Laboratory of Solid State Physics

Laboratory calibration of acoustic emission (AE) behaviour in active waveguide system (AWS) is crucial for AE-based landslide monitoring. This study proposes a novel strategy to analyse the AE signal parameters generated during AWS deformations, aimed at predicting landslide velocity scales corresponding to distinct slope instability states. Compression tests were conducted on models of AWS using a universal testing machine to simulate strain-induced interactions within backfill material, thereby generating AE signals. Deformation rates ranged from extremely slow (0.003 mm/min) to rapid (30.0 mm/min), incorporating two intermediate scales (0.03 and 3.0 mm/min) within the Varnes’ landslide velocity framework. Key AE signal parameters including signal duration, counts, acoustic signal level, amplitude, signal strength, and their derivatives, were systematically analyzed for each velocity scale. A strong proportional relationship was observed between cumulative AE counts and deformation rate, while signal strength exhibited a quadratic correlation with amplitude. AE activity or order of AE signals per unit time, corresponding to each velocity scale were also analyzed. Significant results and correlations were verified using a different model of AWS. Additionally, a single test consisting of all the velocity scales in sequential order was conducted on the AWS and results were in consistence. The findings offer valuable insights for developing real-time landslide early warning systems that issue alerts based on varying landslide velocities and slope instability stages, as reflected in the AE data of AWS.

With increasing research in sensors development and fabrications, the sensitivity is found to be a foremost factor which demands optimization to attain desirable response. In order to do so, network density need to be subjected and investigates its correlations with sensor sensitivity. This particular study examines the impact of network density on sensor responsiveness. In order to explore the impact of SWNTs concentration density onto the fabricated sensor behaviour, the surface morphology has been examined by Raman Spectroscopy and resistance analysis onto as fabricated sensor samples. Furthermore, flexible SWNTs thick film gas resistor (CNT-TFR) has been generated using the vacuum filtering technique. The sensing measures of these manufactured sensors are examined by exposing them to NO2 concentrations ranging from 0.5 ppm to 10 ppm for duration of 3 min. The sensor exhibiting a concentration of 5 mg/L demonstrates the most pronounced response compared to the other sensors. The influence of network density on the ability to adsorb, heterogeneity, signal-to-noise ratio, and detection limit was also examined. The repeatability and selectivity were further examined to determine the ideal density of the sensor.

A large-area centimeter-scale (2 cm × 1 cm) high-quality continuous MoS2 film was grown on a SiO2/Si substrate via the Chemical Vapor Deposition (CVD) technique to ensure the scalability and uniformity of the MoS2 film across a large area, rendering it suitable for wafer-scale applications. We further establish the transfer of MoS2 film from the grown substrate (SiO2/Si) to Interdigitated Electrodes (IDE) structures fabricated on GaAs substrate via a wet etching process utilizing Hydrogen Fluoride (HF) solution, effectively removing the MoS2 layer from SiO2/Si substrate within 2–3 min, while preserving the structural integrity and quality of the MoS2 film. Characterization studies involving Raman analysis, Photoluminescence (PL) mapping, SEM imaging, and optoelectronics measurements confirm the high quality and integrity of the transferred MoS2 film onto IDE structures fabricated on GaAs substrate for photodetection application. Optoelectronic measurements revealed a significant responsivity enhancement from 2.13 to 26.4 mA/W at a 20 V bias under 780 nm laser illuminations (5 mW), due to the incorporation of gold nanoparticles between the IDE fingers by employing RF sputtering. Thus, integrating nanoparticles in the active region of optoelectronic devices can markedly enhance the optical efficiency of 2D material-based optoelectronic systems. Overall, this CVD technique presents a viable approach for the scalable production of large-area MoS2 films and their transfer onto fabricated structures, opening avenues for the integration of MoS2 films into advanced technological devices and systems, particularly in micro and Nano-electromechanical systems.

This study analyzes the arguments about the humanitarian tragedy involving the Yanomami people published on Twitter between January 21 and 23, 2023. Based on the theories of social representations and dehumanization, we investigated the construction of arguments through intergroup relations. We collected 506,773 messages containing the term “Yanomami”. A Social Network Analysis (SNA) revealed two main groups: a group made up of profiles linked to the Lulista left and another made up of profiles linked to the Bolsonaro right. The 15 profiles with the highest indegree in each group made up a corpus of 148 texts, shared 170,168 times, analyzed by similarity in the IRaMuTeQ software. All profiles were anonymized. The analysis revealed strong polarization. The group linked to President Lula emphasized the Bolsonaro government’s negligence in the face of repeated warnings about the Yanomami crisis. On the other hand, the group aligned with former president Bolsonaro downplayed the crisis and defended his actions, such as food distribution, indicating that the left was organizing a “narrative” against the former President. This polarization reflects the “battle of ideas” taking place in Brazil, making it difficult for the debate on the issue to focus on the humanitarian crisis of indigenous peoples. The study recommends network analysis combined with lexicographic analysis for future research into social representations, highlighting its effectiveness in identifying groups formed by interactions in network conversations. Understanding these dynamics is crucial to promoting justice and dignity for the Yanomami people.

A novel creation procedure for the nitrogen-vacancy (NV) center in diamond is investigated. After shallow nitrogen implantation, a continuous-wave laser is used to induce NV formation, while simultaneously exciting fluorescence to enable live observation. Our investigations imply that a different mechanism than heat induced vacancy diffusion causes the formation of NV centers with this method and we suggest possible alternative pathways which could be responsible, based on the observed properties. Furthermore, we test the procedure for its capabilities for the controlled creation of single centers and show that the emergence of individual centers can be tracked, while achieving sub-micrometer spatial precision.

Semiconductor‐superconductor hybrid materials are used as a platform to realize Andreev bound states, which hold great promise for quantum applications. These states require transparent interfaces between the semiconductor and superconductor, which are typically realized by in‐situ deposition of an Al superconducting layer. Here a hybrid material is presented, based on an InAs 2D electron gas (2DEG) combined with in‐situ deposited Nb and NbTi superconductors, which offer a larger operating range in temperature and magnetic field due to their larger superconducting gap. The inherent difficulty associated with the formation of an amorphous interface between III‐V semiconductors and Nb‐based superconductors is addressed by introducing a 7 nm Al interlayer. The Al interlayer provides an epitaxial connection between an in‐situ magnetron sputtered Nb or NbTi thin film and a shallow InAs 2DEG. This metal‐to‐metal epitaxy is achieved by optimization of the material stack and results in an induced superconducting gap of approximately 1 meV, determined from transport measurements of superconductor‐semiconductor Josephson junctions. This induced gap is approximately five times larger than the values reported for Al‐based hybrid materials and indicates the formation of highly‐transparent interfaces that are required in high‐quality hybrid material platforms.

Efficient and accurate characterization of an experimental setup is a critical requirement in any physical setting. In the quantum realm, the characterization of an unknown operator is experimentally accomplished via Quantum Process Tomography (QPT). This technique combines the outcomes of different projective measurements to reconstruct the underlying process matrix, typically extracted from maximum-likelihood estimation. Here, we exploit the logical correspondence between optical polarization and two-level quantum systems to retrieve the complex action of structured metasurfaces within a QPT-inspired context. In particular, we investigate a deep-learning approach that allows for fast and accurate reconstructions of space-dependent SU(2) operators by only processing a minimal set of measurements. We train a convolutional neural network based on a scalable U-Net architecture to process entire experimental images in parallel. Synthetic processes are reconstructed with average fidelity above 90%. The performance of our routine is experimentally validated in the case of space-dependent polarization transformations acting on a classical laser beam. Our approach further expands the toolbox of data-driven approaches to QPT and shows promise in the real-time characterization of complex optical gates.

The transition metal dichalcogenide 1T‐TaS2 exhibits a Charge Density Wave (CDW) with in‐plane chirality. Due to the rich phase diagram, the Ferro‐Rotational Order (FRO) can be tuned by external stimuli. The FRO is studied by Angle‐Resolved Photoelectron Spectroscopy (ARPES), Raman spectroscopy, and Selected Area Electron Diffraction (SAED). The in‐plane chirality of the CDW is lost at the transition from Nearly‐Commensurate (NC) to In‐Commensurate (IC) phase and can be controlled by applying shear stress to the sample while cooling it through the transition from IC‐CDW to NC‐CDW. Based on these observations, a protocol is proposed to achieve reliable, non‐volatile state switching of the FRO configuration in 1T‐TaS2 bulk crystals. These results pave the way for new functional devices in which in‐plane chirality can be set on demand.

The gynaecological examination (GE) is a major public health issue, with bad experiences of this examination widely reported as a disincentive to cervical cancer screening. In France, a movement to denounce gynaecological and obstetrical violence is expressed through a massive publication of testimonies on social networks. Via a socio-representational approach and from a critical gender perspective, this article aims to explore how people use digital media to communicate about the GE, and to analyse the experiences related to the GE and the representation systems underlying them. Using an inductive strategy, a corpus of discussion from the Doctissimo forum, and testimonies and comments from the PayeTonGynéco Facebook pages and Tumblr was created and submitted to lexicographical analysis. Our results suggest that the GE is indicative of a broader social function. People seem to use digital media to cope with a form of social ignorance of women’s experience in gynaecology with a certain ambivalence regarding their liberating potential.

We perform systematic investigation on (1-x)Ba(Zr0.20Ti0.80)O3-x(Ba0.70Ca0.30)TiO3 ceramics prepared by solid state reaction technique. We thoroughly investigate the effect of synthesis procedure on crystal structure, microstructure, dielectric, ferroelectric, and piezoelectric properties. Room temperature X-Ray diffraction (XRD) patterns reveal that the as synthesized samples crystallize with desired perovskite phase. Scanning electron microscopy depicts that the grain size shows significant enhancement in size. Large grains having size ~ 36 μm were observed in 50(BZT-BCT) composition prepared using modified synthesis route. Dielectric analysis depicts that the Curie temperature ‘Tc’ and diffusive coefficient ‘γ’ are considerably affected by the synthesis process. Ferroelectric studies show the well saturated loops at 30 kV/cm, and observed maximum values of remnant polarization (Pr), saturation polarization (Ps) and low values of coercive field (Ec) ~ 12.39 μC/cm², 22.67 μC/cm² and 3.05 kV/cm, respectively for 50(BZT-BCT) composition. Excellent piezoelectric properties (d33 ~ 520 pC/N and kp ~ 57.5%) were observed in 50(BZT-BCT) ceramic. The present manuscript highlights the various parameters affected the synthesis process. The results show that the modified synthesis route enhanced the properties of the ceramic and are promising candidates for lead-free piezoelectric applications.

During coating processes, dust deposition can lead to an uneven thickness in the resulting film, posing significant problems in industrial processes. Our study explores the effects of solid defects using...

The photocatalytic (PC) behavior of CeO2–TiO2 hollow composites with different heterojunction structures are investigated. The composites are fabricated by combining TiO2 hollow spheres and CeO2 nanoparticles with changing the ratio between Ce and Ti. High‐resolution microscopic and spectroscopic analysis demonstrates that three types of cerium‐bearing structures form on the surface of the titania. The first involves Ce atoms adsorbed onto the surface of TiO2 particles. The second occurs with small CeO2 particles, ≈2 nm in size, resulting from the aggregation of the adsorbed Ce atoms, thus forming a CeO2–TiO2 heterojunction. The last type is obtained through the growth of the CeO2 particles up to 10 nm in size. All the CeO2–TiO2 composites exhibit enhanced photocatalytic degradation of methyl orange under visible light irradiation compared to mere CeO2 or TiO2 nanoparticles. The synergistic effect of these three structures leads to a competition between size effects and interface interactions, which affects the band alignment, the number of defects, and, consequently, the PC activity. The highest PC reaction rate constant under visible light reaches up to 0.017 min⁻¹ and is achieved when the CeO2 nanoparticle size is smaller than its Debye length.

We study the effect of the pseudospin ferromagnetism with the aid of an electrically detected electron spin resonance in a wide AlAs quantum well containing a high quality two-dimensional electron system. Here, pseudospin emerges as a two-component degree of freedom, that labels degenerate energy minima in momentum space populated by electrons. The built-in mechanical strain in the sample studied imposes a finite “Zeeman” splitting between the pseudospin “up” and “down” states. Because of the anisotropy of the electron spin splitting we were able to independently measure the electron spin resonances originating from the two in-plane valleys. By analyzing the relative resonance amplitudes, we were able to investigate the ferromagnetic phase transitions taking place at integer filling factors of the quantum Hall effect when the magnetic field is tilted. The pseudospin nature of these transitions is demonstrated.

The properties of superconducting devices depend sensitively on the parity (even or odd) of the quasiparticles that they contain. Encoding quantum information in the parity degree of freedom is central in several emerging solid-state qubit architectures, including in hybrid superconductor-semiconductor devices. In the latter case, accurate, nondestructive, and time-resolved parity measurements are a challenging issue. Here, we report on control and real-time parity measurement in a superconducting island embedded in a superconducting loop and realized in a hybrid two-dimensional heterostructure using a microwave resonator. To avoid microwave losses impeding time-resolved measurements, the device and readout resonator are located on separate chips, connected via flip-chip bonding, and couple inductively through vacuum. The superconducting resonator detects the parity-dependent circuit inductance, allowing for fast parity readout. We have resolved even- and odd-parity states with a signal-to-noise ratio of SNR ≈ 3 for an integration time of 20 μ s and a detection fidelity exceeding 98 % . The real-time parity measurement shows a state lifetime extending into the millisecond range. Our approach will lead to a better understanding of coherence-limiting mechanisms in superconducting quantum hardware and help to advance inductive-readout schemes for hybrid qubits. Published by the American Physical Society 2024

Hybrid Josephson junctions (JJs) realized in superconductor-semiconductor heterostructures host fermionic modes known as Andreev bound states (ABSs). In these structures, a promising and yet unexplored avenue for harnessing spin and parity degrees of freedom is offered by JJs with three or more superconducting terminals, where phase-induced spin polarization and transitions of the ground state to an odd parity were predicted to arise. Here we spectroscopically probe the two-dimensional band structure of ABSs in a phase-controlled InAs / Al three-terminal JJ. Andreev bands show signatures of spin-degeneracy breaking, with level splitting in excess of ∼ 9 GHz , and zero-energy crossings associated to ground state fermion parity transitions. Spin splitting and parity transitions are enabled and controlled by locally applied magnetic fluxes, in the absence of Zeeman effect or Coulomb blockade. Our results underscore the potential of multiterminal hybrid devices for phase engineering ABSs, with significant implications for spin- and parity-based quantum devices. Published by the American Physical Society 2024

Zinc telluride (ZnTe) epitaxial layers were grown on gallium arsenide (GaAs) (211) substrate at different growth temperatures by molecular beam epitaxy. The fabricated interdigitated metal semiconductor metal configuration-based photodetector (PD) on ZnTe epitaxial layers exhibited a stable and excellent photo response in a broad spectral range (250–550 nm) up to 125 °C. The room temperature and higher temperature (125 °C) values of maximum current, spectral responsivity and detectivity at an applied bias of 5 V and 550 nm wavelength were 3.5 × 10⁻⁸ A, 0.1 A W⁻¹ and 1 × 10¹¹ Jones and 1.7 × 10⁻⁶ A, 2.5 A W⁻¹ and 1.5 × 10¹¹ Jones, respectively. The maximum photo-to-dark-current ratio (PDCR) value at zero bias and 100 °C was obtained for the ZnTe layer grown at an optimum growth temperature of 380 °C. The high PDCR value exhibits the self-powered capability of the detector. Furthermore, the detector exhibits good on–off switching to the illuminating light with rise and decay times less than 0.29 s and 0.4 s, respectively, at room temperature. The dependence of the photo response on material quality was analysed by varying the substrate growth temperature. The broadband responsivity of the ZnTe-based PD shows its capability as a multicolour detector in the UV and visible region with the use of suitable blocking filters.

Perovskite rare‐earth titanates RTiO3 display a rich array of magnetic and electronic properties, with a Mott‐insulating ground state and ferro‐ or antiferromagnetic spin orders depending on the rare‐earth R. The nominal Ti valence is 3+ with a corresponding 3d¹ configuration. Yet, at the surface of both bulk and thin films of RTiO3, the Ti valence has been found to strongly deviate towards the more stable 4+ state, adversely affecting magnetic properties. While this finding is rather ubiquitous, its exact origin is still poorly understood, which hampers the integration of RTiO3 into complex heterostructures harnessing their rich physics. Here, scanning transmission electron microscope and electron energy loss spectroscopy experiments are used to analyze the top part of an epitaxial DyTiO3 thin film displaying a well‐developed Ti⁴⁺‐rich layer over several nanometres. It shows that this valence evolution is related to a combination of short‐range ordered interstitial oxygen planes and Ti‐Dy cationic imbalance. Both defects synergistically contribute to enough hole doping for a complete transition toward Ti⁴⁺ over a few unit‐cells from the surface while a structure primarily of the perovskite‐type is maintained.

Soft solid emulsions are liquid droplets encapsulated in a soft solid material. Typical of dispersed systems, they can combine properties from both the liquid inclusions and the soft solids. The relative importance of the two phases in the rheological response is captured through the elastocapillary number, which compares capillary forces in the liquid inclusions to the matrix rigidity. We work with solid emulsions formed of poly(ethylene glycol) droplets in a poly(dimethylsiloxane) (PDMS) continuous phase. We create three families of emulsions with varying elastocapillary numbers, and range of inclusion volume fractions from 0 to 0.5. Through oscillatory rheology we probe both the elastic response and the dissipative effects of liquid droplets. In the case of a dominant response from the continuous phase or the drops, the results can be described with Palierne’s model. However, for the intermediate elastocapillary series we show that the evolution of the storage and loss moduli decouple with dispersed phase volume fraction. We attribute the increase of loss factor with volume fraction to the high polydispersity in droplet size. We can further modulate the response of the materials by cooling to freeze the droplets. This approach allows us to compare these soft solid emulsions with theories related to solid dispersions.