In 2023 the shocking news that a bilayer Ni-based oxide superconductor was found with a Tc of 80 K quickly spread, starting the current frenzy of Ni-based high-Tc superconductors [1]. Although superconductivity at present is only achieved at high pressure, strain may reduce this requirement, and ambient pressure Ni-based high Tc may occur in the near future. My presentation will start with a quick review of the precursors of the present frenzy in thin films of the infinite-layer phase [2], followed by the current experimental situation on bilayers and trilayers, the confirmation of strictly zero resistivity and the Meissner effect [3,4], as well as alternative atomic structures proposed for these compounds [5]. Then, I will move to theoretical development with focus on the results of our group on band structure, Fermi surface, the importance of “dimers” along the z-axis, and the random-phase approximation results for magnetism and pairing, via a collaboration between the University of Tennessee and Oak Ridge National Laboratory [6-13]. Although I will focus on our own results, our publications contain references to dozens of other theoretical, and experimental, efforts that interested readers can consult as well. The field is rapidly evolving and surprises are published in the arXiv on a weekly basis, making this area quite exciting and one of the hottest topics of research in present day Condensed Matter Physics.

[1] H. Sun,…, and M. Wang, Nature 621, 493 (2023).
[2] D. Li,…, and H. Hwang, Nature 572, 624 (2019).
[3] N. Wang,…, and J. Cheng, Nature 634, 579 (2024).
[4] Y. Zhu,…, and J. Zhao, Nature 631, 531 (2024).
[5] X. Chen,…, and J. Mitchell, J. Am. Chem. Soc. 146, 23640 (2024).
[6] Y. Zhang et al., Physical Review B 108, 165141 (2023).
[7] Y. Zhang et al., Physical Review B 108, L180510 (2023).  Letter. Editor’s Sugg.
[8] Y. Zhang et al., Nat Commun 15, 2470 (2024).
[9] Y. Zhang et al., Physical Review B 109, 045151 (2024). Editor’s Suggestion.
[10] Y. Zhang et al., Physical Review Letters 133, 136001 (2024).
[11] L.-F. Lin et al., Physical Review B 110, 195135 (2024). Editor’s Suggestion.
[12] Y. Zhang et al., Physical Review B 110, L060510 (2023).  Letter.
[13] Y. Zhang et al., arXiv:2408.07690.

Liquified noble gases are frequently the choice of target for neutrino and dark matter experiments which require an extremely high grade of purity of the liquids (in particular, in terms of oxygen contamination (< 100 ppt). Ultra-pure Liquid Argon (LAr) is the chosen target for the Long Baseline Neutrino Facility (LBNF) – Deep Underground Neutrino Experiment (DUNE) and related experiments. Brazil in-Kind contribution includes R&D, testing, construction and commissioning (including Facility Technical description, Facility lay-out, facility assembly process description, Master Plan encompass detailing, implementation and commissioning phases and commercial data) to complete engineering, design, manufacturing, testing, shipping and delivery of the Gaseous Argon (GAr) purification, LAr purification and Regeneration Systems for Detectors #1(Horizontal Drift)  and 2# (Vertical Drift).
As such, we will describe the conceptual Project Design of these systems and the proposals for innovative methods of LA purification, including capturing of nitrogen, which is a desirable additional feature to increase the control of the LAr purity in case of unexpected leaks and to allow the advanced use of the LAr scintillation light beyond the initial requirements of LBNF-DUNE. FAPESP Project # 2024/07128-7

Quantum materials encompass a wide family of systems that display many fascinating phenomena, from high-temperature superconductivity to topological order. They stand out not only as promising candidates for new technological applications, but also as windows into the fundamental microscopic properties of interacting electrons, whose collective behavior can be very different from the behavior of an individual electron. Macroscopically, these electronic correlations are manifested by the emergence of complex phase diagrams displaying a plethora of electronic states that are not independent, but intertwined. In this talk, I will present a theoretical framework that captures the intricate interplay between electronic states of matter that may seem unrelated at first sight. Based on the concept of vestigial orders, it generalizes to the quantum realm concepts common to the description of liquid crystals. More specifically, in this approach, thermal or quantum fluctuations cause an electronically ordered state to partially melt in multiple stages, leading to the emergence of two or more intertwined phases with comparable energy scales. This framework not only sheds new light on the known phase diagrams of various quantum materials, such as iron-based superconductors, but it also provides new insights into the experimental realization of exotic states, such as a charge-4e superconducting phase in twisted bilayer graphene.

Descrevemos um programa de pesquisa com antihidrogênio (antiH) que evoluiu pelas etapas de: formação dos primeiros anti-átomos a baixas energias[1]; aprisionamento magnético[2]; medida da constante hiperfina[3]; medida da transição 1S-2S com 12 algarismos significativos[4], medida mais precisa já realizada com antimatéria; resfriamento a laser[5]; primeira medida direta da aceleração da gravidade terrestre sobre o anti-átomo[6,7] e às novas medidas espectroscópicas em análise que apontam para partes em 10^13. As pesquisas visam testes de fundamentos da física como a simetria Carga-Paridade-Tempo (CPT) e Princípio de Equivalência Fraco (WEP) em buscas de explicações para nosso Universo desprovido de antimatéria, um dos grandes mistérios da física atual. Na direção de aumentar a precisão, desenvolvemos uma técnica na UFRJ[8] para gerar e aprisionar ânions de H- para permitir ao experimento ALPHA obter H na mesma armadilha de antiH[9] e assim obter controle sobre diversos efeitos sistemáticos.

[1] Amoretti, M. et al.[ATHENA Collab.] Production and detection of cold antihydrogen atoms. Nature 419, 456 (2002)
[2] Andresen, G. B. et al.[ALPHA Collab.] Trapped antihydrogen. Nature 468, 673 (2010)
[3] Ahmadi, M. et al.[ALPHA Collab.] Observation of the hyperfine spectrum of antihydrogen. Nature 548, 66 (2017)
[4] Ahmadi, M. et al. [ALPHA Collab.] Characterization of the 1S–2S transition in antihydrogen. Nature 557, 71 (2018).
[5] Baker, C. J. et al. Laser cooling of antihydrogen atoms. Nature 592, 35 (2021).
Azevedo, L.O.A. et al. Adaptable platform for trapped cold electrons, hydrogen and lithium anions and cations. Commun Phys 6, 112 (2023)
[6] Cesar, C. L., Trapping and spectroscopy of hydrogen. Hyp. Interact. 109, 293 (1997).
[7] E.K. Anderson et al. [ALPHA Collab.] Observation of the effect of gravity on the motion of antimatter, Nature (in the press) (2023); https://www.nature.com/articles/s41586-023-06527-1
[8] Azevedo, L.O.A., et al. Adaptable platform for trapped cold electrons, hydrogen and lithium anions and cations. Commun Phys 6, 112 (2023)
[9] Cesar, C. L. A sensitive detection method for high resolution spectroscopy of trapped antihydrogen, hydrogen and other trapped species. J. Phys. B 49, 074001 (2016).

Consider a composite quantum system (finite-dimensional Hilbert space) with many interacting degrees of freedom. However, suppose we do not have access to all of these degrees of freedom; we only have access to a part, a subsystem. In this context, the following questions arise: What are the quantum resources that exist in the subsystem to which we have access? What are the physical processes that can influence the subsystem? How can we determine these details with a bona-fide quantifier? Given resources and processes, what can be done operationally with the subsystem? The goal is to analyze how quantum resources and physical processes help us understand the transformations of systems. In this sense, two perspectives will be taken: One related to quantum speed limits and another related to the information flow between the system and the surrounding environment. We will see how information is transformed by the action of the environment and the impact that the return of information can have on a temperature estimation protocol.

Nanoconfined matter naturally occurs in many contexts. Nanoconfined water exists in the interior of micelles, membranes, inside the nanopores of concrete and other synthetic materials. Its unique properties control chemical, biochemical and physical processes. The way it interacts with other molecules and materials defines solubility constants, reaction speeds, reaction routes and supramolecular arrangement. Aside from liquids, nanoconfined environments also host a range of other molecules, including anions and organic matter. Interacting with the confining media, these molecules have their properties altered and at the same time modify the properties of the confining walls. Controlling the way these subsystems interact with each other and probing their properties is a challenging task that invariably requires multi-diagnostic approaches utilizing multiple advanced characterization techniques. In this talk, the unconventional properties of nanoconfined matter and new ways of controlling and probing them will be discussed.

Neste colóquio, apresentarei alguns resultados da pesquisa em Física de Partículas -- com foco na Cromodinâmica Quântica (QCD) -- realizada por nosso grupo, no IFSC-USP, nos últimos anos. Irei focar, na segunda metade do colóquio, no momento magnético anômalo do múon (conhecido como "g-2"), sua importância para a física atual e qual o status da determinação desta grandeza no Modelo Padrão da Física de Partículas. Nossas contribuições recentes à compreensão detalhada da componente de g-2 devida à QCD serão também discutidas.

The kp method, combined with group theory, is an efficient approach to obtain the low energy effective Hamiltonians of crystalline materials. Although the Hamiltonian coefficients are written as matrix elements of the generalized momentum operator π = p + pSOC (including spin-orbit coupling corrections), their numerical values must be determined from outside sources, such as experiments or ab initio methods. In Ref. [1], we develop a code to explicitly calculate the Kane (linear in crystal momentum) and Luttinger (quadratic in crystal momentum) parameters of kp effective Hamiltonians directly from ab initio wavefunctions provided by Quantum ESPRESSO. Additionally, the code analyzes the symmetry transformations of the wavefunctions to optimize the final Hamiltonian. This is an optional step in the code, where it numerically finds the unitary transformation U that rotates the basis towards an optimal symmetry-adapted representation informed by the user. In this talk, we present the methodology in detail and illustrate the capabilities of the code applying it to a selection of relevant materials. Particularly, we show a "hands-on" example of how to run the code for graphene (with and without spin-orbit coupling), results for the effective parameters for seminal materials, like GaAs. We'll finish the talk point towards the next steps in hte code development.

The code is open source and available at https://gitlab.com/dft2kp/dft2kp. We acknowledge funding from CNPQ, CAPES and FAPEMIG.

[1] J. V. V. Cassiano, A. L. Araújo, P. E. Faria Junior, G. J. Ferreira, SciPost Phys. Codebases 25 (2024)

Neutrinos are among the most abundant particles in the Universe and one of the most elusive. We are continuously traversed by millions of neutrinos which are copiously produced by our star, the Sun. Every centimeter of our body is crossed by 100 billions of neutrinos, per second! Despite being so abundant neutrinos are still mysterious particles, which probably carries the secret of why, in our Universe, we have matter and not an equal amount of anti-matter... Brazilian researchers are participating to one of the most intriguing and challenging neutrino experiment of the world, the Deep Underground Neutrino Experiment (DUNE) and a Brazilian technology has been developed to capture neutrinos, the ARAPUCA.

Rare-earth (RE) elements are vital for high technological applications due to their typically large magnetic moments and signature optical transitions associated with the 4f electron shell.  In addition to considering single atoms or ions, one can study them inside coordination complexes, allowing for the design and synthesis of structures with desirable functions.  We study different complexes: from ions deposited on surfaces and explore their magnetic interactions to RE ionic clusters self-assembled on a gold crystal surface. Experiments on the ionic complexes find them highly mobile at ~100 K, indicating a liquid-like state. Their mobility is greatly reduced below 5K, revealing self-limiting clusters with RE complexes joined by electrostatic and molecular interactions.  We also study possible arrangements of RE ion chains and clusters on gold.  The magnetic ground state configurations are found to be dominated by magnetic anisotropy effects, which can be explored using scanning tunneling techniques to investigate spin-flip excitations. RE ion clusters can also be employed to analyze entanglement entropy and their signatures in differential conductance experiments.