arXiv subjects

Silvia Giménez-Santamarina

Publications and source records attributed to Silvia Giménez-Santamarina.

7 recordsLinked to original sources

arXiv2026

An expandable kinetic Monte Carlo platform for modelling electron transport through chiral molecules

Chirality from molecular structures interacts with the spin angular momentum of electrons and photons giving rise to a variety of interesting phenomena. Among these, the observation of spin selective transport at room temperature is particularly attractive for the development of functional spintronic devices. During the past twenty five years, two effects have attracted considerable experimental and theoretical attention: electric Magnetochiral Anisotropy (eMChA) and Chirality Induced Spin Selectivity (CISS). In spite of the large body of work devoted to these phenomena, there is still no clear agreement on their microscopic origin(s). It even remains an open question whether eMChA and CISS arise from fundamentally different mechanisms or whether they are different experimental manifestations of the same underlying microscopic effects. In this work, we have developed the core of an efficient kinetic Monte Carlo code for the modeling of electron transport under an applied voltage, where the alpha and beta spin channels are treated independently. Each transport channel is characterized through its intrinsic electron mobility and an effective coupling between charge motion, spin, and chirality. This framework makes it possible to quantify the spin filtering that emerges from the interplay of these properties. From a set of simple rules emerges a voltage- and field-dependent effect that vanishes at low bias and shows the asymmetry between positive and negative voltages that is typically reported in electrical magnetochiral anisotropy experiments. We then move on to relate the internal parameters of our code with parameterization that has been used to describe the eMChA effect.

cond-mat.mes-hall↗

arXiv2023

Lanthanide molecular nanomagnets as probabilistic bits

Over the decades, the spin dynamics of a large set of lanthanide complexes have been explored. Lanthanide-based molecular nanomagnets are bistable spin systems, generally conceptualized as classical bits, but many lanthanide complexes have also been presented as candidate quantum bits (qubits). Here we offer a third alternative and model them as probabilistic bits (p-bits), where their stochastic behavior constitutes a computational resource instead of a limitation. We present a modelling tool for molecular spin p-bits, we demonstrate its capability to simulate bulk magnetic relaxation data and ac experiments and to simulate a minimal p-bit network under realistic conditions. Finally, we go back to a recent systematic data gathering and screen the best lanthanide complexes for p-bit behavior, lay out the performance of the different lanthanide ions and chemical families and offer some chemical design considerations.

cond-mat.mes-hall↗

arXiv2022

Data mining, dashboard and statistical analysis: a powerful framework for the chemical design of molecular nanomagnets

Three decades of research in molecular nanomagnets have raised their magnetic memories from liquid helium to liquid nitrogen temperature thanks to a wise choice of the magnetic ion and coordination environment. Still, serendipity and chemical intuition played a main role. In order to establish a powerful framework for statistically driven chemical design, we collected chemical and physical data for lanthanide-based nanomagnets, catalogued over 1400 published experiments, developed an interactive dashboard (SIMDAVIS) to visualise the dataset, and applied inferential statistical analysis. Our analysis showed that the Arrhenius energy barrier correlates unexpectedly well with the magnetic memory, as both Orbach and Raman processes can be controlled by vibronic coupling. Indeed, only bis-phthalocyaninato sandwiches and metallocenes, with rigid ligands, consistently present magnetic memory up to high temperature. Analysing magnetostructural correlations, we offer promising strategies for improvement, in particular for the preparation of pentagonal bipyramids, where even "softer" complexes are protected against molecular vibrations.

cond-mat.mes-hall↗

arXiv2021

Polymer-based composites for engineering organic memristive devices

Memristive materials are related to neuromorphic applications as they can combine information processing with memory storage in a single computational element, just as biological neurons. Many of these bioinspired materials emulate the characteristics of memory and learning processes that happen in the brain. In this work, we report the memristive properties of a two-terminal (2-T) organic device based on ionic migration mediated by an ion-transport polymer. The material possesses unique memristive properties: it is reversibly switchable, shows tens of conductive states, presents Hebbian learning demonstrated by spiking time dependent plasticity (STDP), and behaves with both short- (STM) and long-term memory (LTM) in a single device. The origin and synergy of both learning phenomena were theoretically explained by means of the chemical interaction between ionic electrolytes and the ion-conductive mediator. Further discussion on the transport mechanism was included to explain the dynamic behaviour of these ionic devices under a variable electric field. We propose this polymer-based composite as an outstanding neuromorphic material for being tunable, cheap, flexible, easy to process, reproducible, and more biocompatible than their inorganic analogues.

cond-mat.soft↗

arXiv2020

Reinforced Room temperature spin filtering in chiral paramagnetic metallopeptides

Chiral-induced spin selectivity (CISS), whereby helical molecules polarize the spin of electrical current, is an intriguing effect with potential applications in nanospintronics. In this nascent field, the study of paramagnetic chiral molecules, which could introduce another degree of freedom in the control of the spin transport, remains so far unexplored. To address this challenge, herein, we propose the use of self-assembled monolayers of helical lanthanide-binding peptides. In order to elucidate the effect of the paramagnetic nuclei, monolayers of the peptide coordinating paramagnetic or diamagnetic ions are prepared. By means of spin-dependent electrochemistry, CISS effect is demonstrated by cyclic voltammetry and impedance measurements for both samples. Additionally, an implementation of the standard liquid-metal drop electron transport setup has been carried out, demonstrating their suitability for solid-state devices. Remarkably, the inclusion of a paramagnetic center in the peptide increases the spin polarization as independently proved by different techniques. These findings permit the inclusion of magnetic biomolecules in the CISS field, paving the way to their implementation in a new generation of spintronic nanodevices.

physics.app-ph↗

arXiv2019

Theoretical insights on the importance of anchoring vs molecular geometry in magnetic molecules acting as junctions

The anchoring of the molecule to an electrode is known to be a key factor in single-molecule spintronics experiments. Likewise, a relaxation down to the most stable geometry is a critical step in theoretical simulations of transport through single-molecule junctions. Herein we present a set of calculations designed to analyze and compare the effect of different anchoring points and the effect of perturbations in the molecular geometry and interelectrode distance. As model system we chose the [V($α$-C$_3$S$_5$)$_3$]$^{2-}$ complex connecting two Au(111) electrodes in a slightly compressed geometry. In our calculations, the attachment happens through an S-Au bond, a common anchoring strategy in molecular spintronics experiments. Our results confirm that small alterations in the molecular geometry have important effects in the conductance. We were able to compare these effects with the ones arising from changing the anchoring position with a constant molecular geometry. Unexpectedly, we demonstrate that the anchoring position has only a lesser relevance in the spintronic behavior of the device, as long as all other parameters are kept frozen. As a consequence, we predict that for experimentalists aiming for reproducibility, the molecular design of rigid linkers is more relevant than the design of univocal anchoring positions.

cond-mat.mes-hall↗

arXiv2019

Exploring the transport properties of equatorially low coordinated erbium single ion magnets

Single-molecule spin transport represents the lower limit of miniaturization of spintronic devices. These experiments, although extremely challenging, are key to understand the magneto-electronic properties of a molecule in a junction. In this context, theoretical screening of new magnetic molecules provides invaluable knowledge before carrying out sophisticated experiments. Herein, we investigate the transport properties of three equatorially low-coordinated erbium single ion magnets with $C_{3v}$ symmetry: Er[N(SiMe$_3$)$_2$]$_3$ (1), Er(btmsm)$_3$ (2) and Er(dbpc)$_3$ (3), where btmsm = bis(trimethylsilyl)methyl and dbpc = 2,6-di-tert-butyl-p-cresolate. Our ligand field analysis, based on previous spectroscopic data, confirms a ground state mainly characterized by $M_J$ =$\pm$15/2 in all three of them. The relaxation of their molecular structures when placed between two Au (111) electrodes leads to an even more symmetric $\sim D_{3h}$ environment, which ensures that these molecules would retain their single-molecule magnet behavior in the device setup. Hence, we simulate spin dependent transport using the DFT optimized structures on the basis of the non-equilibrium Green's function formalism, which, in 1 and 2, suggests a remarkable molecular spin filtering under the effect of an external magnetic field.

cond-mat.mes-hall↗