Study Of Condensed Matter Research Articles

Modeling the Temperature-Dependent Size Change of Polydisperse Nano-objects using a Deep Generative Model.

Modern microscopy techniques can be used to investigate soft nano-objects at the nanometer scale. However, time-consuming microscopy measurements combined with low numbers of observable polydisperse objects often limit the statistics. We propose a method for identifying the most representative objects from their respective point clouds. These point cloud data are obtained, for example, through the localization of single emitters in super-resolution fluorescence microscopy. External stimuli, such as temperature, can cause changes in the shape and properties of adaptive objects. Due to the demanding and time-consuming nature of super-resolution microscopy experiments, only a limited number of temperature steps can be performed. Therefore, we propose a deep generative model that learns the underlying point distribution of temperature-dependent microgels, enabling the reliable generation of unlimited samples with an arbitrary number of localizations. Our method greatly cuts down the data collection effort across diverse experimental conditions, proving invaluable for soft condensed matter studies.

Probing Quantum Phases in Ultra-High-Mobility Two-Dimensional Electron Systems Using Surface Acoustic Waves.

Transport measurement, which applies an electric field and studies the migration of charged particles, i.e., the current, is the most widely used technique in condensed matter studies. It is generally assumed that the quantum phase remains unchanged when it hosts a sufficiently small probing current, which is, surprisingly, rarely examined experimentally. In this Letter, we study the ultra-high-mobility two-dimensional electron system using a propagating surface acoustic wave, whose traveling speed is affected by the electrons' compressibility. The acoustic power used in our Letter is several orders of magnitude lower than previous reports, and its induced perturbation to the system is smaller than the transport current. Therefore we are able to observe the quantum phases become more incompressible when hosting a perturbative current.

Entanglement entropy, single-particle occupation probabilities, and short-range correlations

For quantum many-body systems with short-range correlations (SRCs), the intimate relationship between their magnitude, the behavior of the single-particle occupation probabilities at momenta larger than the Fermi momentum, and the entanglement entropy is a new qualitative aspect not studied and exploited yet. A large body of recent condensed matter studies indicates that the time evolution of the entanglement entropy describes the nonequilibrium dynamics of isolated and strongly interacting many-body systems, in a manner similar to the Boltzmann entropy, which is strictly defined for dilute and weakly interacting many-body systems. Both theoretical and experimental studies in nuclei and cold atomic gases have shown that the fermion momentum distribution has a generic behavior $n(k)=C/{k}^{4}$ at momenta larger than the Fermi momentum, due to the presence of SRCs, with approximately 20% of the particles having momenta larger than the Fermi momentum. The presence of the long momentum tails in the presence of SRCs changes the textbook relation between the single-particle kinetic energy and occupation probabilities, ${n}_{\text{mf}}(k)=1/{1+exp\ensuremath{\beta}[\ensuremath{\epsilon}(k)\ensuremath{-}\ensuremath{\mu}]}$ for momenta very different form the Fermi momentum, particularly for dynamics processes. SRCs induced high-momentum tails of the single-particle occupation probabilities increase the entanglement entropy of fermionic systems, which in its turn affects the dynamics of many nuclear reactions, such as heavy-ion collisions and nuclear fission.

Realizing Attosecond Core-Level X-ray Spectroscopy for the Investigation of Condensed Matter Systems

Unraveling the exact nature of nonequilibrium and correlated interactions is paramount for continued progress in many areas of condensed matter science. Such insight is a prerequisite to develop an engineered approach for smart materials with targeted properties designed to address standing needs such as efficient light harvesting, energy storage, or information processing. For this goal, it is critical to unravel the dynamics of the energy conversion processes between carriers in the earliest time scales of the excitation dynamics. We discuss the implementation and benefits of attosecond soft x-ray core-level spectroscopy up to photon energies of 600 eV for measurements in solid-state systems. In particular, we examine how the pairing between coherent spectral coverage and temporal resolution provides a powerful new insight into the quantum dynamic interactions that determine the macroscopic electronic and optical response. We highlight the different building blocks of the methodology and point out the important aspects for its application from condensed matter studies to materials as thin as 25 nm. Furthermore, we discuss the technological developments in the field of tabletop attosecond soft x-ray sources with time-resolved measurements at the near and extended edge simultaneously and investigate the exciting prospective of extending such technique to the study of 2-dimensional materials.

Gas phase Photoemission studies in the hard X-ray domain

Recent results obtained in gas phase photoemission studies are presented in this article with particular emphasis on recoil, Double Core Hole and Post Collision Interaction. These three important effects are not specific to the gas phase and could have more general applications in condensed matter studies.

Crystal Growth, Tetrahertz Generation, and Optical Characterization of EHPSI-4NBS

Nonlinear optical (NLO) organic crystals such as DAST, OH1, HMQ-TMS, and BNA have shown value as highly efficient terahertz (THz) generators, compared to their inorganic crystal counterparts. This is due to their higher peak electric fields and THz pulses with broader bandwidths generated with simple optical rectification setups. However, organic crystals exhibit phonon absorptions that reduce the THz output at specific frequencies. This is clearly appreciated in the state-of-the-art DAST crystal, which shows a significant generation dip at 1.1 THz. To solve this problem, new NLO organic crystals capable of producing THz radiation with unique spectra are under constant development, and the discovery of improved THz sources can help accelerate a host of condensed matter studies that are enabled with high-field THz science. In this article, we introduce the crystal growth and optical characterization of EHPSI-4NBS, and a comprehensive comparison of THz generation with benchmark organic crystals, showing that this novel crystal features higher generated electric fields. EHPSI-4NBS covers the electromagnetic spectrum from 0.1 to 3.8 THz without significant generation dips. These advantages make EHPSI-4NBS a promising crystalline material for THz generation applications.

A Primer on Weyl Semimetals: Down the Discovery of Topological Phases

Recently discovered Weyl semimetals (WSM) have found special place in topological condensed matter studies for they represent first example of massless Weyl fermions found in electronic condensed matter systems. A WSM shows gapless bulk energy spectra with Dirac-like point degeneracies, famously called Weyl nodes, which carry with themselves well defined chiralities and topologically protected chiral charges. One finds the Berry curvature of the Bloch bands to become singular, like in a magnetic monopole, at these Weyl nodes. Moreover, these systems feature topological surface states in the form of open Fermi arcs. In this review, we undergo a concise journey from graphene based Dirac physics to Weyl semimetals: the underlying Hamiltonians, their basic features and their unique response to external electric and magnetic fields in order to provide a basic walk-through of how the Weyl physics unfolded with time starting from the discovery of Graphene.

High accuracy characterisation for the absolute energy of scandium Kα

This work reports the absolute characterisation of the Sc Kα profile. All component peaks are characterised for the first time. The satellite component centroids, line-widths, and relative intensities are determined. Energies are calibrated on an absolute basis. Sc and peak energies of 4090.699(10) eV and 4085.926(18) eV are reported, respectively, with estimated standard error uncertainties of 2.4 and 4.4 ppm. In this work, an electron gun operating at 20 kV, incident on high purity metals, produces the x-ray fluorescence, which Bragg diffracts via a Germanium (220) crystal to permit high-accuracy measurement of energy. The Kα emission spectrum of scandium (Z = 21) has not been measured in absolute energy in over 50 years. At the time the data was reported in ‘x units’ and the angstrom was not a well defined unit. That reported uncertainty was estimated to be approximately 50 ppm (parts per million) or 0.2 eV. The new profile characterisation combined with the absolute energy calibration provides an important definition for future studies in chemical speciation and condensed matter studies. Furthermore, the methodology described obtains a level of accuracy from relatively low energy x-rays to provide an important insight for future studies in fundamental parameters, pionic spectra and high-accuracy tests of QED.

Optimization of moderators and beam extraction at the ESS.

A global approach coupling the moderator to the beam extraction system has been applied for the design optimization of the thermal and cold moderators of the European Spallation Source (ESS), which will be the brightest neutron source in the world for condensed-matter studies. The design is based on the recently developed high-brightness low-dimensional moderator concepts. Para-hydrogen is used for the cold neutron source, while thermal neutrons are provided by moderation in water. The overall moderation configuration was chosen in order to satisfy a range of requirements on bispectral extraction, beamport configuration and instrument performance. All instruments are served by a single moderator assembly above the target, arranged in a 'butterfly' geometry with a height of 3 cm. This was determined to be the optimal height for trade-off between high brightness and efficient guide illumination, by analysis of the performance of 23 instruments, based on the reference suite of the ESS Technical Design Report. The concept of 'brilliance transfer' is introduced to quantify the performance of the neutron optical system from the source to the sample. The target monolith incorporates a grid of 42 neutron beamports with an average separation of 6°, allowing a free choice between cold and thermal neutron sources at all instrument positions. With the large number of beamports and the space below the target available for future moderators, ample opportunities are available for future upgrades.

Hydrostatic pressure dependence on the collapsing of heptamer clusters in the charge ordered spinel AlV2O4

Charge frustrated spinels have engaged the interest of condensed matter studies due to the novel formation of multimer molecular sub units that lifts the degeneracy in the ground state. An exhaustive study on the stability of these molecular sub units is not available in the literature. In the present study, evidence has been obtained for the first time that hydrostatic pressure beyond 21 GPa, destabilizes the vanadium heptamer molecular sub units reversibly in the unique ambient temperature charge ordered spinel AlV2O4. The bulk modulus and its pressure derivative of the charge ordered phase are constrained. In addition a systematic structural analysis as a function of temperature shows destabilization of vanadium trimers those stack up to make the heptamer units. The crystal structure and total energy have been calculated using first principles density functional formalism (GGA approximation) as a function of pressure. The results obtained corroborate the stability of the frustrated phase beyond 20 GPa.

Testing a newly developed single-sphere neutron spectrometer in reference monochromatic fields from 147 keV to 14.8 MeV

A new neutron spectrometer, designed to simultaneously respond from the thermal domain up to hundreds of MeV neutrons, was designed and built in the framework of the INFN project NESCOFI@BTF. It has been called SP2 (SPherical SPectrometer) and it consists of 31 thermal neutron detectors embedded in a 25cm diameter polyethylene sphere with an internal 1cm thick lead shell. The new spectrometer shows similar performance as the Bonner sphere spectrometer, but has the notable advantage of requiring only one exposure to determine the whole spectrum. The SP2 response matrix, previously calculated with MCNP, has been experimentally evaluated with monochromatic reference neutron fields from 147keV to 14.8MeV at PTB Braunschweig. As suitable thermal neutron detectors, Dysprosium activation foils were adopted at this stage. The results of the experiment confirmed the correctness of the response matrix within an overall uncertainty of ±3%. The next phase of the NESCOFI@BTF project will be the replacement of passive detectors with active counters, thus leading to a real-time spectrometric monitor that is expected to significantly innovate the neutron control task in neutron-producing facilities, such as the beam-lines for industrial irradiation or condensed matter studies.

Applications of low temperature nuclear orientation

The techniques of low temperature nuclear orientation (LTNO) and nuclear magnetic resonance on oriented nuclei (NMRON) are versatile tools used across a range of applications. Such applications include nuclear moment and hyperfine field measurements and testing of nuclear decay models, as well as condensed matter studies, particularly applied to magnetism. Following the tradition of such presentations, the techniques LTNO and NMRON, are briefly outlined along with the principal applications with a focus on some recent works.

A PHYLLOTACTIC APPROACH TO THE STRUCTURE OF COLLAGEN FIBRILS

Collagen fibrils, cable-like assemblies of long biological molecules, the so-called triple helices, are dominant components of connective tissues. Their determinant morphological and functional roles motivated a large number of studies concerning their formation and structure. However, these two points are still open questions and, particularly, that of the lateral assembly of the triple helices which is certainly dense but not strictly that of a well-ordered molecular crystal. We examine here the geometrical template provided by the algorithm of phyllotaxis which gives to each element of an assembly of points or parallel rods the most homogeneous and isotropic dense environment in a situation of cylindrical symmetry. The scattered intensity obtained from a phyllotactic distribution of triple helices in collagen fibrils presents features which could contribute to the scattering observed along the equatorial direction of their X-ray patterns. Following this approach, the aggregation of triple helices in fibrils should be considered within the frame of soft condensed matter studies rather than that of molecular crystal studies.

Rattling the cage: Micro- to mesoscopic structure in liquids as simple as argon and as complicated as water

The water molecule has the convenient property that its molecular polarizability tensor is nearly isotropic while its dipole moment is large. As a result, the low-frequency anisotropic Raman spectrum of liquid water is mostly collision-induced and therefore reports primarily translational motions while the far-infrared (terahertz) and dielectric spectrum is dominated by rotational modes. Atomic and globular–molecular liquids have a zero dipole moment as well as an isotropic polarizability tensor. These spectrum-simplifying properties were exploited in a study of a number of liquids and solutions using ultrafast optical Kerr-effect (OKE) spectroscopy combined with dielectric relaxation spectroscopy (DRS), terahertz time-domain spectroscopy (THz-TDS), and terahertz field-induced second-harmonic generation (TFISH) spectroscopy. For room-temperature ionic liquids (RTILs), liquid water, aqueous salt solutions, noble gas liquids, and globular–molecular liquids it was found that, in each case, surprising structure and/or inhomogeneity is observed, ranging from mesoscopic clustering in RTILs to stretched-exponential dynamics in the noble gas liquids. For aqueous electrolyte solutions it is shown that the viscosity, normally described by the Jones–Dole expression, can be explained in terms of a jamming transition, a concept borrowed from soft condensed matter studies of glass transitions in colloidal suspensions.

Properties of indium phosphite and selected compounds under irradiation with swift heavy ions

Surface and bulk properties of indium phosphate single crystals with initial and previously irradiated by 25 MeV electrons structures were irradiated with 86Kr (253 MeV) and 197Au (200 MeV) up to various fluences. The modern methods of condensed matter studies were used for research of InP property changes before and after irradiation as scanning (SEM) and high resolution transmission electronic microscopy (HTEM), Rutherford backscattering spectroscopy (RBS/C) and atomic force microscopy (AFM). The comparison of obtained results with the results of other authors is carried out. The surface structure change of InP single crystal irradiated by high-energy 86Kr ions and electrons is studied. It is shown the changes of the InP surface have complicated character and caused by inelastic sputtering processes. It is observed the twice irradiated layer swells with the cracks creation on the surface. The swelling with cracks and strong sputtering of twice irradiated by electrons and ions with high energy layers of the InP and GaAs surfaces are explained using the model based on the influence of ionizing energy loss of swift 86Kr ions. The small crystalline objects are detected on the InP surface irradiated with 86Kr ions which may be nano- and micro-crystals of InP. All obtained effects are discussed in frame of models based on ionizing energy loss of swift heavy ions.

History of the Conferences on Application of Neutron Scattering in Condensed Matter Studies from 1964 to 2006

History of the Conferences on Application of Neutron Scattering in Condensed Matter Studies from 1964 to 2006

Use of the Z Accelerator for Condensed Matter Studies at Multi-Mbar Pressures

The ability to study material response during isentropic compression has been a grand challenge of the scientific community for several decades. However, development of precision techniques for producing isentropic compression at high pressures has been limited. The revolutionary advance for using planar magnetic loading on the Z accelerator accelerated this goal by enabling quasi-isentropic studies on macroscopically sized materials to over 5 Mbar. In addition, the accelerator is easily configured to launch flyer plates to velocities more than four times higher than possible with conventional launchers, thus allowing shock compression studies in the laboratory to pressures exceeding 20 Mbar.

Applications of Neutron Radiography and Neutron Tomography

In radiographic methods, the attenuation of an incident beam on passing through an object is used to study the internal structure of this object. The availability of techniques to “look inside” large, optically intransparent objects without having to destroy them is obviously appealing and has had a profound impact in many fields, most clearly in medicine, but also in condensed matter studies. The development of radiography started with Rontgen’s discovery of X-rays in 1895, where the absorption of X-rays by bones were demonstrated publicly in 1896 by obtaining a radiograph of a hand. The medical applications were obvious, and already in World War I, mobile X-ray units were routinely deployed. The main shortcoming of X-ray radiography in early medical applications is that often it cannot be used to distinguish different kinds of soft tissue and that the two dimensional projections are sometimes difficult to interpret. This changed dramatically with the development of “computerized axial tomography” for which the Nobel prize was awarded in 1979 to Hounsfield and Cormack. Computed tomography, as it is now frequently called, is the three-dimensional reconstruction of the interior of an object from many radiographs taken at different angles, and this combination of data sets enables to distinguish between different soft tissues, such as kidneys and liver. Medical computed X-ray tomography scanners were used soon afterwards to investigate minerals and rocks, for example in an early study of chondritic meteorites (Arnold et al. 1983). These had a comparatively poor spatial resolution of ~1 mm. As there is no need for low radiation doses in material science studies, and as the penetrating power of high energy X-rays is larger and higher spatial resolutions can be obtained, dedicated scanners for material science have been developed. Commercially available “table top” scanners now offer spatial resolution of less than 1 …

Radioactive Ion Beams as Microscopic Probes into Matter

During the last decade there has been a remarkable progress in technologies concerning beams of radioactive ions, and based on this, nuclear physics has enjoyed an expanding interest in the newly accessible regions of nuclide. The opportunities are now getting practicable to other fields where even improved production yields and/or ease-of-use of the beams are essential. In particular, the upcoming facility at RIKEN called RIBF is intended to magnify these opportunities with increased available intensities and varieties. After an introduction of principles and methods in the experimental techniques, we describe the characteristics of radioactive ion beams presently available at RIKEN as well as of those to be available at RIBF in a few years, and discuss material science studies to be enabled by the incorporation of radioactive beams. In particular, we focus our discussion on spin-oriented radioactive ion beams. β-rays or other radiations emitted in decays of spin polarized radioactive nuclei show asymmetric or anisotropic angular distributions, and provide unique tool to detect the spin precession and relaxation in material where they are implanted. A method of p olarization taking advantage of the projectile fragmentation kinematics has been developed to produce polarized radioactive beams at RIKEN. Furthermore, a new method to obtain highly polarized slow radioactive ions at RIBF is being developed. We report on the present status, and discuss possible applications to condensed matter studies.

Natural crystals selection process for neutron diffraction applications

This work aims to show a selection process for natural crystals that considers the major characteristics and performance as gratings for neutron monochromators using the neutron diffraction technique. A total of 19 crystals have been selected and classified regarding their adequacy for use as neutron diffraction devices. Applying special criteria, method and the rocking curve technique, the measurements have been performed and the theoretically available values compared with the experimental results, obtained directly from a neutron diffractometer in operation at the IEA-R1 (5 MW) nuclear research reactor. The choice for natural crystals, expanding the operational range of the neutron diffraction instruments, is related with the purpose of getting monochromatic neutron sources suitable for the applications. The neutron has proved to be the most powerful microscopic testing particle in condensed matter studies and in many other areas of application.