Hole Doping Research Articles

Manipulating ambient pressure superconductivity in metal borocarbides through hole doping.

A Ca2B4C4 ternary compound obtained by using a machine learning (ML) guided structure search is found to be metastable with a formation energy of only 18 meV/atom above the convex hull but exhibits only marginal superconducting transition temperature (Tcc). By replacing Ca with Na, the electronic density of states (DOS) at the Fermi level is significantly enhanced, increasing the predicted Tc to 21.9 K. Extending this hole-doping strategy to other Ca-B-C compounds, we found that while Na4B2C22 remains superconducting with a Tc of 4.0 K, Na substitution in Ca2B4C8 transforms it from a semiconductor to a superconductor with a Tc of 28.9 K. The flat σ bands, particularly from the 2px and 2py orbitals of carbon, and a Van Hove singularity at the Fermi level, play crucial roles in enhancing the superconductivity. This work introduces a new class of B-C-based superconductors and broadens the compositional space for high-temperature superconducting materials.&#xD.

Is p-Type Doping in TeO2 Feasible?

Abstract Wide-bandgap two-dimensional (2D) β-TeO2 has been reported as a high-mobility p-type transparent semiconductor (Nat. Electron. 2021, 4, 277-283), attracting significant attention. This “breakthrough” not only challenges the conventional characterization of TeO2 as an insulator but also conflicts with the anticipated difficulty in hole doping of TeO2 by established chemical trends. Notably, the reported Fermi level of 0.9 eV above the valence band maximum actually suggests that the material is an insulator, contradicting the high hole density obtained by Hall effect measurement. Furthermore, the detected residual Se and the possible reduced elemental Te in the 2D β-TeO2 samples introduces complexity, considering that elemental Se, Te, and Te1-x Se x themselves are high-mobility p-type semiconductors. Therefore, doubts regarding the true cause of the p-type conductivity observed in the 2D β-TeO2 samples arise. In this Letter, we employ density functional theory calculations to illustrate that TeO2, whether in its bulk forms of α-, β-, or γ-TeO2, or in the 2D β-TeO2 nanosheets, inherently exhibits insulating properties and poses challenges in carrier doping due to its shallow conduction band minimum and deep valence band maximum. Our findings shed light on the insulating properties and doping difficulty of TeO2, contrasting with the claimed p-type conductivity in the 2D β-TeO2 samples, prompting inquiries into the true origin of the p-type conductivity.

Fluctuating charge-density-wave correlations in the three-band Hubbard model

The high-temperature superconducting cuprates host unidirectional spin- and charge-density-wave orders that can intertwine with superconductivity in nontrivial ways. While the charge components of these stripes have now been observed in nearly all cuprate families, their detailed evolution with doping varies across different materials and at high and low temperatures. We address this problem using nonperturbative determinant quantum Monte Carlo calculations for the three-band Hubbard model. Using an efficient implementation, we can resolve the model's fluctuating spin and charge modulations and map their evolution as a function of the charge transfer energy and doping. We find that the incommensurability of the charge modulations is decoupled from the spin modulations and decreases with hole doping, consistent with experimental measurements at high temperatures. These findings support the proposal that the high-temperature charge correlations are distinct from the intertwined stripe order observed at low-temperature and in the single-band Hubbard model.

Ohmic contact mechanism and charge redistribution of MoS2/Mn+1XnO2 heterostructures

Abstract Several M n+1 X n O2 compounds exhibit work functions higher than those of three-dimensional metals, enabling the formation of Ohmic contact heterostructures with MoS2, which enhances the catalytic activity of MoS2 for the hydrogen evolution reaction. However, the Schottky barrier height (SBH) in these Ohmic contact heterostructures does not adhere to the Schottky-Mott limit, leaving the Ohmic contact mechanism between MoS2 and M n+ 1X n O2 unclear and hindering further investigations into these heterostructures. In this study, we investigate 22 MoS2/M n+ 1X n O2 heterostructures using the unfolding method. Among these, the eight M n+ 1X n O2 compounds—Cr2CO2, Mo2CO2, V2CO2, W2CO2, Cr2NO2, V2NO2, Ti3C2O2 and V4C3O2—form p-type Ohmic contacts with MoS2. In contrast, the twelve compounds—Hf2CO2, Nb2CO2, Ta2CO2, Ti2CO2, Zr2CO2, Mo2NO2, Ti2NO2, Ti3N2O2, Zr3C2O2, Nb4C3O2, Ta4C3O2 and Ti4N3O2—create p-type Schottky contacts, while Hf2NO2 and Zr2NO2 form n-type Schottky contacts with MoS2. In the Ohmic contact heterostructures, out-of-plane orbital states hybridize to form a splitting band, allowing the highest valence band of MoS2 to cross the Fermi level and achieve hole doping. This splitting band not only results in a SBH that does not conform to the Schottky–Mott limit but also redistributes charge density. Notably, the heterostructures formed by Cr2CO2, Mo2CO2, V2CO2, W2CO2, Cr2NO2, V2NO2, V4C3O2, and MoS2 exhibit charge polarity distribution, whereas MoS2/Ti3C2O2 does not demonstrate charge polarity distribution.

Controllable half-metallicity in MnPX3 monolayer

Modulable electronic and magnetic structures significantly extend the properties and applications of two-dimensional (2D) materials. 2D antiferromagnets (AFM) can even become ferromagnets (FM) by various approaches, which ignites growing research interests in 2D AFM. Through first-principles calculations, we find that the adsorption of Li (electron doping) and F (hole doping) on the surface of MnPSe3 can induce half-metallicity with opposite spin polarizations. The adsorption site, concentration, charge transfer, and the exchange energy are investigated in detail, indicating the robustness of half-metallicity. At the interface of MnPS3/Au(111) heterostructure, we find electrons transfer from Au(111) to MnPS3, forming the Ohmic contact and inducing AFM-FM transition. All our results show that ferromagnetic MnPX3 (X = S and Se) monolayer with half-metallicity can be easily obtained, which may be of great significance in 2D spintronic materials and devices.

Hole doping and electronic correlations in Cr substituted BaFe$_{2}$As$_{2}$

Hole doping and electronic correlations in Cr substituted BaFe$_{2}$As$_{2}$

Lattice study of SU(2) gauge theory coupled to four adjoint Higgs fields

Gauge theories with matter fields in various representations play an important role in different branches of physics. Recently, it was proposed that several aspects of the pseudogap phase of cuprate superconductors near optimal doping may be explained by an emergent SU(2) gauge symmetry. Around the transition with positive hole doping, one can construct a (2+1)−dimensional SU(2) gauge theory coupled to four adjoint scalar fields which gives rise to a rich phase diagram with a myriad of phases having different broken symmetries. We study the phase diagram of this model on the Euclidean lattice using the hybrid Monte Carlo algorithm. We find the existence of multiple broken phases as predicted by previous mean-field studies. Depending on the quartic couplings, the SU(2) gauge symmetry is broken down either to U(1) or Z2 in the perturbative description of the model. We further study the confinement-deconfinement transition in this theory, and find that both the broken phases are deconfining in the range of volumes that we studied. However, there exists a marked difference in the behavior of the Polyakov loop between the two phases. Published by the American Physical Society 2024

Controllable p-type doping and improved conductance of few-layer WSe2 via Lewis acid

Manipulation of the electronic properties of layered transition-metal dichalcogenides (TMDs) is of fundamental significance for a wide range of electronic and optoelectronic applications. Surface charge transfer doping is considered to be a powerful technique to regulate the carrier density of TMDs. Herein, the controllable p-type surface modification of few-layer WSe2by FeCl3Lewis acid with different doping concentrations have been achieved. Effective hole doping of WSe2has been demonstrated using Raman spectra and XPS. Transport properties indicated the p-type FeCl3surface functionalization significantly increased the hole concentration with 1.2 × 1013cm-2, resulting in 6 orders of magnitude improvement for the conductance of FeCl3-modified WSe2compared with pristine WSe2. This work provides a promising approach and facilitate the further advancement of TMDs in electronic and optoelectronic applications.

Thickness and Doping Density Influence of a High-Voltage Inorganic Perovskite Solar Cell: A SCAPS 1-D Simulation Study

Recently, all inorganic perovskite solar cells have triggered great attention thanks to the rising performance during their development in solid state photovoltaics showing enhanced characteristics, such as: good stability, high photoluminescence quantum yield, tunable size, and morphology. In this work, a high open-circuit voltage solar cell based on all-inorganic perovskite through SCAPS simulator program is presented by analysing electron transport layer (ETL), perovskite layer, hole transport layer (HTL) thickness and doping density from a FTO/TiO2/CsPbBr3/Spiro-OMeTAD/Au structure were modified to observe its influence on solar cell performance. Therefore, simulation results show that a thicker ETL hinders carrier transport towards the FTO layer due to larger distance which leads to higher recombination rate, reducing carrier’s lifetime. Albeit high doping density values in ETL enhances the overall solar cell performance. As for the absorber layer, while its thickness increases, carrier collection rate decreases due to recombination impacting Voc, which results from thickness increase. Based on the results, solar cell efficiency improvement is attributed to the built-in electric field as absorber layer doping density increases. While HTL thickness has minimum impact on the solar cell output, doping density enhances device parameters significantly. Summarising the results obtained from thickness and doping density simulations, the optimal solar cell operation was obtained at 10 nm, 600 nm, and 100 nm layer thickness as well as 1020 cm-3, 1016 cm-3, and 1020 cm-3 doping density (TiO2, CsPbBr3 and Spiro-OMeTAD). Results from three different sources, collected from literature, were used to compare, and fitting them along with simulation results.

Realizing synergistic optimization of electrical and thermal transport properties in BiCuSeO ceramics via multi-element doping

In this study, the design of high-entropy alloys (multi-element substitution, Al3+/La3+/Sb3+/Y3+) was used to increase material entropy and improve heat scattering to further reduce thermal conductivity. Concurrently, Ca2+ ion hole doping was used to improve its electrical conductivity. Therefore, a series of Bi0.92−xAl0.02La0.02Sb0.02Y0.02CaxCuSeO (x = 0, 0.02, 0.06, 0.10, and 0.14) ceramics was prepared using a combination of high-energy ball milling and cold isostatic pressing. The multi-element substitution of Al0.02La0.02Sb0.02Y0.02Ca0.02 in the Bi site resulted in a minimum thermal conductivity of 0.35 Wm−1K−1, which is one-third of that of intrinsic BiCuSeO. Simultaneously, the conductivity increased up to 10–20 times that of intrinsic BiCuSeO, proportional to the amount of Ca2+ doping. Furthermore, the optimum component Bi0.82Al0.02La0.02Sb0.02Y0.02Ca0.10CuSeO exhibited an extremely high power factor of 568.55 μWm−1K−2 at 773 K, significantly higher than that of pure BiCuSeO (148.7 μWm−1K−2). Consequently, a peak ZT value of approximately 1.12 was achieved at 773 K, which was 4.48 times higher than that of the pristine BiCuSeO specimen (approximately 0.25). Our findings provide a novel strategy to optimize the thermoelectric properties of BiCuSeO and other materials.

Charge stripe manipulation of superconducting pairing symmetry transition

Charge stripes have been widely observed in many different types of unconventional superconductors, holding varying periods (P\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\\mathcal{P}}}$$\\end{document}) and intensities. However, a general understanding on the interplay between charge stripes and superconducting properties is still incomplete. Here, using large-scale unbiased numerical simulations on a general inhomogeneous Hubbard model, we discover that the charge-stripe period P\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\\mathcal{P}}}$$\\end{document}, which is variable in different real material systems, could dictate the pairing symmetries—d wave for P≥4,s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\\mathcal{P}}}\\ge 4,s$$\\end{document} and d waves for P≤3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\\mathcal{P}}}\\le 3$$\\end{document}. In the latter, tuning hole doping and charge-stripe amplitude can trigger a d-s wave transition and magnetic-correlation shift, where the d-wave state converts to a pairing-density wave state, competing with the s wave. These interesting phenomena arise from an unusual stripe-induced selection rule of pairing symmetries around on-stripe region and within inter-stripe region, giving rise to a critical point of P=3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\\mathcal{P}}}=3$$\\end{document} for the phase transition. In general, our findings offer important insights into the differences in the superconducting pairing mechanisms across many P\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\\mathcal{P}}}$$\\end{document}-dependent superconducting systems, highlighting the decisive role of charge stripe.

Geometric structure and electronic properties of bilayer graphene with a Moire superlattice by interlayer asymmetric tensile strain

Using the density functional theory combined with the effective screening medium method, we investigated the energetics and electronic properties of bilayer graphene, comprising graphene layers without and with tensile strain. An interlayer interaction does not affect the structural reconstruction of each graphene layer despite the bilayer structure possessing a Moire superlattice. The structural asymmetry between the graphene layers causes a potential difference across the layers, leading to electron and hole doping in the layers without and with the tensile strain. Accumulated carriers show unique lateral distribution in each graphene layer, which depends on the interlayer atomic arrangements.

Trion sensing of a zero-field composite Fermi liquid.

The half-filled lowest Landau level is a fascinating platform for researching interacting topological phases. A celebrated example is the composite Fermi liquid, a non-Fermi liquid formed by composite fermions in strong magnetic fields1-10. Its zero-field counterpart is predicted in atwisted MoTe2 bilayer (tMoTe2)11,12-a recently discovered fractional Chern insulator exhibiting the fractional quantum anomalous Hall effect13-16. Although transport measurements at ν = -1/2 show signatures consistent with a zero-field composite Fermi liquid14, new probes are crucial to investigate the state and its elementary excitations. Here, by using the unique valley properties of tMoTe2, we report optical signatures of a zero-field composite Fermi liquid. We measured the degree of circular polarization (ρ) of trion photoluminescence versus hole doping and electric field. We found that, within the phase space showing robust ferromagnetism, ρ is near unity for Fermi liquid states. However, ρ is quenched at both integer andfractional Chern insulators, and in a holedoping range near ν = -1/2. Temperature, optical excitation power and electric-field-dependence measurements demonstrate that the quenching of ρ is a direct consequence of an energy gap (pseudogap) for electronic excitations of the Chern insulators (composite Fermi liquid): because the local spin-polarized excitations necessary to form trions are strongly suppressed, trion formation at the corresponding filling factors relies on optically generated unpolarized itinerant holes. Our work highlights a new excitonic probe of zero-field fractional Chern insulator physics, unique to tMoTe2.

The mysterious magnetic ground state of Ba14MnBi11 is likely self-doped and altermagnetic

Magnetism in the Zintl compound Ba14MnBi11 is rather poorly understood. Experimental claims are largely inconsistent with ab initio calculations, much beyond typical errors of the latter. We revisit this old problem, assuming that the root of the problem may be in nonstoichiometry of existing samples. Our key finding is that the magnetic ground state is indeed very susceptible to charge doping (band filling). Calculations for stoichiometric Ba14MnBi11 give a rather stable ferromagnetic metallic state, in agreement with previous publications. However, by adding exactly one electron per Mn, the system becomes semiconducting as expected, and becomes weakly antiferromagnetic (AF). On the other hand, upon small amount of hole doping, the system transitions to a special type of AF state known as altermagnetism. Furthermore, hole and electron doping-induced phase transitions result from different underlying mechanisms, influencing different exchange pathways. We propose that the inconsistency between experiment and theory is not a failure of the latter, but results from a nontrivial ramification of nonstoichiometry. The possibility of doping-stabilized altermagnetism is exciting.

Possible Superconductivity for Layered Metal Boride Carbide Compounds MB2C2 (M = Alkali, Alkaline-Earth, or Rare-Earth Metals).

The possible emergence of superconductivity in layered metal boride carbide compounds MB2C2 (M = Sc, Y, Be, Ca) was investigated using density functional theory calculations upon the topology of a boron-carbon network and the nature of the metal. ScB2C2 and YB2C2 show metallic and superconductive properties with low critical temperatures (Tcs). The semiconducting BeB2C2 compound may show superconductivity upon carrier doping with a high Tc of 47.8 K by hole doping─comparable to the structurally related MgB2 superconductor─but with a low Tc by electron doping. In contrast, the semiconducting CaB2C2 compound is predicted to be a superconductor by hole and electron doping but with low Tcs. These differences arise from the spatial distribution of electrons at the Fermi level. For compounds with low Tcs, electrons at the Fermi level are localized primarily on B and C π states perpendicular to the BC layers, experiencing minimal influence from atomic oscillations and resulting in weak electron-phonon interactions. Conversely, for a high Tc, electrons are found in σ-bonding states, leading to strong electron-phonon interactions. Electrons at the Fermi level in boron-carbon σ-bonding states seem to be a prerequisite to expect high Tc superconductivity in this kind of compound.

Ultrasensitive and durable borophene-based humidity sensors for advanced human-centric applications

Borophene, a novel two-dimensional (2D) nanomaterials with high surface-to-volume ratio and abundant active sites, show great promise for humidity sensing applications, which are crucial for improving human comfort, public health, and device safety. However, traditional fabrication methods, such as drop-coating, face limitations including uncontrollable sensing layer thickness, poor water-damage resistance, and inherent variability between devices. In this work, we present a high-performance humidity sensor fabricated using borophene glass. The sensor demonstrates an impressive detection range (11–97 % RH), exceptional sensitivity (up to 1.83×105% at 97 % RH), low hysteresis (1.245 %), excellent repeatability, and relatively fast response (28.8 s)/recovery (2.6 s) times. Notably, the sensor exhibits thickness-dependent sensing performance, long-term stability, high selectivity, and water-damage resistance. First-principles calculations show that borophene exhibits an adsorption energy of 0.208 eV for H2O molecules, with the hole doping effect following adsorption driving the sensor’s response to varying relative humidity levels. The sensor’s sustained heightened sensitivity under high humidity conditions is attributed to the Grotthuss mechanism. Additionally, the sensor has been successfully integrated into various human-centric applications, including speech recognition, wireless monitoring of respiratory patterns, and non-contact switches. These advancements pave the way for the integration of borophene humidity sensors into smart devices and non-contact control systems, driving innovation in human–computer interaction and healthcare technologies.

Thermal and photochemical degradation of CsGeI3 and CsGeBr3: XPS and optical studies

The toxicity of complex lead halides significantly limits the commercialization and practical application of perovskite solar cells. In recent days, lead-free complex lead halides with a perovskite structure have become increasingly popular, among which germanium systems are the least studied. Here we present for the first time a systematic study of the thermal and photochemical stability of perovskite thin films of CsGeI3 and CsGeBr3. The measurements of optical absorbance and X-ray photoelectron spectra (XPS) of core levels and valence bands of Ge-based halide perovskites after light soaking and heat stress were thoroughly performed. It has been found the effect of thermal and photochemical degradation of Ge perovskites which is accompanied by reduction of I:Ge and Br:Ge ratios and appearance of tetravalent metal species fixed in XPS Ge 2p and Ge 3d spectra. The XPS O 1s measurements of irradiated and annealed Ge-based perovskites and their comparison with spectra of GeO2 have shown that formation of Ge4+-species is not due to metal oxidation but owing to defect-mediated hole-doping. While the Ge2+→Ge4+ process lowers the thermal and photochemical stability of Ge-based perovskites and limits their use in photovoltaics, the temperature induced hole doping is favorable for thermoelectric applications.

Fermi and Luttinger Arcs: Two Concepts, Realized on One Surface.

We present an analytically solvable model for correlated electrons, which is able to capture the major Fermi surface modifications occurring in both hole- and electron-doped cuprates as a function of doping. The proposed Hamiltonian qualitatively reproduces the results of numerically demanding many-body calculations, here obtained using the dynamical vertex approximation. Our analytical theory provides a transparent description of a precise mechanism, capable of driving the formation of disconnected segments along the Fermi surface (the highly debated "Fermi arcs"), as well as the opening of a pseudogap in hole and electron doping. This occurs through a specific mechanism: The electronic states on the Fermi arcs remain intact, while the Fermi surface part where the gap opens transforms into a Luttinger arc.

Electrical Transport Properties of PbS Quantum Dot/Graphene Heterostructures.

The integration of PbS quantum dots (QDs) with graphene represents a notable advancement in enhancing the optoelectronic properties of quantum-dot-based devices. This study investigated the electrical transport properties of PbS quantum dot (QD)/graphene heterostructures, leveraging the high carrier mobility of graphene. We fabricated QD/graphene/SiO2/Si heterostructures by synthesizing p-type monolayer graphene via chemical vapor deposition and spin-coating PbS QDs on the surface. Then, we used a low-temperature electrical transport measurement system to study the electrical transport properties of the heterostructure under different temperature, gate voltage, and light conditions and compared them with bare graphene samples. The results indicated that the QD/graphene samples exhibited higher resistance than graphene alone, with both resistances slightly increasing with temperature. The QD/graphene samples exhibited significant hole doping, with conductivity increasing from 0.0002 Ω-1 to 0.0007 Ω-1 under gate voltage modulation. As the temperature increased from 5 K to 300 K, hole mobility decreased from 1200 cm2V-1s-1 to 400 cm2V-1s-1 and electron mobility decreased from 800 cm2V-1s-1 to 200 cm2V-1s-1. Infrared illumination reduced resistance, thereby enhancing conductivity, with a resistance change of about 0.4%/mW at a gate voltage of 125 V, demonstrating the potential of these heterostructures for infrared photodetector applications. These findings offer significant insights into the charge transport mechanisms in low-dimensional materials, paving the way for high-performance optoelectronic devices.

Superconductivity in Diamond-Like BC15.

Advancing the compositional space of a compound class can result in intriguing superconductors, such as LaH10. Herein, we performed a comprehensive first-principles structural search on a binary B-C system with various chemical compositions. The identified diamond-like BC15, named d-BC15, is thermodynamically superior to the synthesized BC3 and BC5. Interestingly, d-BC15 shows anisotropic superconductivity resulting from three distinct Fermi surfaces. Its predicted critical temperature (Tc) is 43.6 K at ambient pressure, beyond the McMillan limit. d-BC15 reaches a maximum of around 75 K at 0.43% hole doping due to the substantially enhanced density of states at the Fermi level. Additionally, d-BC15 demonstrates superhard characteristics with a Vickers hardness of 75 GPa. The calculated tensile and shear stresses are 72 and 73 GPa, respectively. The combination of high superconductivity and superhardness in d-BC15 offers new insights into the design of multifunctional materials.