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

Seminar DMONS/DSI – Axis 1 : presented by Anna Galler

Anna GALLER / Institute of Theoretical and Computational Physics, Graz University of Technology, Austria

Abstract : Optical phenomena in solids are fascinating and of great importance for technological applications. In this talk, I will first present a novel approach to compute the optical response and color of new inorganic pigment materials from first principles. I will show that the brilliant colors of my target materials, certain transition-metal oxides and rare-earth semiconductors, are strongly influenced by the presence of transition-metal and rare-earth electronic states, whose theoretical treatment requires elaborate many-body techniques.
The second part of the seminar will be focused on nonlinear optical phenomena. I will investigate the response of monolayer hexagonal boron nitride, a prototypical 2D semiconductor, to intense ultrafast laser pulses. I will show that the conduction band charge occupation induced by an elliptically polarized laser can be understood in a multi-photon resonant picture, but remarkably, only if using the Floquet light-dressed states instead of the undressed matter states.
[1] Ransmayr, Tomczak and Galler, PRM 6, 105003 (2022)
[2] Galler, Rubio and Neufeld, J. Phys. Chem. Lett. 14, 50, 11298–11304 (2023)

Pour tout contact : Mébarek ALOUANI : mebarek.alouani@ipcms.unistra.fr

Seminar DON, axes 1 and 4 presented Abdelghani Laraoui

Abdelghani Laraoui (Department of Mechanical & Materials Engineering, University of Nebraska-Lincoln)

Abstract :
Magnetic microscopy based on nitrogen vacancy (NV) centers in diamond has become a versatile tool to detect magnetic fields with an unprecedented combination of spatial resolution and magnetic sensitivity, opening up new frontiers in biological [1] and condensed physics matter research [2]. In this seminar, I will present two examples of using NV magnetic microscopy in both scanning probe microscopy (SPM) and wide-field microscopy (WFM) geometries to study nanoscale magnetic phenomena in different materials. First, I will discuss NV-SPM measurements of antiferromagnetic (AFM) domains switching in Cr2O3 and B-Cr2O3 thin films and device structures [3, 4]. Cr2O3 is an archetypical AFM oxide that permits voltage-control of the Néel vector. In addition, boron doping increases Néel temperature from 307 K to 400 K and allows realizing voltage controlled Néel vector at zero applied magnetic field, a promising finding to AFM spintronics. Then, I will discuss NV-WFM measurements on individual Fe(Htrz)2(trz)](BF4)] (Fe triazole) spin-crossover (SCO) nano-rods of size varying from 20 to 1000 nm [5]. Fe triazole SCO complexes exhibit thermal switching between low spin (LS) and high spin (HS) states which are applicable in thermal sensors and molecular switches. While the bulk magnetic properties of these molecules are widely studied by bulk magnetometry techniques their properties at the individual level are missing. The stray magnetic fields produced by individual Fe-triazole nano-rods are imaged by NV magnetic microscopy as a function of temperature (up to 150 0C) and applied magnetic field (up to 3500 G). We found that in most of the nanorods the LS state is slightly paramagnetic, possibly originating from the surface oxidation and/or the greater Fe(III) presence along the nanorods’ edges [5].

References: [1] I. Fescenko, A. Laraoui, et al., Phys. Rev. App. 11, 034029 (2019). [2] A. Laraoui and K.
Ambal, Appl. Phys. Lett. 121, 060502 (2022). [3] A. Erickson, A. Laraoui, et al., RSC Adv. 13, 178-185 (2023).
[4] A. Erickson, A. Laraoui, et al., to be submitted to Nat. Mat. (2023). [5] S. Lamichhane, A. Laraoui, et al.,
ACS Nano 17, 9, 8694–8704 (2023).

Contact : Valérie Halté (valerie.halte@ipcms.unistra.fr)

Mini-Symposium DMONS, QMat and Axis 1

10:15 – 10:45: Paloma Arroyo Huidobro
Departamento de Física Téorica de la Materia Condensada, Uni. Autónoma de Madrid

Controlling light-matter interactions with subwavelength emitter arrays

10:45 – 11:00: coffee break

11:00 – 11:30: Denis Basko
Université Grenoble Alpes, CNRS, LPMMC, Grenoble
Local bistability under microwave heating for spatially mapping
disordered superconductors

11:30 – 12:00: Jean-Noël Fuchs
Sorbonne Université, CNRS, LPTMC, Paris
The SSH model and the Zak phase