Most recent publications
 | Martin Schlipf; Feliciano Giustino Dynamic Rashba-Dresselhaus Effect Journal Article Phys. Rev. Lett., 127 , pp. 237601, 2021. @article{PhysRevLett.127.237601, title = {Dynamic Rashba-Dresselhaus Effect}, author = {Martin Schlipf and Feliciano Giustino}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.127.237601}, doi = {10.1103/PhysRevLett.127.237601}, year = {2021}, date = {2021-12-02}, journal = {Phys. Rev. Lett.}, volume = {127}, pages = {237601}, publisher = {American Physical Society}, abstract = {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.}, keywords = {}, pubstate = {published}, tppubtype = {article} } 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. |
 | 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 Physical Review Research, 3 (4), 2021, ISSN: 2643-1564. @article{2021b, title = {First-principles predictions of Hall and drift mobilities in semiconductors}, author = {Samuel Poncé and Francesco Macheda and Elena Roxana Margine and Nicola Marzari and Nicola Bonini and Feliciano Giustino}, url = {http://dx.doi.org/10.1103/PhysRevResearch.3.043022}, doi = {10.1103/physrevresearch.3.043022}, issn = {2643-1564}, year = {2021}, date = {2021-10-08}, journal = {Physical Review Research}, volume = {3}, number = {4}, publisher = {American Physical Society (APS)}, abstract = {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.}, keywords = {}, pubstate = {published}, tppubtype = {article} } 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. |
 | 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 The Journal of Physical Chemistry C, 125 (39), pp. 21689-21700, 2021. @article{doi:10.1021/acs.jpcc.1c06542, title = {Quasiparticle Band Structure and Phonon-Induced Band Gap Renormalization of the Lead-Free Halide Double Perovskite Cs_{2}InAgCl_{6}}, author = {Viet-Anh Ha and George Volonakis and Hyungjun Lee and Marios Zacharias and Feliciano Giustino}, url = {https://doi.org/10.1021/acs.jpcc.1c06542}, doi = {10.1021/acs.jpcc.1c06542}, year = {2021}, date = {2021-09-22}, journal = {The Journal of Physical Chemistry C}, volume = {125}, number = {39}, pages = {21689-21700}, abstract = {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.}, keywords = {}, pubstate = {published}, tppubtype = {article} } 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. |
 | Joshua Leveillee; George Volonakis; Feliciano Giustino Phonon-Limited Mobility and Electron–Phonon Coupling in Lead-Free Halide Double Perovskites Journal Article The Journal of Physical Chemistry Letters, 12 (18), pp. 4474-4482, 2021, (PMID: 33956454). @article{doi:10.1021/acs.jpclett.1c00841, title = {Phonon-Limited Mobility and Electron–Phonon Coupling in Lead-Free Halide Double Perovskites}, author = {Joshua Leveillee and George Volonakis and Feliciano Giustino}, url = {https://doi.org/10.1021/acs.jpclett.1c00841}, doi = {10.1021/acs.jpclett.1c00841}, year = {2021}, date = {2021-05-06}, journal = {The Journal of Physical Chemistry Letters}, volume = {12}, number = {18}, pages = {4474-4482}, abstract = {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}, note = {PMID: 33956454}, keywords = {}, pubstate = {published}, tppubtype = {article} } 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 |