Effect Of Hole Doping Research Articles

Electron and hole doping in the relativistic Mott insulator Sr2IrO4 : A first-principles study using band unfolding technique

We study the effects of dilute La and Rh substitutional doping on the electronic structure of the relativistic Mott insulator ${{\mathrm{Sr}}_{2}\mathrm{IrO}}_{4}$ using fully relativistic and magnetically noncollinear density functional theory with the inclusion of an on-site Hubbard $U$. To model doping effects, we have adopted the supercell approach, that allows for a realistic treatment of structural relaxations and electronic effects beyond a purely rigid band approach. By means of the band unfolding technique we have computed the spectral function and constructed the effective band structure and Fermi surface (FS) in the primitive cell, which are readily comparable with available experimental data. Our calculations clearly indicate that La and Rh doping can be interpreted as effective electron and (fractional) hole doping, respectively. We found that both electron and hole doping induce an insulating-to-metal transition (IMT) but with different characteristics. In ${\mathrm{Sr}}_{2\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{IrO}}_{4}$ the IMT is accompanied by a moderate renormalization of the electronic correlation substantiated by a reduction of the effective on-site Coulomb repulsion $U\ensuremath{-}J$ from 1.6 eV $(x=0)$ to 1.4 eV (metallic regime of $x=12.5%$). The progressive closing of the relativistic Mott gap leads to the emergence of connected elliptical electron pockets at $(\ensuremath{\pi}/2,\ensuremath{\pi}/2)$ and less intense features at $X$ on the Fermi surface. The average ordered magnetic moment is slightly reduced upon doping, but the canted antiferromagnetic state is perturbed on the Ir-O planes located near the La atoms. The substitution of Ir with the nominally isovalent Rh is accompanied by a substantial hole transfer from the Rh site to the nearest-neighbor Ir sites. This shifts down the chemical potential, creates almost circular disconnected hole pockets in the FS, and establishes the emergence of a two-dimensional metallic state formed by conducting Rh planes intercalated by insulating Ir planes. Finally, our data indicate that hole doping causes a flipping of the in-plane net ferromagnetic moment on the Rh plane and induces a magnetic transition from the antiferromagnetic (AF)-I to the AF-II ordering.

Tunable Conductivity and Half Metallic Ferromagnetism in Monolayer Platinum Diselenide: A First-Principles Study

On basis of the first-principles calculations, we have studied the effects of hole doping and biaxial tensile strain on the electronic and magnetic properties of monolayer of platinum diselenide (PtSe2). Due to the large density of states near the valence band edge, this nonmagnetic monolayer semiconductor switches to a ferromagnetic half metal within a small range of hole doping. With an increase of hole density, average magnetic moment per carrier also increases and reaches at its maximum value over a specific range of carrier density, while the system remains in a half metal state before the magnetic moment abruptly begins to fall. We also predict a critical value of biaxial tensile strain (5%) for doped monolayer PtSe2, after which the optimal carrier density becomes constant, while the magnetic moment/carrier gradually increases and the ferromagnetic state of the system becomes more stable with increasing values of strain. This work paves a possible way to engineer the magnetic properties of the two-...

Electronic and magnetic properties of MnF3(4) superhalogen cluster-sandwiched bilayer graphene: First-principles calculations

By conducting first-principles calculations with van der Waals correction, we investigate the structural, electronic, and magnetic properties of Gr/MnF3(4)/Gr sandwiched structures. The calculated binding energies were within 54–79meV per carbon atom for the four Gr/MnF3(4)/Gr sandwiched structures tested in our study. This result implies that the MnF3(4) clusters stabilize the AA and AB stacking in the Gr/MnF3(4)/Gr sandwich structures because of the high electronegativity of the clusters. Charge transfer from bilayer graphene to the MnF3(4) clusters is noted to induce effective hole doping in graphene. Spin polarization in the graphene layer is approximately 100% along the majority direction on the position of the Fermi level in the MnF3-doped structures. The band gaps of the spin-up and spin-down branches and the magnetic moments of the C atoms are increased by compression interlayer spacing. The MnF3 clusters affect the electronic and magnetic properties of graphene in the vicinity of the Fermi level; thus, the clusters are highly suitable for use as a dopant in spintronic applications.

First principle study of inducing superconductivity in α-graphyne by hole-doping and biaxial tensile strain

First-principle calculations within Eliashberg theory framework have been utilized to investigate theoretically the effect of hole-doping along with applying strain on superconductivity in α-graphyne and graphene as a benchmark. We show how the electronic properties, electron-phonon interaction strength and superconducting critical temperature TC of α-graphyne and graphene are affected by hole-doping and biaxial tensile strain. Although, intrinsic α-graphyne is semi-metal but it is found that increasing hole-doped concentration of 12.5–25% changes its electronic properties from metal to semiconductor with a band gap energy of 0.46eV. Furthermore, we demonstrate that it is not possible to induce superconductivity in α-graphyne by the conspiracy of 12.5% hole-doping and critical strain (8%) contrary to 12.5% hole-doped graphene under critical strain (12%) which becomes superconductor with TC∼12K. It seems that the presence of CC bond suppresses the effect of strain significantly and hole-doping slightly on improving electron-phonon coupling constant and TC in contrast to graphene.

Hallmarks of the Mott-metal crossover in the hole-doped pseudospin-1/2 Mott insulator Sr2IrO4.

The physics of doped Mott insulators remains controversial after decades of active research, hindered by the interplay among competing orders and fluctuations. It is thus highly desired to distinguish the intrinsic characters of the Mott-metal crossover from those of other origins. Here we investigate the evolution of electronic structure and dynamics of the hole-doped pseudospin-1/2 Mott insulator Sr2IrO4. The effective hole doping is achieved by replacing Ir with Rh atoms, with the chemical potential immediately jumping to or near the top of the lower Hubbard band. The doped iridates exhibit multiple iconic low-energy features previously observed in doped cuprates—pseudogaps, Fermi arcs and marginal-Fermi-liquid-like electronic scattering rates. We suggest these signatures are most likely an integral part of the material's proximity to the Mott state, rather than from many of the most claimed mechanisms, including preformed electron pairing, quantum criticality or density-wave formation.

Electronic structure and O vacancy formation/migration in La0.825(Mg/Ca/Ba)0.125CoO3

The effect of A-site hole doping (Mg2+, Ca2+ or Ba2+) on the electronic and magnetic properties as well as the O vacancy formation and migration in perovskite LaCoO3 is studied using first-principles calculations. All three dopants are found to facilitate O vacancy formation. Substitution of La3+ with Ba2+/Mg2+ yields the lowest O vacancy formation energy for low/intermediate spin Co, implying that not only the structure but also the spin state of Co is a key parameter. Only for low spin Co the ionic radius is correlated with the O migration barrier. Enhanced migration for intermediate spin Co is ascribed to the availability of additional space at the transition state.

Temperature and doping dependence of normal state spectral properties in a two-orbital model for ferropnictides

Using a second-order perturbative Green's functions approach we determined the normal state spectral function A(k→,ω) employing a minimal model for ferropnictides. Used before to study magnetic fluctuations and superconducting properties, it includes the two effective bands related to Fe-3d orbitals proposed by S. Raghu et al. [Phys. Rev. B 77 (2008) 220503(R)], and local intra- and inter-orbital correlations for the effective orbitals. Here, we focus on the normal state electronic properties, in particular the temperature and doping dependence of the total density of states, A(ω), and of A(k→,ω) in different Brillouin zone regions, comparing them with existing angle resolved photoemission spectroscopy (ARPES) and theoretical results. We obtain an asymmetric effect of electron and hole doping, quantitative agreement with the experimental chemical potential shifts, as well as spectral weight redistributions near the Fermi level with temperature consistent with the available experiments. In addition, we predict a non-trivial dependence of A(ω) with temperature, exhibiting clear renormalization effects by correlations. Interestingly, investigating the origin of this predicted behavior by analyzing the evolution with temperature of the k-dependent self-energy obtained in our approach, we could identify a number of Brillouin zone points, not probed by ARPES yet, where the largest non-trivial effects of temperature on the renormalization are predicted for the parent compounds.

Crystal structure and electronic states of Co and Gd ions in a Gd0.4Sr0.6CoO2.85 single crystal

X-ray diffraction and X-ray absorption near edge structure (XANES) spectra have been measured at the Со K-edge and Gd L 3-edge in GdCoO3 and Gd0.4Sr0.6CoO2.85 cobaltites. The effect of Sr substitution on the crystal structure and electronic and magnetic states of Co3+ ions in a Gd0.4Sr0.6CoO2.85 single crystal has been analyzed. The XANES measurements at the Co K-edge have not showed a noticeable shift of the absorption edge with an increase in the concentration of Sr. This indicates that the effective valence of cobalt does not change. An increase in the intensity of absorption at the Gd L 3-edge is due to an increase in the degree of hybridization of the Gd(5d) and O(2p) states. The effect of hole doping on the magnetic properties results in the appearance of the ferromagnetic component and in a significant increase in the magnetic moment.

Chemical doping and high-pressure studies of layeredβ−PdBi2single crystals

We have systematically grown large single crystals of the layered compounds $\ensuremath{\beta}\ensuremath{-}\mathrm{PdB}{\mathrm{i}}_{2}$, and both the hole-doped $\mathrm{PdB}{\mathrm{i}}_{2\ensuremath{-}x}\mathrm{P}{\mathrm{b}}_{x}$ and the electron-doped $\mathrm{N}{\mathrm{a}}_{x}\mathrm{PdB}{\mathrm{i}}_{2}$, and studied their magnetic and transport properties. Hall effect measurements on $\mathrm{PdB}{\mathrm{i}}_{2}$, $\mathrm{PdB}{\mathrm{i}}_{1.8}\mathrm{P}{\mathrm{b}}_{0.2}$, and $\mathrm{N}{\mathrm{a}}_{0.057}\mathrm{PdB}{\mathrm{i}}_{2}$ show that the charge transport is dominated by electrons in all of the samples. The electron concentration is substantially reduced upon Pb doping in $\mathrm{PdB}{\mathrm{i}}_{2\ensuremath{-}x}\mathrm{P}{\mathrm{b}}_{x}$ and increased upon Na intercalation in $\mathrm{N}{\mathrm{a}}_{x}\mathrm{PdB}{\mathrm{i}}_{2}$, indicating effective hole doping by Pb and electron doping by Na. We observed a monotonic decrease of the superconducting transition temperature $({T}_{c})$ from 5.4 K in undoped $\mathrm{PdB}{\mathrm{i}}_{2}$ to less than 2 K for $x>0.35$ in hole-doped $\mathrm{PdB}{\mathrm{i}}_{2\ensuremath{-}x}\mathrm{P}{\mathrm{b}}_{x}$. Meanwhile, a rapid decrease of ${T}_{c}$ with Na intercalation is also observed in the electron-doped $\mathrm{N}{\mathrm{a}}_{x}\mathrm{PdB}{\mathrm{i}}_{2}$, which is in disagreement with the theoretical expectation. In addition, both the magnetoresistance and Hall resistance further reveal evidence for a possible spin excitation associated with Fermi surface reconstruction at \ensuremath{\sim}50 K in the Na-intercalated $\mathrm{PdB}{\mathrm{i}}_{2}$ sample. The complete phase diagram is thus established from hole doping to electron doping. Meanwhile, a high-pressure study of the undoped $\mathrm{PdB}{\mathrm{i}}_{2}$ shows that the ${T}_{c}$ is linearly suppressed under pressure with a $d{T}_{c}/dP$ coefficient of \ensuremath{-}0.28 K/GPa.

High temperature thermoelectric properties of Bi2−xNaxSr2Co2Oy ceramics

The Na doping effects on the high temperature thermoelectric properties of [Formula: see text] ([Formula: see text] = 0, 0.05, 0.10, 0.15, 0.20 and 0.30) ceramics were investigated from 343 K to 973 K. When [Formula: see text], the electrical resistivity of [Formula: see text] decreases with increasing Na doping amount due to the hole-doping effect, which exhibits metallic electrical conductivity behavior. While, at the temperature range of 480–830 K, the samples with [Formula: see text] exhibit semiconductor electrical conductivity behavior instead. The Seebeck coefficients are improved by Na doping at lower temperature, but they decrease slightly at higher temperature except for [Formula: see text]. Roughly, the thermal conductivity is depressed by the doping defects. As an overall result, the dimensionless figure of merit [Formula: see text] of [Formula: see text] reaches the maximum value of 0.3 K at 973 K, which is nearly twice the value of the undoped sample [Formula: see text].

Evaluation of Ca3(Co,M)2O6 (M=Co, Fe, Mn, Ni) as new cathode materials for solid-oxide fuel cells

Series compounds Ca3(Co0.9M0.1)2O6 (M=Co, Fe, Mn, Ni) with hexagonal crystal structure were prepared by sol–gel route as the cathode materials for solid oxide fuel cells (SOFCs). Effects of the varied atomic compositions on the structure, electrical conductivity, thermal expansion and electrochemical performance were systematically evaluated. Experimental results showed that the lattice parameters of Ca3(Co0.9Fe0.1)2O6 and Ca3(Co0.9Mn0.1)2O6 were both expanded to certain degree. Electron-doping and hole-doping effects were expected in Ca3(Co0.9Mn0.1)2O6 and Ca3(Co0.9Ni0.1)2O6 respectively according to the chemical states of constituent elements and thermal-activated behavior of electrical conductivity. Thermal expansion coefficients (TEC) of Ca3(Co0.9M0.1)2O6 were measured to be distributed around 16×10−6K−1, and compositional elements of Fe, Mn, and Ni were especially beneficial for alleviation of the thermal expansion problem of cathode materials. By using Ca3(Co0.9M0.1)2O6 as the cathodes operated at 800°C, the interfacial area-specific resistance varied in the order of M=Co<M=Fe<M=Ni<M=Mn, and the over-potential increased in the order of M=Fe≈M=Co<M=Mn<M=Ni. Among all of these compounds, Ca3(Co0.9Fe0.1)2O6 showed the best electrochemical performance and the power density as high as ca. 500mWcm−2 at 800°C achieved in the single cell with La0.8Sr0.2Ga0.83Mg0.17O2.815 as electrolyte and Ni–Ce0.8Sm0.2O1.9 as anode. Ca3(Co0.9M0.1)2O6 (M=Co, Fe, Mn, Ni) can be used as the cost-effective cathode materials for SOFCs.

Electronic structure of phosphorene nanoribbons

Abstract Density Functional Theory employing periodic boundary conditions at the VSXC/6-31G level is used to calculated the dependence of the energy levels of phosphorene nanoribbons on the wave vector. The ribbons are shown to be small band gap semiconductors having band gaps at K=0 less than 0.81 eV. The electronic structure is shown to be dependent on the direction in the unit cell in which the ribbons are formed. The unit cell is predicted to be a ground state triplet suggesting that ribbons formed from it could be ferromagnetic semiconductors. The effect of hole (Si) doping and electron (S) doping on the electronic structure of the ribbons is investigated.

Negative Colossal Magnetoresistance Driven by Carrier Type in the Ferromagnetic Mott Insulator GaV4S8

We report here a study on the evolution of structural and electronic properties of the lacunar spinel compounds GaV4S8 with charge doping. In this ferromagnetic (FM) Mott insulator, the heterovalent substitutions of Ga3+ by Zn2+ or Ge4+ allow induction of charge doping either by holes or by electrons. We show that electron-doped GaV4S8 displays a bulk, negative, and colossal magnetoresistance (CMR) with a relative drop of resistivity reaching −80% at 7 T in the vicinity of the Curie temperature. Conversely, hole-doped GaV4S8 does not display any negative CMR but a classical positive magnetoresistance. This asymmetric electron–hole doping effect challenges the common view stating that CMR effects in doped FM Mott insulators depends only on the density of carrier and not on their electron/hole nature. We show that a simple model based on multiorbital effects and Hund’s rule is able to capture the presence (absence) of negative CMR in electron- (hole-) doped GaV4S8.

Surface transfer doping induced effective modulation on ambipolar characteristics of few-layer black phosphorus.

Black phosphorus, a fast emerging two-dimensional material, has been configured as field effect transistors, showing a hole-transport-dominated ambipolar characteristic. Here we report an effective modulation on ambipolar characteristics of few-layer black phosphorus transistors through in situ surface functionalization with caesium carbonate (Cs2CO3) and molybdenum trioxide (MoO3), respectively. Cs2CO3 is found to strongly electron dope black phosphorus. The electron mobility of black phosphorus is significantly enhanced to ~27 cm(2) V(-1) s(-1) after 10 nm Cs2CO3 modification, indicating a greatly improved electron-transport behaviour. In contrast, MoO3 decoration demonstrates a giant hole-doping effect. In situ photoelectron spectroscopy characterization reveals significant surface charge transfer occurring at the dopants/black phosphorus interfaces. Moreover, the surface-doped black phosphorus devices exhibit a largely enhanced photodetection behaviour. Our findings coupled with the tunable nature of the surface transfer doping scheme ensure black phosphorus as a promising candidate for further complementary logic electronics.

Modification of electronic structure and thermoelectric properties of hole-doped tungsten dichalcogenides

We present a study on the modification of the electronic structure and hole-doping effect for the layered dichalcogenide ${\mathrm{WSe}}_{2}$ with a multivalley band structure, where Ta is doped on the W site along with a partial substitution of Te for its lighter counterpart Se. By means of band-structure calculations and specific-heat measurements, the introduction of Te is theoretically and experimentally found to change the electronic states in ${\mathrm{WSe}}_{2}$. While in ${\mathrm{WSe}}_{2}$ the valence-band maximum is located at the $\ensuremath{\Gamma}$ point, the introduction of Te raises the bands at the $K$ point with respect to the $\ensuremath{\Gamma}$ point. In addition, thermal-transport measurements reveal a smaller thermal conductivity at room temperature of ${\mathrm{W}}_{1\ensuremath{-}x}{\mathrm{Ta}}_{x}{\mathrm{Se}}_{1.6}{\mathrm{Te}}_{0.4}$ than reported for ${\mathrm{W}}_{1\ensuremath{-}x}{\mathrm{Ta}}_{x}{\mathrm{Se}}_{2}$. However, when approaching 900 K, the thermal conductivities of both systems converge while the resistivity in ${\mathrm{W}}_{1\ensuremath{-}x}{\mathrm{Ta}}_{x}{\mathrm{Se}}_{1.6}{\mathrm{Te}}_{0.4}$ is larger than in ${\mathrm{W}}_{1\ensuremath{-}x}{\mathrm{Ta}}_{x}{\mathrm{Se}}_{2}$, leading to comparable but slightly smaller values of the figure of merit in ${\mathrm{W}}_{1\ensuremath{-}x}{\mathrm{Ta}}_{x}{\mathrm{Se}}_{1.6}{\mathrm{Te}}_{0.4}$.

Structural evolution in CVD graphene chemically oxidized by sulphuric acid

The role of sulphuric acid (H2SO4) in fabrication graphene oxide besides as intercalant has not been well addressed. In this work, Raman spectroscopy is used to monitor structural evolution in chemical vapor deposition (CVD) graphene chemically oxidized by dilute H2SO4. From the analysis of Raman spectra of oxidized graphene, we propose that oxidation first initiates at preexisting defects, and vacancy‐like defects are formed. Following is the radial growth of the vacancy, and oxidation pits appear in graphene. This assumption is further confirmed by atomic force microscope measurement. It is also found that with increase of amounts of defects, G peak is blue shift, and this is explained by defect and hole doping effect. Hole doping in graphene is much stronger at hexagon regions near the oxidation pits. This work helps in understanding the role of H2SO4 in fabrication graphene oxide as oxidizer as well as helps in obtaining structure information of graphene oxide. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Computational Investigation of the Electronic and Optical Properties of Planar Ga-Doped Graphene

We simulate the optical and electrical responses in gallium-doped graphene. Using density functional theory with a local density approximation, we simulate the electronic band structure and show the effects of impurity doping (0–3.91%) in graphene on the electron density, refractive index, optical conductivity, and extinction coefficient for each doping percentage. Here, gallium atoms are placed randomly (using a 5-point average) throughout a 128-atom sheet of graphene. These calculations demonstrate the effects of hole doping due to direct atomic substitution, where it is found that a disruption in the electronic structure and electron density for small doping levels is due to impurity scattering of the electrons. However, the system continues to produce metallic or semimetallic behavior with increasing doping levels. These calculations are compared to a purely theoretical 100% Ga sheet for comparison of conductivity. Furthermore, we examine the change in the electronic band structure, where the introduction of gallium electronic bands produces a shift in the electron bands and dissolves the characteristic Dirac cone within graphene, which leads to better electron mobility.

Effect of hole doping on the magnetism of point defects in graphene: A theoretical study

Using ab initio methods based on the density functional theory, we study the magnetic properties of different point defects in graphene. We consider separately, atomic hydrogen, atomic fluorine, and single vacancies. The three defects have completely different magnetic properties. A local spin one-half magnetic moment is well defined at a hydrogen impurity, while single fluorine adatoms do not induce a well-defined magnetic moment unless there is a fluorine concentration of at least of a 0.5%. In this case, the induced magnetic moment is of the order of 0.45 ${\ensuremath{\mu}}_{B}$ per defect. This behavior is interpreted as being due to the charge transfer between fluorine and graphene. The case of magnetic moments localized at $\ensuremath{\pi}$ electrons near vacancies is different from both previous cases; the size of the induced magnetic moment decreases with the dilution of defects and it is compatible with zero in the isolated vacancy. The effect of hole doping on these magnetic behaviors is studied and compared with the available experimental data. In the three cases, hole doping inhibits the formation of $\ensuremath{\pi}$ states magnetic moments.

Effects of hole doping and chemical pressure on the average superconducting kinetic energy of YBa2Cu3O7-δ single crystals

We reported on MZFC(T) and MFCC(T) reversible dc magnetizations of YBa2Cu3O7-δ, Y0.99Ca0.01Ba2Cu3O7-δ and YBa1.75Sra0.25Cu3O7-δ single crystals with a strong focus on the effects of Ca and Sr doping on the average superconducting kinetic energy density, k(T) of the YBa2Cu3O7-δ The k(T) is used as a relevant tool to provide physical information about the HTSC paring mechanism. The determination of the k(T) from MZFC(T) and MFCC(T) data is supported by virial theorem of superconductivity [k(T) = – MB]. The MZFC(T) and MFCC(T) measurements were performed with a SQUID magnetometer to H ≤ 50kOe applied parallel to the c axis of the samples. The results show that the samples present a common k(T) behavior that is characterized by a maximum value for T ≤ Tc that gradually decreases as the temperature rises towards to the Tc, becoming null to T ≤ Tc. The magnetic field affects smoothly the k(T) data behavior. The k(T) results contrasting of our samples shows that the Ca and Sr doping promotes a reduction of its amplitude. A possible explanation to this feature could be associated to the fact that the hole doping character promoted by Ca doping and the chemical pressure effect motivated by Sr doping affects considerably the superconducting paring mechanism of the YBa2Cu3O7-δ.

Contrasting carrier doping effects in the Kondo insulatorCeOs2Al10: The influential role ofc−fhybridization in spin-gap formation

The effects of electron (Ir) and hole (Re) doping on the hybridization gap and antiferromagnetic order have been studied by magnetization, muon spin relaxation ($\mu^+$SR), and inelastic neutron scattering on the polycrystalline samples of Ce(Os$_{1-x}$Ir$_x$)$_2$Al$_{10}$ ($x$ = 0.08 and 0.15) and CeOs$_{1.94}$Re$_{0.06}$Al$_{10}$. $\mu^+$SR spectra clearly reveals magnetic ordering below 20 and 10 K for $x$ = 0.08 and 0.15 samples respectively with a very weak signature of oscillations of the muon initial asymmetry at very short time scale. Our important findings are that small amount of electron doping (i) completely suppress the inelastic magnetic excitations near 11 meV down to 2K, which were observed in the undoped compound, and the response transforms into a broad quasielastic response and (ii) the internal field at the corresponding muon site is remarkably enhanced by about ten times compared with the parent compound. On the other hand with small amount of hole (3\% Re) doping the intensity of the inelastic magnetic excitations near 11 meV is reduced significantly. The main origin of the observed doping effect is an extra 5$d$ electrons being carried by Ir and a hole carried by Re compared with that the Os atom. The obtained results demonstrate a great sensitivity of the carrier doping and provides additional ways to study their anomalous magnetic properties.