2024 |
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Yanxing Li, Fan Zhang, Viet-Anh Ha, Yu-Chuan Lin, Chengye Dong, Qiang Gao, Zhida Liu, Xiaohui Liu, Sae Hee Ryu, Hyunsue Kim, Chris Jozwiak, Aaron Bostwick, Kenji Watanabe, Takashi Taniguchi, Bishoy Kousa, Xiaoqin Li, Eli Rotenberg, Eslam Khalaf, Joshua A. Robinson, Feliciano Giustino & Chih-Kang Shih Tuning commensurability in twisted van der Waals bilayers Journal Article In: Nature, vol. 625, pp. 494–499, 2024. @article{Li2024, Moiré superlattices based on van der Waals bilayers created at small twist angles lead to a long wavelength pattern with approximate translational symmetry. At large twist angles (θt), moiré patterns are, in general, incommensurate except for a few discrete angles. Here we show that large-angle twisted bilayers offer distinctly different platforms. More specifically, by using twisted tungsten diselenide bilayers, we create the incommensurate dodecagon quasicrystals at θt = 30° and the commensurate moiré crystals at θt = 21.8° and 38.2°. Valley-resolved scanning tunnelling spectroscopy shows disparate behaviours between moiré crystals (with translational symmetry) and quasicrystals (with broken translational symmetry). In particular, the K valley shows rich electronic structures exemplified by the formation of mini-gaps near the valence band maximum. These discoveries demonstrate that bilayers with large twist angles offer a design platform to explore moiré physics beyond those formed with small twist angles. | |
2023 |
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Hyungjun Lee, Samuel Poncé, Kyle Bushick, Samad Hajinazar, Jon Lafuente-Bartolome, Joshua Leveillee, Chao Lian, Francesco Macheda, Hari Paudyal, Weng Hong Sio, Marios Zacharias, Xiao Zhang, Nicola Bonini, Emmanouil Kioupakis, Elena R Margine, Feliciano Giustino Electron-phonon physics from first principles using the EPW code Journal Article In: npj Computational Materials, vol. 8, no. 156, 2023. @article{Lee2023, EPW is an open-source software for ab initio calculations of electron–phonon interactions and related materials properties. The code combines density functional perturbation theory and maximally localized Wannier functions to efficiently compute electron–phonon coupling matrix elements, and to perform predictive calculations of temperature-dependent properties and phonon-assisted quantum processes in bulk solids and low-dimensional materials. Here, we report on significant developments in the code since 2016, namely: a transport module for the calculation of charge carrier mobility under electric and magnetic fields using the Boltzmann transport equation; a superconductivity module for calculations of phonon-mediated superconductors using the anisotropic multi-band Eliashberg theory; an optics module for calculations of phonon-assisted indirect transitions; a module for the calculation of small and large polarons without supercells; and a module for calculating band structure renormalization and temperature-dependent optical spectra using the special displacement method. For each capability, we outline the methodology and implementation and provide example calculations. | |
Marios Zacharias, George Volonakis, Feliciano Giustino, Jacky Even Anharmonic electron-phonon coupling in ultrasoft and locally disordered perovskites Journal Article In: npj Computational Materials, vol. 9, no. 153, 2023. @article{Zacharias2023b, Anharmonicity and disorder are ubiquitous in the physics of perovskites and give rise to several unique phenomena observed in scattering and spectroscopy experiments with profound consequences for device applications. Several of these phenomena still lack interpretation from a first-principles perspective since, hitherto, no approach is available to account for anharmonicity and disorder in the phonon dynamics and electron-phonon couplings. Here, relying on the special displacement method, we develop a unified framework for the treatment of both and demonstrate that electron-phonon coupling in cubic oxide and halide perovskites is strongly influenced by the multi-well potential energy landscape. We uncover that disorder is at the origin of phonon bunching and overdamping in halide perovskites leading to vibrational dynamics far from the ideal phonon picture. We also clarify a long standing problem in electronic structure calculations of cubic perovskites and show that band gap corrections arising from disorder, spin-orbit coupling, more accurate exchange-correlation functionals, and electron-phonon coupling are all essential. Our results are in excellent agreement with scattering and optical spectroscopy measurements, suggesting that disorder is the key to address pending questions on perovskites' technological applications. | |
Marios Zacharias, George Volonakis, Feliciano Giustino, Jacky Even Anharmonic lattice dynamics via the special displacement method Journal Article In: Physical Review B, vol. 108, iss. 3, pp. 035155, 2023. @article{Zacharias2023, On the basis of the self-consistent phonon theory and the special displacement method, we develop an approach for the treatment of anharmonicity in solids. We show that this approach enables the efficient calculation of temperature-dependent anharmonic phonon dispersions, requiring very few steps to achieve minimization of the system's free energy. We demonstrate this methodology in the regime of strongly anharmonic materials, which exhibit a multiwell potential energy surface, like cubic SrTiO3, CsPbBr3, CsPbI3, CsSnI3, and Zr. Our results are in good agreement with experiments and previous first-principles studies relying on stochastic nonperturbative and molecular dynamics simulations. We achieve a very robust workflow by using harmonic phonons of the polymorphous ground state as the starting point and an iterative mixing scheme of the dynamical matrix. We also suggest that the phonons of the polymorphous ground state might provide an excellent starting approximation to explore anharmonicity. Given the simplicity, efficiency, and stability of the present treatment to anharmonicity, it is especially suitable for use with any electronic structure code and for investigating electron-phonon couplings in strongly anharmonic systems. | |
Mir Mohammad Sadeghi, Yajie Huang, Chao Lian, Feliciano Giustino, Emanuel Tutuc, Allan H MacDonald, Takashi Taniguchi, Kenji Watanabe, Li Shi Tunable electron–flexural phonon interaction in graphene heterostructures Journal Article In: Nature, vol. 617, pp. 282-286, 2023. @article{Sadeghi2023, Peculiar electron–phonon interaction characteristics underpin the ultrahigh mobility, electron hydrodynamics superconductivity and superfluidity observed in graphene heterostructures. The Lorenz ratio between the electronic thermal conductivity and the product of the electrical conductivity and temperature provides insight into electron–phonon interactions that is inaccessible to past graphene measurements. Here we show an unusual Lorenz ratio peak in degenerate graphene near 60 kelvin and decreased peak magnitude with increased mobility. When combined with ab initio calculations of the many-body electron–phonon self-energy and analytical models, this experimental observation reveals that broken reflection symmetry in graphene heterostructures can relax a restrictive selection rule to allow quasielastic electron coupling with an odd number of flexural phonons, contributing to the increase of the Lorenz ratio towards the Sommerfeld limit at an intermediate temperature sandwiched between the low-temperature hydrodynamic regime and the inelastic electron–phonon scattering regime above 120 kelvin. In contrast to past practices of neglecting the contributions of flexural phonons to transport in two-dimensional materials, this work suggests that tunable electron–flexural phonon coupling can provide a handle to control quantum matter at the atomic scale, such as in magic-angle twisted bilayer graphene where low-energy excitations may mediate Cooper pairing of flat-band electrons. | |
Joshua Leveillee, Xiao Zhang, Emmanouil Kioupakis, Feliciano Giustino Ab initio calculation of carrier mobility in semiconductors including ionized-impurity scattering Journal Article In: Physical Review B, vol. 107, iss. 12, pp. 125207, 2023. @article{Leveillee2023, The past decade has seen the emergence of ab initio computational methods for calculating phonon-limited carrier mobilities in semiconductors with predictive accuracy. More realistic calculations ought to take into account additional scattering mechanisms such as, for example, impurity and grain-boundary scattering. In this paper, we investigate the effect of ionized-impurity scattering on the carrier mobility. We model the analytical impurity potential parameterized from first principles by a collection of randomly distributed Coulomb scattering centers, and we include this relaxation channel into the ab initio Boltzmann transport equation, as implemented in the EPW code. We demonstrate this methodology by considering silicon, silicon carbide, and gallium phosphide, for which detailed experimental data are available. Our calculations agree well with experiments over a broad range of temperatures and impurity concentrations. For each compound investigated here, we compare the relative importance of electron-phonon scattering and ionized-impurity scattering, and we critically assess the reliability of Matthiessen's rule. We also show that an accurate description of dielectric screening and carrier effective masses can improve quantitative agreement with experiments. | |
Weng Hong Sio, Feliciano Giustino Polarons in two-dimensional atomic crystals Journal Article In: Nature Physics, vol. 19, pp. 629-636, 2023. @article{Sio2023, Polarons are quasiparticles that emerge from the interaction of fermionic particles with bosonic fields. In crystalline solids, polarons form when electrons and holes become dressed by lattice vibrations. While experimental signatures of polarons in bulk three-dimensional materials abound–, only rarely have polarons been observed in two-dimensional atomic crystals. Here, we shed light on this asymmetry by developing a quantitative ab initio theory of polarons in atomically thin crystals. Using this conceptual framework, we determine the real-space structure of the recently observed hole polaron in hexagonal boron nitride, discover a critical condition for the existence of polarons in two-dimensional crystals and establish the key materials descriptors and the universal laws that underpin polaron physics in two dimensions. | |
Hwijong Lee, Yuanyuan Zhou, Sungyeb Jung, Hongze Li, Zhe Cheng, Jiaming He, Jie Chen, Peter Sokalski, Andrei Dolocan, Raluca Gearba‐Dolocan, Kevin C Matthews, Feliciano Giustino, Jianshi Zhou, Li Shi High‐Pressure Synthesis and Thermal Conductivity of Semimetallic θ‐Tantalum Nitride Journal Article In: Advanced Functional Materials, vol. 33, iss. 17, no. 2370102, 2023. @article{Lee2023b, The lattice thermal conductivity (κph) of metals and semimetals is limited by phonon-phonon scattering at high temperatures and by electron-phonon scattering at low temperatures or in some systems with weak phonon-phonon scattering. Following the demonstration of a phonon band engineering approach to achieve an unusually high κph in semiconducting cubic-boron arsenide (c-BAs), recent theories have predicted ultrahigh κph of the semimetal tantalum nitride in the θ-phase (θ-TaN) with hexagonal tungsten carbide (WC) structure due to the combination of a small electron density of states near the Fermi level and a large phonon band gap, which suppress electron-phonon and three-phonon scattering, respectively. Here, measurements on the thermal and electrical transport properties of polycrystalline θ-TaN converted from the ε phase via high-pressure synthesis are reported. The measured thermal conductivity of the θ-TaN samples shows weak temperature dependence above 200 K and reaches up to 90 Wm−1K−1, one order of magnitude higher than values reported for polycrystalline ε-TaN and δ-TaN thin films. These results agree with theoretical calculations that account for phonon scattering by 100 nm-level grains and suggest κph increase above the 249 Wm−1 K−1 value predicted for single-crystal WC when the grain size of θ-TaN is increased above 400 nm. | |
2022 |
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Xiao Zhang, Guangsha Shi, Joshua A Leveillee, Feliciano Giustino, Emmanouil Kioupakis Ab initio theory of free-carrier absorption in semiconductors Journal Article In: Physical Review B, vol. 106, iss. 20, pp. 205203, 2022. @article{Zhang2022, The absorption of light by free carriers in semiconductors results in optical loss for all photon wavelengths. Since free-carrier absorption competes with optical transitions across the band gap, it also reduces the efficiency of optoelectronic devices such as solar cells because it does not generate electron-hole pairs. In this work, we develop a first-principles theory of free-carrier absorption taking into account both single-particle excitations and the collective Drude term, and we demonstrate its application to the case of doped Si. We determine the free-carrier absorption coefficient as a function of carrier concentration and we obtain excellent agreement with experimental data. We identify the dominant processes that contribute to free-carrier absorption at various photon wavelengths, and analyze the results to evaluate the impact of this loss mechanism on the efficiency of Si-based optoelectronic devices. | |
Jon Lafuente-Bartolome, Chao Lian, Weng Hong Sio, Idoia G Gurtubay, Asier Eiguren, Feliciano Giustino Ab initio self-consistent many-body theory of polarons at all couplings Journal Article In: Physical Review B, vol. 106, iss. 7, pp. 075119, 2022. @article{Lafuente-Bartolome2022, We present a theoretical framework to describe polarons from first principles within a many-body Green's function formalism. Starting from a general electron-phonon Hamiltonian, we derive a self-consistent Dyson equation in which the phonon-mediated self-energy is composed by two distinct terms. One term is the Fan-Migdal self-energy and describes dynamic electron-phonon processes, the other term is a contribution to the self-energy originating from the static displacements of the atomic nuclei in the polaronic ground state. The lowest-order approximation to the present theory yields the standard many-body perturbation theory approach to electron-phonon interactions in the limit of large polarons, and the ab initio polaron equations introduced [Sio et al., Phys. Rev. B 99, 235139 (2019); Phys. Rev. Lett. 122, 246403 (2019)] in the limit of small polarons. A practical recipe to implement the present unifying formalism in first-principles calculations is outlined. We apply our method to the Fröhlich model, and obtain remarkably accurate polaron energies at all couplings, in line with Feynman's polaron theory and diagrammatic Monte Carlo calculations. We also recover the well-known results of Fröhlich and Pekar at weak and strong coupling, respectively. The present approach enables predictive many-body calculations of polarons in real materials at all couplings. | |
Jon Lafuente-Bartolome, Chao Lian, Weng Hong Sio, Idoia G Gurtubay, Asier Eiguren, Feliciano Giustino Unified approach to polarons and phonon-induced band structure renormalization Journal Article In: Physical Review Letters, vol. 129, iss. 7, pp. 076402, 2022. @article{Lafuente-Bartolome2022b, Ab initio calculations of the phonon-induced band structure renormalization are currently based on the perturbative Allen-Heine theory and its many-body generalizations. These approaches are unsuitable to describe materials where electrons form localized polarons. Here, we develop a self-consistent, many-body Green’s function theory of band structure renormalization that incorporates localization and self-trapping. We show that the present approach reduces to the Allen-Heine theory in the weak-coupling limit, and to total energy calculations of self-trapped polarons in the strong-coupling limit. To demonstrate this methodology, we reproduce the path-integral results of Feynman and diagrammatic Monte Carlo calculations for the Fröhlich model at all couplings, and we calculate the zero point renormalization of the band gap of an ionic insulator including polaronic effects. | |
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. |
2024 |
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Tuning commensurability in twisted van der Waals bilayers Journal Article In: Nature, vol. 625, pp. 494–499, 2024. | |
2023 |
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Electron-phonon physics from first principles using the EPW code Journal Article In: npj Computational Materials, vol. 8, no. 156, 2023. | |
Anharmonic electron-phonon coupling in ultrasoft and locally disordered perovskites Journal Article In: npj Computational Materials, vol. 9, no. 153, 2023. | |
Anharmonic lattice dynamics via the special displacement method Journal Article In: Physical Review B, vol. 108, iss. 3, pp. 035155, 2023. | |
Tunable electron–flexural phonon interaction in graphene heterostructures Journal Article In: Nature, vol. 617, pp. 282-286, 2023. | |
Ab initio calculation of carrier mobility in semiconductors including ionized-impurity scattering Journal Article In: Physical Review B, vol. 107, iss. 12, pp. 125207, 2023. | |
Polarons in two-dimensional atomic crystals Journal Article In: Nature Physics, vol. 19, pp. 629-636, 2023. | |
High‐Pressure Synthesis and Thermal Conductivity of Semimetallic θ‐Tantalum Nitride Journal Article In: Advanced Functional Materials, vol. 33, iss. 17, no. 2370102, 2023. | |
2022 |
|
Ab initio theory of free-carrier absorption in semiconductors Journal Article In: Physical Review B, vol. 106, iss. 20, pp. 205203, 2022. | |
Ab initio self-consistent many-body theory of polarons at all couplings Journal Article In: Physical Review B, vol. 106, iss. 7, pp. 075119, 2022. | |
Unified approach to polarons and phonon-induced band structure renormalization Journal Article In: Physical Review Letters, vol. 129, iss. 7, pp. 076402, 2022. | |
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. |