Condens. Matter, Volume 4, Issue 1 (March 2019) – 34 articles

It has been recently shown that fast oscillating control fields can be used to speed up an otherwise slow adiabatic process, making the system always follow an instantaneous eigenvector closely. In applying this method though, one typically assumes perfect phase relations among the control fields. In this work, we discuss the effect of potential static phase errors. We show that the latter can in some cases produce higher fidelities, leading to an unexpected improvement of the method. This is shown numerically and explained via a perturbative expansion of the error produced by the control strategy. When high-precision phase control is accessible, the results suggest that the phases of the control field can be used as free parameters whose optimization can be beneficial for the control protocol. Full article

In this short communication, we report a new carbon material prepared from meta-linked polyaniline that exhibits weak antiferromagnetic interactions at low temperature. The synthesis of poly(meta-aniline), abbreviated as m-PANI, was conducted using the Ullmann reaction with the aid of Cu⁺ as a catalyst in the presence of K₂CO₃. After the generation of radical cations by vapor-phase doping with iodine, carbonization was performed to prepare carbon polyaniline (C-PANI), which comprises condensed benzene rings. Analysis with a superconducting quantum interference device revealed that the resultant carbon exhibits antiferromagnetism at low temperatures. The discovery of this weak antiferromagnetic carbon may contribute to the development of carbon magnets. Full article

Out-of-equilibrium phenomena are attracting high interest in physics, materials science, chemistry and life sciences. In this state, the study of structural fluctuations at different length scales in time and space are necessary to achieve significant advances in the understanding of the structure-functionality relationship. The visualization of patterns arising from spatiotemporal fluctuations is nowadays possible thanks to new advances in X-ray instrumentation development that combine high-resolution both in space and in time. We present novel experimental approaches using high brilliance synchrotron radiation sources, fast detectors and focusing optics, joint with advanced data analysis based on automated statistical, mathematical and imaging processing tools. This approach has been used to investigate structural fluctuations in out-of-equilibrium systems in the novel field of inhomogeneous quantum complex matter at the crossing point of technology, physics and biology. In particular, we discuss how nanoscale complexity controls the emergence of high-temperature superconductivity (HTS), myelin functionality and formation of hybrid organic-inorganic supramolecular assembly. The emergent complex geometries, opening novel venues to quantum technology and to the development of quantum physics of living systems, are discussed. Full article

Novel, large-area silicon drift detectors (SDDs) have been developed to perform precision measurements of kaonic atom X-ray spectroscopy, for the study the $\overline{K}$ N strong interaction in the low-energy regime. These devices have special geometries, field configurations and read-out electronics, resulting in excellent performances in terms of linearity, stability and energy resolution. In this work the SDDs energy response in the energy region between 4000 eV and 12,000 eV is reported, revealing a stable linear response within 1 eV and good energy resolution. Full article

A proposal for building a Free Electron Laser, EuPRAXIA@SPARC_LAB, at the Laboratori Nazionali di Frascati, is at present under consideration. This FEL facility will provide a unique combination of a high brightness GeV-range electron beam generated in a X-band RF linac, a 0.5 PW-class laser system and the first FEL source driven by a plasma accelerator. The FEL will produce ultra-bright pulses, with up to 10 ${}^{12}$ photons/pulse, femtosecond timescale and wavelength down to 3 nm, which lies in the so called “water window”. The experimental activity will be focused on the realization of a plasma driven short wavelength FEL able to provide high-quality photons for a user beamline. In this paper, we describe the main classes of experiments that will be performed at the facility, including coherent diffraction imaging, soft X-ray absorption spectroscopy, Raman spectroscopy, Resonant Inelastic X-ray Scattering and photofragmentation measurements. These techniques will allow studying a variety of samples, both biological and inorganic, providing information about their structure and dynamical behavior. In this context, the possibility of inducing changes in samples via pump pulses leading to the stimulation of chemical reactions or the generation of coherent excitations would tremendously benefit from pulses in the soft X-ray region. High power synchronized optical lasers and a TeraHertz radiation source will indeed be made available for THz and pump–probe experiments and a split-and-delay station will allow performing XUV-XUV pump–probe experiments. Full article

The effect of surface roughness on angular distributions of reflected and physically sputtered particles is investigated by ultra-high vacuum (UHV) ion-surface interaction experiments. For this purpose, a smooth (R_a = 5.9 nm) and a rough (R_a = 20.5 nm) tungsten (W) surface were bombarded with carbon ions ¹³C⁺ under incidence angles of 30° and 80°. Reflected and sputtered particles were collected on foils to measure the resulting angular distribution as a function of surface morphology. For the qualitative and quantitative analysis, secondary ion mass spectrometry (SIMS) and nuclear reaction analysis (NRA) were performed. Simulations of ion-surface interactions were carried out with the SDTrimSP (Static Dynamic Transport of Ions in Matter Sputtering) code. For rough surfaces, a special routine was derived and implemented. Experimental as well as calculated results prove a significant impact of surface roughness on the angular distribution of reflected and sputtered particles. It is demonstrated that the effective sticking of C on W is a function of the angle of incidence and surface morphology. It is found that the predominant ion-surface interaction process changes with fluence. Full article

The electronic band structure, namely energy band surfaces and densities-of-states (DoS), of a hypothetical flat and ideally perfect, i.e., without any type of holes, boron sheet with a triangular network is calculated within a quasi-classical approach. It is shown to have metallic properties as is expected for most of the possible structural modifications of boron sheets. The Fermi curve of the boron flat sheet is found to be consisted of 6 parts of 3 closed curves, which can be approximated by ellipses representing the quadric energy-dispersion of the conduction electrons. The effective mass of electrons at the Fermi level in a boron flat sheet is found to be too small compared with the free electron mass $m_0$ and to be highly anisotropic. Its values distinctly differ in directions Γ–K and Γ–M: $m_{\mathsf{\Gamma }–\mathrm{K}}/m_0\approx 0.480$ and $m_{\mathsf{\Gamma }–\mathrm{M}}/m_0\approx 0.052$ , respectively. The low effective mass of conduction electrons, $m_{\sigma }/m_0\approx 0.094$ , indicates their high mobility and, hence, high conductivity of the boron sheet. The effects of buckling/puckering and the presence of hexagonal or other type of holes expected in real boron sheets can be considered as perturbations of the obtained electronic structure and theoretically taken into account as effects of higher order. Full article

We report on the comparison between temperature-dependent magneto-absorption and magnetotransport spectroscopy of HgTe/CdHgTe quantum wells in terms of the detection of the phase transition between the topological insulator and band insulator states. Our results demonstrate that temperature-dependent magnetospectroscopy is a powerful tool to discriminate trivial and topological insulator phases, yet the magnetotransport method is shown to have advantages for the clear manifestation of the phase transition with accurate quantitative values of the transition parameter (i.e., critical magnetic field B_c). Full article

The principle of the electrodeposition method is to immerse the coated products in a water electrolyte solution, the main components of which are salts or other soluble compounds—metal coatings. The software COMSOL Multiphysics was allowed to perform a simulation of the processes of electrodeposition of the metals copper and silver in the groove of the trapezoidal profile. Full article

In this paper, we study an atomic chain in the presence of modulated charge potential and modulated Rashba spin-orbit coupling (RSOC) of equal periods. We show that for commensurate periodicities, $\lambda =4n$ with integer n, the three-dimensional synthetic space obtained by sliding the two phases of the charge potential and RSOC features a topological nodal-line semimetal protected by an anti-unitary particle-hole symmetry. The location and shape of the nodal lines strongly depend on the relative amplitude between the charge potential and RSOC. Full article

The Compton scattering of gamma rays is commonly detected using two detector layers, the first for detection of the recoil electron and the second for the scattered gamma. We have assembled detector modules consisting of scintillation pixels, which are able to detect and reconstruct the Compton scattering of gammas with only one readout layer. This substantially reduces the number of electronic channels and opens the possibility to construct cost-efficient Compton scattering detectors for various applications such as medical imaging, environment monitoring, or fundamental research. A module consists of a 4 × 4 matrix of lutetium fine silicate scintillators and is read out by a matching silicon photomultiplier array. Two modules have been tested with a ${}^{22}$ Na source in coincidence mode, and the performance in the detection of 511 keV gamma Compton scattering has been evaluated. The results show that Compton events can be clearly distinguished with a mean energy resolution of 12.2% ± 0.7% in a module and a coincidence time resolution of $0.56\pm 0.02$ ns between the two modules. Full article

Graphite intercalation via chemical strategies is a common procedure to delaminate stratified crystals and obtain a suspension of graphene flakes. The intercalation mechanism at the molecular level is still under investigation in view of enhancing graphene production and reducing damage to the original pristine crystal. The latter, in particular, can undergo surface detriment due to both blister evolution and carbon dissolution. The role of the electrolyte temperature in this process has never been investigated. Here, by using an in-situ atomic force microscopy (AFM) apparatus, we explore surface morphology changes after the application of fast cyclic-voltammetries at 343 K, in view of de-coupling the crystal swelling phenomenon from the other electrochemical processes. We find that blisters do not evolve as a consequence of the increasing temperature, while the quality of the graphite surface becomes significantly worse, due to the formation of some adsorbates on possible defect sites of the electrode surface. Our results suggest that the chemical baths used in graphite delamination must be carefully monitored in temperature for avoiding undesired electrode detriment. Full article

We present a summary of some recent theoretical results for matter-wave patterns in Fermi and Bose–Fermi degenerate gases, obtained in the framework of the quasi-mean-field approximation. We perform a dimensional reduction from the three-dimensional (3D) equations of motion to 2D and 1D effective equations. In both cases, comparison of the low-dimensional reductions to the full model is performed, showing very good agreement for ground-state solutions. Some complex dynamical regimes are reported too for the corresponding 1D systems. Full article

Graphene has shown great potential for ultra-high frequency electronics. However, using graphene in electronic devices creates a requirement for electrodes with low contact resistance. Thermal annealing is sometimes used to improve the performance of contact electrodes. However, high-temperature annealing may introduce additional doping or defects to graphene. Moreover, an extensive increase in temperature may damage electrodes by destroying the metal–graphene contact. In this work, we studied the effect of high-temperature annealing on graphene and nickel–graphene contacts. Annealing was done in the temperature range of 200–800 °C and the effect of the annealing temperature was observed by two and four-point probe resistance measurements and by Raman spectroscopy. We observed that the annealing of a graphene sample above 300 °C increased the level of doping, but did not always improve electrical contacts. Above 600 °C, the nickel–graphene contact started to degrade, while graphene survived even higher process temperatures. Full article

We derive the two-dimensional equation of state for a bosonic system of ultracold atoms interacting with a finite-range effective interaction. Within a functional integration approach, we employ a hydrodynamic parameterization of the bosonic field to calculate the superfluid equations of motion and the zero-temperature pressure. The ultraviolet divergences, naturally arising from the finite-range interaction, are regularized with an improved dimensional regularization technique. Full article

In this work, the possibility of modeling the process of thermal decomposition in the COMSOL Multiphysics program for the preparation of nanoparticles of metals and their alloys was determined. To identify the most suitable pyrolysis medium, two environments are presented: a water solution and ethanol. Full article

X-ray graphite optics consists of thin layers of Pyrolytic Graphite (PG) attached to a substrate of focusing shape. Pyrolytic Graphite is a perfect artificial graphite obtained by annealing of carbon deposit at temperatures about 3000 °C under deformation. By varying the annealing conditions, one could get PG of different mosaic structure and mechanical properties. A wide variability of the reflecting layer characteristics and optics shape makes the graphite optics useful in an extended range of applications. The optics could be adjusted to applications that require moderate resolution as EDXRF (energy dispersive X-Ray fluorescence) and as well as for high-resolution applications as EXAFS (extended X-ray absorption fine structure), XANES (X-ray absorption near-edge structure) and XES (X-ray emission spectroscopy). To realize the optics with theoretically optimized parameters the relationship between the production procedure and the mosaicity and reflectivity of the optics was experimentally studied. The influence of thickness, the type of PG (Highly Oriented PG (HOPG) or Highly Annealed PG (HAPG)) and substrate characteristics on the optics performance is presented. Full article

Crystallization is a generic phenomenon in classical and quantum mechanics arising in a variety of physical systems. In this work, we focus on a specific platform, ultracold dipolar bosons, which can be realized in experiments with dilute gases. We reviewed the relevant ingredients leading to crystallization, namely the interplay of contact and dipole–dipole interactions and system density, as well as the numerical algorithm employed. We characterized the many-body phases investigating correlations and superfluidity. Full article

There is growing compelling experimental evidence that a quantum complex matter scenario made of multiple electronic components and competing quantum phases is needed to grab the key physics of high critical temperature (T_c) superconductivity in layered cuprates. While it is known that defect self-organization controls T_c, the mechanism remains an open issue. Here we focus on the theoretical prediction of the multiband electronic structure and the formation of broken Fermi surfaces generated by the self-organization of oxygen interstitials O_i atomic wires in the spacer layers in HgBa₂CuO_4+δ, La₂CuO_4+δ and La₂NiO_4+δ, by means of self-consistent Linear Muffin-Tin Orbital (LMTO) calculations. The electronic structure of a first phase of ordered O_i atomic wires and of a second glassy phase made of disordered O_i impurities have been studied through supercell calculations. We show the common features of the influence of O_i wires in the electronic structure in three types of materials. The ordering of O_i into wires leads to a separation of the electronic states between the O_i ensemble and the rest of the bulk. The wire formation first produces quantum confined localized states near the wire, which coexist with, Second, delocalized states in the Fermi surface (FS) of doped cuprates. A new scenario emerges for high T_c superconductivity, where Kitaev wires with Majorana bound states are proximity-coupled to a 2D d-wave superconductor. Full article

A novel bulk optics scheme for quantum walks is presented. It consists of a one-dimensional lattice built on two concatenated displaced Sagnac interferometers that make it possible to reproduce all the possible trajectories of an optical quantum walk. Because of the closed loop configuration, the interferometric structure is intrinsically stable in phase. Moreover, the lattice structure is highly configurable, as any phase component perceived by the walker is accessible, and finally, all output modes can be measured at any step of the quantum walk evolution. We report here on the experimental implementation of ordered and disordered quantum walks. Full article

The amyloidogenic islet amyloid polypeptide (IAPP) and the associated pro-peptide ProIAPP_1–48 are involved in cell death in type 2 diabetes mellitus. It has been observed that interactions of this peptide with metal ions have an impact on the cytotoxicity of the peptides as well as on their deposition in the form of amyloid fibrils. In particular, Cu(II) seems to inhibit amyloid fibril formation, thus suggesting that Cu homeostasis imbalance may be involved in the pathogenesis of type 2 diabetes mellitus. We performed X-ray Absorption Spectroscopy (XAS) measurements of Cu(II)-ProIAPP complexes under near-physiological (10 μM), equimolar concentrations of Cu(II) and peptide. Such low concentrations were made accessible to XAS measurements owing to the use of the High Energy Resolved Fluorescence Detection XAS facility recently installed at the ESRF beamline BM16 (FAME-UHD). Our preliminary data show that XAS measurements at micromolar concentrations are feasible and confirm that ProIAPP_1–48-Cu(II) binding at near-physiological conditions can be detected. Full article

LISA (Linea Italiana per la Spettroscopia di Assorbimento di raggi X) is the new Italian Collaborating Research Group (CRG) beamline at the European Synchrotron Radiation Facility (ESRF) dedicated to X-ray absorption spectroscopy (XAS). The beamline covers a wide energy range, 4 < E < 90 keV, which offers the possibility for probe the K and L edges of elements that are heavier than Ca. A liquid He/N₂ cryostat and a compact furnace are available for measurements in a wide temperature range (10–1000 K), allowing for in situ chemical treatments and measurements under a controlled atmosphere. The sub-millimetric beam size, the high photon flux provided, and the X-ray fluorescence detectors available (HP-Ge, SDD) allow for the study of liquid and highly diluted samples. Trace elements in geological or environmental samples can be analyzed, even for very small sample areas, gaining information on oxidation states and host phases. Full article

A partial substitution such as Ce in SmCo ${}_5$ could be a brilliant way to improve the magnetic performance, because it will introduce strain in the structure and breaks the lattice symmetry in a way that enhances the contribution of the Co atoms to magnetocrystalline anisotropy. However, Ce substitutions, which are benefit to improve the magnetocrystalline anisotropy, are detrimental to enhance the Curie temperature ( $T_{\mathrm{C}}$ ). With the requirements of wide operating temperature range of magnetic devices, it is important to quantitatively explore the relationship between the $T_{\mathrm{C}}$ and ferromagnetic exchange energy. In this paper we show, based on mean-field approximation, artificial tensile strain in SmCo ${}_5$ induced by substitution leads to enhanced effective ferromagnetic exchange energy and $T_{\mathrm{C}}$ , even though Ce atom itself reduces $T_{\mathrm{C}}$ . Full article

We investigate the effect of amplitude and phase noise on the dynamics of a discrete-time quantum walk and its related evolution. Our findings underline the robustness of the motion with respect to these noise sources, and can explain the stability of quantum walks that has recently been observed experimentally. This opens the road to measure topological properties of an atom-optics double kicked rotor with an additional internal spin degree of freedom. Full article

We studied magnetized topological insulator/superconductor junctions with the expectation of unconventional superconductive states holding Majorana fermions induced by superconductive proximity effects on the surface states of magnetized topological insulators (TIs), attached by conventional superconductors. We introduced Fe-doped BiSbTe₂Se as an ideal magnetic TI and used the developed junction fabrication process to access the proximity-induced surface superconducting states. The bulk single crystals of the Fe-doped TI showed excellent bulk-insulating properties and ferromagnetism simultaneously at a low temperature. Meanwhile, the fabricated junctions also showed an insulating behavior above 100 K, as well as metallic conduction at a low temperature, which reflects bulk carrier freezing. In addition, we observed a proximity-induced gap structure in the conductance spectra. These results indicate that the junctions using the established materials and process are preferable to observe unconventional superconducting states which are induced via the surface channels of the magnetized TI. We believe that the developed process can be applied for the fabrication of complicated junctions and suites for braiding operations. Full article

Polarization selection of the reflected radiation has been employed in Mössbauer reflectivity measurements with a synchrotron Mössbauer source (SMS). The polarization of resonantly scattered radiation differs from the polarization of an incident wave so the Mössbauer reflectivity contains a scattering component with 90° rotated polarization relative to the π-polarization of the SMS for some hyperfine transitions. We have shown that the selection of this rotated π→σ component from total reflectivity gives an unusual angular dependence of reflectivity characterized by a peak near the critical angle of the total external reflection. In the case of collinear antiferromagnetic interlayer ordering, the “magnetic” maxima on the reflectivity angular curve are formed practically only by radiation with this rotated polarization. The first experiment on Mössbauer reflectivity with a selection of the rotated polarization discovers the predicted peak near the critical angle. The measurement of the rotated π→σ polarization component in Mössbauer reflectivity spectra excludes the interference with non-resonant electronic scattering and simplifies the spectrum shape near the critical angle allowing for an improved data interpretation in the case of poorly resolved spectra. It is shown that the selected component of Mössbauer reflectivity with rotated polarization is characterized by enhanced surface sensitivity, determined by the “squared standing waves” depth dependence. Therefore, the new approach has interesting perspectives for investigations of surfaces, ultrathin layers and multilayers having complicated magnetic structures. Full article

X-ray Absorption Fine Structure Spectroscopy (XAFS) is a powerful technique to investigate the local atomic geometry and the chemical state of atoms in different types of materials, especially if lacking a long-range order, such as nanomaterials, liquids, amorphous and highly disordered systems, and polymers containing metallic atoms. The INFN-LNF DAΦNE-Light DXR1 beam line is mainly dedicated to soft X-ray absorption spectroscopy; it collects the radiation of a wiggler insertion device and covers the energy range from 0.9 to 3.0 keV or the range going from the K-edge of Na through to the K-edge of Cl. The characteristics of the beamline are reported here together with the XAFS spectra of reference compounds, in order to show some of the information achievable with this X-ray spectroscopy. Additionally, some examples of XAFS spectroscopy applications are also reported. Full article

High-quality single crystals are essentially needed for the investigation of the novel bulk properties of unconventional superconductors. The availability of such crystals grown by the floating-zone method has helped to unveil the unconventional superconductivity of the layered perovskite Sr₂RuO₄, which is considered as a strong candidate of a topological spin-triplet superconductor. Yet, recent progress of investigations urges further efforts to obtain ultimately high-quality crystalline samples. In this paper, we focus on the method of preparation of feed rods for the floating-zone melting and report on the improvements of the crystal growth. We present details of the improved methods used to obtain crystals with superconducting transition temperatures T_c that are consistently as high as 1.4 K, as well as the properties of these crystals. Full article

Realizing reversible reduction-oxidation (redox) reactions of lattice oxygen in batteries is a promising way to improve the energy and power density. However, conventional oxygen absorption spectroscopy fails to distinguish the critical oxygen chemistry in oxide-based battery electrodes. Therefore, high-efficiency full-range mapping of resonant inelastic X-ray scattering (mRIXS) has been developed as a reliable probe of oxygen redox reactions. Here, based on mRIXS results collected from a series of Li_1.17Ni_0.21Co_0.08Mn_0.54O₂ electrodes at different electrochemical states and its comparison with peroxides, we provide a comprehensive analysis of five components observed in the mRIXS results. While all the five components evolve upon electrochemical cycling, only two of them correspond to the critical states associated with oxygen redox reactions. One is a specific feature at 531.0 eV excitation and 523.7 eV emission energy, the other is a low-energy loss feature. We show that both features evolve with electrochemical cycling of Li_1.17Ni_0.21Co_0.08Mn_0.54O₂ electrodes, and could be used for characterizing oxidized oxygen states in the lattice of battery electrodes. This work provides an important benchmark for a complete assignment of all mRIXS features collected from battery materials, which sets a general foundation for future studies in characterization, analysis, and theoretical calculation for probing and understanding oxygen redox reactions. Full article