Novel electronic states close to Mott transition in low-dimensional and frustrated systems

Recent studies demonstrated that there may appear different novel states in correlated systems close to localized-itinerant crossover. Especially favourable conditions for that are met in low-dimensional and in frustrated systems. In this paper I discuss on concrete examples some of such novel states. In particular, for some spinels and triangular systems there appears a "partial Mott transition", in which first some finite clusters (dimers, trimes, tetramers, heptamers) go over to the itinerant regime, and the real bulk Mott transition occurs only later. Also some other specific possibilities in this crossover regime are shortly discussed, such as spin-Peierls-Peierls transition in TiOCl, spontaneous charge disproportionation in some cases, etc.Comment: To be published in Journal of Physics - Condensed Matter, conference serie

Subthreshold and near-threshold kaon and antikaon production in proton-nucleus reactions

The differential production cross sections of K^+ and K^- mesons have been measured at the ITEP proton synchrotron in p+Be, p+Cu collisions under lab angle of 10.5^0, respectively, at 1.7 and 2.25, 2.4 GeV beam energies. A detailed comparison of these data with the results of calculations within an appropriate folding model for incoherent primary proton-nucleon, secondary pion-nucleon kaon and antikaon production processes and processes associated with the creation of antikaons via the decay of intermediate phi mesons is given. We show that the strangeness exchange process YN->NNK^- gives a small contribution to the antikaon yield in the kinematics of the performed experiment. We argue that in the case when antikaon production processes are dominated by the channels with KK^- in the final state, the cross sections of the corresponding reactions are weakly influenced by the in-medium kaon and antikaon mean fields.Comment: 24 pages. accepted for publication at J.Phys.

Electrostriction measurements in gadolinium doped cerium oxide

The equipment of the Ural Center for Shared Use “Modern nanotechnology” UrFU was used. The research was made possible with the financial support of Russian Foundation for Basic Research grant (15-52-06006-MNTI_a)

Singlet-triplet excitations and high-field magnetization in CuTe2O5

By measuring the THz electron spin resonance (ESR) transmission spectra and high-field magnetization on the spin-gapped system CuTe$_2$O$_5$, we identified the singlet-triplet excitations in the dimerized non-magnetic ground state. The determined spin-gap value of $h\nu_0=4.94$ meV at the $\Gamma$ point ($\mathbf{Q}\simeq\mathbf{0}$) is significantly smaller than the strongest antiferromagnetic exchange interaction between the Cu ions predicted by theoretical investigations. We also observed the critical field $H_{c1}^{a^*}=37.6$ T for \textbf{H} $\bot$ \emph{bc}-plane and $H_{c1}^{bc}=40.6$ T for \textbf{H} $\|$ \emph{bc}-plane at the onset of non-zero magnetization, consistent with the gap value and corresponding anisotropic \emph{g}-factors determined previously. The observed singlet-triplet excitations in Faraday and Voigt configurations suggest a mixing of the singlet state with the $S_z=0$ triplet state and the $S_z=\pm 1$ triplet states, respectively, due to the Dzyaloshinskii-Moriya (DM) interaction with a DM vector perpendicular to the crystalline \emph{bc}-plane.Comment: 5 pages, 4 figure

Tunka Advanced Instrument for cosmic rays and Gamma Astronomy

The paper is a script of a lecture given at the ISAPP-Baikal summer school in 2018. The lecture gives an overview of the Tunka Advanced Instrument for cosmic rays and Gamma Astronomy (TAIGA) facility including historical introduction, description of existing and future setups, and outreach and open data activities.Comment: Lectures given at the ISAPP-Baikal Summer School 2018: Exploring the Universe through multiple messengers, 12-21 July 2018, Bol'shie Koty, Russi

Uncovering the origin of local electrochemical response in Ce1.9Gd0.1O2

Cerium oxide (CeO) has a wide range of different applications such as gas sensing, water splitting and others. CeO is an attractive alternative to yttria-stabilized zirconia as an electrolyte for low-temperature fuel cells because of its high ionic conductivity, low reactivity and good chemical compatibility with many mixed conducting cathode materials [1].The equipment of the Ural Center for Shared Use"Modern nanotechnology" UrFU was used. This research was made possible in part by RFBR (Grant No. 15-52-06006 MNTI_a). This work was supported by the Israeli Ministry of Science and Technology within the program of Israel Russian Federation Scientific Collaboration, Grant No. 12421-3. A.L.K. and A.T. acknowledge the CICECO– Aveiro Institute of Materials POCI-01-0145-FEDER-007679 (Ref. FCT UID /CTM /50011/2013), financed by national funds through the FCT/MEC and when applicable co- financed by FEDER under the PT2020 Partnership Agreement. This work has been supported in part by the Ministry of Education and Science of the Russian Federation under Project No. 3.9534.2017/BP

Silvanite AuAgTe4: a rare case of gold superconducting material

Gold is one of the most inert metals, forming very few compounds, some with rather interesting properties, and only a few of them are currently known to be superconducting under certain conditions. Compounds of another noble element, Ag, are also relatively rare, and very few of them are superconducting. Finding new superconducting materials containing gold (and silver) is a challenge - especially having in mind that the best high-Tc superconductors under normal conditions are based upon their rather close congener, Cu. Here we report combined X-ray diffraction, Raman, and resistivity measurements, as well as first-principles calculations, to explore the effect of hydrostatic pressure on the properties of the sylvanite mineral, AuAgTe4. Our experimental results, supported by density functional theory, reveal a structural phase transition at ∼5 GPa from a monoclinic P2/c to P2/m phase, resulting in almost identical coordinations of Au and Ag ions, with rather uniform interatomic distances. Furthermore, resistivity measurements show the onset of superconductivity at ∼1.5 GPa in the P2/c phase, followed by a linear increase of Tc up to the phase transition, with a maximum in the P2/m phase, and a gradual decrease afterwards. Our calculations indicate phonon-mediated superconductivity, with the electron-phonon coupling coming predominantly from the low-energy phonon modes. Thus, along with the discovery of a new superconducting compound of gold/silver, our results advance the understanding of the mechanism behind superconductivity in Au-containing compounds and dichalcogenides of other transition metals. © 2023 The Royal Society of Chemistry.EAR – 1606856; EAR – 1634415; National Science Foundation, NSF: ACI-1548562, DMR-2035518, OAC-1818253, OAC-2103991; U.S. Department of Energy, USDOE: DE-FG02-94ER14466; Office of Science, SC: DE-AC02-06CH11357; Argonne National Laboratory, ANL; University of Chicago; Israel Science Foundation, ISF: 1552/18, 1748/20We are grateful to Prof. L. Bohatý and Prof. P. Becker-Bohatý for providing us with natural single-crystals. We thank I. Silber and G. Tuvia for assisting with the resistance measurements. This work was supported by the National Science Foundation under grant no. DMR-2035518 (for superconductivity analysis) and grant no. OAC-2103991 (for code development). This research was supported by the Israel Science Foundation (grants no. 1552/18 and 1748/20). This work used the Expanse system at the San Diego Supercomputer Center via allocation TG-DMR180071 and the Frontera supercomputer at the Texas Advanced Computing Center via the Leadership Resource Allocation (LRAC) award DMR22004. Expanse is supported by the Extreme Science and Engineering Discovery Environment (XSEDE) program40 through NSF award no. ACI-1548562, and Frontera is supported by NSF award no. OAC-1818253.41 Portions of this work were performed at GeoSoilEnviroCARS (The University of Chicago, Sector 13), Advanced Photon Source (APS), Argonne National Laboratory. GeoSoilEnviroCARS is supported by the National Science Foundation – Earth Sciences (EAR – 1634415). Use of the COMPRES-GSECARS gas loading system was supported by COMPRES under NSF Cooperative Agreement EAR – 1606856 and by GSECARS through NSF grant EAR – 1634415 and DOE grant DE-FG02-94ER14466. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. E. V. K., Yu. S. P., A. V. U., and S. V. S., thank the Russian Ministry of Science and High Education (project “Quantum” no. 122021000038-7)