A. Leonardo - Academia.edu (original) (raw)
Papers by A. Leonardo
Proceedings of the 9th International Conference on Computer Supported Education, 2017
In the Physics Degree it is of fundamental importance to practice in an Experimental Laboratory. ... more In the Physics Degree it is of fundamental importance to practice in an Experimental Laboratory. The standard Laboratory Sessions consist of two main parts: data handling and data processing. The session should also have a prologue, where students get to know the underlaying theory of the practical session and an epilogue, where students present the results obtained and the difficulties encountered. The prologue and the epilogue naturally decouple from the work in the laboratory. Data processing, in most cases, is effectively decoupled from the work in the laboratory, as well. In this short paper we present a tool, the Jupyter Notebook, an electronic laboratory logbook, which conveniently facilitates the decoupling of the data handling and processing, but which merges almost completely into an electronic notebook the four parts of the laboratory practical session: theory, data, processing and presentation. But, interestingly, the notebook goes beyond that: it allows the students to explore the data in an interactive way (simulating variants), to acquire a deeper knowledge of the data (by digitally altering the experiment or simulating new ones), to propose new experiments, etcetera. We strongly believe that this tool can also motivate the students: the results are obtained interactively, immediately, visually, and they can be shared and even improved. Moreover, the laboratory sessions get optimized: simulations make the sessions be focused on obtaining data and in its variants.
ABSTRACTAdvances in DNA sequencing technologies have revolutionized rare disease diagnosis, resul... more ABSTRACTAdvances in DNA sequencing technologies have revolutionized rare disease diagnosis, resulting in an increasing volume of available genomic data. Despite this wealth of information and improved procedures to combine data from various sources, identifying the pathogenic causal variants and distinguishing between severe and benign variants remains a key challenge. Mutations in the Kv7.2 voltage-gated potassium channel gene (KCNQ2) have been linked to different subtypes of epilepsies, such as benign familial neonatal epilepsy (BFNE) and epileptic encephalopathy (EE). To date, there is a wide variety of genome-wide computational tools aiming at predicting the pathogenicity of variants. However, previous reports suggest that these genome-wide tools have limited applicability to theKCNQ2gene related diseases due to overestimation of deleterious mutations and failure to correctly identify benign variants, being, therefore, of limited use in clinical practice. In this work, we found ...
Journal of Physics: Conference Series, 2019
Going one step further in the use and impact measurement of new strategies to improve the teachin... more Going one step further in the use and impact measurement of new strategies to improve the teaching-learning process during lecturing General Physics courses, the current contribution reports the last results/observations obtained by the authors on the combination of simple classroom experiments with active methodologies and new technologies (media). Cross-checking the answers in multiple choice questions done online during the lectures and in exams at the end of the term shows that this strategy has, at least partly, a positive effect on clarifying misconceptions. The overall opinion of the students was assessed and it showed that this lecturing approach is useful and motivating, making the lectures more attractive and stimulating eagerness to understand Physics.
Nature Communications
Electron band topology is combined with intrinsic magnetic orders in MnBi2Te4, leading to novel q... more Electron band topology is combined with intrinsic magnetic orders in MnBi2Te4, leading to novel quantum phases. Here we investigate collective spin excitations (i.e. magnons) and spin fluctuations in atomically thin MnBi2Te4 flakes using Raman spectroscopy. In a two-septuple layer with non-trivial topology, magnon characteristics evolve as an external magnetic field tunes the ground state through three ordered phases: antiferromagnet, canted antiferromagnet, and ferromagnet. The Raman selection rules are determined by both the crystal symmetry and magnetic order while the magnon energy is determined by different interaction terms. Using non-interacting spin-wave theory, we extract the spin-wave gap at zero magnetic field, an anisotropy energy, and interlayer exchange in bilayers. We also find magnetic fluctuations increase with reduced thickness, which may contribute to a less robust magnetic order in single layers.
arXiv: Materials Science, Aug 24, 2021
Structural, electronic and magnetic properties of bulk ilmenite CoTiO$_3$ are analyzed in the fra... more Structural, electronic and magnetic properties of bulk ilmenite CoTiO$_3$ are analyzed in the framework of density functional theory (DFT), using the generalized gradient approximation (GGA) and Hubbard-corrected approaches. We find that the G-type antiferromagnetic (G-AFM) structure, which consists of antiferromagnetically coupled ferromagnetic ababab planes, is the ground-state of the system, in agreement with experiments. Furthermore, cobalt titanates present two critical temperatures related to the breaking of the inter- and intra-layer magnetic ordering. This would result in the individual planes remaining ferromagnetic even at temperatures above the Néel temperature. When spin-orbit coupling is included in our calculations, we find an out-of-plane magnetic anisotropy, which can be converted to an in-plane anisotropy with a small doping of electrons corresponding to about 2.5% Ti substitution for Co, consistent with experimental expectations. We thus present a disorder-dependent study of the magnetic anisotropy in bulk textCoTiO_3\text{CoTiO}_3textCoTiO_3, which will determine its magnon properties, including topological aspects.
Structural, electronic and magnetic properties of bulk ilmenite CoTiO_3 are analyzed in the frame... more Structural, electronic and magnetic properties of bulk ilmenite CoTiO_3 are analyzed in the framework of Density Functional Theory (DFT), using the Generalized Gradient Approximation (GGA) and Hubbard-corrected approaches. We find that the G-type antiferromagnetic (G-AFM) structure, which consists of antiferromagnetically coupled ferromagnetic ab planes, is the ground-state of the system, in agreement with experiments. Furthermore, cobalt titanates present two critical temperatures related to the breaking of the inter- and intra-layer magnetic ordering. This would result in the individual planes remaining ferromagnetic even at temperatures above the Néel temperature. When spin-orbit coupling is included in our calculations, we find an out-of-plane magnetic anisotropy, which can be converted to an in-plane anisotropy with a small doping of electrons corresponding to about 2.5% Ti substitution for Co, consistent with experimental expectations. We thus present a disorder-dependent stud...
Physical review B, Jul 7, 2021
An ab-initio study of beta-As2Te3 (R3m symmetry) at hydrostatic pressures shows that this compoun... more An ab-initio study of beta-As2Te3 (R3m symmetry) at hydrostatic pressures shows that this compound is a trivial small band-gap semiconductor at room pressure that undergoes a quantum topological phase transition to a 3D topological Dirac semi-metal around 2 GPa. At higher pressures, the band-gap reopens and again decreases above 4 GPa. Our calculations predict an insulator-metal transition above 6 GPa due to the closing of the band-gap, with strong topological features persisting between 2 and 10 GPa with Z4=3 topological index. By investigating the lattice thermal-conductivity (κL), we observe that close to room conditions κL is very low, either for the in-plane and the out-of-plane axis, with 0.098 and 0.023 Wm −1 K −1 , respectively. This effect occurs due to the presence of two low-frequency optical modes, namely Eu and Eg, which increase the phononphonon scattering rate. Therefore, our work suggests that ultra-low lattice thermal-conductivities, which enable highly efficient thermoelectric materials, can be engineered in systems that are close to a structural instability derived from phonon Kohn anomalies. At higher pressures, the values of the in-and out-of-plane thermal-conductivities not only increase in magnitude, but also approximate in value as the layered character of the compound decreases.
M. Arruabarrena, A. Leonardo, 3 M. Rodriguez-Vega, Gregory A. Fiete, 6 and A. Ayuela 3 Materials ... more M. Arruabarrena, A. Leonardo, 3 M. Rodriguez-Vega, Gregory A. Fiete, 6 and A. Ayuela 3 Materials Physics Center (CFM), 20018 Donostia, Spain Department of Applied Physics II, University of the Basque Country UPV/ EHU, Bilbao, Spain. Donostia International Physics Center (DIPC), 20018 Donostia, Spain Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Department of Physics, Northeastern University, Boston, MA 02115, USA Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA (Dated: August 25, 2021)
Physical Review B, 2007
The temperature-dependent linewidth of the ⌫ surface state on Al͑100͒ was measured. The result ca... more The temperature-dependent linewidth of the ⌫ surface state on Al͑100͒ was measured. The result cannot be reconciled, not even qualitatively, with the well-known model for describing the influence of electron-phonon coupling on the lifetime broadening on electronic surface states. It is argued that this is due to the presence of thermally excited defects on the surface. Incorporating this possibility into the analysis, the measured temperature dependence is found to be consistent with that expected from an ab initio calculation of the electronphonon coupling strength. This phenomenon should be quite general and, indeed, a reanalysis of recently published data of Au͑111͒ ͓S. LaShell et al., Phys. Rev. B 74, 033410 ͑2006͔͒ resolves an apparent discrepancy between the measured and calculated electron-phonon coupling strengths.
Physical Review B, 2007
We report a detailed ab initio study of the electron-phonon ͑e-ph͒ interaction contribution to th... more We report a detailed ab initio study of the electron-phonon ͑e-ph͒ interaction contribution to the linewidth ⌫ e-ph ͑⑀ k,i ͒ of electron and hole states for bulk magnesium and the Mg͑0001͒ surface. The calculations are based on density functional theory and linear response approach. For bulk Mg, we find a large contribution of optical phonons to the Eliashberg spectral function and to ⌫ e-ph ͑⑀ k,i ͒. The e-ph coupling parameter at the Fermi level ͑mass enhancement parameter͒ has been found to be = 0.30. In the case of the surface, we have focused on the study of the ⌫ and M surface states for which we find = 0.28 and = 0.38, respectively. We show an important role of the Rayleigh vibrational mode in the e-ph coupling in the ⌫ surface state. These results are in a very good agreement with tunneling spectroscopic data and recent photoemission measurements of .
Journal of Physics: Condensed Matter, 2006
We present an ab initio study of the electron-phonon (e-ph) coupling and its contribution to the ... more We present an ab initio study of the electron-phonon (e-ph) coupling and its contribution to the phonon linewidths and to the lifetime broadening of excited electron and hole states in bulk Pd. The calculations, based on density-functional theory, were carried out using a linear-response approach in the plane-wave pseudopotential representation. The obtained results for the Eliashberg spectral function α 2 F(ω), e-ph coupling constant λ, and the contribution to the lifetime broadening, e−ph , show strong dependence on both the energy and momentum of an electron (hole) state. The calculation of phonon linewidths gives, in agreement with experimental observations, an anomalously large broadening for the transverse phonon mode T 1 in the direction. In addition, this mode is found to contribute most strongly to the electron-phonon scattering processes on the Fermi surface.
arXiv: Materials Science, 2020
We report a theoretical \textit{ab-initio} study of beta\betabeta-As$_2$Te$_3$ ($R\bar{3}m$ symmetry) a... more We report a theoretical \textit{ab-initio} study of beta\betabeta-As$_2$Te$_3$ ($R\bar{3}m$ symmetry) at hydrostatic pressures up to 12 GPa. We have systematically characterized the vibrational and electronic changes of the system induced by the pressure variation. The electronic band dispersions calculated at different pressures using \textit{QS}GW show an insulator-metal transition. At room pressure the system is a semiconductor with small band-gap, and the valence and conduction bands present a parabolic conventional dispersion. However around 2 GPa the parabolic shape of the bands become linear and touch at the Fermi level. This means that this compound undergoes a pressure-induced topological phase transition to a 3D analog of graphene, known as a 3D Dirac semi-metal, with gapless electronic excitations. At increasing pressures the gap reopens and variation of the character of the electronic band-gap from direct to indirect is evidenced. At 7 GPa we observe the formation of a negativ...
We theoretically study the effect of low-frequency light pulses in resonance with phonons in the ... more We theoretically study the effect of low-frequency light pulses in resonance with phonons in the topological and magnetically ordered two septuple-layer (2-SL) MnBi2Te4 (MBT) and MnSb2Te4 (MST). These materials share symmetry properties and an antiferromagnetic ground state in pristine form but present different magnetic exchange interactions. In both materials, shear and breathing Raman phonons can be excited via non-linear interactions with photo-excited infrared phonons using intense laser pulses attainable in current experimental setups. The light-induced transient lattice distortions lead to a change in the sign of the effective interlayer exchange interaction and magnetic order accompanied by a topological band transition. Furthermore, we show that moderate anti-site disorder, typically present in MBT and MST samples, can facilitate such an effect. Therefore, our work establishes 2-SL MBT and MST as candidate platforms to achieve non-equilibrium magneto-topological phase trans...
Martin Rodriguez-Vega, Ze-Xun Lin, 3 A. Leonardo, 5 A. Ernst, 7 M. G. Vergniory, 8 and Gregory A.... more Martin Rodriguez-Vega, Ze-Xun Lin, 3 A. Leonardo, 5 A. Ernst, 7 M. G. Vergniory, 8 and Gregory A. Fiete 9 Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Department of Physics, The University of Texas at Austin, Austin, TX 78712, USA Department of Physics, Northeastern University, Boston, MA 02115, USA Donostia International Physics Center, Paseo Manuel de Lardizabal 4, 20018 San Sebastian, Spain Department of Physics, University of the Basque Country UPV/ EHU, Leioa, Spain. Institut für Theoretische Physik, Johannes Kepler Universität, A 4040 Linz, Austria Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, D-06120 Halle, Germany Max Planck Institute for Chemical Physics of Solids, Dresden, D-01187, Germany Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA (Dated: August 31, 2021)
Physical Review B
In bilayer CrI 3 , experimental and theoretical studies suggest that the magnetic order is closel... more In bilayer CrI 3 , experimental and theoretical studies suggest that the magnetic order is closely related to the layer staking configuration. In this work, we study the effect of dynamical lattice distortions, induced by nonlinear phonon coupling, in the magnetic order of the bilayer system. We use density functional theory to determine the phonon properties and group theory to obtain the allowed phonon-phonon interactions. We find that the bilayer structure possesses low-frequency Raman modes that can be nonlinearly activated upon the coherent photoexcitation of a suitable infrared phonon mode. This transient lattice modification in turn inverts the sign of the interlayer spin interaction for parameters accessible in experiments, indicating a low-frequency light-induced antiferromagnet-to-ferromagnet transition.
Journal of Physics: Condensed Matter, 2016
First-principles calculations based on density-functional theory including anharmonicity within t... more First-principles calculations based on density-functional theory including anharmonicity within the variational stochastic self-consistent harmonic approximation are applied to understand how the quantum character of the proton affects the candidate metallic molecular Cmca - 4 structure of hydrogen in the 400-450 GPa pressure range, where metallization of hydrogen is expected to occur. Anharmonic effects, which become crucial due to the zero-point motion, have a large impact on the hydrogen molecules by increasing the intramolecular distance by approximately a 6%. This induces two new electron pockets at the Fermi surface opening new scattering channels for the electron-phonon interaction. Consequently, the electron-phonon coupling constant and the superconducting critical temperature are approximately doubled by anharmonicity and Cmca - 4 hydrogen becomes a superconductor above 200 K in all the studied pressure range. Contrary to many superconducting hydrides, where anharmoncity tends to lower the superconducting critical temperature, our results show that it can enhance superconductivity in molecular hydrogen.
Surface Science, 2006
We report ab initio study of the electron-phonon coupling in a free standing Beryllium monolayer.... more We report ab initio study of the electron-phonon coupling in a free standing Beryllium monolayer. The calculations were carried out using a linear-response approach in the plane-wave pseudopotential representation. The Eliashberg spectral function a 2 F(x) and the electron-phonon coupling parameter k are evaluated at the Fermi level. The obtained results show a large contribution to the electron-phonon coupling from the low-energy transverse mode scattering.
Surface Science, 2007
We report ab initio study of the electron–phonon coupling in a free standing magnesium monolayer ... more We report ab initio study of the electron–phonon coupling in a free standing magnesium monolayer and at the Mg(0001) surface. The calculations were carried out using a linear-response approach in the plane-wave pseudopotential representation. Eliashberg spectral function α2F(ω) averaged over electron states at the Fermi surface is presented for the monolayer while for the Mg(0001) surface, we compute the electron–phonon spectral function α2Fk,i(ω) for surface states at the Γ¯ and M¯ points.
Surface Science, 2006
ABSTRACT
Proceedings of the 9th International Conference on Computer Supported Education, 2017
In the Physics Degree it is of fundamental importance to practice in an Experimental Laboratory. ... more In the Physics Degree it is of fundamental importance to practice in an Experimental Laboratory. The standard Laboratory Sessions consist of two main parts: data handling and data processing. The session should also have a prologue, where students get to know the underlaying theory of the practical session and an epilogue, where students present the results obtained and the difficulties encountered. The prologue and the epilogue naturally decouple from the work in the laboratory. Data processing, in most cases, is effectively decoupled from the work in the laboratory, as well. In this short paper we present a tool, the Jupyter Notebook, an electronic laboratory logbook, which conveniently facilitates the decoupling of the data handling and processing, but which merges almost completely into an electronic notebook the four parts of the laboratory practical session: theory, data, processing and presentation. But, interestingly, the notebook goes beyond that: it allows the students to explore the data in an interactive way (simulating variants), to acquire a deeper knowledge of the data (by digitally altering the experiment or simulating new ones), to propose new experiments, etcetera. We strongly believe that this tool can also motivate the students: the results are obtained interactively, immediately, visually, and they can be shared and even improved. Moreover, the laboratory sessions get optimized: simulations make the sessions be focused on obtaining data and in its variants.
ABSTRACTAdvances in DNA sequencing technologies have revolutionized rare disease diagnosis, resul... more ABSTRACTAdvances in DNA sequencing technologies have revolutionized rare disease diagnosis, resulting in an increasing volume of available genomic data. Despite this wealth of information and improved procedures to combine data from various sources, identifying the pathogenic causal variants and distinguishing between severe and benign variants remains a key challenge. Mutations in the Kv7.2 voltage-gated potassium channel gene (KCNQ2) have been linked to different subtypes of epilepsies, such as benign familial neonatal epilepsy (BFNE) and epileptic encephalopathy (EE). To date, there is a wide variety of genome-wide computational tools aiming at predicting the pathogenicity of variants. However, previous reports suggest that these genome-wide tools have limited applicability to theKCNQ2gene related diseases due to overestimation of deleterious mutations and failure to correctly identify benign variants, being, therefore, of limited use in clinical practice. In this work, we found ...
Journal of Physics: Conference Series, 2019
Going one step further in the use and impact measurement of new strategies to improve the teachin... more Going one step further in the use and impact measurement of new strategies to improve the teaching-learning process during lecturing General Physics courses, the current contribution reports the last results/observations obtained by the authors on the combination of simple classroom experiments with active methodologies and new technologies (media). Cross-checking the answers in multiple choice questions done online during the lectures and in exams at the end of the term shows that this strategy has, at least partly, a positive effect on clarifying misconceptions. The overall opinion of the students was assessed and it showed that this lecturing approach is useful and motivating, making the lectures more attractive and stimulating eagerness to understand Physics.
Nature Communications
Electron band topology is combined with intrinsic magnetic orders in MnBi2Te4, leading to novel q... more Electron band topology is combined with intrinsic magnetic orders in MnBi2Te4, leading to novel quantum phases. Here we investigate collective spin excitations (i.e. magnons) and spin fluctuations in atomically thin MnBi2Te4 flakes using Raman spectroscopy. In a two-septuple layer with non-trivial topology, magnon characteristics evolve as an external magnetic field tunes the ground state through three ordered phases: antiferromagnet, canted antiferromagnet, and ferromagnet. The Raman selection rules are determined by both the crystal symmetry and magnetic order while the magnon energy is determined by different interaction terms. Using non-interacting spin-wave theory, we extract the spin-wave gap at zero magnetic field, an anisotropy energy, and interlayer exchange in bilayers. We also find magnetic fluctuations increase with reduced thickness, which may contribute to a less robust magnetic order in single layers.
arXiv: Materials Science, Aug 24, 2021
Structural, electronic and magnetic properties of bulk ilmenite CoTiO$_3$ are analyzed in the fra... more Structural, electronic and magnetic properties of bulk ilmenite CoTiO$_3$ are analyzed in the framework of density functional theory (DFT), using the generalized gradient approximation (GGA) and Hubbard-corrected approaches. We find that the G-type antiferromagnetic (G-AFM) structure, which consists of antiferromagnetically coupled ferromagnetic ababab planes, is the ground-state of the system, in agreement with experiments. Furthermore, cobalt titanates present two critical temperatures related to the breaking of the inter- and intra-layer magnetic ordering. This would result in the individual planes remaining ferromagnetic even at temperatures above the Néel temperature. When spin-orbit coupling is included in our calculations, we find an out-of-plane magnetic anisotropy, which can be converted to an in-plane anisotropy with a small doping of electrons corresponding to about 2.5% Ti substitution for Co, consistent with experimental expectations. We thus present a disorder-dependent study of the magnetic anisotropy in bulk textCoTiO_3\text{CoTiO}_3textCoTiO_3, which will determine its magnon properties, including topological aspects.
Structural, electronic and magnetic properties of bulk ilmenite CoTiO_3 are analyzed in the frame... more Structural, electronic and magnetic properties of bulk ilmenite CoTiO_3 are analyzed in the framework of Density Functional Theory (DFT), using the Generalized Gradient Approximation (GGA) and Hubbard-corrected approaches. We find that the G-type antiferromagnetic (G-AFM) structure, which consists of antiferromagnetically coupled ferromagnetic ab planes, is the ground-state of the system, in agreement with experiments. Furthermore, cobalt titanates present two critical temperatures related to the breaking of the inter- and intra-layer magnetic ordering. This would result in the individual planes remaining ferromagnetic even at temperatures above the Néel temperature. When spin-orbit coupling is included in our calculations, we find an out-of-plane magnetic anisotropy, which can be converted to an in-plane anisotropy with a small doping of electrons corresponding to about 2.5% Ti substitution for Co, consistent with experimental expectations. We thus present a disorder-dependent stud...
Physical review B, Jul 7, 2021
An ab-initio study of beta-As2Te3 (R3m symmetry) at hydrostatic pressures shows that this compoun... more An ab-initio study of beta-As2Te3 (R3m symmetry) at hydrostatic pressures shows that this compound is a trivial small band-gap semiconductor at room pressure that undergoes a quantum topological phase transition to a 3D topological Dirac semi-metal around 2 GPa. At higher pressures, the band-gap reopens and again decreases above 4 GPa. Our calculations predict an insulator-metal transition above 6 GPa due to the closing of the band-gap, with strong topological features persisting between 2 and 10 GPa with Z4=3 topological index. By investigating the lattice thermal-conductivity (κL), we observe that close to room conditions κL is very low, either for the in-plane and the out-of-plane axis, with 0.098 and 0.023 Wm −1 K −1 , respectively. This effect occurs due to the presence of two low-frequency optical modes, namely Eu and Eg, which increase the phononphonon scattering rate. Therefore, our work suggests that ultra-low lattice thermal-conductivities, which enable highly efficient thermoelectric materials, can be engineered in systems that are close to a structural instability derived from phonon Kohn anomalies. At higher pressures, the values of the in-and out-of-plane thermal-conductivities not only increase in magnitude, but also approximate in value as the layered character of the compound decreases.
M. Arruabarrena, A. Leonardo, 3 M. Rodriguez-Vega, Gregory A. Fiete, 6 and A. Ayuela 3 Materials ... more M. Arruabarrena, A. Leonardo, 3 M. Rodriguez-Vega, Gregory A. Fiete, 6 and A. Ayuela 3 Materials Physics Center (CFM), 20018 Donostia, Spain Department of Applied Physics II, University of the Basque Country UPV/ EHU, Bilbao, Spain. Donostia International Physics Center (DIPC), 20018 Donostia, Spain Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Department of Physics, Northeastern University, Boston, MA 02115, USA Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA (Dated: August 25, 2021)
Physical Review B, 2007
The temperature-dependent linewidth of the ⌫ surface state on Al͑100͒ was measured. The result ca... more The temperature-dependent linewidth of the ⌫ surface state on Al͑100͒ was measured. The result cannot be reconciled, not even qualitatively, with the well-known model for describing the influence of electron-phonon coupling on the lifetime broadening on electronic surface states. It is argued that this is due to the presence of thermally excited defects on the surface. Incorporating this possibility into the analysis, the measured temperature dependence is found to be consistent with that expected from an ab initio calculation of the electronphonon coupling strength. This phenomenon should be quite general and, indeed, a reanalysis of recently published data of Au͑111͒ ͓S. LaShell et al., Phys. Rev. B 74, 033410 ͑2006͔͒ resolves an apparent discrepancy between the measured and calculated electron-phonon coupling strengths.
Physical Review B, 2007
We report a detailed ab initio study of the electron-phonon ͑e-ph͒ interaction contribution to th... more We report a detailed ab initio study of the electron-phonon ͑e-ph͒ interaction contribution to the linewidth ⌫ e-ph ͑⑀ k,i ͒ of electron and hole states for bulk magnesium and the Mg͑0001͒ surface. The calculations are based on density functional theory and linear response approach. For bulk Mg, we find a large contribution of optical phonons to the Eliashberg spectral function and to ⌫ e-ph ͑⑀ k,i ͒. The e-ph coupling parameter at the Fermi level ͑mass enhancement parameter͒ has been found to be = 0.30. In the case of the surface, we have focused on the study of the ⌫ and M surface states for which we find = 0.28 and = 0.38, respectively. We show an important role of the Rayleigh vibrational mode in the e-ph coupling in the ⌫ surface state. These results are in a very good agreement with tunneling spectroscopic data and recent photoemission measurements of .
Journal of Physics: Condensed Matter, 2006
We present an ab initio study of the electron-phonon (e-ph) coupling and its contribution to the ... more We present an ab initio study of the electron-phonon (e-ph) coupling and its contribution to the phonon linewidths and to the lifetime broadening of excited electron and hole states in bulk Pd. The calculations, based on density-functional theory, were carried out using a linear-response approach in the plane-wave pseudopotential representation. The obtained results for the Eliashberg spectral function α 2 F(ω), e-ph coupling constant λ, and the contribution to the lifetime broadening, e−ph , show strong dependence on both the energy and momentum of an electron (hole) state. The calculation of phonon linewidths gives, in agreement with experimental observations, an anomalously large broadening for the transverse phonon mode T 1 in the direction. In addition, this mode is found to contribute most strongly to the electron-phonon scattering processes on the Fermi surface.
arXiv: Materials Science, 2020
We report a theoretical \textit{ab-initio} study of beta\betabeta-As$_2$Te$_3$ ($R\bar{3}m$ symmetry) a... more We report a theoretical \textit{ab-initio} study of beta\betabeta-As$_2$Te$_3$ ($R\bar{3}m$ symmetry) at hydrostatic pressures up to 12 GPa. We have systematically characterized the vibrational and electronic changes of the system induced by the pressure variation. The electronic band dispersions calculated at different pressures using \textit{QS}GW show an insulator-metal transition. At room pressure the system is a semiconductor with small band-gap, and the valence and conduction bands present a parabolic conventional dispersion. However around 2 GPa the parabolic shape of the bands become linear and touch at the Fermi level. This means that this compound undergoes a pressure-induced topological phase transition to a 3D analog of graphene, known as a 3D Dirac semi-metal, with gapless electronic excitations. At increasing pressures the gap reopens and variation of the character of the electronic band-gap from direct to indirect is evidenced. At 7 GPa we observe the formation of a negativ...
We theoretically study the effect of low-frequency light pulses in resonance with phonons in the ... more We theoretically study the effect of low-frequency light pulses in resonance with phonons in the topological and magnetically ordered two septuple-layer (2-SL) MnBi2Te4 (MBT) and MnSb2Te4 (MST). These materials share symmetry properties and an antiferromagnetic ground state in pristine form but present different magnetic exchange interactions. In both materials, shear and breathing Raman phonons can be excited via non-linear interactions with photo-excited infrared phonons using intense laser pulses attainable in current experimental setups. The light-induced transient lattice distortions lead to a change in the sign of the effective interlayer exchange interaction and magnetic order accompanied by a topological band transition. Furthermore, we show that moderate anti-site disorder, typically present in MBT and MST samples, can facilitate such an effect. Therefore, our work establishes 2-SL MBT and MST as candidate platforms to achieve non-equilibrium magneto-topological phase trans...
Martin Rodriguez-Vega, Ze-Xun Lin, 3 A. Leonardo, 5 A. Ernst, 7 M. G. Vergniory, 8 and Gregory A.... more Martin Rodriguez-Vega, Ze-Xun Lin, 3 A. Leonardo, 5 A. Ernst, 7 M. G. Vergniory, 8 and Gregory A. Fiete 9 Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Department of Physics, The University of Texas at Austin, Austin, TX 78712, USA Department of Physics, Northeastern University, Boston, MA 02115, USA Donostia International Physics Center, Paseo Manuel de Lardizabal 4, 20018 San Sebastian, Spain Department of Physics, University of the Basque Country UPV/ EHU, Leioa, Spain. Institut für Theoretische Physik, Johannes Kepler Universität, A 4040 Linz, Austria Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, D-06120 Halle, Germany Max Planck Institute for Chemical Physics of Solids, Dresden, D-01187, Germany Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA (Dated: August 31, 2021)
Physical Review B
In bilayer CrI 3 , experimental and theoretical studies suggest that the magnetic order is closel... more In bilayer CrI 3 , experimental and theoretical studies suggest that the magnetic order is closely related to the layer staking configuration. In this work, we study the effect of dynamical lattice distortions, induced by nonlinear phonon coupling, in the magnetic order of the bilayer system. We use density functional theory to determine the phonon properties and group theory to obtain the allowed phonon-phonon interactions. We find that the bilayer structure possesses low-frequency Raman modes that can be nonlinearly activated upon the coherent photoexcitation of a suitable infrared phonon mode. This transient lattice modification in turn inverts the sign of the interlayer spin interaction for parameters accessible in experiments, indicating a low-frequency light-induced antiferromagnet-to-ferromagnet transition.
Journal of Physics: Condensed Matter, 2016
First-principles calculations based on density-functional theory including anharmonicity within t... more First-principles calculations based on density-functional theory including anharmonicity within the variational stochastic self-consistent harmonic approximation are applied to understand how the quantum character of the proton affects the candidate metallic molecular Cmca - 4 structure of hydrogen in the 400-450 GPa pressure range, where metallization of hydrogen is expected to occur. Anharmonic effects, which become crucial due to the zero-point motion, have a large impact on the hydrogen molecules by increasing the intramolecular distance by approximately a 6%. This induces two new electron pockets at the Fermi surface opening new scattering channels for the electron-phonon interaction. Consequently, the electron-phonon coupling constant and the superconducting critical temperature are approximately doubled by anharmonicity and Cmca - 4 hydrogen becomes a superconductor above 200 K in all the studied pressure range. Contrary to many superconducting hydrides, where anharmoncity tends to lower the superconducting critical temperature, our results show that it can enhance superconductivity in molecular hydrogen.
Surface Science, 2006
We report ab initio study of the electron-phonon coupling in a free standing Beryllium monolayer.... more We report ab initio study of the electron-phonon coupling in a free standing Beryllium monolayer. The calculations were carried out using a linear-response approach in the plane-wave pseudopotential representation. The Eliashberg spectral function a 2 F(x) and the electron-phonon coupling parameter k are evaluated at the Fermi level. The obtained results show a large contribution to the electron-phonon coupling from the low-energy transverse mode scattering.
Surface Science, 2007
We report ab initio study of the electron–phonon coupling in a free standing magnesium monolayer ... more We report ab initio study of the electron–phonon coupling in a free standing magnesium monolayer and at the Mg(0001) surface. The calculations were carried out using a linear-response approach in the plane-wave pseudopotential representation. Eliashberg spectral function α2F(ω) averaged over electron states at the Fermi surface is presented for the monolayer while for the Mg(0001) surface, we compute the electron–phonon spectral function α2Fk,i(ω) for surface states at the Γ¯ and M¯ points.
Surface Science, 2006
ABSTRACT