arXiv subjects

Frederico Gil Alabarse

Publications and source records attributed to Frederico Gil Alabarse.

3 recordsLinked to original sources

arXiv2025

Ternary superhydrides under pressure of Anderson's theorem: Near-record superconductivity in (La,Sc)H$_{12}$

Lanthanum-hydrogen system and its derivatives remain among the most promising for achieving room-temperature superconductivity. In this study, we examined the formation of ternary lanthanum-scandium superhydrides at pressures up to 220 GPa. The primary product of the LaSc alloy's reaction with hydrogen is newly discovered cubic (La,Sc)H$_{12}$, demonstrating clear superconducting transition in all six channels of the van der Pauw scheme below 244-248 K. In this compound with an unusually large unit cell volume, virtually no magnetoresistance was observed in fields up to 68 Tesla. Synthesized samples of (La,Sc)H$_{12}$ demonstrate pronounced superconducting diode and SQUID-like effects at a record high temperature of 233 K. Furthermore, our analysis revealed the formation of lower hexagonal polyhydrides (La,Sc)H$_{6-7}$, which could potentially account for the anomaly in electrical resistance observed near 274 K. This anomaly between 265-290 K also appears in the radio-frequency transmission measurements and may be of a superconducting nature.

cond-mat.supr-con↗

arXiv2024

Raisins in a Hydrogen Pie: Ultrastable Cesium and Rubidium Polyhydrides

We proposed a new method for synthesis of metal polyhydrides via high-pressure thermal decomposition of corresponding amidoboranes in diamond anvil cells. Within this approach, we synthesized molecular semiconducting cesium ($\textit P4/nmm$-CsH$_7$, $\textit P$1-CsH$_{15+x}$) and rubidium (RbH$_{9-x}$) polyhydrides with a very high hydrogen content reaching 93 at%. Preservation of CsH$_7$ at near ambient conditions, confirmed both experimentally and theoretically, represents a significant advance in the stabilization of hydrogen-rich compounds. In addition, we synthesized two crystal modifications of RbH$_{9-x}$ with pseudo hexagonal and pseudo tetragonal structures identified by synchrotron X-ray diffraction and Raman measurements. Both phases are stable at 8-10 GPa. This is an unprecedented low stabilization pressure for polyhydrides. These discoveries open up possibilities for modifying existing hydrogen storage materials to increase their efficiency.

cond-mat.mtrl-sci↗

arXiv2023

Structural, Vibrational, and Electronic Behavior of Two GaGeTe Polymorphs under compression

GaGeTe is a layered topological semimetal that has been recently found to exist in at least two different polytypes, $α$-GaGeTe ($R\bar{3}m$) and $β$-GaGeTe ($P6_3 mc$). Here we report a joint experimental and theoretical study of the structural, vibrational, and electronic properties of these two polytypes at high pressure. Both polytypes show anisotropic compressibility and two phase transitions, above 7 and 15 GPa, respectively, as confirmed by XRD and Raman spectroscopy measurements. Although the nature of the high-pressure phases is not confirmed, comparison with other chalcogenides and total-energy calculations allow us to propose possible high-pressure phases for both polytypes with an increase in coordination for Ga and Ge atoms from 4 to 6. In particular, the simplification of the X-ray patterns for both polytypes above 15 GPa suggests a transition to a structure of relatively higher symmetry than the original one. This result is consistent with the rocksalt-like high-pressure phases observed in parent III-VI semiconductors, such as GaTe, GaSe, and InSe. Pressure-induced amorphization is observed upon pressure release. The electronic band structures of $α$-GaGeTe and $β$-GaGeTe and their pressure dependence also show similarities to III-VI semiconductors, thus suggesting that the germanene-like sublayer induces a semimetallic character in both GaGeTe polytypes. Above 3 GPa, both polytypes lose their topological features, due to the opening of the direct band gap, while the reduction of the interlayer space increases the thermal conductivity at high pressure.

cond-mat.mtrl-sci↗