Organic mixed ion-electron conductors are renowned for their unique ability to efficiently conduct both electrons and ions, finding applications across various fields such as electronics and bioelectronics. In this colloquium, I will delve into the fundamentals of ionic-electronic transport in organic mixed conductors and showcase their applications in electrochemical transistors, biosensors, and low-voltage artificial synapse memory systems, which emulate the function of neurons (also known as neuromorphic devices).

Graphene is a crystalline 2D material and considered the thinnest possible membrane. Because of its high chemical stability, combined with its physical properties, graphene is promising in a variety of applications. Particularly, liquid/graphene interfaces have been exploited for bio-applications on cellular flow sensing, liquid sensing, DNA sequencing, and transparent windows in liquid cells. In such devices, understanding the interaction between water and graphene is crucial for building up novel and smart bio-interfaces. Additionally, the study of reactivity and structure of water at the graphene interface has also generated intriguing questions and controversial results. For instance, several experimental works demonstrate that the charge transfer process that happens between graphene and water molecules is highly dependent on the underlying substrate. Thus, it would be highly desirable to elucidate the above discussion by probing the electrical response of a suspended graphene membrane in contact with water without the presence of any substrate. We also believe that a precise understanding of the electrochemical behavior of water/graphene interface would be fundamental for developing novel and superior electrical, mechanical and optical devices. In this work, we develop a microfluidic platform that integrates suspended graphene membrane windows (with electrical contacts) with buried fluid channels to probe the electrical response of a graphene membrane in contact with water [1,2,3]. The platform design provides a direct probing of the electrical response of the air/graphene/liquid interface without the presence of any underlying substrate.

 I will present a detailed study of the water-induced electromechanical response in suspended graphene atop a microfluidic channel. The graphene membrane resistivity rapidly decreases ~ 25% upon water injection into the channel, defining a sensitive “channel wetting” device – a wetristor. The physical mechanism of the wetristor operation is investigated using two graphene membrane geometries, either uncovered or covered by an inert and rigid lid (h-BN multilayer or PMMA film). The wetristor effect, namely the water-induced resistivity collapse, occurs in uncovered devices only. AFM and Raman spectroscopy indicate substantial morphology changes of graphene membranes in such devices, while covered membranes suffer no changes, upon channel water filling. Our results suggest an electromechanical nature for the wetristor effect, where the resistivity reduction is caused by un-wrinkling of the graphene membrane through channel filling, with an eventual direct doping caused by water being of much smaller magnitude, if any. The wetristor device should find useful sensing applications in general micro- and nano-fluidics and provides novel insights on the interface interactions of 2D materials with liquids.

Acknowledgments: The authors acknowledge the support of FAPEMIG (Rede 2D), CNPQ/MCTI, and INCT de Nanocarbono.

[1] Ferrai et al., Graphene nanoencapsulation action at an air/lipid interface Journal of Materials Science 57, 6223 (2022).

[2] Ferrari et al., Apparent Softening of Wet Graphene Membranes on a Microfluidic Platform ACS Nano 12, 5, 4312 (2018)

[3] Meireles, Leonel et al., Graphene Electromechanical Water Sensor: The Wetristor. Advanced Electronic Materials, 6, 1901167, 2020.

Since the breakdown of Dennard scaling approximately 15 years ago, the clock frequency of processors has remained stalled at a few GHz. Although all-optical transistors that can switch at THz speed could bring a leap in performance, this promise was not fulfilled during decades of research due to low optical nonlinearities and bulky components. Now the foundations of a new generation of devices are investigated that harnesses the so-called strong light-matter interaction regime with novel materials and integrated photonic structures that could enable compact, ultrafast all-optical logic circuits with attojoule switching energy [1,2].

In this talk, the experimental progress towards this goal will be presented, including a cascading setup where a spontaneous polariton condensate is created in one cavity (Seed) and fed into another cavity (Transistor) to induce polariton condensation [3]. Additionally, rapid polariton condensation dynamics on a sub-picosecond timescale will be presented, and important transistor metrics such as signal amplification (up to a factor of 60) and on/off extinction ratio (up to 9:1) will be determined.

These findings indicate the potential for developing integrated, ultrafast all-optical transistors that are scalable, allowing for more complex all-optical logic circuits.

This work was funded by EU H2020 EIC Pathfinder Open project “PoLLoC” (grant agreement no. 899141) and EU H2020 MSCA-ITN project “AppQInfo” (grant agreement no. 956071).

References

[1] Anton V. Zasedatelev, Anton V. Baranikov, Denis Sannikov, Darius Urbonas, Fabio Scafirimuto, Vladislav Yu. Shishkov, Evgeny S. Andrianov, Yurii E. Lozovik, Ullrich Scherf, Thilo Stöferle, Rainer F. Mahrt, Pavlos G. Lagoudakis, “A room-temperature organic polariton transistor,” Nat. Photonics 13, 378–383 (2019).

[2] Anton V. Zasedatelev, Anton V. Baranikov, Darius Urbonas, Fabio Scafirimuto, Ullrich Scherf, Thilo Stöferle, Rainer F. Mahrt, Pavlos G. Lagoudakis, “Single-photon nonlinearity at room temperature,” Nature 597, 493–497 (2021).

[3] P. Tassan, D. Urbonas, B. Chmielak, J. Bolten, T. Wahlbrink, M. C. Lemme, M. Forster, U.Scherf, R.F. Mahrt, T. Stöferle, “Integrated ultrafast all-optical polariton transistors,” arXiv:2404.01868v1, (2024).

Scanning probe microscopy allows a better understanding of phenomena at the nanoscale. The advent of CO-functionalized tips allowed for something extraordinary: atomically resolved images on planar molecules and the elucidation of chemical structures.  
The combination of high-resolution scanning tunneling microscopy and atomic force microscopy has allowed different textbook chemistry concepts (e.g. bond-order, aromaticity and oxidation states) to be probed in unforeseen ways. Moreover, it is possible to characterize batches of synthesized products one-molecule-at-a-time and create a library of observed chemical structures in ways that are prohibitive to standard analytical tools. Here, I will show how high-resolution AFM measurements are performed. Then, we will peruse through different aspects of on-surface reactions and its wonders.

   The symmetries of crystals play an important role in the properties of their phonons. When the mirror symmetries are broken, the lattice ions can display circular motion with finite angular momentum. These modes, known as chiral phonons, have recently been demonstrated in both rotating and propagating lattice motions. Usually, phonons are insensitive to magnetic fields. On the contrary, chiral phonons carry magnetic moment and directly couple to magnetic fields.
    In this talk, I will present a review of the recent progress on the study of chiral phonons using terahertz time-domain spectroscopy. Our contributions to this exciting new field will be highlighted [1-3]. In particular, I will show that the phonon magnetic moment is largely enhanced in topological materials. Furthermore, unpublished results will be discussed to provide future perspectives.
    Our research was supported by FAPESP Grants No. 2015/16191-5 and 2018/06142-5, 2021/12470-8, 2023/04245-0, and CNPq Grants No. 307737/2020-9 and 409245/2022-4.

[1] A. Baydin et al., Physical Review Letters 128, 075901 (2022).
[2] F. G. G. Hernandez et al., Science Advances 9, eadj4074 (2023).
[3] N. M. Kawahala et al., Coatings 13, 1855 (2023).

Transition metal dichalcogenides (TMDs) are one of the most explored classes of two-dimensional materials. The experimental routes for synthesis and device construction in these materials are well established allowing future applications. Materials with topological phases of matter present the possibility of electronic transport with long coherence length, due to the protection of their surface states by time-reversal symmetry. Such systems allow for the development of low-power electronics and new device functionalities. We show that energetically favorable defects in TMDs, Hg doping, and chalcogen vacancies, introduce topological states in their semiconductor gap. The transition from trivial to non-trivial occurs at a critical concentration of defects and is robust against disorder.

Qubits are the standard basis for quantum computation with many competing host platforms such as superconducting circuits, trapped ions, and quantum dots, to name a few. Part of the recent efforts with these platforms focused on simulations of fermionic systems. However, the mapping from qubits to local fermionic modes is inefficient because it introduces additional overhead to the calculations. To overcome this limitation, we propose a practical implementation of a universal quantum computer that uses local fermionic modes rather than qubits. Our design consists of quantum dots tunnel coupled by a hybrid superconducting island together with a tunable capacitive coupling between the dots. We show that coherent control of Cooper pair splitting, elastic cotunneling, and Coulomb interactions allows us to implement the universal set of quantum gates. Finally, we discuss possible limitations of the device and list necessary experimental efforts to overcome them. Particularly, we predict short coherence times due to charge noise and develop an alternative operational regime using neutral Andreev fermions.

We study the projective nature of quantum measurements to achieve quantum-enhanced magnetometry using a spin chain probe for remotely detecting a local magnetic field [1, 2]. Our protocol involves performing a sequence of local measurements followed by free evolution on a spin chain probe initialized in a separable state. The local magnetic field to be estimated acts on one end of the probe, inducing an evolution through the whole system. On the other hand, the readout spin, measured sequentially at regular intervals on a fixed basis, is located at the other end, enabling remote sensing of the local field. The system is not reset until the entire sequence of measurements is completed. Increasing the sequence length demonstrates that sensing precision can be enhanced beyond the standard limit. The sequential protocol has both fundamental and practical implications. From a fundamental point of view, it introduces a new methodology for achieving quantum-enhanced sensitivity by exploiting the quantum nature of measurements and their subsequent wave-function collapse. From a practical perspective, our protocol provides remote quantum sensing while avoiding the need for complex entangled states and challenging adaptive measurements.
[1] V Montenegro, GS Jones, S Bose, A Bayat - Physical Review Letters 129, 120503, 2022
[2] Y Yang, V Montenegro, A Bayat - Physical Review Research 5, 043273, 2023

Após a Revolução Industrial o mundo vivenciou mudanças profundas na sociedade. Industrialização de países, urbanização e desenvolvimento de grandes cidades e uma cultura de consumo por bens, trouxe consigo geração de poluentes, demanda por recursosnaturais e uma dependência profunda por energia para poder manter esse novo estilo devida.

É dentro desse contexto que nasce a necessidade pelo desenvolvimento de novastecnologias capazes de garantir uma geração de energia sustentável e eficiente e por soluções que possam identificar e captar poluentes no meio ambiente.

Assim, este trabalho tem por objetivo sintetizar óxidos mistos do tipo perovskitas,estudar as suas propriedades físicas e químicas obtidas a partir da sua fabricação por diferentes elementosquímicos, estequiometria e geometria visando a sua aplicação como fotossensores e células fotovoltaicas. A síntese e caracterização de monocristais serão produzidos através da técnica detransporte químico em fase vapor (CVT), nanocompostos serão obtidos pelo método sol-gel e filmes finos por meio da técnica sputtering. Mais especificamente procura-se desenvolver sensores de gases de pequeno porte que sejam mais acessíveis, apresentando alta sensibilidade e uma melhor capacidade de seleção.

Skyrmionics stands as one of physics' most promising areas, with the potential to innovate and develop future devices and technologies. Magnetic skyrmions are nanoscale magnetic whirls that are topologically protected and can be moved by currents, leading to the prediction of several applications. Its topological charge leads to high stability; however, it also leads to the skyrmion Hall effect. From memory storage devices, like the racetrack memory, to computing devices, like artificial neurons, this shortcoming is one of the primary reasons why skyrmion-based spintronic devices have yet to be achieved. Here, we study the motion of skyrmions with different topological charges and helicities. Using an effective center-of-mass description of these magnetic quasiparticles, namely, the Thiele equation, we analyze their dynamics under different gradient landscapes and interactions aiming to suppress or take advantage of the skyrmion Hall effect. Following a neuroscience approach, we also discuss possible applications in neuromorphic computing.

[1] I.R, de Assis, et al. Phys. Rev. B 108, 144438 (2023)
[2] I.R, de Assis, et al. Neuromorph. Comput. Eng. 3 014012 (2023)