Webinar DMONS presented by M. Benjamin Bacq-Labreuil

Benjamin BACQ-LABREUIL (Institut Quantique de l’Université de Sherbrooke – Canada)

Abstract : High-temperature n-layer cuprate superconductors have the remarkable universal feature that the maximum transition temperature Tc is always obtained for the tri-layer compound. It remains unclear how the recent breakthroughs, highlighting the relation of the charge transfer gap (CTG) and the spin exchange J with the pairing density, can be related to this universality. By integrating an exact diagonalization solver to a density functional theory (DFT) plus cluster dynamical mean-field theory (CDMFT) framework, we were able to carry charge self-consistent DFT+CDMFT calculations for n =1-5 multilayer cuprates. Remarkably, the undoped compounds already host a peculiar behavior as a function of n: the CTG first decreases until reaching a minimum at n=3, and then stabilizes. The CTG is smaller in the inner CuO2 planes, and consequently the spin exchange J is larger as compared to the outer planes, which corroborates the experimental evidence of stronger antiferromagnetic spin fluctuations in the inner planes. We trace back the miscroscopic origin of these observations to the existence of interstitial conduction states confined between the CuO2 layers which favor the inner planes. Our work paves the way towards ab initio material-specific predictions of the superconducting order parameter.

Contact : Mébarek ALOUANI : mebarek.alouani@ipcms.unistra.fr

Connexion links on March 5th, 2024  from 14h50 :

https://cnrs.zoom.us/j/94911816568?pwd=c0JoY2EyU1VJOG5SN2NsQXNDRG81Zz09
Meeting ID: 949 1181 6568
Secret code: 0FaFbn

Seminar Axis 3 presented by Dr. Maurizio Mastropasqua Talamo

Dr. Maurizio Mastropasqua Talamo (Laboratoire Moltech-Anjou, Université d’Angers)

Abstract :

Starting from initial purposes of molecular recognition, the study of chiral pi-conjugated molecules and supramolecular assemblies have led over time to a deeper understanding of chirality-related properties which do not only rely upon geometric pairing but also involve polarization in light-matter interaction and spin selectivity in charge transport. These new properties have boosted the interest in the development of chiral organic semiconductors for advanced optoelectronics applications.

Many asymmetric synthetic techniques which are particularly important in the field of pharmaceutical synthesis, can enable the practical modification of pi-conjugated scaffolds with various stereogenic motifs, resulting in molecular semiconductors and chromophores showcasing diverse chirality-related properties.

Some examples of asymmetric modification of molecular semiconductors and chromophores will be given in this lecture along with a discussion about chirality-related properties observed within the newly synthesized materials.

Seminar IPCMS presented by Dr. Laurence CROGUENNEC

Dr. Laurence CROGUENNEC  (Institut de Chimie de la Matière Condensée de Bordeaux)

Directrice de recherche CNRS, directrice adjointe de l’ICMCB

Abstract :

Known from all chemists for decades, the sodium-ion battery technology was dethroned in the 1980s by the lithium-ion battery that offered better performance. The major interest of sodium is to be a sustainable resource in comparison to lithium. The technology is thus back on the scene as an ecological, economical and reliable alternative to the lithium-ion battery. I will present the challenges of this research field, and highlight some of our results. I will show how we were able to (i) discover a new family of NASICON structural type materials NaxV2(PO4)3, and (ii) demonstrate how the chemistry of mixed anions and in particular the competition between the ionic bond V-F and the very covalent vanadyle-type bond V=O has an impact on the properties of Na3V2(PO4)2F3-yOy. I will demonstrate that only the in-depth control of the relationship synthesis/composition/atomic and electronic structure allows to tune the properties in the battery. I will illustrate also that monitoring in situ and operando, especially at large scale facilities, the synthesis of electrode materials and their evolution when used in batteries is essential. Changes in the composition and structure of the materials must be studied in their environment (in situ), and in real time (operando) during their preparation or operation of the battery because they are most often in conditions out of equilibrium. The experiments thus conducted allow to study the dynamics of reactions, essential for the understanding of the material and optimization of its performance in the electrochemical storage system.

Seminar DMONS/DSI presented by Sophie WEBER

Sophie WEBER (ETH-Zurich, Department of Materials, Zurich, Switzerland)

Theoretical arguments [1,2] and experimental measurements [3-6] have definitively shown that antiferromagnets (AFMs) with particular bulk symmetries can possess a nonzero magnetic dipole moment per unit area or “surface magnetization” on certain surface facets. Such surface magnetization underlies intriguing physical phenomena like interfacial magnetic coupling, and can be used as a readout method of antiferromagnetic domains. However, a universal description and understanding of antiferromagnetic surface magnetization is lacking. I first introduce a classification system based on whether the surface magnetization is sensitive or robust to roughness, and on whether the magnetic dipoles at the surface of interest are compensated or uncompensated. I then show that every type of surface magnetization can be identified and understood in terms of bulk magnetic multipoles, which are already established as symmetry indicators for bulk magnetoelectric responses [7]. This intimate correspondence between antiferromagnetic surface magnetization and magnetoelectric responses at both linear and higher orders reveals that selection and control of the antiferromagnetic order parameter via magnetoelectric annealing may be possible in many more materials and surfaces than previously believed. I use density functional calculations to illustrate that nominally compensated (10-10) and (-12-10) surfaces in magnetoelectric Cr2O3 develop a finite magnetization density at the surface, in agreement with our predictions based on both group theory and the ordering of the bulk multipoles. Finally, I present magnetotransport results by collaborators confirming our ab-initio and theoretical predictions of finite magnetization on these surfaces. Our analysis [8,9] provides a comprehensive basis for understanding the surface magnetic properties and their intimate correspondence to bulk magnetoelectric effects in antiferromagnets, and may have important implications for technologically relevant phenomena such as exchange bias coupling.
[1] A. F. Andreev, JETP Lett. 63, 756 (1996)
[2] K. D. Belashchenko, Phys. Rev. Lett. 105, 147204 (2010)
[3] X. H et al, Nature Mat. 9, 579 (2010)
[4] N. Wu et al., Phys. Rev. Lett. 106, 087202 (2011)
[5] P. Appel et al., Nano Lett. 19, 1682 (2019)
[6] M. S. Wörnle et al., Phys. Rev. B 103, 094426 (2021)
[7] N. A. Spaldin et al., Phys. Rev. B 88, 094429 (2013)
[8] S. F. Weber et al., arXiv:2306.06631 (2023)
[9] O. V. Pylypovskyi, S. F. Weber et al., arXiv 2310.13438 (2023)

Contact : Mébarek ALOUANI : mebarek.alouani@ipcms.unistra.fr

Seminar DMONS – Axis 1 presented by Horacio Miguel PASTAWSKI

Horacio Miguel PASTAWSKI (Instituto de Física Enrique Gaviola, Universidad Nacional de Córdoba-CONICET, Academia Nacional de Ciencias-Argentina)

Abstract :

I will describe the qualitative features of our three-decade long experimental and theoretical quest to
identify emergent phenomena within the quantum dynamics of spin and charge excitations. A quantum
phase transition occurs as an analytical discontinuity of a physical observable, as illustrated by the
Anderson metal-insulator transition in disordered systems. We observed a clear phase transition in the
case of two interacting nuclear spins undergoing Rabi oscillations in presence of a spin environment [1],
that, according to the Fermi Golden Rule, results in an imaginary energy in a 2×2 non-Hermitian effective
Hamiltonian [2]. The oscillations became a purely exponential decay when their coupling strength fell
below a critical value. Our first experimental hint that many-body interactions could lead to irreversible
dynamics, appeared when confronting the insurmountable limitations in performing a perfect time-
reversal procedure, even in a fairly well-controlled setting of nuclear spins [3]. After a decade of work,
we experimentally observed [4] a phase transition to an intrinsically irreversible regime in the
thermodynamic limit. However, its analytical proof has initially eluded us [5]. Recently, we observed a
striking universal stability of coherently diffusive one-dimensional systems with respect to decoherence
[6]. This approach gives a new insight to the “poised realm” hypothesis, promoted for biological systems,
stating that the edge of chaos is a favorable condition to charge and excitonic transport. As pointed out
by R. Laughlin, classical chaos can lead to diffusion, and hence, to a form of quantum dynamics extremely
robust against environmental noise.


[1] Environmentally induced quantum dynamical phase transition in a spin swapping operation, G.A. Álvarez, E.P.Danieli,
P.R.Levstein, and H.M. Pastawski,J. Chem. Phys. 124, 1 (2006);
[2] Revisiting the Fermi Golden Rule: Quantum dynamical phase transition as a paradigm shift H. M. Pastawski Physica B 398,
278 (2007);
[3] Attenuation of polarization echoes in NMR: A test for the emergence of Dynamical Irreversibility in Many-Body Quantum
Systems. P.R. Levstein, G. Usaj, H.M. Pastawski, J. Chem. Phys. 108, 2718 (1998);
[4] Perturbation-independent decay of the Loschmidt echo in a many-spin system studied through scaled dipolar dynamics. C.M.
Sánchez, A.K. Chattah, K.X. Wei, L. Buljubasich, P. Cappellaro, and H.M. Pastawski, Phys. Rev. Lett. 124, 030601 (2020);
[5] Loschmidt echo in many-spin systems: a quest for intrinsic decoherence and emergent irreversibility P. R. Zangara and H. M.
Pastawski, Phys. Scr. 92, 033001(2017);
[6] Universal stability of coherently diffusive 1D systems with respect to decoherence. F.S. Lozano-Negro, E. Alvarez Navarro,
N.C. Chávez, F. Mattiotti, F. Borgonovi, H.M. Pastawski, G.L.Celardo, arXiv.2307.05656.

Contact : Rodolfo JALABERT : rodolfo.jalabert@ipcms.unistra.fr