2022 |
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 | Chao-Sheng Lian, Christoph Heil, Xiaoyu Liu, Chen Si, Feliciano Giustino, Wenhui Duan Intrinsic and doping-enhanced superconductivity in monolayer 1T-TaS2: Critical role of charge ordering and spin-orbit coupling Journal Article In: Physical Review B, vol. 105, iss. 18, pp. L180505, 2022. @article{Lian2022,The interplay of superconductivity with charge density wave (CDW) in metallic transition-metal dichalcogenides has been widely debated, and viable strategies manipulating these quantum states in the two-dimensional (2D) limit remain unclear. Using the ab initio anisotropic Migdal-Eliashberg theory, we successfully explain the superconductivity observed in monolayer 1H−TaS2 by simultaneously determining its precise CDW structure and treating the marked modification of electron-phonon interaction and critical temperature Tc by spin-orbit coupling effects. With this paradigm, we further show that electron doping weakens the CDW order leading to increased Tc up to 11 K, along with a single-gap to two-gap superconductivity transition due to the suppression of the CDW gap. By contrast, a low hole doping barely affects the CDW but still yields a significantly enhanced superconducting order, implying their good coexistence. Combined with the synergistic behavior of CDW and superconductivity, which cooperate upon TaS2 thickness reduction causing an unusual rise of Tc, our results unravel diversified interactions between the two collective orders in ultrathin TaS2, being competition, coexistence or cooperation depending on external stimuli, which provide key clues for controlling correlated states in devices based on 2D CDW superconductors. |
Feliciano Giustino, Henry James Snaith, Nobuya Sakai, Yorgos Volonakis Double perovskite Patent 2022. @patent{nokey,The invention relates to an optoelectronic material comprising a compound, wherein the compound comprises: (i) one or more cations, A; (ii) one or more first B cations, Bn+; (iii) one or more second B cations, Bm+; and (iv) one or more chalcogen anions, X; wherein the one or more first B cations, Bn+ are different from the one or more second B cations, Bm+; n represents the oxidation state of the first B cation and is a positive integer of from 1 to 7 inclusive; m represents the oxidation state of the second B cation and is a positive integer of from 1 to 7 inclusive; and n+m is equal to 8. | |
 | Joshua Leveillee, Samuel Poncé, Nicholas L Adamski, Chris G Van de Walle, Feliciano Giustino Anisotropic-strain-enhanced hole mobility in GaN by lattice matching to ZnGeN2 and MgSiN2 Journal Article In: Applied Physics Letters, vol. 120, iss. 20, 2022. @article{Leveillee2022,The key obstacle toward realizing integrated gallium nitride (GaN) electronics is its low hole mobility. Here, we explore the possibility of improving the hole mobility of GaN via epitaxial matching to II–IV nitride materials that have recently become available, namely, ZnGeN2 and MgSiN2. We perform state-of-the-art calculations of the hole mobility of GaN using the ab initio Boltzmann transport equation. We show that effective uniaxial compressive strain of GaN along the [1-100] by lattice matching to ZnGeN2 and MgSiN2 results in the inversion of the heavy hole band and split-off hole band, thereby lowering the effective hole mass in the compression direction. We find that lattice matching to ZnGeN2 and MgSiN2 induces an increase in the room-temperature hole mobility by 50% and 260% as compared to unstrained GaN, respectively. Examining the trends as a function of strain, we find that the variation in mobility is highly nonlinear; lattice matching to a hypothetical solid solution of Zn0.75Ge0.75Mg0.25Si0.25N2 would already increase the hole mobility by 160%. |
 | Kevin Hurlbutt, Feliciano Giustino, George Volonakis, Mauro Pasta Origin of the high specific capacity in sodium manganese hexacyanomanganate Journal Article In: Chemistry of Materials, vol. 34, iss. 10, pp. 4336-4343, 2022. @article{Hurlbutt2022,Sodium manganese hexacyanomanganate, NaxMn[Mn(CN)6], is an electrochemically active Prussian blue analogue (PBA) that has been studied experimentally as an electrode material in rechargeable sodium-ion batteries. It has a reversible specific capacity of 209 mA h g–1, which is substantially higher than the theoretical specific capacity of 172 mA h g–1 expected for two reduction events conventional in PBAs. It has been suggested that the high specific capacity originates from this compound’s unique ability to insert a third sodium ion per formula unit. However, the plausibility of this mechanism has remained ambiguous. Here, we use density functional theory (DFT) with a hybrid functional to calculate the formation energies of various oxidation states and magnetic phases of the NaxMn[Mn(CN)6] system. We confirm that the compound Na3MnII[MnI(CN)6] is, indeed, thermodynamically stable. It contains manganese(I), and the sodium ions occupy the interfacial position of the lattice subcubes. We also provide strong evidence that the phase of the fully oxidized Mn[Mn(CN)6] compound is charge-disproportionated, containing manganese(II) and manganese(IV). We proceed to show that the presence of crystalline water increases the reduction potential of the system and that the hydrated compounds have theoretical crystal geometries and reduction potentials that closely match the experiment. This work clarifies the charge-storage mechanism in a well-known but less-understood PBA. |
 | Weng Hong Sio, Feliciano Giustino Unified ab initio description of Fröhlich electron-phonon interactions in two-dimensional and three-dimensional materials Journal Article In: Physical Review B, vol. 105, iss. 11, pp. 115414, 2022. @article{Sio2022,Ab initio calculations of electron-phonon interactions including the polar Fröhlich coupling have advanced considerably in recent years. The Fröhlich electron-phonon matrix element is by now well understood in the case of bulk three-dimensional (3D) materials. In the case of two-dimensional (2D) materials, the standard procedure to include Fröhlich coupling is to employ Coulomb truncation, so as to eliminate artificial interactions between periodic images of the 2D layer. While these techniques are well established, the transition of the Fröhlich coupling from three to two dimensions has not been investigated. Furthermore, it remains unclear what error one makes when describing 2D systems using the standard bulk formalism in a periodic supercell geometry. Here we generalize previous work on the ab initio Fröhlich electron-phonon matrix element in bulk materials by investigating the electrostatic potential of atomic dipoles in a periodic supercell consisting of a 2D material and a continuum dielectric slab. We obtain a unified expression for the matrix element, which reduces to the existing formulas for three-dimensional and 2D systems when the interlayer separation tends to zero or infinity, respectively. This expression enables an accurate description of the Fröhlich matrix element in 2D systems without resorting to Coulomb truncation. We validate our approach by direct ab initio density-functional perturbation theory calculations for monolayer BN and MoS2, and we provide a simple expression for the 2D Fröhlich matrix element that can be used in model Hamiltonian approaches. The formalism outlined in this work may find applications in calculations of polarons, quasiparticle renormalization, transport coefficients, and superconductivity, in 2D and quasi-2D materials. |
 | Nikolaus Kandolf, Carla Verdi, Feliciano Giustino Many-body Green's function approaches to the doped Fröhlich solid: Exact solutions and anomalous mass enhancement Journal Article In: Physical Review B, vol. 105, iss. 8, pp. 085148, 2022. @article{10.1103/PhysRevB.105.085148,In polar semiconductors and insulators, the Fröhlich interaction between electrons and long-wavelength longitudinal optical phonons induces a many-body renormalization of the carrier effective masses and the appearance of characteristic phonon sidebands in the spectral function, commonly dubbed “polaron satellites.” The simplest model that captures these effects is the Fröhlich model, whereby electrons in a parabolic band interact with a dispersionless longitudinal optical phonon. The Fröhlich model has been employed in a number of seminal papers, from early perturbation-theory approaches to modern diagrammatic Monte Carlo calculations. One limitation of this model is that it focuses on undoped systems, thus ignoring carrier screening and Pauli blocking effects that are present in real experiments on doped samples. To overcome this limitation, we here extend the Fröhlich model to the case of doped systems, and we provide exact solutions for the electron spectral function, mass enhancement, and polaron satellites. We perform the analysis using two approaches, namely, Dyson's equation with the Fan-Migdal self-energy, and the second-order cumulant expansion. We find that these two approaches provide qualitatively different results. In particular, Dyson's approach yields better quasiparticle masses and worse satellites, while the cumulant approach provides better satellite structures, at the price of worse quasiparticle masses. Both approaches yield an anomalous enhancement of the electron effective mass at finite doping levels, which in turn leads to a breakdown of the quasiparticle picture in a significant portion of the phase diagram. |
 | VA Ha, H Lee, F Giustino CeTaN3 and CeNbN3: Prospective Nitride Perovskites with Optimal Photovoltaic Band Gaps Journal Article In: Chemistry of Materials, vol. 34, iss. 5, pp. 2107-2122, 2022. @article{Ha2022,Perovskites constitute an exceptionally tunable materials familywith diverse applications in electronics, optoelectronics, energy, and quantumtechnologies. Out of the thousands of known perovskites, the majority ofcompounds are oxides, halides, and chalcogenides. In contrast, only two nitrideperovskites are currently known. In this work we perform a thoroughab initiocomputational screening of possible nitride perovskites, and we identify two newcompounds, CeNbN3and CeTaN3, with band gaps in the near-infrared to visiblerange, depending on temperature. In their room-temperature orthorhombic phase,we predict that both compounds exhibit direct or quasidirect band gaps in therange 1.1−2.0 eV, with thePnmaphases matching the Shockley−Queisser limit for photovoltaic energy conversion efficiency. Thesecompounds are also predicted to be strong light absorbers, with absorption coefficients surpassing those of high-performancesemiconductors such as GaAs and CH3NH3PbI3. The presentfindings reveal a potentially new class of nitride semiconductors withpromise for electronics, optoelectronics, and light harvesting and for integration with existing nitride-based lighting technology. |
2021 |
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 | Martin Schlipf; Feliciano Giustino Dynamic Rashba-Dresselhaus Effect Journal Article In: Phys. Rev. Lett., vol. 127, pp. 237601, 2021. @article{Schlipf2021,The Rashba-Dresselhaus effect is the splitting of doubly degenerate band extrema in semiconductors, accompanied by the emergence of counterrotating spin textures and spin-momentum locking. Here we investigate how this effect is modified by lattice vibrations. We show that, in centrosymmetric nonmagnetic crystals, for which a bulk Rashba-Dresselhaus effect is symmetry-forbidden, electron-phonon interactions can induce a phonon-assisted, dynamic Rashba-Dresselhaus spin splitting in the presence of an out-of-equilibrium phonon population. In particular, we show how Rashba, Dresselhaus, or Weyl spin textures can selectively be established by driving coherent infrared-active phonons, and we perform ab initio calculations to quantify this effect for halide perovskites. |
 | Mengke Liu; Joshua Leveillee; Shuangzan Lu; Jia Yu; Hyunsue Kim; Cheng Tian; Youguo Shi; Keji Lai; Chendong Zhang; Feliciano Giustino; Chih-Kang Shih Monolayer 1T-NbSe2 as a 2D-correlated magnetic insulator Journal Article In: Science Advances, vol. 7, no. 47, pp. eabi6339, 2021. @article{doi:10.1126/sciadv.abi6339,1T-NbSe2 is a correlated insulator with localized magnetic moments exhibiting Kondo resonances when exchange-coupled to 2H-NbSe2. Monolayer group V transition metal dichalcogenides in their 1T phase have recently emerged as a platform to investigate rich phases of matter, such as spin liquid and ferromagnetism, resulting from strong electron correlations. Newly emerging 1T-NbSe2 has inspired theoretical investigations predicting collective phenomena such as charge transfer gap and ferromagnetism in two dimensions; however, the experimental evidence is still lacking. Here, by controlling the molecular beam epitaxy growth parameters, we demonstrate the successful growth of high-quality single-phase 1T-NbSe2. By combining scanning tunneling microscopy/spectroscopy and ab initio calculations, we show that this system is a charge transfer insulator with the upper Hubbard band located above the valence band maximum. To demonstrate the electron correlation resulted magnetic property, we create a vertical 1T/2H NbSe2 heterostructure, and we find unambiguous evidence of exchange interactions between the localized magnetic moments in 1T phase and the metallic/superconducting phase exemplified by Kondo resonances and Yu-Shiba-Rusinov–like bound states. |
 | Marios Zacharias; Hélène Seiler; Fabio Caruso; Daniela Zahn; Feliciano Giustino; Pantelis C Kelires; Ralph Ernstorfer Efficient First-Principles Methodology for the Calculation of the All-Phonon Inelastic Scattering in Solids Journal Article In: Phys. Rev. Lett., vol. 127, pp. 207401, 2021. @article{PhysRevLett.127.207401,Inelastic scattering experiments are key methods for mapping the full dispersion of fundamental excitations of solids in the ground as well as nonequilibrium states. A quantitative analysis of inelastic scattering in terms of phonon excitations requires identifying the role of multiphonon processes. Here, we develop an efficient first-principles methodology for calculating the all-phonon quantum mechanical structure factor of solids. We demonstrate our method by obtaining excellent agreement between measurements and calculations of the diffuse scattering patterns of black phosphorus, showing that multiphonon processes play a substantial role. The present approach constitutes a step towards the interpretation of static and time-resolved electron, x-ray, and neutron inelastic scattering data. |
 | Marios Zacharias; Hélène Seiler; Fabio Caruso; Daniela Zahn; Feliciano Giustino; Pantelis C Kelires; Ralph Ernstorfer Multiphonon diffuse scattering in solids from first principles: Application to layered crystals and two-dimensional materials Journal Article In: Physical Review B, vol. 104, no. 20, 2021, ISSN: 2469-9969. @article{2021,Time-resolved diffuse scattering experiments have gained increasing attention due to their potential to reveal nonequilibrium dynamics of crystal lattice vibrations with full momentum resolution. Although progress has been made in interpreting experimental data on the basis of one-phonon scattering, understanding the role of individual phonons can be sometimes hindered by multiphonon excitations. In Ref. [M. Zacharias, H. Seiler, F. Caruso, D. Zahn, F. Giustino, P. C. Kelires, and R. Ernstorfer, Phys. Rev. Lett. 127, 207401 (2021)], we have introduced a rigorous approach for the calculation of the all-phonon inelastic scattering intensity of solids from first-principles. In the present work, we describe our implementation in detail and show that multiphonon interactions are captured efficiently by exploiting translational and time-reversal symmetries of the crystal. We demonstrate its predictive power by calculating the scattering patterns of monolayer molybdenum disulfide (MoS2), bulk MoS2, and black phosphorus (bP), and we obtain excellent agreement with our measurements of thermal electron diffuse scattering. Remarkably, our results show that multiphonon excitations dominate in bP across multiple Brillouin zones, while in MoS2 they play a less pronounced role. We expand our analysis for each system and examine the effect of individual atomic and interatomic vibrational motion on the diffuse scattering signals. We further demonstrate the high-throughput capability of our approach by reporting all-phonon scattering maps of two-dimensional MoSe2, WSe2, WS2, graphene, and CdI2, rationalizing in each case the effect of multiphonon processes. As a side point, we show that the special displacement method reproduces the thermally distorted configuration that generates precisely the all-phonon diffuse pattern. The present methodology opens the way for systematic calculations of the scattering intensity in crystals and the accurate interpretation of static and time-resolved inelastic scattering experiments. |
 | Samuel Poncé; Francesco Macheda; Elena Roxana Margine; Nicola Marzari; Nicola Bonini; Feliciano Giustino First-principles predictions of Hall and drift mobilities in semiconductors Journal Article In: Physical Review Research, vol. 3, no. 4, 2021, ISSN: 2643-1564. @article{2021b,Carrier mobility is at the root of our understanding of electronic devices. We present a unified methodology for the parameter-free calculations of phonon-limited drift and Hall carrier mobilities in real materials within the framework of the Boltzmann transport equation. This approach enables accurate and parameter-free calculations of the intrinsic mobility and will find applications in the design of electronic devices under realistic conditions of strain and temperature. The methodology exploits a novel approach for incorporating the effect of long-range quadrupole fields in the electron-phonon scattering rates and capitalizes on a rigorous and efficient procedure for numerical convergence. The accuracy reached in this work allows us to assess the impact of common approximations employed in transport calculations, including the role of exchange and correlation functionals, spin-orbit coupling, pseudopotentials, Wannier interpolation, Brillouin-zone sampling, dipole and quadrupole corrections, and the relaxation-time approximation. We study diamond, silicon, GaAs, 3C-SiC, AlP, GaP, c-BN, AlAs, AlSb, and SrO, and find that our most accurate calculations predict Hall mobilities significantly larger than the experimental data in the case of SiC, AlAs, and GaP. We identify possible improvements to the theoretical and computational frameworks to reduce this discrepancy, and we argue that new experimental data are needed to perform a meaningful comparison, since almost all existing data are more than two decades old. By setting tight standards for reliability and reproducibility, the present work aims to facilitate validation and verification of data and software towards predictive calculations of transport phenomena in semiconductors. |
 | Chelsea Q Xia; Samuel Poncé; Jiali Peng; Aleksander M Ulatowski; Jay B Patel; Adam D Wright; Rebecca L Milot; Hans Kraus; Qianqian Lin; Laura M Herz; Feliciano Giustino; Michael B Johnston Ultrafast photo-induced phonon hardening due to Pauli blocking in MAPbI3 single-crystal and polycrystalline perovskites Journal Article In: Journal of Physics: Materials, vol. 4, no. 4, pp. 044017, 2021. @article{Xia_2021,Metal-halide perovskite semiconductors have attracted intense interest over the past decade, particularly for applications in photovoltaics. Low-energy optical phonons combined with significant crystal anharmonicity play an important role in charge-carrier cooling and scattering in these materials, strongly affecting their optoelectronic properties. We have observed optical phonons associated with Pb–I stretching in both MAPbI3 single crystals and polycrystalline thin films as a function of temperature by measuring their terahertz conductivity spectra with and without photoexcitation. An anomalous bond hardening was observed under above-bandgap illumination for both single-crystal and polycrystalline MAPbI3. First-principles calculations reproduced this photo-induced bond hardening and identified a related lattice contraction (photostriction), with the mechanism revealed as Pauli blocking. For single-crystal MAPbI3, phonon lifetimes were significantly longer and phonon frequencies shifted less with temperature, compared with polycrystalline MAPbI3. We attribute these differences to increased crystalline disorder, associated with grain boundaries and strain in the polycrystalline MAPbI3. Thus we provide fundamental insight into the photoexcitation and electron–phonon coupling in MAPbI3. |
 | Viet-Anh Ha; George Volonakis; Hyungjun Lee; Marios Zacharias; Feliciano Giustino Quasiparticle Band Structure and Phonon-Induced Band Gap Renormalization of the Lead-Free Halide Double Perovskite Cs2InAgCl6 Journal Article In: The Journal of Physical Chemistry C, vol. 125, no. 39, pp. 21689-21700, 2021. @article{doi:10.1021/acs.jpcc.1c06542,The lead-free halide double perovskite Cs2InAgCl6 was recently designed in silico and subsequently synthesized in the lab. This perovskite is a wide-gap semiconductor with a direct band gap and exhibits extraordinary photoluminescence in the visible range upon Na doping. The light emission properties of Cs2InAgCl6 have successfully been exploited to fabricate stable single-emitter-based white-light LEDs with near unity quantum efficiency. An intriguing puzzle in the photophysics of this compound is that the onset of optical absorption is around 3 eV, but the luminescence peak is found around 2 eV. As a first step toward elucidating this mismatch and clarifying the atomic-scale mechanisms underpinning the observed luminescence, here, we report a detailed investigation of the quasiparticle band structure of Cs2InAgCl6 as well as the phonon-induced renormalization of the band structure. We perform calculations of bang gaps and effective masses using the GW method, and we calculate the phonon-induced band structure renormalization using the special displacement method. We find that GW calculations are rather sensitive to the functional used in the density functional theory calculations and that self-consistency on the eigenvalues is necessary to achieve quantitative agreement with experiments. Our most accurate band gap at room temperature is in the range of 3.1–3.2 eV and includes a phonon-induced gap renormalization of 0.2 eV. By computing the phonon-induced mass enhancement, we find that the electron carriers are in the weak polaronic coupling regime, while hole carriers are in the intermediate coupling regime as a result of the localized and directional nature of the Ag eg 4d states at the valence band top. |
 | Kevin Hurlbutt; Feliciano Giustino; Mauro Pasta; George Volonakis Electronic Structure and Electron-Transport Properties of Three Metal Hexacyanoferrates Journal Article In: Chemistry of Materials, vol. 33, no. 17, pp. 7067-7074, 2021. @article{doi:10.1021/acs.chemmater.1c02183,Metal hexacyanometallates, or Prussian blue analogs (PBAs), are active materials in important electrochemical technologies, including next-generation sodium- and potassium-ion batteries. They have tunable properties, including reduction potential, ionic conductivity, and color. However, little is known about their electronic conductivities. In this work, we use density-functional theory to model the electronic structure and to explore the likely electron-conduction mechanism in three promising cathodes (manganese, iron, and cobalt hexacyanoferrate) in each of three oxidation states. First, we demonstrate that hybrid functionals reliably reproduce experimentally observed spin configurations and geometric phase changes. We confirm these materials are semiconductors or insulators with band gaps ranging from 1.90 eV up to 4.94 eV. We further identify that for most of the compounds, the electronic band edges originate from carbon-coordinated iron orbitals, suggesting that doping at the carbon-coordinated site may strongly affect carrier conductivity. Finally, we calculate charge-carrier effective masses, which we find are very heavy. This study is an important foundation for making electronic conductivity a tunable PBA material property. |
 | Sai Mu; Andrew J E Rowberg; Joshua Leveillee; Feliciano Giustino; Chris G Van de Walle First-principles study of electron transport in ScN Journal Article In: Physical Review B, vol. 104, no. 7, 2021, ISSN: 2469-9969. @article{2021c,We investigate the conduction-band structure and electron mobility in rocksalt ScN based on density functional theory. The first-principles band structure allows us to obtain band velocities and effective masses as a function of energy. Electron-phonon scattering is assessed by explicitly computing the q-dependent electron-phonon matrix elements, with the inclusion of the long-range electrostatic interaction. The influence of free-carrier screening on the electron transport is assessed using the random-phase approximation. We find a notable enhancement of electron mobility when the carrier concentration exceeds 1020 cm−3. We calculate the room-temperature electron mobility in ScN to be 587 cm2/Vs at low carrier concentrations. When the carrier concentration is increased, the electron mobility starts to decrease significantly around n = 1019 cm−3 and drops to 240 cm2/Vs at n = 1021 cm−3. We also explore the influence of strain in (111)- and (100)-oriented ScN films. For (111) films, we find that a 1.0% compressive epitaxial strain increases the in-plane mobility by 72 cm2/Vs and the out-ofplane mobility by 50 cm2/Vs. For (100) films, a 1.0% compressive epitaxial strain increases the out-of-plane mobility by as much as 172 cm2/Vs, but has a weak impact on the in-plane mobility. Our study sheds light on electron transport in ScN at different electron concentrations and shows how strain engineering could increase the electron mobility |
 | Joshua Leveillee; George Volonakis; Feliciano Giustino Phonon-Limited Mobility and Electron–Phonon Coupling in Lead-Free Halide Double Perovskites Journal Article In: The Journal of Physical Chemistry Letters, vol. 12, no. 18, pp. 4474-4482, 2021, (PMID: 33956454). @article{doi:10.1021/acs.jpclett.1c00841,Lead-free halide double perovskites have attracted considerable attention as complements to lead-based halide perovskites in a range of optoelectronic applications. Experiments on Cs2AgBiBr6 indicate carrier mobilities in the range of 0.3−11 cm2 /(V s) at room temperature, considerably lower than in lead-based perovskites. The origin of low mobilities is currently unclear, calling for an atomic-scale investigation. We report state-of-the-art ab initio calculations of the phonon-limited mobility of charge carriers in lead-free halide double perovskites Cs2AgBiX6 (X = Br, Cl). For Cs2AgBiBr6, we obtain room temperature electron and hole mobilities of 17 and 14 cm2/(V s), respectively, in line with experiments. We demonstrate that the cause for the lower mobility of this compound, compared to CH3NH3PbI3, resides in the heavier carrier effective masses. A mode-resolved analysis of scattering rates reveals the predominance of Fröhlich electron−phonon scattering, similar to lead-based perovskites. Our results indicate that, to increase the mobility of lead-free perovskites, it is necessary to reduce the effective masses, for example by cation engineering |
 | Tianlun Allan Huang; Marios Zacharias; Kirk D Lewis; Feliciano Giustino; Sahar Sharifzadeh Exciton–Phonon Interactions in Monolayer Germanium Selenide from First Principles Journal Article In: The Journal of Physical Chemistry Letters, vol. 12, no. 15, pp. 3802-3808, 2021, (PMID: 33848154). @article{doi:10.1021/acs.jpclett.1c00264,We investigate from first principles exciton–phonon interactions in monolayer germanium selenide, a direct gap two-dimensional semiconductor. By combining the Bethe–Salpeter approach and the special displacement method, we explore the phonon-induced renormalization of the exciton wave functions, excitation energies, and oscillator strengths. We determine a renormalization of the optical gap of 0.1 eV at room temperature, which results from the coupling of the exciton with both acoustic and optical phonons, with the strongest coupling to optical phonons at ∼100 cm–1. We also find that the exciton–phonon interaction is similar between monolayer and bulk GeSe. Overall, we demonstrate that the combination of many-body perturbation theory and special displacements offers a new route to investigate electron–phonon couplings in excitonic spectra, the resulting band gap renormalization, and the nature of phonons that couple to the exciton. |
 | Chelsea Q Xia; Jiali Peng; Samuel Poncé; Jay B Patel; Adam D Wright; Timothy W Crothers; Mathias Uller Rothmann; Juliane Borchert; Rebecca L Milot; Hans Kraus; Qianqian Lin; Feliciano Giustino; Laura M Herz; Michael B Johnston Limits to Electrical Mobility in Lead-Halide Perovskite Semiconductors Journal Article In: The Journal of Physical Chemistry Letters, vol. 12, no. 14, pp. 3607-3617, 2021, (PMID: 33822630). @article{doi:10.1021/acs.jpclett.1c00619,Semiconducting polycrystalline thin films are cheap to produce and can be deposited on flexible substrates, yet high-performance electronic devices usually utilize singlecrystal semiconductors, owing to their superior charge-carrier mobilities and longer diffusionlengths. Here we show that the electrical performance of polycrystalline films of metal-halide perovskites (MHPs) approaches that of single crystals at room temperature. Combining temperature-dependent terahertz conductivity measurements and ab initio calculations we uncover a complete picture of the origins of charge-carrier scattering in single crystals and polycrystalline films of CH3NH3PbI3. We show that Fröhlich scattering of charge carriers with multiple phonon modes is the dominant mechanism limiting mobility, with grain-boundary scattering further reducing mobility in polycrystalline films. We reconcile the large discrepancy in charge-carrier diffusion lengths between single crystals and films by considering photon reabsorption. Thus, polycrystalline films of MHPs offer great promise for devices beyond solar cells, including light-emitting diodes and modulators. |
 | Nourdine Zibouche; Martin Schlipf; Feliciano Giustino GW band structure of monolayer MoS2 using the SternheimerGW method and effect of dielectric environment Journal Article In: Phys. Rev. B, vol. 103, pp. 125401, 2021. @article{PhysRevB.103.125401,Monolayers of transition-metal dichalcogenides (TMDs) hold great promise as future nanoelectronic and optoelectronic devices. An essential feature for achieving high device performance is the use of suitable supporting substrates, which can affect the electronic and optical properties of these two-dimensional (2D) materials. Here, we perform many-body GW calculations using the SternheimerGW method to investigate the quasiparticle band structure of monolayer MoS2 subject to an effective dielectric screening model, which is meant to approximately describe substrate polarization in real device applications. We show that, within this model, the dielectric screening has a sizable effect on the quasiparticle band gap; for example, the gap renormalization is as large as 250 meV for MoS2 with model screening corresponding to SiO2. Within the G0W0 approximation, we also find that the inclusion of the effective screening induces a direct band gap, in contrast to the unscreened monolayer. We also find that the dielectric screening induces an enhancement of the carrier effective masses by as much as 27% for holes, shifts plasmon satellites, and redistributes quasiparticle weight. Our results highlight the importance of the dielectric environment in the design of 2D TMD-based devices. |
Publicationssysnet2024-11-05T15:43:52+00:00
2022 |
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| Intrinsic and doping-enhanced superconductivity in monolayer 1T-TaS2: Critical role of charge ordering and spin-orbit coupling Journal Article In: Physical Review B, vol. 105, iss. 18, pp. L180505, 2022. |
Double perovskite Patent 2022. | |
| Anisotropic-strain-enhanced hole mobility in GaN by lattice matching to ZnGeN2 and MgSiN2 Journal Article In: Applied Physics Letters, vol. 120, iss. 20, 2022. |
| Origin of the high specific capacity in sodium manganese hexacyanomanganate Journal Article In: Chemistry of Materials, vol. 34, iss. 10, pp. 4336-4343, 2022. |
| Unified ab initio description of Fröhlich electron-phonon interactions in two-dimensional and three-dimensional materials Journal Article In: Physical Review B, vol. 105, iss. 11, pp. 115414, 2022. |
| Many-body Green's function approaches to the doped Fröhlich solid: Exact solutions and anomalous mass enhancement Journal Article In: Physical Review B, vol. 105, iss. 8, pp. 085148, 2022. |
| CeTaN3 and CeNbN3: Prospective Nitride Perovskites with Optimal Photovoltaic Band Gaps Journal Article In: Chemistry of Materials, vol. 34, iss. 5, pp. 2107-2122, 2022. |
2021 |
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| Dynamic Rashba-Dresselhaus Effect Journal Article In: Phys. Rev. Lett., vol. 127, pp. 237601, 2021. |
| Monolayer 1T-NbSe2 as a 2D-correlated magnetic insulator Journal Article In: Science Advances, vol. 7, no. 47, pp. eabi6339, 2021. |
| Efficient First-Principles Methodology for the Calculation of the All-Phonon Inelastic Scattering in Solids Journal Article In: Phys. Rev. Lett., vol. 127, pp. 207401, 2021. |
| Multiphonon diffuse scattering in solids from first principles: Application to layered crystals and two-dimensional materials Journal Article In: Physical Review B, vol. 104, no. 20, 2021, ISSN: 2469-9969. |
| First-principles predictions of Hall and drift mobilities in semiconductors Journal Article In: Physical Review Research, vol. 3, no. 4, 2021, ISSN: 2643-1564. |
| Ultrafast photo-induced phonon hardening due to Pauli blocking in MAPbI3 single-crystal and polycrystalline perovskites Journal Article In: Journal of Physics: Materials, vol. 4, no. 4, pp. 044017, 2021. |
| Quasiparticle Band Structure and Phonon-Induced Band Gap Renormalization of the Lead-Free Halide Double Perovskite Cs2InAgCl6 Journal Article In: The Journal of Physical Chemistry C, vol. 125, no. 39, pp. 21689-21700, 2021. |
| Electronic Structure and Electron-Transport Properties of Three Metal Hexacyanoferrates Journal Article In: Chemistry of Materials, vol. 33, no. 17, pp. 7067-7074, 2021. |
| First-principles study of electron transport in ScN Journal Article In: Physical Review B, vol. 104, no. 7, 2021, ISSN: 2469-9969. |
| Phonon-Limited Mobility and Electron–Phonon Coupling in Lead-Free Halide Double Perovskites Journal Article In: The Journal of Physical Chemistry Letters, vol. 12, no. 18, pp. 4474-4482, 2021, (PMID: 33956454). |
| Exciton–Phonon Interactions in Monolayer Germanium Selenide from First Principles Journal Article In: The Journal of Physical Chemistry Letters, vol. 12, no. 15, pp. 3802-3808, 2021, (PMID: 33848154). |
| Limits to Electrical Mobility in Lead-Halide Perovskite Semiconductors Journal Article In: The Journal of Physical Chemistry Letters, vol. 12, no. 14, pp. 3607-3617, 2021, (PMID: 33822630). |
| GW band structure of monolayer MoS2 using the SternheimerGW method and effect of dielectric environment Journal Article In: Phys. Rev. B, vol. 103, pp. 125401, 2021. |