Fecha  Evento 

12/09/2019  12/09/2019  Magic Angle Graphene: a New Platform for Strongly Correlated Physics
SPEAKER: Pablo JarilloHerrero, Massachusetts Institute of Technology. Abstract The understanding of stronglycorrelated quantum matter has challenged physicists for decades. Such difficulties have stimulated new research paradigms, such as ultracold atom lattices for simulating quantum materials. In this talk I will present a new platform to investigate strongly correlated physics, based on graphene moiré superlattices. In particular, I will show that when two graphene sheets are twisted by an angle close to the theoretically predicted ‘magic angle’, the resulting flat band structure near the Dirac point gives rise to a stronglycorrelated electronic system. These flat bands exhibit halffilling insulating phases at zero magnetic field, which we show to be a correlated insulator arising from electrons localized in the moiré superlattice. Moreover, upon doping, we find electrically tunable superconductivity in this system, with many characteristics similar to hightemperature cuprates superconductivity. These unique properties of magicangle twisted bilayer graphene open up a new playground for exotic manybody quantum phases in a 2D platform made of pure carbon and without magnetic field. The easy accessibility of the flat bands, the electrical tunability, and the bandwidth tunability though twist angle may pave the way towards more exotic correlated systems, such as quantum spin liquids or correlatedtopological insulators.
More information: http://www.ifimac.uam.es/category/conferencesevents

19/06/2019  11/10/2019  25º PREMIO CARMEN Y SEVERO OCHOA DE INVESTIGACIÓN EN BIOLOGÍA MOLECULAR

07/11/2018  07/11/2018  Las nuevas Neurotecnologías: impacto en la Ciencia, Medicina y Sociedad SPEAKER: DR. Rafael Yuste Professor of Biological Sciences, Director NeuroTechnology Center, Columbia University, New York.

15/12/2017  15/12/2017  Geometry invariant phenomena in near zero index media Abstract: Continuous media and metamaterials with a nearzero refractive index (NZI media) provide alternative pathways for the control and manipulation of lightmatter interactions. The exotic behavior of NZI media is rooted in the fact that the wavelength gets effectively stretched as the refractive index vanishes. This allows for pathological solutions to the wave equation, including spatially static fields distributions which nevertheless dynamically oscillate in time. This paradoxical behavior gives access to a regime of qualitatively different wave dynamics, where the importance of the geometry is lessened, and certain observables are invariant with respect to geometrical deformations, even including changes in the topology of the system.
In this talk, I’ll review and discuss some of the geometryinvariant phenomena related to nearzeroindex media. Examples will include: (i) transmission (tunneling) of waves through deformed waveguides. (ii) Unconventional resonators supporting modes whose eigenfrequency is independent of the geometry of their external boundary. (iii) Violation of effective medium theory geometrical restrictions, enabling, for example, single unitcell metamaterials. (iv) Existence of bound states in open 3D compact resonators with arbitrarily shaped boundaries. Different technological applications and implementations of these concepts will be discussed.
Más información: http://www.ifimac.uam.es/category/seminars/

12/12/2017  12/12/2017  Charge and energy noise in ac driven conductors
Abstract: The timedependent driving of nanoscale conductors allows for the controlled creation of singleelectron excitations. This effect has been demonstrated experimentally both by application of timedependent driving to gates coupled to confined systems, such as quantum dots [1], and by specifically shaped acdriving of twodimensional conductors [2,3]. However, the spectral properties of the injected signal are in general not known; moreover, the particle emission goes along with the excitation of electronhole pairs with some unknown energy distribution. These issues can be addressed by studying fluctuations in the detected currents: not only do such fluctuations provide more insight into how to increase the precision of the singleparticle emission, but also they allow for obtaining more information about the character of the emitted signal.
Here, I will present a theoretical study of charge and energy currents and their fluctuations in coherent conductors driven by different types of timeperiodic bias voltages, based on a scattering matrix approach [4,5]. Specifically, we investigate the role of electronlike and holelike excitations created by the driving in the charge current noise, where they only contribute separately. In contrast, additional features due to electronhole correlations appear in the energy noise. We then compare two different types of driving schemes [6], that is for a driven mesoscopic capacitor [1] as well as for a Lorentzianshaped bias voltage [3], which do not differ in the number of injected particles, but only in their energetic properties. Finally, I will discuss proposals for the detection of charge and energy noise, either through power fluctuations [4], or via frequencydependent temperature and electrochemicalpotential fluctuations in a probe reservoir [7]. References: [1] G. Fève, A. Mahé, J.M. Berroir, T. Kontos, B. Plaçais, D. C. Glattli, A. Cavanna, B. Etienne, Y. Jin: Science 316, 1169 (2007). [2] J. Gabelli and B. Reulet, Phys. Rev. B 87, 075403 (2013). [3] J. Dubois, T. Jullien, F. Portier, P. Roche, A. Cavanna, Y. Jin, W. Wegscheider, P. Roulleau, and D. C. Glattli, Nature 502, 659 (2013). [4] F. Battista, F. Haupt, and J. Splettstoesser, Phys. Rev. B 90, 085418 (2014) [5] F. Battista, F. Haupt, and J. Splettstoesser, J. Phys. Conf. Ser. 568, 052008 (2014) [6] N. Dashti, M. Misiorny, P. Samuelsson, and J. Splettstoesser, in preparation [7] N. Dashti, M. Misiorny, P. Samuelsson, and J. Splettstoesser, in preparation.
Más información: http://www.ifimac.uam.es/category/seminars/ 
Fecha  Evento 

12/09/2019  12/09/2019  Magic Angle Graphene: a New Platform for Strongly Correlated Physics
SPEAKER: Pablo JarilloHerrero, Massachusetts Institute of Technology. Abstract The understanding of stronglycorrelated quantum matter has challenged physicists for decades. Such difficulties have stimulated new research paradigms, such as ultracold atom lattices for simulating quantum materials. In this talk I will present a new platform to investigate strongly correlated physics, based on graphene moiré superlattices. In particular, I will show that when two graphene sheets are twisted by an angle close to the theoretically predicted ‘magic angle’, the resulting flat band structure near the Dirac point gives rise to a stronglycorrelated electronic system. These flat bands exhibit halffilling insulating phases at zero magnetic field, which we show to be a correlated insulator arising from electrons localized in the moiré superlattice. Moreover, upon doping, we find electrically tunable superconductivity in this system, with many characteristics similar to hightemperature cuprates superconductivity. These unique properties of magicangle twisted bilayer graphene open up a new playground for exotic manybody quantum phases in a 2D platform made of pure carbon and without magnetic field. The easy accessibility of the flat bands, the electrical tunability, and the bandwidth tunability though twist angle may pave the way towards more exotic correlated systems, such as quantum spin liquids or correlatedtopological insulators.
More information: http://www.ifimac.uam.es/category/conferencesevents

19/06/2019  11/10/2019  25º PREMIO CARMEN Y SEVERO OCHOA DE INVESTIGACIÓN EN BIOLOGÍA MOLECULAR

07/11/2018  07/11/2018  Las nuevas Neurotecnologías: impacto en la Ciencia, Medicina y Sociedad SPEAKER: DR. Rafael Yuste Professor of Biological Sciences, Director NeuroTechnology Center, Columbia University, New York.

15/12/2017  15/12/2017  Geometry invariant phenomena in near zero index media Abstract: Continuous media and metamaterials with a nearzero refractive index (NZI media) provide alternative pathways for the control and manipulation of lightmatter interactions. The exotic behavior of NZI media is rooted in the fact that the wavelength gets effectively stretched as the refractive index vanishes. This allows for pathological solutions to the wave equation, including spatially static fields distributions which nevertheless dynamically oscillate in time. This paradoxical behavior gives access to a regime of qualitatively different wave dynamics, where the importance of the geometry is lessened, and certain observables are invariant with respect to geometrical deformations, even including changes in the topology of the system.
In this talk, I’ll review and discuss some of the geometryinvariant phenomena related to nearzeroindex media. Examples will include: (i) transmission (tunneling) of waves through deformed waveguides. (ii) Unconventional resonators supporting modes whose eigenfrequency is independent of the geometry of their external boundary. (iii) Violation of effective medium theory geometrical restrictions, enabling, for example, single unitcell metamaterials. (iv) Existence of bound states in open 3D compact resonators with arbitrarily shaped boundaries. Different technological applications and implementations of these concepts will be discussed.
Más información: http://www.ifimac.uam.es/category/seminars/

12/12/2017  12/12/2017  Charge and energy noise in ac driven conductors
Abstract: The timedependent driving of nanoscale conductors allows for the controlled creation of singleelectron excitations. This effect has been demonstrated experimentally both by application of timedependent driving to gates coupled to confined systems, such as quantum dots [1], and by specifically shaped acdriving of twodimensional conductors [2,3]. However, the spectral properties of the injected signal are in general not known; moreover, the particle emission goes along with the excitation of electronhole pairs with some unknown energy distribution. These issues can be addressed by studying fluctuations in the detected currents: not only do such fluctuations provide more insight into how to increase the precision of the singleparticle emission, but also they allow for obtaining more information about the character of the emitted signal.
Here, I will present a theoretical study of charge and energy currents and their fluctuations in coherent conductors driven by different types of timeperiodic bias voltages, based on a scattering matrix approach [4,5]. Specifically, we investigate the role of electronlike and holelike excitations created by the driving in the charge current noise, where they only contribute separately. In contrast, additional features due to electronhole correlations appear in the energy noise. We then compare two different types of driving schemes [6], that is for a driven mesoscopic capacitor [1] as well as for a Lorentzianshaped bias voltage [3], which do not differ in the number of injected particles, but only in their energetic properties. Finally, I will discuss proposals for the detection of charge and energy noise, either through power fluctuations [4], or via frequencydependent temperature and electrochemicalpotential fluctuations in a probe reservoir [7]. References: [1] G. Fève, A. Mahé, J.M. Berroir, T. Kontos, B. Plaçais, D. C. Glattli, A. Cavanna, B. Etienne, Y. Jin: Science 316, 1169 (2007). [2] J. Gabelli and B. Reulet, Phys. Rev. B 87, 075403 (2013). [3] J. Dubois, T. Jullien, F. Portier, P. Roche, A. Cavanna, Y. Jin, W. Wegscheider, P. Roulleau, and D. C. Glattli, Nature 502, 659 (2013). [4] F. Battista, F. Haupt, and J. Splettstoesser, Phys. Rev. B 90, 085418 (2014) [5] F. Battista, F. Haupt, and J. Splettstoesser, J. Phys. Conf. Ser. 568, 052008 (2014) [6] N. Dashti, M. Misiorny, P. Samuelsson, and J. Splettstoesser, in preparation [7] N. Dashti, M. Misiorny, P. Samuelsson, and J. Splettstoesser, in preparation.
Más información: http://www.ifimac.uam.es/category/seminars/ 