RESUMEN
For over a decade, iron-based superconductors (IBSCs) have been the subject of intense scientific research, yet the underlying principle of their pairing mechanism remains elusive. To address this, we have developed a simulation tool that reasonably predicts the regional superconducting phase diagrams of key IBSCs, incorporating factors such as anisotropic superconducting gap, spin-orbital coupling, electron-phonon coupling, antiferromagnetism, spin density wave, and charge transfer. Our focus has been on bulk FeSe, LiFeAs, NaFeAs, and FeSe films on SrTiO3 substrates. By incorporating angle-resolved photoemission spectroscopy (ARPES) data to fine-tune the electron concentration in the superconducting state, our simulations have successfully predicted the theoretical superconducting transition temperature (Tc) of these compounds, closely matching experimental results. Our research not only aids in identifying patterns and establishing correlations with Tc but also provides a simulation tool for potentially predicting high-pressure phase diagrams.
RESUMEN
Why are materials with specific characteristics more abundant than others? This is a fundamental question in materials science and one that is traditionally difficult to tackle, given the vastness of compositional and configurational space. We highlight here the anomalous abundance of inorganic compounds whose primitive unit cell contains a number of atoms that is a multiple of four. This occurrence-named here the rule of four-has to our knowledge not previously been reported or studied. Here, we first highlight the rule's existence, especially notable when restricting oneself to experimentally known compounds, and explore its possible relationship with established descriptors of crystal structures, from symmetries to energies. We then investigate this relative abundance by looking at structural descriptors, both of global (packing configurations) and local (the smooth overlap of atomic positions) nature. Contrary to intuition, the overabundance does not correlate with low-energy or high-symmetry structures; in fact, structures which obey the rule of four are characterized by low symmetries and loosely packed arrangements maximizing the free volume. We are able to correlate this abundance with local structural symmetries, and visualize the results using a hybrid supervised-unsupervised machine learning method.
RESUMEN
In this work, we consider the physical basis of deformation and fracture in layered composite nanocrystalline/amorphous material-low-melting crystalline alloy in a wide temperature range. Deformation and fracture at the crack tip on the boundary of such materials as nanocrystalline alloy of the trademark 5BDSR, amorphous alloy of the trademark 82K3XSR and low-melting crystalline alloy were experimentally investigated. The crack was initiated by uniaxial stretching in a temperature range of 77-293 K. A theoretical description of the processes of deformation and fracture at the crack tip is proposed, with the assumption that these processes lead to local heating and ensure the plastic character of crack growth at liquid nitrogen temperatures. The obtained results improve the theoretical understanding of the physics of fracture at the boundary of nanocrystalline and crystalline alloys in a wide temperature range. The possibility of preserving the plastic nature of fracture in a thin boundary layer of crystalline-nanocrystalline material at cryogenic temperatures has been experimentally shown.
RESUMEN
Reliable synthesis methods for high-quality, large-sized, and uniform two-dimensional (2D) transition-metal dichalcogenides (TMDs) are crucial for their device applications. However, versatile approaches to growing high-quality, large-sized, and uniform 2D transition-metal tellurides are rare. Here, we demonstrate an ion adsorption strategy that facilitates the Frank-van der Merwe growth of 2D transition-metal tellurides. By employing this method, we grow MoTe2 and WTe2 with enhanced lateral size, reduced thickness, and improved uniformity. Comprehensive characterizations confirm the high quality of as-grown MoTe2. Moreover, various characterizations verify the adsorption of K+ and Cl- ions on the top surface of MoTe2. X-ray photoelectron spectroscopy (XPS) analysis reveals that the MoTe2 is stoichiometric without K+ and Cl- ions and exhibits no discernable oxidation after washing. This top surface control strategy provides a new controlling knob to optimize the growth of 2D transition-metal tellurides and holds the potential for generalized to other 2D materials.
RESUMEN
Discovery of iron-based superconductors paved the way to a competitor of high-temperature superconductors, easier to produce, better performing in high fields, and promising to be less expensive. Critical parameters are investigated by resistivity measurements as a function of temperature, field, and angle R(T,H,θ). This work presents a deep analysis of H-θ phase diagram of PLD-processed Fe(Se,Te) superconducting films, thus revealing material and pinning anisotropy at once. By selecting different thresholds along the R(T,H,θ) curves, all possible regimes emerge. Surprisingly, anisotropy arises moving from the upper critical field toward the irreversibility line: gradually a non-monotonous transition from 3D to 2D, and backward to 3D occurs. Although Fe(Se,Te) appears as a 3D superconductor, its anisotropic pinning landscape shows up similarities with an intrinsic layered superconductor and Fe(Se,Te) definitively mimics YBCO. We propose a general method to disentangle, in any other superconductor, material dimensionality and pinning anisotropy that are key constraints for applications.
RESUMEN
To enhance the use of Cr2TiC2Tx MXene in spin electronics, it is essential to transform its spin-disordered state into a long-range ordered spin state. In this study, first-principles calculations show that Rh layers adhered to the Cr2TiC2Tx surfaces can transform its spin disordered state into a long-range spin order by donating electrons to the O terminations, resulting in Cr2TiC2Tx becoming a single-layer A-type antiferromagnet. As the proportion of F termination increases from 0 to 100%, the exchange coupling constant J1 of the compound escalates from 0.5 to 15.9 meV. Concurrently, the Néel temperature experiences a significant rise from 8 K to 110 K. The analysis of the density of states reveals that the obtained Cr2TiC2Tx exhibits excellent conductivity with O termination and semiconductor characteristics with F termination. These unique features make Cr2TiC2Tx a promising magnetic material for application in spin electronics.