arXiv subjects

Mario Rentería

Publications and source records attributed to Mario Rentería.

4 recordsLinked to original sources

arXiv2026

First-Principles Study of the Temperature Dependence of Structural, Electronic, and Hyperfine Properties of the Cu(100) Surface

In this work, we investigate the temperature-dependent behavior of the pure (undoped) Cu(100) surface using first-principles calculations within the Density Functional Theory framework. One of the main objectives is to determine, as a first step, whether the unexpected linear dependence of the electric-field gradient (EFG) tensor observed in TDPAC experiments on $^{111}$Cd probes deposited on Cu(100) surfaces could arise from the surface generation itself or from surface reconstruction. To this end, we perform a comprehensive $\it{ab}$ $\it{initio}$ study of the Cu(100) surface reconstruction and its associated structural, electronic, and hyperfine properties as a function of temperature, not only at the outermost atomic layer (i.e., the topmost Cu atom) but also as a function of atomic depth relative to the surface. To study the temperature dependence of the EFG, we use experimentally determined temperature-dependent lattice parameters for bulk copper in our calculations. The anisotropic relaxation that arises when bulk symmetry is broken helps unravel the potential sources of EFG temperature dependence at the surface. Studying the electron density of conduction electrons $\rho$($\bf{r}$) at the atomic scale near the Cu nucleus and the atom-resolved partial density of states at the topmost Cu atom allows us to correlate the surface effect on the EFG with respect to the bulk value. Finally, we discuss the linear temperature dependence found for the EFG on the undoped Cu(100) surface in relation to the temperature dependence of the "lattice" contribution to the EFG in the framework of the universal correlation found by Raghavan $\it{et}$ $\it{al.}$ [PRL 34, 1280 (1975)] for noncubic metals, showing that the linear decrease of the EFG as T increases in the $^{111}$Cd-doped Cu(100) surface is probably mostly caused by the generation of the pure Cu(100) surface and its reconstruction.

cond-mat.mtrl-sci↗

arXiv2025

"Aftereffects'' Phenomenon in $^{111}$In($\rightarrow$$^{111}$Cd)-Implanted $\alpha$-Al$_2$O$_3$ Single Crystals: Novel Approach Integrating Experimental Double-Model Analysis with Density-Functional Theory

We develop an experimental double-model analysis, combined with density-functional theory (DFT), to explore the origins of dynamic hyperfine interactions (HFIs) linked to the electron-capture decay ''aftereffects ''(ECAE) phenomenon. This electronic effect, reversible with temperature, has been observed in time-differential perturbed $\gamma$-$\gamma$ angular correlations (TDPAC) experiments on oxides doped with ($^{111}$In (EC)$\rightarrow$)$^{111}$Cd probe atoms. Besides identifying the electronic configuration that yields the stable final electric-field gradient (EFG) after the dynamic process ends, we determine the initial configurations around the probe nucleus and their corresponding EFGs whose fluctuations produce these dynamic HFIs. We demonstrate the equivalence between parameters of the two most widely used methods for analyzing this type of dynamic HFI, enabling us to obtain these initial electronic configurations at each temperature. In this framework, to unravel controversial TDPAC results reported for $^{111}$In-implanted $\alpha$-Al$_2$O$_3$ single crystals, we perform a DFT study of Cd-doped $\alpha$-Al$_2$O$_3$, examining their defect-formation energies, as functions of the Cd impurity level's charge state. We show that the stable final EFG for the expected interaction HFI$_u$ originates from $^{111}$Cd probes located at defect-free substitutional Al sites (without trapped electron holes) across all measured temperatures. Those of the unexpected HFI$_d$ originate from probes at Al sites, but with different degrees of occupation of the Cd impurity level. We show that one trapped hole for HFI$_u$ and at least five for HFI$_d$ are responsible for the dynamic regime when the ''aftereffects'' are more pronounced. The proposed scenario accounts for the observation of well-defined EFGs when the dynamic regime does not end.

cond-mat.mes-hall↗

arXiv2018

Experimental TDPAC and Theoretical DFT Study of Structural, Electronic, and Hyperfine Properties in ($^{111}$In-->) $^{111}$Cd-Doped SnO$_2$ Semiconductor: Ab Initio Modeling of the Electron-Capture-Decay After-Effects Phenomenon

In this paper we investigate the effect of Cd doping at ultra-low concentrations in SnO$_2$ both experimentally, by measuring the temperature dependence of the electric quadrupole hyperfine interactions with time-differential perturbed angular correlation (TDPAC) spectroscopy using $^{111}$Cd as probe nuclei, and theoretically, by performing first-principles calculations based on the density functional theory. TDPAC spectra were successfully analyzed with a time-dependent on-off model for the perturbation factor. These results show combined dynamic plus static interactions whose electric-field gradients were associated in this model to different stable electronic configurations close to the Cd atoms. The dynamic regime is then originated in fast fluctuations between these different electronic configurations. First-principles calculations results show that the Cd impurity introduces a double acceptor level in the top of the valence band of the doped semiconductor and produces isotropic outward relaxations of the nearest oxygen neighbors. The variation of the calculated electric-field gradient tensor as a function of the charge state of the Cd impurity level shows an interesting behavior that explains the experimental results, giving strong support from first-principles to the electron-capture after-effects proposed scenario. The electron-capture decay of the parent $^{111}$In to $^{111}$Cd as well as the double acceptor character of the $^{111}$Cd impurity and the electric nature of the host are shown to contribute to the existence of these type of time-dependent hyperfine interactions.

cond-mat.mtrl-sci↗

arXiv2005

Non-ionic contributions to the electric-field gradient at $^{181}$Ta and $^{111}$Cd impurity sites in R$_2$O$_3$ (R= Sc, In, Lu, Yb, Tm, Er, Y, Ho, Dy, Gd, Eu, Sm) bixbyites

The time-differential perturbed-angular-correlation (TDPAC) technique was applied to the study of the internal electric-field gradient (EFG) in Eu- and Ho-sesquioxides in their cubic bixbyite phases. The results, as well as previous characterizations of the EFG at $^{181}$Ta sites in oxides with the bixbyite structure, were compared to those obtained in experiments using $^{111}$Cd as probe, and to point-charge model and {\it ab initio} results calculations for the EFG tensor at impurity sites in binary oxides. These studies provide quantitative information about electronic processes and the structural relaxations induced by the presence of impurity probes in the host lattices, and confirm the existence of nonionic contributions to the EFG in these systems. Our FP-LAPW calculations show that this nonionic contribution to the EFG is the dominating one, and that it is originated in the population of {\it p} states (5{\it p} in the case of Cd, 6{\it p} for Ta).

cond-mat.mtrl-sci↗