430 results on '"Kuneš, P."'
Search Results
2. Fingerprints of Mott and Slater gaps in the core-level photoemission spectra of antiferromagnetic iridates
- Author
-
Nakagawa, K., Hariki, A., Okauchi, T., Fujiwara, H., Ahn, K. -H., Murakami, Y., Hamamoto, S., Kanai-Nakata, Y., Kadono, T., Higashiya, A., Tamasaku, K., Yabashi, M., Ishikawa, T., Sekiyama, A., Imada, S., Kuneš, J., Takase, K., and Yamasaki, A.
- Subjects
Condensed Matter - Strongly Correlated Electrons - Abstract
We present Ir $4f$ core-level hard-x-ray photoemission spectroscopy (HAXPES) experiments conducted across antiferromagnetic (AFM) ordering transition in Ruddlesden-Popper iridates Sr$_2$IrO$_4$ and Sr$_3$Ir$_2$O$_7$. The Ir $4f$ spectra exhibit distinct changes between the AFM and paramagnetic (PM) phases, with the spectral difference $I_\text{PM}-I_\text{AFM}$ showing a contrasting behavior in the two compounds. By employing computational simulations using the local-density approximation combined with the dynamical mean-field theory method, we elucidate that $I_\text{PM}-I_\text{AFM}$ primary reflects the Slater or Mott-Hubbard character of the AFM insulating state rather than material specific details. This sensitivity to fine low-energy electronic structure arises from the dependence of charge-transfer responses to the sudden creation of a localized core hole on both metal-insulator transitions and long-range AFM ordering. Our result broadens the applications of core-level HAXPES as a tool for characterization of electronic structure., Comment: Main: 7 pages, 3 figures ; SM: 4 pages, 4 figures
- Published
- 2024
3. Wasserstein Wormhole: Scalable Optimal Transport Distance with Transformers
- Author
-
Haviv, Doron, Kunes, Russell Zhang, Dougherty, Thomas, Burdziak, Cassandra, Nawy, Tal, Gilbert, Anna, and Pe'er, Dana
- Subjects
Computer Science - Machine Learning ,Computer Science - Computational Geometry ,Quantitative Biology - Genomics - Abstract
Optimal transport (OT) and the related Wasserstein metric (W) are powerful and ubiquitous tools for comparing distributions. However, computing pairwise Wasserstein distances rapidly becomes intractable as cohort size grows. An attractive alternative would be to find an embedding space in which pairwise Euclidean distances map to OT distances, akin to standard multidimensional scaling (MDS). We present Wasserstein Wormhole, a transformer-based autoencoder that embeds empirical distributions into a latent space wherein Euclidean distances approximate OT distances. Extending MDS theory, we show that our objective function implies a bound on the error incurred when embedding non-Euclidean distances. Empirically, distances between Wormhole embeddings closely match Wasserstein distances, enabling linear time computation of OT distances. Along with an encoder that maps distributions to embeddings, Wasserstein Wormhole includes a decoder that maps embeddings back to distributions, allowing for operations in the embedding space to generalize to OT spaces, such as Wasserstein barycenter estimation and OT interpolation. By lending scalability and interpretability to OT approaches, Wasserstein Wormhole unlocks new avenues for data analysis in the fields of computational geometry and single-cell biology., Comment: Published at the Forty-first International Conference on Machine Learning (ICML2024)
- Published
- 2024
4. Quantifying the U $5f$ covalence and degree of localization in U intermetallics
- Author
-
Marino, Andrea, Christovam, Denise S., Takegami, Daisuke, Falke, Johannes, Carvalho, Miguel M. F., Okauchi, Takaki, Chang, Chun-Fu, Altendorf, Simone G., Amorese, Andrea, Sundermann, Martin, Gloskovskii, Andrei, Gretarsson, Hlynur, Keimer, Bernhard, Andreev, Alexandr V., Havela, Ladislav, Leithe-Jasper, Andreas, Severing, Andrea, Kunes, Jan, Tjeng, Liu Hao, and Hariki, Atsushi
- Subjects
Condensed Matter - Strongly Correlated Electrons - Abstract
A procedure for quantifying the U $5f$ electrons' covalence and degree of localization in U intermetallic compounds is presented. To this end, bulk sensitive hard and soft x-ray photoelectron spectroscopy were utilized in combination with density-functional theory (DFT) plus dynamical mean-field theory (DMFT) calculations. The energy dependence of the photoionization cross-sections allows the disentanglement of the U\,$5f$ contribution to the valence band from the various other atomic subshells so that the computational parameters in the DFT\,+\,DMFT can be reliably determined. Applying this method to UGa$_2$ and UB$_2$ as model compounds from opposite ends of the (de)localization range, we have achieved excellent simulations of the valence band and core-level spectra. The width in the distribution of atomic U\,$5f$ configurations contributing to the ground state, as obtained from the calculations, quantifies the correlated nature and degree of localization of the U\,5$f$. The findings permit answering the longstanding question why different spectroscopic techniques give seemingly different numbers for the U 5$f$ valence in intermetallic U compounds., Comment: 14 pages, 9 figures
- Published
- 2024
- Full Text
- View/download PDF
5. Mechanism of intermetallic charge transfer and bond disproportionation in BiNiO$_3$ and PbNiO$_3$ revealed by hard x-ray photoemission spectroscopy
- Author
-
Yamaguchi, Tatsuya, Furo, Mizuki, Sakai, Yuki, Nishikubo, Takumi, Hojo, Hajime, Azuma, Masaki, Oka, Kengo, Mori, Daisuke, Inaguma, Yoshiyuki, Mizumaki, Masaichiro, Yamamoto, Kento, Kuneš, Jan, Mizokawa, Takashi, and Hariki, Atsushi
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science - Abstract
Perovskites with Bi or Pb on the A-site host a number of interesting and yet to be understood phenomena such as negative thermal expansion in BiNiO$_3$. We employ hard x-ray photoemission spectroscopy of Ni 2$p$ core-level as well as valence band to probe the electronic structure of BiNiO$_3$ and PbNiO$_3$. The experimental results supported by theoretical calculations using dynamical mean-field theory reveal essentially identical electronic structure of the Ni-O subsystem typical of Ni$^{2+}$ charge-transfer insulators. The two materials are distinguished by filling of the Bi(Pb)-O antibonding states in the vicinity of the Fermi level, which is responsible for the Bi disproportionation in BiNiO$_3$ at ambient pressure and absence of similar behavior in PbNiO$_3$. The present experiments provide evidence for this conclusion by revealing the presence/absence of Bi/Pb $6s$ states at the top of the valence band in the two materials.
- Published
- 2023
- Full Text
- View/download PDF
6. X-ray Magnetic Circular Dichroism in RuO$_2$
- Author
-
Hariki, A., Takahashi, Y., and Kuneš, J.
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science - Abstract
We present numerical simulation of the X-ray magnetic circular dichroism (XMCD) of the $L_{2,3}$ and $M_{2,3}$ edges of Ru in antiferromagnetic RuO$_2$ using a combination of density functional + dynamical mean-field theory and configuration interaction treatment of Anderson impurity model. We study the dependence of the dichroic spectra on the orientation of the N\'eel vector and discuss it in the context of altermagnetism. Approximate equivalence between the XMCD spectra for geometries with X-rays propagating parallel and perpendicular to the N\'eel vector is found and shown to be exact in absence of valence spin-orbit coupling and core-valence multipolar interaction., Comment: 7 pages, 6 figures
- Published
- 2023
- Full Text
- View/download PDF
7. Hidden covalent insulator and spin excitations in SrRu$_2$O$_6$
- Author
-
Csontosová, D., Chaloupka, J., Shinaoka, H., Hariki, A., and Kuneš, J.
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science - Abstract
The density functional plus dynamical mean-field theory is used to study the spin excitation spectra of SrRu$_2$O$_6$. A good quantitative agreement with experimental spin excitation spectra is found. Depending on the size of the Hund's coupling $J_H$ the systems chooses either Mott insulator or covalent insulator state when magnetic ordering is not allowed. We find that the nature of the paramagnetic state has negligible influence on the charge and spin excitation spectra. We find that antiferromagnetic correlations hide the covalent insulator state for realistic choices of the interaction parameters., Comment: 15 pages, 4 figures
- Published
- 2023
8. X-ray Magnetic Circular Dichroism in Altermagnetic $\alpha$-MnTe
- Author
-
Hariki, A., Din, A. Dal, Amin, O. J., Yamaguchi, T., Badura, A., Kriegner, D., Edmonds, K. W., Campion, R. P., Wadley, P., Backes, D., Veiga, L. S. I., Dhesi, S. S., Springholz, G., Šmejkal, L., Výborný, K., Jungwirth, T., and Kuneš, J.
- Subjects
Condensed Matter - Materials Science ,Condensed Matter - Strongly Correlated Electrons - Abstract
Altermagnetism is a recently identified magnetic symmetry class combining characteristics of conventional collinear ferromagnets and antiferromagnets, that were regarded as mutually exclusive, and enabling phenomena and functionalities unparalleled in either of the two traditional elementary magnetic classes. In this work we use symmetry and ab initio theory to explore X-ray magnetic circular dichroism (XMCD) in the altermagnetic class. Our results highlight the distinct phenomenology in altermagnets of this time-reversal symmetry breaking response, and its potential utility for element-specific spectroscopy and microscopy in altermagnets. As a representative material for our XMCD study we choose $\alpha$-MnTe with the compensated antiparallel magnetic order in which an anomalous Hall effect has been already demonstrated both in theory and experiment. The predicted magnitude of XMCD lies well within the resolution of existing experimental techniques., Comment: Experimental data added
- Published
- 2023
- Full Text
- View/download PDF
9. Single- and Multimagnon Dynamics in Antiferromagnetic $\alpha$-Fe$_2$O$_3$ Thin Films
- Author
-
Li, Jiemin, Gu, Yanhong, Takahashi, Yoshihiro, Higashi, Keisuke, Kim, Taehun, Cheng, Yang, Yang, Fengyuan, Kunes, Jan, Pelliciari, Jonathan, Hariki, Atsushi, and Bisogni, Valentina
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science - Abstract
Understanding the spin dynamics in antiferromagnetic (AFM) thin films is fundamental for designing novel devices based on AFM magnon transport. Here, we study the magnon dynamics in thin films of AFM $S=5/2$ $\alpha$-Fe$_2$O$_3$ by combining resonant inelastic x-ray scattering, Anderson impurity model plus dynamical mean-field theory, and Heisenberg spin model. Below 100 meV, we observe the thickness-independent (down to 15 nm) acoustic single-magnon mode. At higher energies (100-500 meV), an unexpected sequence of equally spaced, optical modes is resolved and ascribed to $\Delta S_z = 1$, 2, 3, 4, and 5 magnetic excitations corresponding to multiple, noninteracting magnons. Our study unveils the energy, character, and momentum-dependence of single and multimagnons in $\alpha$-Fe$_2$O$_3$ thin films, with impact on AFM magnon transport and its related phenomena. From a broader perspective, we generalize the use of L-edge resonant inelastic x-ray scattering as a multispin-excitation probe up to $\Delta S_z = 2S$. Our analysis identifies the spin-orbital mixing in the valence shell as the key element for accessing excitations beyond $\Delta S_z = 1$, and up to, e.g., $\Delta S_z = 5$. At the same time, we elucidate the novel origin of the spin excitations beyond the $\Delta S_z = 2$, emphasizing the key role played by the crystal lattice as a reservoir of angular momentum that complements the quanta carried by the absorbed and emitted photons., Comment: Accepted in Physical Review X
- Published
- 2022
- Full Text
- View/download PDF
10. Gradient Estimation for Binary Latent Variables via Gradient Variance Clipping
- Author
-
Kunes, Russell Z., Yin, Mingzhang, Land, Max, Haviv, Doron, Pe'er, Dana, and Tavaré, Simon
- Subjects
Computer Science - Machine Learning ,Statistics - Machine Learning - Abstract
Gradient estimation is often necessary for fitting generative models with discrete latent variables, in contexts such as reinforcement learning and variational autoencoder (VAE) training. The DisARM estimator (Yin et al. 2020; Dong, Mnih, and Tucker 2020) achieves state of the art gradient variance for Bernoulli latent variable models in many contexts. However, DisARM and other estimators have potentially exploding variance near the boundary of the parameter space, where solutions tend to lie. To ameliorate this issue, we propose a new gradient estimator \textit{bitflip}-1 that has lower variance at the boundaries of the parameter space. As bitflip-1 has complementary properties to existing estimators, we introduce an aggregated estimator, \textit{unbiased gradient variance clipping} (UGC) that uses either a bitflip-1 or a DisARM gradient update for each coordinate. We theoretically prove that UGC has uniformly lower variance than DisARM. Empirically, we observe that UGC achieves the optimal value of the optimization objectives in toy experiments, discrete VAE training, and in a best subset selection problem.
- Published
- 2022
11. Chemical forest amelioration: Experience from the Czech Republic and other selected countries - A review
- Author
-
Martin Baláš, Ivan Kuneš, Vilém Podrázský, Josef Gallo, and František Lopot
- Subjects
afforestation and forest regeneration ,forest fertilisation ,macronutrients ,tree growth ,soil and foliage chemistry ,soil remediation ,Forestry ,SD1-669.5 - Abstract
This review article summarises the results of research on forest liming, fertilisation, nutrition flows and cycles in selected European and other countries. The presented studies mostly deal with assessing the effect of liming and fertilisation applied during planting or shortly after planting. The sporadic studies on fertilisation in older stands are also presented. The application of crushed limestone, dolomite or other alkaline rocks or their mixtures is usually used to improve the soil conditions on a large area through the adjustment of soil acidity and to supply any deficient elements, especially calcium and magnesium. These amendments are typically used on naturally nutrient-poor soils or as a curative technique to neutralise the soil chemistry affected by anthropogenic acidification. Artificial fertilisers are usually applied on small spots to individual trees on the surface of the soil shortly after planting or into a planting hole during planting. The purpose is to give some initial support to young trees to better overcome the post-planting shock and to accelerate the height growth. Less frequently, artificial fertilisers are used on large areas of forest stands for the purpose of increasing stem growth. The methods and the extent of forest fertilisation substantially vary in individual countries and different time periods.
- Published
- 2024
- Full Text
- View/download PDF
12. Administrative system of afforestation in the Czech Republic: A long journey to a new forest
- Author
-
Martin Baláš, Josef Gallo, Marcin Czacharowski, Michal Pástor, Jaroslav Jankovič, Igor Štefančík, Ivan Kuneš, and Hubert Hasenauer
- Subjects
administration ,afforestation of agricultural land ,forest establishment ,land-use change ,spatial planning policy ,Forestry ,SD1-669.5 - Abstract
This review uses a case study based on an executed afforestation project to comprehensively describe the administrative procedure regarding afforestation of agricultural land in the Czech Republic, Central Europe. We consider the official proceedings for obtaining a permit to land-use change (i.e. changing the nature of land use and the mode of land use in the real estate cadastre) as a very complex and protracted procedure, which can substantially reduce the motivation of people to establish new forests. Therefore, we propose a simplification of the administration process of land-use change. The main idea is to make the procedure as simple as possible in those areas where afforestation is desirable, especially from the environmental point of view. It assumes the possibility of quick, precise and, if possible, automatic distinction whether the afforestation is suitable or not. The situation in the Czech Republic is compared with the surrounding Central-European countries: Poland and Slovakia. In these countries, the official procedure connected with afforestation seems to be rather less complicated.
- Published
- 2024
- Full Text
- View/download PDF
13. Use of brassinosteroids to overcome unfavourable climatic effects on seed germination in Pinus nigra J. F. Arnold
- Author
-
Suraweera PACNB, Kuneš I, Baláš M, Podrázský V, Šulitka M, and Remeš J
- Subjects
Brassinosteroids ,Pinus nigra ,Germination Capacity ,Germination Energy ,Germination Rate ,Forestry ,SD1-669.5 - Abstract
Seeds of forest species can show germination and survival problems if they are exposed to adverse climatic conditions in the course of germination. Brassinosteroids could help seeds to overcome such environmental stress. We tested the effects of exogenous application of a chosen brassinosteroid compound 2α,3α,17β-trihydroxy-5α-androstan-6-one on the germination capacity and germination energy of European black pine (Pinus nigra J. F. Arnold) seeds. Before germination, the seeds were soaked for 24 hours either in demineralised water (control treatment) or in brassinosteroid solutions of four concentrations (high, higher-medium, lower-medium and low-concentration treatments). In the course of germination, the control and all four concentration treatments were subjected to two alternative temperature regimes: the optimal (unstressed) regime (20/30°C) and the stress regime, during which the seeds were exposed to temporary temperature stress (peaking at 42°C). In the optimal temperature regime, the highest germination energy was recorded in the higher-medium-concentration treatment and a significantly increased germination energy when compared to the control was also observed in a high-concentration treatment. The brassinosteroid, when applied in high, higher-medium and lower-medium concentrations, significantly increased the germination capacity compared to the control. The highest germination capacity was recorded in the high-concentration treatment. The temperature stress substantially reduced the germination of P. nigra. In the stress regime, the seeds of the higher-medium-concentration treatment decidedly showed the highest germination energy and capacity and those of the control treatment the lowest. The seed germination energy in the control was significantly lower than that recorded in the high and higher-medium-concentration treatments. The seed germination capacity in the control was significantly lower than those found in all concentration treatments, except for the seeds in the low-concentration treatment. The brassinosteroid application promoted the germination of black pine and partly alleviated the impact of the temporary heat stress. However, this application did not compensate for the heat stress effects completely. The potential for the use of the brassinosteroid may exist chiefly for seedings of Pinus nigra in forest nurseries where the nursery staff try to maintain optimal climatic conditions, and deviations from these conditions are usually only temporary.
- Published
- 2024
- Full Text
- View/download PDF
14. Kondo quasiparticle dynamics observed by resonant inelastic x-ray scattering
- Author
-
Rahn, M. C., Kummer, K., Hariki, A., Ahn, K. -H., Kunes, J., Amorese, A., Denlinger, J. D., Lu, D. -H., Hashimoto, M., Rienks, E., Valvidares, M., Haslbeck, F., Byler, D. D., McClellan, K. J., Bauer, E. D., Zhu, J. -X., Booth, C. H., Christianson, A. D., Lawrence, J. M., Ronning, F., and Janoschek, M.
- Subjects
Condensed Matter - Strongly Correlated Electrons - Abstract
Effective models focused on pertinent low-energy degrees of freedom have substantially contributed to our qualitative understanding of quantum materials. An iconic example, the Kondo model, was key to demonstrating that the rich phase diagrams of correlated metals originate from the interplay of localized and itinerant electrons. Modern electronic structure calculations suggest that to achieve quantitative material-specific models, accurate consideration of the crystal field and spin-orbit interactions is imperative. This poses the question of how local high-energy degrees of freedom become incorporated into a collective electronic state. Here, we use resonant inelastic x-ray scattering (RIXS) on CePd$_3$ to clarify the fate of all relevant energy scales. We find that even spin-orbit excited states acquire pronounced momentum-dependence at low temperature - the telltale sign of hybridization with the underlying metallic state. Our results demonstrate how localized electronic degrees of freedom endow correlated metals with new properties, which is critical for a microscopic understanding of superconducting, electronic nematic, and topological states.
- Published
- 2022
- Full Text
- View/download PDF
15. CaCu$_3$Ru$_4$O$_{12}$: a high Kondo-temperature transition metal oxide
- Author
-
Takegami, D., Kuo, C. Y., Kasebayashi, K., Kim, J. -G., Chang, C. F., Liu, C. E., Wu, C. N., Kasinathan, D., Altendorf, S. G., Hoefer, K., Meneghin, F., Marino, A., Liao, Y. F., Tsuei, K. D., Chen, C. T., Ko, K. -T., Günther, A., Ebbinghaus, S. G., Seo, J. W., Lee, D. H., Ryu, G., Komarek, A. C., Sugano, S., Shimakawa, Y., Tanaka, A., Mizokawa, T., Kuneš, J., Tjeng, L. H., and Hariki, A.
- Subjects
Condensed Matter - Strongly Correlated Electrons - Abstract
We present a comprehensive study of CaCu$_3$Ru$_4$O$_{12}$ using bulk sensitive hard and soft x-ray spectroscopy combined with local-density approximation (LDA) + dynamical mean-field theory (DMFT) calculations. Correlation effects on both the Cu and Ru ions can be observed. From the Cu $2p$ core level spectra we deduce the presence of magnetic Cu$^{2+}$ ions hybridized with a reservoir of itinerant electrons. The strong photon energy dependence of the valence band allows us to disentangle the Ru, Cu, and O contributions and thus to optimize the DMFT calculations. The calculated spin and charge susceptibilities show that the transition metal oxide CaCu$_3$Ru$_4$O$_{12}$ must be classified as a Kondo system and that the Kondo temperature is in the range of 500-1000 K., Comment: Accepted for publication in Phys. Rev. X
- Published
- 2021
- Full Text
- View/download PDF
16. Valence skipping, internal doping and site-selective Mott transition in PbCoO$_3$ under pressure
- Author
-
Hariki, Atsushi, Ahn, Kyo-Hoon, and Kuneš, Jan
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science - Abstract
We present a computational study of PbCoO$_3$ at ambient and elevated pressure. We employ the static and dynamic treatment of local correlation in form of density functional theory + $U$ (DFT+$U$) and + dynamical mean-field theory (DFT+DMFT). Our results capture the experimentally observed crystal structures and identify the unsaturated Pb $6s$ - O $2p$ bonds as the driving force beyond the complex physics of PbCoO$_3$. We provide a geometrical analysis of the structural distortions and we discuss their implications, in particular, the internal doping, which triggers transition between phases with and without local moments and a site selective Mott transition in the low-pressure phase.
- Published
- 2021
- Full Text
- View/download PDF
17. Application of precision agriculture technologies in Central Europe-review
- Author
-
Bojana Petrović, Roman Bumbálek, Tomáš Zoubek, Radim Kuneš, Luboš Smutný, and Petr Bartoš
- Subjects
Smart technologies ,Precision agriculture adoption ,Technology adoption ,Agriculture (General) ,S1-972 ,Nutrition. Foods and food supply ,TX341-641 - Abstract
Precision agriculture (PA) relies on a large amount of precise data about a given area and allows that data to be used in accordance with agronomic practices. It offers farmers greater control over existing processes, from crop placement to soil conditions to chemical use. On the other hand, applying precision livestock solutions to these expanding systems is a way to bring animals closer to producers and minimize waste and costs. In Europe, precision agriculture has emerged as a new way to help farmers increase the quantity and quality of agricultural production while using fewer inputs. The spatial and temporal variability in the application of PA and the implications of site-specific application are documented in this article. The objective of this review article is to provide an overview of the application of precision agriculture in Central European countries (Poland, Czech Republic, Austria, Slovakia, Slovenia, Germany, and Hungary) identified through a systematic literature review (SLR). The analyses revealed that with the rapid development of automation in agriculture, the demand for skilled workers will continue to increase and technology will continue to open up new application areas as well as the development of new AgriTech startups in the future. Currently, there are farmers in Germany and the Czech Republic who are leaders in the use of these technologies. However, the application of precision agriculture requires further research to provide more accurate information and is an area that is constantly evolving.
- Published
- 2024
- Full Text
- View/download PDF
18. Pressure-induced excitations in the out-of-plane optical response of the nodal-line semimetal ZrSiS
- Author
-
Ebad-Allah, J., Rojewski, S., Vöst, M., Eickerling, G., Scherer, W., Uykur, E., Sankar, Raman, Varrassi, L., Franchini, C., Ahn, K., Kuneš, J., and Kuntscher, C. A.
- Subjects
Condensed Matter - Materials Science - Abstract
The anisotropic optical response of the layered, nodal-line semimetal ZrSiS at ambient and high pressure is investigated by frequency-dependent reflectivity measurements for the polarization along and perpendicular to the layers. The highly anisotropic optical conductivity is in very good agreement with results from density functional theory calculations and confirms the anisotropic character of ZrSiS. Whereas the in-plane optical conductivity shows only modest pressure-induced changes, we found strong effects on the out-of-plane optical conductivity spectrum of ZrSiS, with the appearance of two prominent excitations. These pronounced pressure-induced effects can neither be attributed to a structural phase transition according to our single-crystal x-ray diffraction measurements, nor can they be explained by electronic correlation and electron-hole pairing effects, as revealed by theoretical calculations. Our findings are discussed in the context of the recently proposed excitonic insulator phase in ZrSiS., Comment: 6 pages, 3 figures, accepted for publication in Phys. Rev. Lett
- Published
- 2021
- Full Text
- View/download PDF
19. Antiferromagnetic magnons and local anisotropy: dynamical mean-field study
- Author
-
Niyazi, A., Geffroy, D., and Kunes, J.
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Statistical Mechanics - Abstract
We present a dynamical mean-field study of antiferromagnetic magnons in one-, two- and three-orbital Hubbard model of square and bcc cubic lattice at intermediate coupling strength. Weinvestigate the effect of anisotropy introduced by an external magnetic field or single-ion anisotropy.For the latter we tune continuously between the easy-axis and easy-plane models. We also analyzea model with spin-orbit coupling in cubic site-symmetry setting. The ordered states as well as themagnetic excitations are sensitive to even a small breaking ofSU(2)symmetry of the model andfollow the expectations of spin-wave theory as well as general symmetry considerations., Comment: 8 pages, 6 figures
- Published
- 2021
- Full Text
- View/download PDF
20. Core-Level X-Ray Spectroscopy of Infinite-Layer Nickelate: LDA+DMFT Study
- Author
-
Higashi, Keisuke, Winder, Mathias, Kuneš, Jan, and Hariki, Atsushi
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science - Abstract
Motivated by recent core-level x-ray photoemission spectroscopy (XPS), x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS) experiments for the newly-discovered superconducting infinite-layer nickelate, we investigate the core-level spectra of the parent compounds NdNiO$_2$ and LaNiO$_2$ using the combination of local density approximation and dynamical mean-field theory (LDA+DMFT). Adjusting a charge-transfer energy to match the experimental spectra, we determine the optimal model parameters and discuss the nature of the NdNiO$_2$ ground state. We find that self-doping from the Nd 5$d$ states in the vicinity of the Fermi energy prohibits opening of Mott-Hubbard gap in NdNiO$_2$. The present Ni $L_3$ XAS and RIXS calculation for LaNiO$_2$ cannot explain the difference to NdNiO$_2$ spectra.
- Published
- 2021
- Full Text
- View/download PDF
21. Silvicultural potential of the main introduced tree species in the Czech Republic – review
- Author
-
Novotný Stanislav, Gallo Josef, Baláš Martin, Kuneš Ivan, Fuchs Zdeněk, and Brabec Pavel
- Subjects
climatic change ,forest restoration ,assisted migration ,forest productivity ,stability and vitality ,Forestry ,SD1-669.5 - Abstract
Only 1.82% of the Czech forests are covered by the introduced (exotic, non-native) tree species, they represent only a very minor part of the forest area in the Czech Republic. Despite this fact under certain circumstances and locally, they can play an important role in the forest restoration of declined forests. The main non-native tree species used in the Czech Republic are: black locust (Robinia pseudoacacia L.), Douglas-fir (Pseudotsuga menziesii [Mirbel] Franco), grand fir (Abies grandis [Douglas ex D. Don] Lindl.), black walnut (Juglans nigra L.), northern red oak (Quercus rubra L.), and blue spruce (Picea pungens Engelm.). Other tree species are cultivated on very small areas, despite their much larger potential. The aim of the presented review paper is to summarize information on the introduced tree species, available especially from national sources, and give comprehensive information concerning the potential and risk of their use in the conditions of the Czech Republic. The authors mention also other tree species eligible for silviculture under current as well as future climatic circumstances. The current area and silvicultural potential in the climate changing conditions are analysed and summarized.
- Published
- 2023
- Full Text
- View/download PDF
22. Kondo quasiparticle dynamics observed by resonant inelastic x-ray scattering
- Author
-
Rahn, MC, Kummer, K, Hariki, A, Ahn, K-H, Kuneš, J, Amorese, A, Denlinger, JD, Lu, D-H, Hashimoto, M, Rienks, E, Valvidares, M, Haslbeck, F, Byler, DD, McClellan, KJ, Bauer, ED, Zhu, JX, Booth, CH, Christianson, AD, Lawrence, JM, Ronning, F, and Janoschek, M
- Subjects
Chemical Sciences ,Physical Sciences ,Condensed Matter Physics - Abstract
Effective models focused on pertinent low-energy degrees of freedom have substantially contributed to our qualitative understanding of quantum materials. An iconic example, the Kondo model, was key to demonstrating that the rich phase diagrams of correlated metals originate from the interplay of localized and itinerant electrons. Modern electronic structure calculations suggest that to achieve quantitative material-specific models, accurate consideration of the crystal field and spin-orbit interactions is imperative. This poses the question of how local high-energy degrees of freedom become incorporated into a collective electronic state. Here, we use resonant inelastic x-ray scattering (RIXS) on CePd3 to clarify the fate of all relevant energy scales. We find that even spin-orbit excited states acquire pronounced momentum-dependence at low temperature-the telltale sign of hybridization with the underlying metallic state. Our results demonstrate how localized electronic degrees of freedom endow correlated metals with new properties, which is critical for a microscopic understanding of superconducting, electronic nematic, and topological states.
- Published
- 2022
23. Quantifying the U 5f covalence and degree of localization in U intermetallics
- Author
-
Andrea Marino, Denise S. Christovam, Daisuke Takegami, Johannes Falke, Miguel M. F. Carvalho, Takaki Okauchi, Chun-Fu Chang, Simone G. Altendorf, Andrea Amorese, Martin Sundermann, Andrei Gloskovskii, Hlynur Gretarsson, Bernhard Keimer, Alexandr V. Andreev, Ladislav Havela, Andreas Leithe-Jasper, Andrea Severing, Jan Kuneš, Liu Hao Tjeng, and Atsushi Hariki
- Subjects
Physics ,QC1-999 - Abstract
A procedure for quantifying the U 5f electronic covalency and degree of localization in U intermetallic compounds is presented. To this end, bulk sensitive hard and soft x-ray photoelectron spectroscopy were utilized in combination with density-functional theory (DFT) plus dynamical mean-field theory (DMFT) calculations. The energy dependence of the photoionization cross sections allows the disentanglement of the U 5f contribution to the valence band from the various other atomic subshells so the computational parameters in the DFT+DMFT can be reliably determined. Applying this method to UGa_{2} and UB_{2} as model compounds from opposite ends of the (de)localization range, we have achieved excellent simulations of the valence band and core-level spectra. The width in the distribution of atomic U 5f configurations contributing to the ground state, as obtained from the calculations, quantifies the correlated nature and degree of localization of the U 5f. The findings permit answering the longstanding question why different spectroscopic techniques give seemingly different numbers for the U 5f valence in intermetallic U compounds.
- Published
- 2024
- Full Text
- View/download PDF
24. Dynamical response and competing orders in two-band Hubbard model
- Author
-
Niyazi, A., Geffroy, D., and Kuneš, J.
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Quantum Physics - Abstract
We present a dynamical mean-field study of two-particle dynamical response functions in two-band Hubbard model across several phase transitions. We observe that the transition between theexcitonic condensate and spin-state ordered state is continuous with a narrow strip of supersolidphase separating the two. Approaching transition from the excitonic condensate is announced bysoftening of the excitonic mode at theMpoint of the Brillouin zone. Inside the spin-state orderedphase there is a magnetically ordered state with 2x2 periodicity, which has no precursor in thenormal phase., Comment: 8 pages, 9 figures
- Published
- 2020
- Full Text
- View/download PDF
25. X-ray spectroscopy of rare-earth nickelate LuNiO$_3$: LDA+DMFT study
- Author
-
Winder, Mathias, Hariki, Atsushi, and Kuneš, Jan
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science - Abstract
We present a computational study of resonant inelastic x-ray scattering (RIXS) and x-ray absorption in a representative rare-earth nickelate LuNiO$_3$. We study the changes in the spectra across the metal-insulator/site-disproportionation transition. In particular, we address the question of site-selectivity of the two methods in the disproportionated insulating phase and the signature of metal-insulator transition in the fluorescence-like feature of the RIXS spectra. To this end we use the local density approximation + dynamical mean-field theory (LDA+DMFT) approach combined with configuration integration method to compute the core-level spectra.
- Published
- 2020
- Full Text
- View/download PDF
26. Ferromagnetism of LaCoO$_3$ films
- Author
-
Sotnikov, Andrii, Ahn, Kyo-Hoon, and Kuneš, Jan
- Subjects
Condensed Matter - Strongly Correlated Electrons - Abstract
We study ferromagnetic ordering and microscopic inhomogeneity in tensile strained LaCoO$_3$ using numerical simulations. We argue that both phenomena originate from effective superexchange interactions between atoms in the high-spin (HS) state mediated by the intermediate-spin excitations. We derive a model of the HS excitation as a bare atomic state dressed by electron and electron-hole fluctuations on the neighbor atoms. We construct a series of approximations to account for electron correlation effects responsible for HS fluctuations and magnetic exchange. The obtained amplitudes and directional dependence of magnetic couplings between the "dressed" HS states show a qualitative agreement with experimental observations and provide a new physical picture of LaCoO$_3$ films., Comment: 23 pages, 9 figures, Submission to SciPost
- Published
- 2020
- Full Text
- View/download PDF
27. Lipidization as a tool toward peptide therapeutics
- Author
-
Aneta Myšková, David Sýkora, Jaroslav Kuneš, and Lenka Maletínská
- Subjects
Peptide therapeutics ,structure modification ,lipidization ,therapeutic lipopeptides ,Therapeutics. Pharmacology ,RM1-950 - Abstract
AbstractPeptides, as potential therapeutics continue to gain importance in the search for active substances for the treatment of numerous human diseases, some of which are, to this day, incurable. As potential therapeutic drugs, peptides have many favorable chemical and pharmacological properties, starting with their great diversity, through their high affinity for binding to all sort of natural receptors, and ending with the various pathways of their breakdown, which produces nothing but amino acids that are nontoxic to the body. Despite these and other advantages, however, they also have their pitfalls. One of these disadvantages is the very low stability of natural peptides. They have a short half-life and tend to be cleared from the organism very quickly. Their instability in the gastrointestinal tract, makes it impossible to administer peptidic drugs orally. To achieve the best pharmacologic effect, it is desirable to look for ways of modifying peptides that enable the use of these substances as pharmaceuticals. There are many ways to modify peptides. Herein we summarize the approaches that are currently in use, including lipidization, PEGylation, glycosylation and others, focusing on lipidization. We describe how individual types of lipidization are achieved and describe their advantages and drawbacks. Peptide modifications are performed with the goal of reaching a longer half-life, reducing immunogenicity and improving bioavailability. In the case of neuropeptides, lipidization aids their activity in the central nervous system after the peripheral administration. At the end of our review, we summarize all lipidized peptide-based drugs that are currently on the market.
- Published
- 2023
- Full Text
- View/download PDF
28. Damping of spinful excitons in LaCoO$_3$ by thermal fluctuations: Theory and experiment
- Author
-
Hariki, Atsushi, Wang, Ru-Pan, Sotnikov, Andrii, Tomiyasu, Keisuke, Betto, Davide, Brookes, Nicholas B., Uemura, Yohei, Ghiasi, Mahnaz, de Groot, Frank M. F., and Kuneš, Jan
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science - Abstract
We present Co $L_3$-edge resonant inelastic x-ray scattering (RIXS) of bulk LaCoO$_3$ across the thermally-induced spin-state crossover around 100~K. Owing to a high energy resolution of 25~meV, we observe unambiguously the dispersion of the intermediate-spin (IS) excitations in the low temperature regime. Approaching the intermediate temperature regime, the IS excitations are damped and the bandwidth is reduced. The observed behavior can be well described by a model of mobile IS excitons with strong attractive interaction, which we solve using dynamical mean-field theory for hard-core bosons. Our results provide a detailed mechanism of how high-spin (HS) and IS excitations interact to establish the physical properties of cobaltite perovskites.
- Published
- 2019
- Full Text
- View/download PDF
29. LDA+DMFT approach to resonant inelastic x-ray scattering in correlated materials
- Author
-
Hariki, Atsushi, Winder, Mathias, Uozumi, Takayuki, and Kuneš, Jan
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science - Abstract
We present a computational study of $L$-edge resonant inelastic x-ray scattering (RIXS) in correlated 3$d$ transition-metal oxides using an $ab$ $initio$ method based on local density approximation + dynamical mean-field theory (DMFT). The present method, building on Anderson impurity model with an optimized continuum bath within DMFT, is an extension of the cluster model to include unbound electron-hole pair excitations as well as material-specific charge-transfer excitations with less empirical parameters. We find a good agreement with available experimental data. The relationship between correlated bands and fluorescence-like feature in the RIXS spectra is discussed.
- Published
- 2019
- Full Text
- View/download PDF
30. Prediction Focused Topic Models for Electronic Health Records
- Author
-
Ren, Jason, Kunes, Russell, and Doshi-Velez, Finale
- Subjects
Computer Science - Machine Learning ,Statistics - Machine Learning - Abstract
Electronic Health Record (EHR) data can be represented as discrete counts over a high dimensional set of possible procedures, diagnoses, and medications. Supervised topic models present an attractive option for incorporating EHR data as features into a prediction problem: given a patient's record, we estimate a set of latent factors that are predictive of the response variable. However, existing methods for supervised topic modeling struggle to balance prediction quality and coherence of the latent factors. We introduce a novel approach, the prediction-focused topic model, that uses the supervisory signal to retain only features that improve, or do not hinder, prediction performance. By removing features with irrelevant signal, the topic model is able to learn task-relevant, interpretable topics. We demonstrate on a EHR dataset and a movie review dataset that compared to existing approaches, prediction-focused topic models are able to learn much more coherent topics while maintaining competitive predictions., Comment: Machine Learning for Health (ML4H) at NeurIPS 2019 - Extended Abstract. arXiv admin note: substantial text overlap with arXiv:1910.05495
- Published
- 2019
31. Possibilities for dealing with large litters of piglets
- Author
-
Ivan Řezáč, Naděžda Kernerová, Michal Komosný, Radim Kuneš, Nikola Havrdová, Anna Poborská, Denisa Polívková, Martin Kantor, and Luboš Zábranský
- Subjects
piglet ,milk feed mixture ,milk substitute ,nurse sow ,Agriculture - Abstract
The aim of the first experiment was to verify the effectiveness and profitability of providing supplemental feed to piglets. The milk feed mixture of two producers (MFM-1 vs MFM-2) were evaluated (served ad libitum). All piglets were suckled and were fed with the pre-starter feed mixture from the 5th day until the weaning stage. The control group without milk supplements has shown a higher piglet mortality and worse body condition of sows. The usage of milk supplements led to the elimination of the sow body condition loss during the suckling period and reduced feed mixture consumption in sows (P
- Published
- 2023
- Full Text
- View/download PDF
32. Design of semisynthetic derivatives of the Amaryllidaceae alkaloid ambelline and exploration of their in vitro cytotoxic activities
- Author
-
Aneta Ritomská, Darja Koutova, Jana Křoustková, Karel Královec, Darina Muthná, Jiří Kuneš, Lucie Nováková, Radim Havelek, and Lucie Cahlíková
- Subjects
Ambelline ,Amaryllidaceae alkaloids ,Antiproliferative activity ,11-O-(4-Chloro-3-nitrobenzoyl)ambelline ,Cytotoxicity ,In vitro ,Therapeutics. Pharmacology ,RM1-950 - Abstract
Ambelline, an alkaloid from the Amaryllidaceae family with a crinane-type skeleton, has not yet demonstrated any outstanding biological activity. However, its analogues prepared by derivatization of the C-11 hydroxyl group show different interesting effects. Continuing our earlier work, twelve novel aromatic esters were developed (10, 14, 16, 17, 22–25, 30–33) and studied, together with previously synthesized derivatives (2–9, 11–13, 15, 18–21, 26–29) in terms of their cytotoxic activity. The cytotoxic potential was determined on a panel of nine human cancer cell lines and one noncancerous cell line to characterize their biological activity spectrum. To describe and foresee the structure–activity relationship for further research, substances synthesized and described in our previous work were also included in this cytotoxicity study. The most significant activity was associated with analogues having methyl (10), methoxy (14–17), or ethoxy (18) substitution on the phenyl condensed to ambelline. However, the 4-chloro-3-nitrobenzoyl derivative (32) showed the most promising IC50 values, ranging from 0.6 ± 0.1 µM to 9.9 ± 0.2 µM. In vitro cytotoxicity studies indicated the most potent antiproliferative activity of 32 in a dose-dependent and time-dependent manner. Besides, 32 was found to be effective in decreasing viability and triggering apoptosis of MOLT-4 T-lymphoblastic leukemia cells.
- Published
- 2023
- Full Text
- View/download PDF
33. Prediction Focused Topic Models via Feature Selection
- Author
-
Ren, Jason, Kunes, Russell, and Doshi-Velez, Finale
- Subjects
Computer Science - Machine Learning ,Computer Science - Computation and Language ,Statistics - Machine Learning - Abstract
Supervised topic models are often sought to balance prediction quality and interpretability. However, when models are (inevitably) misspecified, standard approaches rarely deliver on both. We introduce a novel approach, the prediction-focused topic model, that uses the supervisory signal to retain only vocabulary terms that improve, or at least do not hinder, prediction performance. By removing terms with irrelevant signal, the topic model is able to learn task-relevant, coherent topics. We demonstrate on several data sets that compared to existing approaches, prediction-focused topic models learn much more coherent topics while maintaining competitive predictions., Comment: AISTATS 2020. arXiv admin note: substantial text overlap with arXiv:1911.08551
- Published
- 2019
34. Metal-insulator transition in CaCu$_3$Fe$_4$O$_{12}$
- Author
-
Hariki, Atsushi, Yamaguchi, Tatsuya, Winder, Mathias, and Kuneš, Jan
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science - Abstract
We study structurally-triggered metal-insulator transition in CaCu$_3$Fe$_4$O$_{12}$ by means of local density approximation (LDA) +$U$ and LDA+dynamical mean-field theory (DMFT). The ferrimagnetic insulating phase is essentially the same within both approaches. While LDA+$U$ describes the metal-insulator transition as a Peierls-like instability driven by Fermi surface nesting in the magnetically ordered phase, LDA+DMFT allows also the site-selective Mott transition without magnetic ordering as well as smooth crossover between the two pictures. We point out similarities and differences to rare-earth nickelates.
- Published
- 2019
- Full Text
- View/download PDF
35. Sparse sampling and tensor network representation of two-particle Green's functions
- Author
-
Shinaoka, Hiroshi, Geffroy, Dominique, Wallerberger, Markus, Otsuki, Junya, Yoshimi, Kazuyoshi, Gull, Emanuel, and Kuneš, Jan
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Physics - Computational Physics - Abstract
Many-body calculations at the two-particle level require a compact representation of two-particle Green's functions. In this paper, we introduce a sparse sampling scheme in the Matsubara frequency domain as well as a tensor network representation for two-particle Green's functions. The sparse sampling is based on the intermediate representation basis and allows an accurate extraction of the generalized susceptibility from a reduced set of Matsubara frequencies. The tensor network representation provides a system independent way to compress the information carried by two-particle Green's functions. We demonstrate efficiency of the present scheme for calculations of static and dynamic susceptibilities in single- and two-band Hubbard models in the framework of dynamical mean-field theory., Comment: 27 pages in single column format, 12 pages (added missing references)
- Published
- 2019
- Full Text
- View/download PDF
36. Pressure-induced spin-state ordering in Sr$_2$CoO$_3$F
- Author
-
Afonso, Juan Fernández, Sotnikov, Andrii, Hariki, Atsushi, and Kuneš, Jan
- Subjects
Condensed Matter - Strongly Correlated Electrons - Abstract
We study theoretically low-temperature phases of a recently synthesized compound Sr$_2$CoO$_3$F under pressure. The analysis combining LDA+DMFT and a strong-coupling effective model points to the existence of not only normal paramagnetic and antiferromagnetic regimes, but also a spin-state ordered phase in a certain range of applied pressure and low temperature. This order is characterized by a checkerboard arrangement of different spin states of cobalt atoms in the lattice., Comment: 7 pages, 7 figures
- Published
- 2019
- Full Text
- View/download PDF
37. Antiferromagnetism in RuO$_2$ as $d$-wave Pomeranchuk instability
- Author
-
Ahn, Kyo-Hoon, Hariki, Atsushi, Lee, Kwan-Woo, and Kuneš, Jan
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science - Abstract
We present a computational study of antiferromagnetic transition in RuO$_2$. The rutile structure with the magnetic sublattices coupled by $\pi/2$-rotation leads to a spin-polarized band structure in the antiferromagnetic state, which gives rise to a $d$-wave modulation of the Fermi surface in the spin-triplet channel. We argue a finite spin conductivity that changes sign in the $ab$ plane is expected RuO$_2$ because of this band structure. We analyze the origin of the antiferromagnetic instability and link it to presence of a nodal line close to the Fermi level., Comment: 5 pages, 5 figures
- Published
- 2019
- Full Text
- View/download PDF
38. Chemical pressure effect on the optical conductivity of the nodal-line semimetals ZrSi$Y$ ($Y$=S, Se, Te) and ZrGe$Y$ ($Y$=S, Te)
- Author
-
Ebad-Allah, J., Afonso, J. Fernández, Krottenmüller, M., Hu, J., Zhu, Y. L., Mao, Z., Kuneš, J., and Kuntscher, C. A.
- Subjects
Condensed Matter - Materials Science ,Condensed Matter - Strongly Correlated Electrons - Abstract
ZrSiS is a nodal-line semimetal, whose electronic band structure contains a diamond-shaped line of Dirac nodes. We carried out a comparative study on the optical conductivity of ZrSiS and related compounds ZrSiSe, ZrSiTe, ZrGeS, and ZrGeTe by reflectivity measurements over a broad frequency range combined with density functional theory calculations. The optical conductivity exhibits a distinct U shape, ending at a sharp peak at around 10000~cm$^{-1}$ for all studied compounds, except for ZrSiTe. The U shape of the optical conductivity is due to transitions between the linearly dispersing bands crossing each other along the nodal line. The sharp high-energy peak is related to transitions between almost parallel bands, and its energy position depends on the interlayer bonding correlated with the $c$/$a$ ratio, which can be tuned by either chemical or external pressure. For ZrSiTe, another pair of crossing bands appears in the vicinity of the Fermi level, corrugating the nodal-line electronic structure and leading to the observed difference in optical conductivity. The findings suggest that the Dirac physics in Zr$XY$ compounds with $X$=Si, Ge and $Y$=S, Se, Te is closely connected to the interlayer bonding., Comment: 9 pages, 6 figures
- Published
- 2019
- Full Text
- View/download PDF
39. Charge-transfer effect in hard x-ray 1$s$ and 2$p$ photoemission spectra: LDA+DMFT and cluster-model analysis
- Author
-
Ghiasi, Mahnaz, Hariki, Atsushi, Winder, Mathias, Kuneš, Jan, Regoutz, Anna, Lee, Tien-Lin, Hu, Yongfeng, Rueff, Jean-Pascal, and de Groot, Frank M. F.
- Subjects
Condensed Matter - Materials Science ,Condensed Matter - Strongly Correlated Electrons - Abstract
We study $1s$ and $2p$ hard x-ray photoemission spectra (XPS) in a series of late transition metal oxides: Fe$_2$O$_3$ (3$d^{5}$), FeTiO$_3$ (3$d^{6}$), CoO (3$d^{7}$) and NiO (3$d^{8}$). The experimental spectra are analyzed with two theoretical approaches: the MO$_6$ cluster model and the local density approximation (LDA) + dynamical mean-field theory (DMFT). Owing to the absence of the core-valence multiplets and spin-orbit coupling, 1$s$ XPS is found to be a sensitive probe of chemical bonding and nonlocal charge-transfer screening, providing complementary information to 2$p$ XPS. The 1$s$ XPS spectra are used to assess the accuracy of the $ab$-initio LDA+DMFT approach, developed recently to study the material-specific charge-transfer effects in core-level XPS.
- Published
- 2018
- Full Text
- View/download PDF
40. Kondo quasiparticle dynamics observed by resonant inelastic x-ray scattering
- Author
-
M. C. Rahn, K. Kummer, A. Hariki, K.-H. Ahn, J. Kuneš, A. Amorese, J. D. Denlinger, D.-H. Lu, M. Hashimoto, E. Rienks, M. Valvidares, F. Haslbeck, D. D. Byler, K. J. McClellan, E. D. Bauer, J. X. Zhu, C. H. Booth, A. D. Christianson, J. M. Lawrence, F. Ronning, and M. Janoschek
- Subjects
Science - Abstract
The fate of high-energy degrees of freedom, such as spin-orbit interactions, in the coherent state of Kondo lattice materials remains unclear. Here, the authors use resonant inelastic x-ray scattering in CePd3 to show how Kondo-quasiparticle excitations are renormalized and develop a pronounced momentum dependence, while maintaining a largely unchanged spin-orbit gap.
- Published
- 2022
- Full Text
- View/download PDF
41. Spatial scaling of pollen-plant diversity relationship in landscapes with contrasting diversity patterns
- Author
-
Vojtěch Abraham, Petr Kuneš, Ondřej Vild, Eva Jamrichová, Zuzana Plesková, Barbora Werchan, Helena Svitavská-Svobodová, and Jan Roleček
- Subjects
Medicine ,Science - Abstract
Abstract Mitigating the effects of global change on biodiversity requires its understanding in the past. The main proxy of plant diversity, fossil pollen record, has a complex relationship to surrounding vegetation and unknown spatial scale. We explored both using modern pollen spectra in species-rich and species-poor regions in temperate Central Europe. We also considered the biasing effects of the trees by using sites in forests and open habitats in each region. Pollen samples were collected from moss polsters at 60 sites and plant species were recorded along two 1 km-transects at each site. We found a significant positive correlation between pollen and plant richness (alpha diversity) in both complete datasets and for both subsets from open habitats. Pollen richness in forest datasets is not significantly related to floristic data due to canopy interception of pollen rather than to pollen productivity. Variances (beta diversity) of the six pollen and floristic datasets are strongly correlated. The source area of pollen richness is determined by the number of species appearing with increasing distance, which aggregates information on diversity of individual patches within the landscape mosaic and on their compositional similarity. Our results validate pollen as a reconstruction tool for plant diversity in the past.
- Published
- 2022
- Full Text
- View/download PDF
42. Collective Modes in Excitonic Magnets: Dynamical Mean-Field Study
- Author
-
Geffroy, D., Kaufmann, J., Hariki, A., Gunacker, P., Hausoel, A., and Kunes, J.
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Statistical Mechanics ,Physics - Computational Physics - Abstract
We present a dynamical mean-field study of dynamical susceptibilities in two-band Hubbard model. Varying the model parameters we analyze the two-particle excitations in the normal as well as in the ordered phase, an excitonic condensate. The two-particle DMFT spectra in the ordered phase reveal the gapless Goldstone modes arising from spontaneous breaking of continuous symmetries. We also observe gapped Higgs mode, characterized by vanishing of the gap at the phase boundary. Qualitative changes observed in the spin susceptibility can be used as an experimental probe to identify the excitonic condensation., Comment: published version
- Published
- 2018
- Full Text
- View/download PDF
43. Continuum Charge Excitations in High-Valence Transition-Metal Oxides Revealed by Resonant Inelastic X-ray Scattering
- Author
-
Hariki, Atsushi, Winder, Mathias, and Kuneš, Jan
- Subjects
Condensed Matter - Strongly Correlated Electrons - Abstract
We present a theoretical investigation of the origin of Raman-like and fluorescencelike (FL) features of resonant inelastic x-ray scattering (RIXS) spectra. Using a combination of local-density approximation + dynamical mean-field theory and a configuration interaction solver for Anderson impurity model, we calculate the $L$-edge RIXS and x-ray absorption spectra of high-valence transition-metal oxides LaCuO$_3$ and NaCuO$_2$. We analyze in detail the behavior of the FL feature and show how it is connected to the details of electronic and crystal structure. On the studied compounds we demonstrate how material details determine whether the electron-hole continuum can be excited in the $L$-edge RIXS process.
- Published
- 2018
- Full Text
- View/download PDF
44. Suppression and revival of long-range ferromagnetic order in the multiorbital Fermi-Hubbard model
- Author
-
Sotnikov, Andrii, Cichy, Agnieszka, and Kuneš, Jan
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Quantum Gases - Abstract
By means of dynamical mean-field theory allowing for complete account of SU(2) rotational symmetry of interactions between spin-1/2 particles, we observe a strong effect of suppression of ferromagnetic order in the multiorbital Fermi-Hubbard model in comparison with a widely used restriction to density-density interactions. In the case of orbital degeneracy, we show that the suppression effect is the strongest in the two-orbital model (with effective spin $S_{\rm eff}=1$) and significantly decreases when considering three orbitals ($S_{\rm eff}=3/2$), thus magnetic ordering can effectively revive for the same range of parameters, in agreement with arguments based on vanishing of quantum fluctuations in the limit of classical spins ($S_{\rm eff}\to\infty$). We analyze a connection to the double-exchange model and observe high importance of spin-flip processes there as well., Comment: 7 pages, 6 figures, final version
- Published
- 2018
- Full Text
- View/download PDF
45. Excitonic magnet in external field: complex order parameter and spin currents
- Author
-
Geffroy, D., Hariki, A., and Kunes, J.
- Subjects
Condensed Matter - Strongly Correlated Electrons - Abstract
We investigate spin-triplet exciton condensation in the two-orbital Hubbard model close to half filling by means of dynamical mean-field theory. Employing an impurity solver that handles complex off-diagonal hybridization functions, we study the behavior of excitonic condensate in stoichiometric and doped systems subject to external magnetic field. We find a general tendency of the triplet order parameter to lay perpendicular with the applied field and identify exceptions from this rule. For solutions exhibiting k-odd spin textures, we discuss the Bloch theorem which, in the absence of spin-orbit coupling, forbids the appearance of spontaneous net spin current. We demonstrate that the Bloch theorem is not obeyed by the dynamical mean-field theory., Comment: 10 pages, 10 figures
- Published
- 2018
- Full Text
- View/download PDF
46. Excitonic dispersion of the intermediate-spin state in LaCoO$_3$ revealed by resonant inelastic X-ray scattering
- Author
-
Wang, Ru-Pan, Hariki, Atsushi, Sotnikov, Andrii, Frati, Federica, Okamoto, Jun, Huang, Hsiao-Yu, Singh, Amol, Huang, Di-Jing, Tomiyasu, Keisuke, Du, Chao-Hung, Kuneš, Jan, and de Groot, Frank M. F.
- Subjects
Condensed Matter - Strongly Correlated Electrons - Abstract
More than 50 years ago the electron-hole attraction was proposed to drive narrow gap semiconductors or semimetals to a new phase, the excitonic insulator. The experimental proof of its existence in bulk materials remains elusive. In strongly correlated insulators, the proximity of the excitonic insulator phase is reflected by the presence of dispersive electron-hole excitations with a small gap above a singlet ground state. Recently, such an excitation spectrum was proposed to be realized in perovskite oxide LaCoO$_3$. In this Letter we use Co $L_3$-edge resonant inelastic X-ray scattering to put this proposal to experimental test.
- Published
- 2017
- Full Text
- View/download PDF
47. Theoretical investigation of excitonic magnetism in LaSrCoO$_{4}$
- Author
-
Afonso, J. Fernández, Sotnikov, A., and Kuneš, J.
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science - Abstract
We use the LDA+U approach to search for possible ordered ground states of LaSrCoO$_4$. We find a staggered arrangement of magnetic multipoles to be stable over a broad range of Co $3d$ interaction parameters. This ordered state can be described as a spin-denity-wave-type condensate of $d_{xy} \otimes d_{x^2-y^2}$ excitons carrying spin $S=1$. Further, we construct an effective strong-coupling model, calculate the exciton dispersion and investigate closing of the exciton gap, which marks the exciton condensation instability. Comparing the layered LaSrCoO$_4$ with its pseudo cubic analog LaCoO$_3$, we find that for the same interaction parameters the excitonic gap is smaller (possibly vanishing) in the layered cobaltite., Comment: 6 pages, 6 figures
- Published
- 2017
- Full Text
- View/download PDF
48. Palmitoylated prolactin-releasing peptide treatment had neuroprotective but not anti-obesity effect in fa/fa rats with leptin signaling disturbances
- Author
-
Lucia Mráziková, Silvie Hojná, Andrea Pačesová, Lucie Hrubá, Veronika Strnadová, Barbora Neprašová, Blanka Železná, Jaroslav Kuneš, and Lenka Maletínská
- Subjects
Nutritional diseases. Deficiency diseases ,RC620-627 - Abstract
Abstract Background/Objective Anorexigenic palmitoylated prolactin-releasing peptide (palm11-PrRP) is able to act centrally after peripheral administration in rat and mouse models of obesity, type 2 diabetes mellitus and/or neurodegeneration. Functional leptin and intact leptin signaling pathways are necessary for the body weight reducing and glucose tolerance improving effect of palm11-PrRP. We have previously shown that palm11-PrRP31 had glucose-lowering properties but not anti-obesity effect in Koletsky rats with leptin signaling disturbances, so improvements in glucose metabolism appear to be completely independent of leptin signaling. The purpose of this study was to describe relationship between metabolic and neurodegenerative pathologies and explore if palm11-PrRP31 could ameliorate them in obese fa/fa rat model with leptin signaling disruption. Subject/Methods The fa/fa rats and their age-matched lean controls at the age 32 weeks were used for this study. The rats were infused for 2 months with saline or palm11-PrRP31 (n = 7–8 per group) at a dose of 5 mg/kg per day using Alzet osmotic pumps. During the dosing period food intake and body weight were monitored. At the end of experiment the oral glucose tolerance test was performed; plasma and tissue samples were collected and arterial blood pressure was measured. Then, markers of leptin and insulin signaling, Tau phosphorylation, neuroinflammation, and synaptogenesis were measured by western blotting and immunohistochemistry. Results Fa/fa rats developed obesity, mild glucose intolerance, and peripheral insulin resistance but not hypertension while palm11-PrRP31 treatment neither lowered body weight nor attenuated glucose tolerance but ameliorated leptin and insulin signaling and synaptogenesis in hippocampus. Conclusion We demonstrated that palm11-PrRP31 had neuroprotective features without anti-obesity and glucose lowering effects in fa/fa rats. This data suggest that this analog has the potential to exert neuroprotective effect despite of leptin signaling disturbances in this rat model.
- Published
- 2022
- Full Text
- View/download PDF
49. Palmitoylated prolactin-releasing peptide treatment had neuroprotective but not anti-obesity effect in fa/fa rats with leptin signaling disturbances
- Author
-
Mráziková, Lucia, Hojná, Silvie, Pačesová, Andrea, Hrubá, Lucie, Strnadová, Veronika, Neprašová, Barbora, Železná, Blanka, Kuneš, Jaroslav, and Maletínská, Lenka
- Published
- 2022
- Full Text
- View/download PDF
50. Spatial scaling of pollen-plant diversity relationship in landscapes with contrasting diversity patterns
- Author
-
Abraham, Vojtěch, Kuneš, Petr, Vild, Ondřej, Jamrichová, Eva, Plesková, Zuzana, Werchan, Barbora, Svitavská-Svobodová, Helena, and Roleček, Jan
- Published
- 2022
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.