Coordinators: Álvaro Gómez León, Sigmund Kohler

06 February 2020, 12:00 h. Sala de Seminarios, 182

Instituto de Ciencia de Materiales de Madrid

After the synthesis of graphene (described at low energies as massless Dirac fermions in 2+1 dimensions) in 2005, Weyl semimetals were synthesized in 2015. Although they can be seen as 3D graphene, a series of new phenomena arise from the fundamental differences between chiral fermions in two and three dimensions. Chiral imbalance in 3D implies a set of anomaly related transport phenomena first discussed in the context of high energy collisions (quark-gluon plasma). Examples are the chiral magnetic effect: generation of an electric current parallel to en applied magnetic field, or the axial magnetic effect: generation of an energy current parallel to an axial magnetic field [1]. In this talk we will see some of the implications of these phenomena to the novel Dirac materials. I will explain the origin of the anomaly--induced response functions and review the experimental evidences found so far. Finally I will describe novel response functions associated to the scale anomaly in Dirac and Weyl semimetals [2]. I will try to be pedagogical.

[1] D. E. Kharzeev, arXiv:1312.3348.

[2] M. N. Chernodub, A. Cortijo, and M. A. H. Vozmediano, Phys. Rev. Lett. 120, 206601 (2018);

M. N. Chernodub, M. A. H. Vozmediano, Phys. Rev. Res. 1, 032002(R) (2019);

V. Arjona, M. N. Chernodub, M. A. H. Vozmediano, Phys. Rev. B 99, 235123 (2019);

M. Chernodub and M. A. H. Vozmediano, Phys. Rev. Res. 1, 032040(R) (2019).

31 January 2020, 12:00 h. Salón de Actos

Regensburg University

The dynamics and spread of quantum information in complex many-body systems is presently attracting a lot of attention across various fields, ranging from cold atom physics via condensed quantum matter to high energy physics and quantum gravity. This includes questions of how a quantum system thermalizes and phenomena like many-body interference and localization, more generally non-classicality in many-particle quantum physics. Here concepts that are based on echoes, i.e. "rewinding" time, provide a powerful way to monitor complex quantum dynamics and its stability. Central to these developments are so-called out-of-time-order correlators (OTOCs) as sensitive probes for chaos and the temporal growth of complexity in interacting systems. We will address such phenomena for quantum critical and quantum chaotic systems using semiclassical path integral techniques based on interfering Feynman paths, thereby bridging the classical and quantum many-body world. These methods enable us to compute echoes and OTOCs including entanglement and correlation effects. Moreover, on the numerical side we devise a semiclassical method for Bose-Hubbard systems far-out-of equilibrium that allows us to calculate many-body quantum interference on time scales far beyond the famous Ehrenfest/scrambling time.

23 January 2020, 12:00 h. Sala de Seminarios, 182

IMDEA

One of the consequences of strong electron-electron interactions in transition metal oxides is the transition from the Mott insulating phase to a metal, and therefore several orders of magnitude change in resistance, as external parameters are varied. The metal-insulator transition (MIT) in these materials has been a long-standing topic of research both from a theoretical and experimental point of view. In particular, two of the phases from the family of vanadium oxides are of great interest, namely vanadium sesquioxide (V_2 O_3) and vanadium dioxide (VO_2). The first one has a very rich phase diagram and is considered a paradigmatic example of a pure metal-Mott insulator phase transition. On the other hand, VO_2 with a phase transition close to room temperature, has gained lot of attention due to the possible applications of MIT materials in devices. In this talk, I will discuss how strain, doping and defects influence the metal-insulator phase transition in V_2 O_3 thin films. Finally, I will also present electrical and optical properties of VO_2 films and their integration in silicon photonic devices.