribute to these PIT peaks. The tunability of PIT on the geometrical parameters is also presented.

We theoretically investigate the optical properties of two-intersecting nanorings (TINR), which exhibit a pronounced Fano resonance in the near-infrared region. A multiple-layer plasmon hybridization model is proposed to explain the reasons and forming processes of the Fano resonance. The dependence of the Fano resonance on the intersecting distance is also demonstrated. Moreover, the presented two-intersecting nanorings are employed as a biosensor exhibiting a 3-fold improvement of the figure of merit than that of a single-ring biosensor with the same resonant wavelength.

Density functional theory calculations by using both generalized gradient approximation (GGA) method and the GGA with considering strong correlation effect (GGA+U) were performed to elucidate the effect of Ce-4f orbit on the electronic structure of ZnO. It is found that after the cerium incorporation, a new localized band appears between the valence and conduction bands, which corresponds to the majority spin of Ce-4f states. It is this localized band that constructs a bridge between the valence and conduction states, which will improve the optical performance of ZnO. ZnO:Ce is a degenerate semiconductor. The strong correlation effect is very important for the 4f orbit of the Ce atom in ZnO:Ce. The mismatch of the majority and minority spin for the Ce-4f, Ce-5d states and the spin-polarized holes in O-2p states induced by Ce doping leads to the presence of the magnetic order for ZnO:Ce. We also studied the band structure and optical properties of ZnO:Ce with lacking one electron and two electrons, respect...