Periodic Reporting for period 1 - DELIGHT (Discovering light-induced phases by first-principles material design)
Período documentado: 2022-10-01 hasta 2025-03-31
Ultrafast lasers sources open new perspectives in exploring broken symmetry phases as it becomes possible to promote a substantial number of electrons in excited states generating a thermalized electron-hole plasma and leading to reversible or irreversible phase transitions. Light-induced charge density waves, order-disorder transitions, melting, stabilization of topological phases and laser-tunable ferroelectricity have been demonstrated. Experiments are far ahead of theory as few (if any) of the demonstrated light-induced phenomena have been predicted by theory.
DELIGHT aims to develop a theoretical strategy to predict and discover photoinduced phases in materials. To accomplish this goal, we will develop quantum-chemical and molecular dynamics schemes including the effect of the thermalized electron-hole plasma on the crystal potential and accounting for light-induced non-perturbative quantum anharmonicity.
DELIGHT will answer these questions: which systems undergo light induced phase transitions ? Can we use light pulses to enhance or tune charge density wave, ferroelectric and magnetic critical temperatures, to generate new topological phases or to optimize the properties of thermoelectric materials ? Can we develop an inverse design strategy, namely given a target property, determine which material will have to be photoexcited and at which fluence to obtain it ?
The proposal will impact chemistry, physics, energy and material engineering. It could lead, for example, to the development of devices with dynamical light switching on/off of magnetism or ferroelectricity, relevant for ultrafast memories, or to the stabilization of new thermoelectric compounds with photo-tunable thermal conductivity and figure of merit. DELIGHT will foster these and similar developments by implementing a fundamentally new and unique database of out-of-equilibrium accessible states of matter that will be a reference for future experiments.
DELIGHT aims to develop a theoretical strategy to predict and discover photoinduced phases in materials. To accomplish this goal, we will develop quantum-chemical and molecular dynamics schemes including the effect of the thermalized electron-hole plasma on the crystal potential and accounting for light-induced non-perturbative quantum anharmonicity.
DELIGHT will answer these questions: which systems undergo light induced phase transitions ? Can we use light pulses to enhance or tune charge density wave, ferroelectric and magnetic critical temperatures, to generate new topological phases or to optimize the properties of thermoelectric materials ? Can we develop an inverse design strategy, namely given a target property, determine which material will have to be photoexcited and at which fluence to obtain it ?
The proposal will impact chemistry, physics, energy and material engineering. It could lead, for example, to the development of devices with dynamical light switching on/off of magnetism or ferroelectricity, relevant for ultrafast memories, or to the stabilization of new thermoelectric compounds with photo-tunable thermal conductivity and figure of merit. DELIGHT will foster these and similar developments by implementing a fundamentally new and unique database of out-of-equilibrium accessible states of matter that will be a reference for future experiments.
The work and the achievements of the first two years of DELIGHT can be summarized in three main points:
1. Design of light induced phase and understanding of ultrafast phase transitions.
(i) we showed that ultrafast lasers impinging on the ground state Pnma structure of SnSe can (i) induce a phase transition to a transient Immm phase and (ii) permanently transform the topologically trivial orthorhombic structure of SnSe into the topological crystalline insulating rocksalt phase via a first-order nonthermal phase transition. One year after that our work was published, an experimental paper (B. J. Dringoli et al., Phys. Rev. Lett. 132, 146901 (2024) ) confirmed our first prediction concerning a transition towards the transient Immm phase and demonstrated the incredible accuracy of our calculation with an error on the critical fluence of only 1 mJ/cm2.
(ii) we performed a joined theoretical and experimental (Berkeley group of Prof. A. Lanzara) work to study of the evolution of the semiconducting phase of TiSe2 after ultrafast photoexcitation. We showed that intense optical excitation can drive 1T-TiSe2, a prototypical charge density wave material, almost instantly from a gapped into a semimetallic state.
(iii) We clarified the transition mechanism of the non-thermal phase transition in photoexcited GeTe from a rhombohedral to a rocksalt crystalline phase
2. Theoretical description of high-order spectroscopies involving light-matter interaction in materials. The development of new modelling and simulations approaches to understand advanced spectroscopies such as photoluminescence or double-resonant Raman is crucial for the characterization of materials and also of new phases arising from photoexcitation.
(i) We developed a first-principles approach based on the many-body cumulant expansion of the charge response to calculate optical absorption and photoluminescence. We applied this method to the optical absorption and photoluminescence spectrum of a single-layer boron nitride.
(ii) In collaboration with the experimental groups of Prof. Leonetta Baldassarre and Prof. Christoph Stampfer and with the theory group of Prof. Francesco Mauri, we provide an explanation of the complicate double resonant Raman effect in graphene and few layer graphene for incoming laser light in the infrared range.
3. Development and distribution under the GNU licence of two codes able to (i) design and understand photoexcited phase transitions in materials and (ii) perform very fast electron-phonon coupling calculation (the EPIq code). The EPIq code is a general purpose interdisciplinary code relevant for many disciplines in condensed matter physics.
(i) we developed a first principles code based on cDFPT for the calculation of structural and harmonic vibrational properties of insulators in the presence of an excited and thermalized electron-hole plasma.In the first year and a half of the ERC, we improve the implementation to include many other options such as different kind of pseudopotentials and others and the code has been released under the GNU licence within the Quantum Espresso suite.
(ii) Development and Distribution (under the GNU licence) of the EPIq code to calculate electron-phonon properties of materials in a Wannier basis approach ( https://the-epiq-team.gitlab.io/epiq-site/ )
1. Design of light induced phase and understanding of ultrafast phase transitions.
(i) we showed that ultrafast lasers impinging on the ground state Pnma structure of SnSe can (i) induce a phase transition to a transient Immm phase and (ii) permanently transform the topologically trivial orthorhombic structure of SnSe into the topological crystalline insulating rocksalt phase via a first-order nonthermal phase transition. One year after that our work was published, an experimental paper (B. J. Dringoli et al., Phys. Rev. Lett. 132, 146901 (2024) ) confirmed our first prediction concerning a transition towards the transient Immm phase and demonstrated the incredible accuracy of our calculation with an error on the critical fluence of only 1 mJ/cm2.
(ii) we performed a joined theoretical and experimental (Berkeley group of Prof. A. Lanzara) work to study of the evolution of the semiconducting phase of TiSe2 after ultrafast photoexcitation. We showed that intense optical excitation can drive 1T-TiSe2, a prototypical charge density wave material, almost instantly from a gapped into a semimetallic state.
(iii) We clarified the transition mechanism of the non-thermal phase transition in photoexcited GeTe from a rhombohedral to a rocksalt crystalline phase
2. Theoretical description of high-order spectroscopies involving light-matter interaction in materials. The development of new modelling and simulations approaches to understand advanced spectroscopies such as photoluminescence or double-resonant Raman is crucial for the characterization of materials and also of new phases arising from photoexcitation.
(i) We developed a first-principles approach based on the many-body cumulant expansion of the charge response to calculate optical absorption and photoluminescence. We applied this method to the optical absorption and photoluminescence spectrum of a single-layer boron nitride.
(ii) In collaboration with the experimental groups of Prof. Leonetta Baldassarre and Prof. Christoph Stampfer and with the theory group of Prof. Francesco Mauri, we provide an explanation of the complicate double resonant Raman effect in graphene and few layer graphene for incoming laser light in the infrared range.
3. Development and distribution under the GNU licence of two codes able to (i) design and understand photoexcited phase transitions in materials and (ii) perform very fast electron-phonon coupling calculation (the EPIq code). The EPIq code is a general purpose interdisciplinary code relevant for many disciplines in condensed matter physics.
(i) we developed a first principles code based on cDFPT for the calculation of structural and harmonic vibrational properties of insulators in the presence of an excited and thermalized electron-hole plasma.In the first year and a half of the ERC, we improve the implementation to include many other options such as different kind of pseudopotentials and others and the code has been released under the GNU licence within the Quantum Espresso suite.
(ii) Development and Distribution (under the GNU licence) of the EPIq code to calculate electron-phonon properties of materials in a Wannier basis approach ( https://the-epiq-team.gitlab.io/epiq-site/ )
All results mentioned in the previous section are novel and beyond state of the art.
The predictions at point 1 (i) have been partially verified experimentally, but we still miss the experimental demonstration of the non-thermal path towards the topologically crystalline phase. More experimental efforts are needed to confirm this theoretical prediction.
All the results 1( ii and iii) aans 2 (i and (ii) ) have been conducted in collaboration with experimentalists and are novel and we believe that they will have a substantial impact.
As a confirmation, at the moment 4 experimental groups have contacted us requiring help to understand their data on other compounds.
For what concern the methodological development (point 3) we are aware that several theoretical groups have started using our cDFPT code and many more are using our EPIq code, so we believe that the impact will grow fast, as it will be demonstrated by the increasing number of citations in the next years.
The predictions at point 1 (i) have been partially verified experimentally, but we still miss the experimental demonstration of the non-thermal path towards the topologically crystalline phase. More experimental efforts are needed to confirm this theoretical prediction.
All the results 1( ii and iii) aans 2 (i and (ii) ) have been conducted in collaboration with experimentalists and are novel and we believe that they will have a substantial impact.
As a confirmation, at the moment 4 experimental groups have contacted us requiring help to understand their data on other compounds.
For what concern the methodological development (point 3) we are aware that several theoretical groups have started using our cDFPT code and many more are using our EPIq code, so we believe that the impact will grow fast, as it will be demonstrated by the increasing number of citations in the next years.