LQMEC - Synergy
#18 LQMEC - Synergy (08/2024)
28/08/2024 (15 - 16 h) Auditório Marcello Damy - Main Building IFUSP
Speaker: Dr. Camila Ianhez
Federal University of São Carlos (UFSCar)
Title: Structural and optical properties of ZnO:Eu under Hydrostatic Pressure
Abstract: The trivalent state of the Eu ion is of particular importance in developing optoelectronic devices due to its broad spectrum of visible emissions. Although the shielding effect of 4f electrons in the lanthanide series is well-known, changes in the symmetry of the chemical environment surrounding Eu³⁺ ions can significantly impact their luminescence. In this presentation, I will explore the synthesis of a europium-doped ZnO thin film using the Spray-Pyrolysis technique and investigate how the host ZnO crystallinity influences europium’s optical emissions. This study employs simultaneous X-ray Diffraction and photoluminescence spectroscopy to examine the effects of varying hydrostatic pressures, with measurements conducted at the Sirius synchrotron facilities.
ONLINE: https://usp-br.zoom.us/j/89433190915
894 3319 0915
SENHA: 469640
#17 LQMEC - Synergy (08/2024)
21/08/2024 (15 - 16 h) Auditório Marcello Damy - Main Building IFUSP
Speaker: Prof. Chihiro Sekine
Muroran Institute of Technology
Title: New development of skutterudite-type thermoelectric materials using high-pressure technique
Abstract: Partially filled skutterudite compounds have been considered as potential candidates for highly efficient thermoelectric materials. The unfilled skutterudite compound MX3 (M = Co, Rh and Ir, X = P, As and Sb), which is a cage-like material, shows excellent thermoelectric (TE) performance. However, the compounds have a disadvantage of high lattice thermal conductivity κL compared to conventional TE materials. The vacancy inside the cage of MX3 (M4X12) can accept a relatively small guest ion R. The vacancy can be partially occupied by R (RxM4X12), such as alkaline-earth, rare-earth and group 13 elements, resulting in a large decrease in κL and improve the TE performance. Namely, R ions are located inside the cages and a marked rattling effect occurs. The reduction in κL for a partially filled skutterudite is a promising method for improving the TE performance. For several RxM4X12, κL decreases with increasing filling ratio x of guest ions. Therefore, partially filled skutterudite compounds with high filling ratio are expected for high-performance TE materials. High pressure benefits the entrance of R into the voids of unfilled skutterudite structure than ambient pressure [1]. We have succeeded in filling unfilled skutterudite compounds with R at a high filling rate x by high-pressure synthesis. Furthermore, we succeeded in filling heavy rare earth ions (Tb and Dy), which cannot be filled at ambient pressure [2]. In this study, we also
focused on a pressure-induced self-insertion reaction. Namely, X atom enters the void of X cage by the reaction under high pressure. The κL of SbxM4Sb12-x (M = Co and Rh) were significantly reduced [3]. This suggests that the pressure-induced structural change could be beneficial for improving TE performance.
*Prof. Sekine is a Visiting Researcher at LQMEC, hosted by Prof. Larrea inside the PRINT USP CAPES grant.
ONLINE: https://usp-br.zoom.us/j/87134
871 3450 5059
SENHA: 575478
#16 LQMEC - Synergy (06/2024)
26/06/2024 (15 - 16 h) Auditório Marcello Damy - Main Building IFUSP
Speaker: Prof. Ivica Zivkovic
École Polytechnique Fédérale de Lausanne
Title:Entropy chase in 5d1 double perovskites
Abstract: A family of double perovskites comprises a very broad range of compounds, displaying a variety of properties and raising interest from physicists, chemists and applied scientists. In this talk I will focus on our recent work on 5d1 compounds, with an emphasis on Ba2MgReO6. Here, the magnetism arises from a single electron occupying t2g orbitals under the influence of strong spin-orbit coupling, resulting in the ground state quartet. Thermodynamic measurements reveal two features, and from resonant x-ray scattering (REXS) it is possible to associate them with long-range order of magnetic dipoles developing below 18 K and charge quadrupoles below 31 K. On the other hand, careful specific heat studies reveal that in the range 2 – 50 K recovered entropy reaches only Rln2, indicating a doublet as a ground state. Contrary to the predominant view, we show evidence of a persisting doublet-doublet gap revealed by resonant inelastic x-ray scattering (RIXS). The puzzle of the ground-state degeneracy and its relation to the observed quadrupolar order can be resolved by invoking a dynamical Jahn-Teller distortion of ReO6 octahedra.
ONLINE: https://usp-br.zoom.us/j/87134
871 3450 5059
SENHA: 575478
#15 LQMEC - Synergy (04/2024)
29/04/2024 (15 - 16 h) Auditório Cesar Lattes - Main Building IFUSP
Speaker: Prof. Ricardo Lobo (1,2)
1 LPEM, ESPCI Paris, CNRS, PSL University, Paris, France
2 Sorbonne Université, ESPCI Paris, LPEM, Paris, France
Title: Localization, disorder, and the chemical bonding in Phase Change Materials
Abstract: Chalcogenide-based phase change materials (PCM) undergo an amorphous to crystalline phase transformation, which shows a metal-insulator transition with significant changes in their optical properties. In addition to the formation of a Drude-like peak, one also observes an intriguing change, of almost one order of magnitude, in the value of the infrared dielectric constant as well as in the Born effective charge [1]. The fundamental origins of the large changes in the optical properties of PCMs are quite intriguing and not fully understood. Here we look at the optical conductivity of a series of PCMs – GeTe, GeSb2Te4, Sb2Te3, and Sb2Se3 – with different degrees of crystallinity and, hence, different conductivities. We highlight three properties of these materials. The first important feature is the role of disorder in the metal-insulator transition. Upon annealing we observe an appearance of a mid-infrared peak that increases in intensity and moves towards a zero-frequency centered Drude peak. Secondly, we closely follow the value of the Born effective charge, extracted from the phonon spectral weight. We observe that this charge increases with the dc conductivity of the material, in contrast to the idea that free carriers compensate for the phonon dipole momentum. Finally, we analyze our data in terms of a “metavalent bonding” [2]. This is a proposed new chemical bonding that would sit between metallic and covalent and which has very particular properties. This metavalent bonding strongly correlates with PCMs that show remarkable optical properties changes.
[1] C. Chen et al. Phys. Rev. B 95, 094111 (2017).
[2] L. Guarneri et al., Adv. Mater. 33, 2102356 (2021).
ONLINE:
https://usp-br.zoom.us/j/82415
824 1511 3194
SENHA:011616
#14 LQMEC - Synergy (03/2024)
20/03/2024 (15 - 16 h) Auditório Cesar Lattes - Main Building IFUSP
Speaker: Prof. Giovanni Hearne Department of Physics, University of Johannesburg, South Africa
Title: 57Fe Mössbauer probe of magnetic-electronic states under extreme conditions
Abstract: 57 Fe Mössbauer spectroscopy (MS) is by now a well known local probe of the magnetic-electronic state of iron-based phases. It provides information on Fe valence, valence dynamics like charge transfer, local coordination changes, spin states and magnetic states. A more challenging, and therefore less common, application of the technique is 57 Fe MS under extreme conditions of high pressure. The above mentioned electronic states can then be probed in-situ as a function of pressure as a “tuning” parameter. I will briefly discuss the methodology of 57 Fe MS implemented under high pressure in the diamond anvil cell. Then I will exemplify its relevance in condensed matter physics, chemistry and geophysics contexts, by reviewing some of the studies mentioned in the references below.
1. “Interplay between H-bonding proton dynamics and Fe valence fluctuations in Fe 3 (PO 4 ) 2 (OH) 2 at high pressure”, G. Hearne, V. Ranieri, P. Hermet, et al., Phys. Rev. B 107, (2023) L060302. DOI: 10.1103/PhysRevB.107.L060302.
2. “Pressure-Induced Spin Crossover at Room Temperature in a Nanoporous Host-Guest Framework Structure”, Banele Vatsha, Rowan Goliath, and Giovanni Hearne, ChemPlusChem 86, (2021) 82–86. DOI:10.1002/cplu.202000557.
3. “Pressure-induced disruption of the local environment of Fe-Fe dimers in FeGa3 accompanied by metallization”, G. R. Hearne, S. Bhattacharjee, B. P. Doyle, et al., Phys. Rev. B 98, (2018) 020101(R). DOI: 10.1103/PhysRevB.98.020101
4. “Interplay between structural and magnetic-electronic responses of FeAl 2 O 4 to a megabar: Site inversion and spin crossover”, W. M. Xu, G. R. Hearne, S. Layek, et al., Phys. Rev. B 97, (2018) 085120. DOI: 10.1103/PhysRevB.97.085120.
ONLINE:
https://usp-br.zoom.us/j/82415
824 1511 3194
SENHA:011616
#13 LQMEC - Synergy (02/2024)
28/02/2024 (15 - 16 h) Auditório Cesar Lattes - Main Building IFUSP
Speaker: Dyon van Dinter (Quantum Materials Sciences Unit at Okinawa Institute of Science and Technology – OIST)
Title: Enhanced Superconductivity in monolayer FeSe on large Fermi Surface perovskite oxide
Abstract: Incorporating AI (big data algorithms, machine learning, large language models) and future Quantum Simulations in the Material Science (MS) process is leading to a substantial increase in efficiency, accuracy, and potential material candidates. For example, DeepMind (a subsidiary of Google) announced late last year that their designed AI model for materials discovery recently completed the discovery of close to 400.000 thermodynamically stable crystalline materials. As they claim, this is equivalent to “800 years” of progress. However, the experimental field of MS is by no means prepared to keep up with the pace of these developments in material discovery. There is too much work to be done by too few experimentalists. A streamlined and standardized infrastructure and workflow are crucial to maximizing the potential these new technologies offer. With this in mind, I will introduce the capabilities of the Quantum Materials Sciences Unit at the Okinawa Institute of Science and Technology (OIST). As a relatively young research unit, we are trying to design and implement a laboratory environment compatible with the in-silico technologies of this new era of big data and quantum information. Functioning as the current ongoing proof of concept study, I will focus on my work on monolayer FeSe on STO and SVO.
ONLINE: https://usp-br.zoom.us/j/82415
Sala zoom: 824 1511 3194
Senha: 011616
#12 LQMEC - Synergy (11/2023)
29/11/2023 (15 - 16 h) Auditório Marcello Damy - Main Building IFUSP
Speaker: Prof. Dr. Pascoal Jose Giglio Pagliuso (UNICAMP)
Title: ESR as a potential probe to search for topologically non-trivial electronic states
Abstract: Topological insulators (TIs) and other non-trivial electronic states have recently attracted great attention from the condensed matter community due to their amazing properties and potential for applications. For the TIs with 3D nature, the promising candidates are supposed to be materials which possess strong spin orbit coupling and no magnetic order. Examples of such materials are the binaries (Bi,Sb)2,(Se,Te)3, several examples of half-Heuslers compounds and the Kondo insulator SmB6. Despite the intense experimental efforts, it has been a great challenge to unambiguously establish the realization of such a state of matter in these compound materials.
In this talk, we will discuss if electron spin resonance (ESR) experiments can be used as a potential probe to detect such topologically protected metallic surface states, based on recent Intriguing ESR results from our group.
ONLINE: https://usp-br.zoom.us/j/84428589569
844 2858 9569
senha: 831613
#11 LQMEC - Synergy (09/2023)
20/09/2023 (15 - 16 h) Auditório Giuseppe Occhialini - Main Building IFUSP
Speaker: Prof. Dr. Marcello Barbosa da Silva Neto (UFRJ)
Title: Topology and the nonreciprocal Hall response in p-type Tellurium
Abstract: Tellurium is a gyrotropic, p-type Weyl semiconductor with remarkable electronic, optical, and transport properties. It has been argued that some of these properties might stem from Weyl nodes at crossing points in the band structure and their nontrivial topological textures. However, Weyl nodes in time-reversal invariant semiconductors are split up in energy, rather than in momentum, and located deep below (far above) the top (bottom) of the valence (conduction) band, challenging such an interpretation. Here, instead, we use a four-band k · p Hamiltonian for p-type tellurium to show how the k-dependent spin-orbit interaction mixes up the top two (Weyl node free) and bottom two (Weyl-node-containing) valence bands, generating a 3D hedgehog orbital magnetic texture at the uppermost valence band, already accessible to transport at the lowest doping. Hedgehog textures are important signatures of Weyl fermion physics, in general, and in the context of condensed matter physics arise from the carriers’ wave packet rotation being locked to their propagation wave vector. For spatially dispersive media, such an induced hedgehog texture/carrier rotation stabilizes two nonreciprocal and antisymmetric components to the Hall transport within different weak-localization (antilocalization) relaxation regimes: the anomalous and planar Hall effects, usually forbidden by time-reversal symmetry. Our AC magnetotransport measurements on Sn-doped tellurium confirm the theoretical predictions and our paper demonstrates how Weyl signatures generally appear in transport on enantiomorphic materials with natural optical activity.
ONLINE: https://usp-br.zoom.us/j/84428589569
844 2858 9569
senha: 831613
#10 LQMEC - Synergy (08/2023)
16/08/2023 (15 - 16 h) Auditório Giuseppe Occhialini - Instituto de Fisica da USP (main building)
Speaker: Prof. Dr. Antonio Jefferson da Silva Machado (EEL – USP)
Title: Crystal Growth and superconducting properties of chalcogenides such as: ZrTe2 and
ZrTe3 intercalated with transition metal and rare earth.
Abstract: In this seminar we will discuss a new method for growth high quality single crystals of ZrTe2 and ZrTe 3 which we call ICVT (Isothermal Chemical Vapor Transport). So, will be discuss the thermodynamic of this new approach and some interesting superconducting properties that emerge from this dichalcogenide in the ZrTe2 intercalated with transition metal and some rare
earths atoms and ZrTe 3 as well. Indeed, ZrTe2 is considered a new Dirac Semimetal example and, therefore, the superconducting behavior that emerge from intercalation can be a new example of topological superconductors.
ONLINE:https://usp-br.zoom.us/j/84428
844 2858 9569 – PASS: 831613
#9 LQMEC - Synergy (07/2023)
13/07/2023 (15 - 16 h) Auditório Giuseppe Occhialini - Instituto de Fisica da USP (main building)
Speaker: Prof. Geetha Balakrishnan (Department of Physics, University of Warwick, UK)
Title: Magnetic skyrmion materials
Abstract: Recently, there has been considerable interest in the physics of magnetic skyrmions due to their potential use in spintronic devices. Non-centrosymmetric magnetic systems have been found to host a variety of exotic, and in some cases topologically protected, magnetic states such as skyrmion lattices, bimerons, chiral solitons and helimagnetism to list a few. More recently skyrmions been found and investigated in centrosymmetric intermetallics as well. To make headway in understanding the physics of these skyrmion materials, high quality single crystals are essential. This has motivated us to embark upon a study of several classes of magnetic materials and to explore a wide composition range of each of the family of compounds. The materials investigated range from lacunar spinels, centrosymmetric intermetallics and layered van der Waals materials.
In this talk, I will present an overview of the crystal growth at Warwick of several of the above materials using a variety of techniques. Investigations of the effects of substitution and the resulting structural order/disorder on the existence of the skyrmions and other related spin structures in these crystals sheds light on the origin and the tuning of these lattices, and important structure –property correlations.
ONLINE: Sala Zoom: https://usp-br.zoom.us/j/89546851611
Room: 895 4685 1611 – Password: 831613
#8 LQMEC - Synergy (04/2023)
14/04/2023 (15 - 16 h) Auditório Gleb Wataghin (Main building) Instituto de Fisica da USP
Speaker: Prof. Narcizo Marques de Souza Neto (Laboratório Nacional de Luz de Síncrotron, CNPEM, Campinas)
Title: Condensed matter at Sirius, the new Brazilian synchrotron source
Abstract: Sirius, the new Brazilian synchrotron light source at Campinas-SP, one of the brightest and first fourth-generation machines in the world, is opening up a plethora of opportunities to study areas such as condensed matter physics with conditions yet nonexistent. Today we have several challenges to provide a complete understanding of physical mechanisms in condensed matter phenomena, as superconductivity for example. That in part can be tackled by employing experimental x-ray techniques, such as XRD, XMCD, RIXS and ARPES, that will be available at Sirius to access, for example, how electronic states are affected depending on multiple factors (temperature, interface, crystallinity, applied fields and pressure, etc). This information could in principle be used to test, validate or propose new physics theories in ways not yet imagined. In this talk I will give an overview of several possibilities for condensed matter and materials research with synchrotron techniques at diverse conditions and sensitivities. The state-of-the-art light source will also be overviewed.
#7 LQMEC - Synergy (03/2023)
24/03/2023 (15 - 16 h) room 3029 IFUSP main building
Speaker: Dr. Mariana Saraiva Leão Lima
Title: Study of structural and electronic properties of Mg2Sn epitaxial thin film for thermoelectric application
Abstract: Mg2X (X =Si, Ge, and Sn) are narrow band gap semiconductors and promising low-cost materials for thermoelectric application. However, the thin film performance is lower than bulk material. In this work, we optimize the fabrication process for Mg2Sn epitaxial thin films and achieve higher thin film’s quality by using molecular beam epitaxy (MBE). Our results suggest
that epitaxial nature is essential for achieving high mobility. Furthermore, we found that Ga incorporation influences the carrier concentration and acts as a phonon-scattering center. The optimal power factor and figure of merit values obtained were 1.49 x 10−3 W ·m−1 ·K−1 and 0.08 at 300 K for Mg2Sn0.97Ga0.03. The values are in the same range as the bulk material of Mg-based II–IV semiconductors, suggesting that the combination of doping and epitaxial nature in thin films can be a promising route for the miniaturization of thermoelectric devices based on Mg-based materials.
#6 LQMEC - Synergy (02/2023)
17/02/2023 (15 - 16 h) Auditório Giuseppe Occhialini, Ala II, Instituto de Fisica da USP
Speaker: Dr. Julio Criginski Cezar (Sabiá Beamline, LNLS Laboratory, Brazil)
Title: Probing magnetism with X-rays
Abstract:
In this talk we will discuss the use of synchrotron radiation to investigate magnetic materials. We will briefly recall the properties of X-rays beams produced by synchrotrons and how one can use their energy and polarization tunability to obtain chemical selective magnetic information.
We will then introduce X-ray magnetic dichroism, a technique with potential to disentangle the spin and orbital contributions to the overall magnetic moment, and how it can be used to obtain images based on magnetic contrast down to resolutions of a few nanometers. We will illustrate the use of these techniques with recent results from our group and collaborations, ranging from proximity induced magnetic moments in ultra thin films, to the characterization of skyrmion carrying artificial antiferromagnets and direct imaging of artificial spin ices. We will end showing the instrumentation available at SIRIUS, the new Brazilian synchrotron, that can be used to obtain this kind of results.
#5 LQMEC - Synergy (12/2022)
16/12/2022 (15 - 16 h) Ed. Principal, Auditório Giuseppe Occhialini
Speaker: Prof. Tulio Costa Rizuti da Rocha (Ipê Beamline, LNLS Laboratory, Brazil)
Title: Probing emerging excitations in solids with Resonant Inelastic X-ray Scattering (RIXS)
Abstract:
Emerging excitations play a central role in understanding the macroscopic properties of quantum materials. The most notable example is the high-temperature superconductors, for which various collective modes such as phonons, polarons, plasmons and magnons might contribute or compete with the formation of Cooper pairs that determine the superconducting state. The dispersion relation of the elementary excitations, i.e., the dependence of their energy on the wave-vector, is one of the most fundamental properties of a quantum many-body system. In this talk, I will show the principles of the resonant inelastic X-ray scattering (RIXS), a technique that can directly probe the momentum resolved excitation spectrum of transition metal compounds.
Particularly, I will show recent results from the investigation of an unusual orbital ordering in CuSb2O6 and the search of collective orbital excitations. Additionally, I will also present details about the RIXS instrument under construction at the IPE beamline of the Sirius synchrotron light source at LNLS/CNPEM.
#4 LQMEC - Synergy (10/2022)
20/10/2022 (15 - 16 h) Ed. Principal, Sala 3029
Speaker: Dr. Goran Nilsen (STFC, Rutherford Appleton Laboratory)
Title: Collinear nematic phase in the breathing pyrochlore spinel LiGa0.95In0.05Cr4O8
Abstract: The A-site ordered spinel chromites AA′ Cr4O8 (A = Li, A′ = Ga, In) realize a so-called breathing pyrochlore lattice, where the B site forms a size-alternating array of corner-sharing Cr3+ (S = 3/2) tetrahedra. This alternation results in different exchanges along the edges of the large (J’) and small (J) tetrahedra. The degree of breathing can then be quantified by Bf = J′/J, whose limiting values 0 and 1 correspond to isolated small tetrahedra and the uniform pyrochlore lattice.
The LiGa1−xInxCr4O8 family has proven to manifest a wide range of magnetic behaviours as a function of the substitution (and hence bond disorder), x. The end member compositions LiGaCr4 O8 (Bf = 0.6) and LiInCr4O8 (Bf = 0.1) exhibit a series of complex magneto-structural transitions resulting in magnetically ordered phases. We have shown that the Néel order is suppressed by even vestigial doping at A′ site; for x = 0.05, magnetic order is replaced with a second-order transition to a possible classical spin nematic phase at Tf ∼ 11 K. Subsequent inelastic neutron scattering experiments reveal a quasi-elastic response at high temperature, as commonly observed in the pyrochlore antiferromagnets. At lower temperatures, this is replaced by an inelastic mode showing a strong resemblance to the broad resonant mode observed in lightly Cd-doped ZnCr2O4. The structure factor of the feature is consistent with “weathervane” modes on hexagonal antiferromagnetic loops, which are abundant in the nematic state. The finite energy of the excitation is proposed to be generated by the biquadratic term in the effective magneto-elastic Hamiltonian, which is also responsible for the onset of the nematic state.
#3 LQMEC - Synergy (09/2022)
16/09/2022 (16 - 17 h) Auditório Giuseppe Occhialini (Sala 2018), Antigo Sul
Speaker: Dr. Muhammad Naveed (LQMEC-IFUSP)
Title: Magneto-transport and Shubnikov-de Haas oscillations in the layered ternary telluride topological semimetal candidate Ta3SiTe6
Abstract: Topological semimetals characterize a unique class of quantum materials hosting Dirac/Weyl fermions. The important features of topological fermions can be exhibited by quantum oscillations. We report the magnetoresistance and Shubnikov-de Haas (SdH) quantum oscillation of longitudinal resistance in the single crystal of topological semimetal candidate Ta3SiTe6 with a magnetic field up to 38 T. The periodic amplitude of the oscillations shows related information about the Fermi surface. The fast Fourier transformation spectra represent a single oscillatory frequency. The analysis of the oscillations shows the Fermi pocket with a cross sectional area of 0.13A˚ -2. Combining magneto-transport measurements and the first-principles calculation, we find that these oscillations come from the hole pocket. Hall resistivity and the SdH oscillations recommend that Ta3SiTe6 is a hole dominated system.
#2 LQMEC - Synergy (08/2022)
19/08/2022 (16 - 17 h) room 3029 IFUSP main building
Speaker: Prof. Dr. Walber Hugo Brito, da Universidade Federal de Minas Gerais (UFMG)
Title: Electronic correlation effects in 3d and 5f
materials
Abstract: In strongly correlated materials the competing energy scales give rise to rich phase diagrams and emergent properties, which can not be properly explained by the usual band theory of solids.
The competition between the kinetic energy and the electron-electron interactions lies at the heart of this problem. In this talk, I will present theoretical studies on the electronic correlation effects in two different materials, namely, iron diantimonide (FeSb2) and elemental plutonium (Pu). The former is a narrow gap correlated semiconductor well-known for its colossal thermopower at low temperatures. In this case, I will discuss the calculated excitation spectra of FeSb2 and its validation using photoemission spectroscopy (ARPES).
In the second part of my talk, I will focus on elemental Pu that exhibits solid state properties which are exceptionally challenging to describe or understand from a theoretical perspective. In this case I will show how many-body calculations have shed a new light on the orbital and site-dependent correlations in elemental Pu.
#1 LQMEC - Synergy (07/2022)
07/07/2022 (10.30-12h) room 3029 IFUSP main building
Speaker: Fernando Almeida de Passos
Title: Magnetic, electronic, and structural investigation of the Sm_{1-x}Y_xCo5 system
Speaker: Cauê Kaufmann Ribeiro
Title: Investigation of role of disorder in pristine cage compound FeGa3
Speaker: Aryella Fae Rabello
Title: Fe1+δGa3: disorder-order phase transitions induced by pressure