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Lisenkov, S.

Publications and source records attributed to Lisenkov, S..

10 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Large Electrically and Chemically Tunable Rashba–Dresselhaus Effects in Ferroelectric CsGeX 3 (X = Cl, Br, I) Perovskites

Rashba–Dresselhaus effects, which originate from spin–orbit coupling and allow for spin manipulations, are actively explored in materials, following the pursuit of spintronics and quantum computing. However, materials that possess practically significant Rashba–Dresselhaus effects often contain toxic elements and offer little opportunity for the tunability of the effects. We used first-principles simulations to reveal that the recently discovered halide ferroelectrics in the CsGeX 3 (X = Cl, Br, I) family possess large and tunable Rashba-Dresselhaus effects. In particular, they give origin to the spin splitting of up to 171 meV in the valence band of CsGeI 3 . The value is chemically tunable and can decrease by 25% and 70% for CsGeBr 3 and CsGeCl 3 , respectively. Such chemical tunability could result in the engineering of desired values through a solid solution technique. Application of an electric field was found to result in structural changes that could decrease and increase spin splitting, leading to electrical tunability of the effect. In the vicinity of conduction and valence band extrema, the spin textures are mostly of the Rashba type, which is promising for spin-to-charge conversion applications. The spin directions are coupled with the polarization direction, leading to Rashba-ferroelectricity cofunctionality. Furthermore, our work identifies lead-free perovskite halides as excellent candidates for spin-based applications and is likely to stimulate further research in this direction.

Electric fields↗
DOE OSTI2023

Machine Learning Reveals Memory of the Parent Phases in Ferroelectric Relaxors Ba(Ti$_{1-x}$,Zr x )O 3

Machine learning has been establishing its potential in multiple areas of condensed matter physics and materials science. Here, in this work, an unsupervised machine learning workflow is developed and used within a framework of first-principles-based atomistic simulations to investigate phases, phase transitions, and their structural origins in ferroelectric relaxors, Ba(Ti 1-x ,Zr x )O 3 . The applicability of the workflow is first demonstrated to identify phases and phase transitions in the parent compound, a prototypical ferroelectric BaTiO 3 . Then the workflow is applied for Ba(Ti 1-x ,Zrx)O 3 with x ≤ 0.25 to reveal i) that some of the compounds bear a subtle memory of BaTiO 3 phases beyond the point of the pinched phase transition, which could contribute to their enhanced electromechanical response; ii) the existence of peculiar phases with delocalized precursors of nanodomains—likely candidates for the controversial polar nanoregions; and iii) nanodomain phases for the largest concentrations of x.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Rashba effects in lead-free ferroelectric semiconductor [CH 3 PH 3 ]SnBr 3

Here, first-principles density functional theory computations are used to predict Rashba effects cofunctional with ferroelectricity in a recently synthesized lead-free hybrid organic-inorganic perovskite MPSnBr 3 (MP=methylphosphonium, [CH 3 PH 3 ] + ). The ground state of the material is polar monoclinic with calculated spontaneous polarization of 3.01 µC/cm 2 . It exhibits near band edges spin-splitting of up to 3.3 meV and Rashba coefficient up to 0.62 eV Å. The spin textures have different topology in the conduction and valence band, which originates from the difference in the spin-momentum coupling strengths. They occur in two orthogonal planes of the Brillouin zone and are coupled to the direction of spontaneous polarization. These features persist at a finite temperature of 293 K. At 333 K, that is above monoclinic to orthorhombic phase transition, spontaneous polarization is reduced to 0.15 µC/cm 2 , while the maximum spin splitting and Rashba coefficient reduce slightly to the value of 2.9 meV and 0.41 eV Å, respectively. The spin textures remain coupled with the polarization direction. We investigate the dependence of the aforementioned properties on the choice of computational methodology to extend the first-principles predictions to include finite temperature effects. We find that the predictions are sensitive to the methodology. Our study reveals the potential of MPSnBr 3 for low-temperature applications in spintronics and quantum computing.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Chemically and electrically tunable spin polarization in ferroelectric Cd-based hybrid organic-inorganic perovskites

Density functional theory computations are used to predict the electronic structure of Cd-based hybrid organic-inorganic high-T C ferroelectric perovskites with TMCM-CdCl 3 being one representative. Here we report Rashba-Dresselhaus spin splitting in the valence band of these nonmagnetic compounds. Interestingly, we find in computations that the splitting is not necessarily sensitive to the polarization of the material but to the organic molecule itself which opens a way to its chemical tunability through the choice of the molecule. Further chemical tunability of spin splitting is shown to be possible through a substitution of Cl in the CdCl 3 chains as the valence band was found to originate from Cl-Cl weekly bonding orbitals. For example, the substitution of Cl with Br in TMCM-CdCl 3 resulted in a ten times increase of spin splitting. Furthermore, the spin polarization in these materials gives origin to persistent spin textures which are coupled to the polarization direction, and, therefore, can be controlled by the electric field. This is promising for spintronics applications.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Structural, Electrical, and Electromechanical Properties of Inverse Hybrid Perovskites from First-Principles: The Case of (CH 3 NH 3 ) 3 OI

Inverse-hybrid perovskites (IHPs) with large polarization have recently been predicted from first-principles computations. Here, we use one representative from the IHP class of materials, (CH 3 NH 3 ) 3 OI (MA3OI), to propose a route to the first-principles prediction of structural and electrical properties, such as polarization, polarization reversibility, and the associated coercive field for hybrid organic–inorganic perovskites. The route relies on the construction of the polarization reversal path that models experimental measurements. Such a path was found to play an important role in the ground-state search as well as in the identification of competing structural variations. The latter is believed to be the origin of the structural disorder that is characteristic of hybrid organic–inorganic perovskites. The application of such an approach to MA3OI leads to the prediction of several structural variations that are expected to result in a structurally disordered phase above 766 K and of the polar ground state with a polarization of 25.3 μC/cm 2 that is reversible with the application of an electric field. The upper estimate for the coercive field associated with homogeneous polarization reversal is 6.9 GV/m. The piezoelectric constants of MA3OI are predicted to be an order of magnitude smaller in comparison with a prototypical inorganic ferroelectric PbTiO 3 ; however, the low symmetry of the MA3OI structure yields finite values for all components of the piezoelectric tensor. The polarization in MA3OI is tunable by the epitaxial strain (11.5% change under 5% epitaxial strain), although less so as compared with PbTiO 3 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Ba ( Ti 1 - x , Zr x ) O 3 relaxors: Dynamic ferroelectrics in the gigahertz frequency range

Relaxor ferroelectrics are of great scientific and technological significance as they exhibit large and unusual responses to external stimuli. Their hallmark features are broadness and frequency dispersion of the peak in the temperature dependence of the dielectric constant. Both are believed to originate from the dynamics of polar nanoregions. Here, we apply first-principles-based molecular dynamics to resolve the gigahertz electric response of dynamically poled Ba (Ti 1 - x , Zr x ) O 3 ferroelectric relaxors that remained overlooked so far. We find that (i) the hallmark relaxor features continue to persist even in the dynamically poled structures, but do not necessarily originate from the polar nanoregions dynamics; (ii) dynamically poled samples exhibit polarization aging which leads to the frequency dependence of both remnant polarization and the Curie temperature; (iii) “dynamical” nature of the latter naturally explains the frequency dependence of the dielectric susceptibility maximum in dynamically poled Ba (Ti 1 - x , Zr x) O 3 ; and (iv) incorporation of the polarization aging into dielectric susceptibility expression explains its enhancing contribution in an intuitive way.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Prediction of high strain polar phases in antiferroelectric PbZrO 3 from multiscale approach

PbZrO 3 is regarded as the first antiferroelectric and currently under intense reexamination. We propose a multiscale approach that combines classical and first principles density functional theory based simulations to explore polar phases in this material. Application of this approach to PbZrO 3 predicts three polar phases, none of which is the common $R3c$. The lowest energy polar phase - $Cc$ - is metastable at zero Kelvin but can be stabilized by application of electric field. Its structural and polarization response to the electric field is in good agreement with experimental data from the literature. The other two phases are $Ima2$ and $I4cm$ of orthorhombic and tetragonal symmetry, respectively, and predicted to stabilize at finite temperatures and under application of larger electric fields. These two phases exhibit very large strain which is of technological significance.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Comparative study of Minnesota functionals performance on ferroelectric BaTiO 3 and PbTiO 3

Density functional theory based simulations are the leading tool for the computational investigation of ferroelectrics and the parametrization of their classical potentials. However, the predictions often depend strongly on the exchange correlation functional. The most popular choices, LDA and GGA, tend to underestimate or overestimate some structural, electric, and energy properties. These impede development of highly accurate classical potentials that extend the reach of first-principles simulations to finite temperatures and realistic sizes. In this work, we investigate the performance of recently developed Minnesota exchange correlation functionals on prototypical ferroelectrics BaTiO 3 , and PbTiO 3 , in comparison with some popular ones. We find that there exists strong correlation between predictions for some properties (tetragonality, phase energy difference, and polarization) by different functionals. Along the correlation line, we find a range of functionals (including some from the Minnesota suite) whose predictions fall in between those of LDA and GGA and, therefore, offer an improvement. A way to relatively rank functional performance with respect to chosen benchmarks is proposed and applied to identify the top performers for BaTiO 3 and PbTiO 3 . Here, the performance is found to be material dependent. Therefore, we propose that the performance assessment carried out in this work is employed to "screen" functionals prior to their use on ferroelectrics. Quick and computationally inexpensive, it is likely to lead to improved descriptions, especially for classical potential parametrization. The Minnesota functional suite is found to be suitable for this task.

36 MATERIALS SCIENCE↗