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15/12/2017 - 15/12/2017Geometry invariant phenomena in near zero index media

Abstract:  

Continuous media and metamaterials with a near-zero refractive index (NZI media) provide alternative pathways for the control and manipulation of light-matter 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 geometry-invariant phenomena related to near-zero-index 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 unit-cell 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/

 

14/12/2017 - 14/12/2017Polariton lattices a novel platform for analogue simulation

 

Abstract:  

A large variety of computationally intractable systems can be mapped into certain univer-

sal classical spin models such as an Ising, X Y or Heisenberg models that are characterised by given degrees of freedom, “spins”, their interactions, “couplings,” and their associated cost function, “Hamiltonian”.  Various physical platforms have been proposed to simulate such models using superconducting  qubits, optical lattices, coupled lasers etc.

We  introduce polariton  lattices as a  new platform  for  analogue  simula- tion;   based on well-established semi- conductor and optical control technolo- gies polariton simulators allow for rapid scalability,  ease  of tunability  and ef- fortless readability.   Polariton conden- sates can be  imprinted  into  any two- dimensional lattices either  by  spatial modulation  of  the  pumping  laser or by lithographic techniques during the growth process, offering straightforward scalability.    In  the  case  of  optically imprinted polariton lattices with freely propagating polariton condensates,  we recently demonstrated that  the phase- configuration acquired in  a  polariton dyad or triad  is chosen  so as to max- imise polariton occupancy [1], while by expanding to square, and rhombic lat- tices as  well as  to arbitrary  polariton graphs we  simulated annealing of the X Y Hamiltonian through bosonic stim- ulation [2]. The bottom-up approach of

bosonic stimulation is achieved here by gradually increasing the excitation density to con- densation threshold. This is an advantage over classical or quantum annealing techniques, where the global ground state is reached through transitions over metastable excited states with an increase of the cost of the search with the size of the system.

By controlling the separation distance, in-plane wavevector, and spin of the injected condensates in polariton graphs, we acquire  several degrees of freedom in the tunability of  inter-site interactions, whilst the continuous coupling of polaritons to free photons offers effortless readability of all the characteristics of the polariton condensates such as energy, momentum, spin, and most critically their phase. The above constitute a unique toolbox for realising intriguing discrete giant vortices, controllable next nearest neighbour interactions, dynamic phase transitions and simulating artificial solids.

References:

 

[1] H. Ohadi, R.L. Gregory, T. Freegarde, Y.G. Rubo, A.V. Kavokin, N.G. Berloff, and

P.G. Lagoudakis, Phys. Rev. X, 6, 031032 (2016)

[2] Natalia G. Berloff, Matteo Silva, Kirill  Kalinin, Alexis Askitopoulos, Julian D. T¨opfer, Pasquale Cilibrizzi, Wolfgang Langbein and Pavlos G. Lagoudakis, Nature Materials in

print DOI: 10.1038/NMAT4971 (2017)

 

Más información: http://www.ifimac.uam.es/category/seminars/

12/12/2017 - 12/12/2017Charge and energy noise in ac driven conductors

 

Abstract:  

The  time-dependent driving of nanoscale conductors allows for the controlled creation of single-electron excitations. This effect has been demonstrated experimentally both by application of time-dependent driving to gates coupled to confined systems, such as quantum dots [1], and by specifically shaped ac-driving of two-dimensional 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 electron-hole 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 single-particle 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 time-periodic bias voltages, based on a scattering matrix approach [4,5].  Specifically, we investigate the role of electron-like and hole-like excitations created by the driving in the charge current noise, where they only contribute separately. In contrast, additional features due to electron-hole 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 Lorentzian-shaped 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 frequency-dependent temperature and electrochemical-potential fluctuations in a probe reservoir [7].

sys

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/

01/12/2017 - 01/12/2017Centrosomes and exosomes molecualr pacemakers of immune synapse

 

 

 

 

 

 

15/11/2017 - 15/11/2017Pair correlation function of a 2D molecular gas directly visualized by scanning tunneling microscopy

 

Abstract:  

The state of matter in fluid phases, determined by the interactions between particles, can be characterized by a pair correlation function (PCF). At the nanoscale, the PCF has been so far obtained experimentally only by means of reciprocal-space techniques. We use scanning tunneling microscopy (STM) at room temperature in combination with lattice-gas kinetic Monte Carlo (KMC) simulations to study a two-dimensional gas of highly mobile molecules of fluorinated copper phthalocyanine on a Si(111)/Tl-(1×1) surface. A relatively slow mechanism of STM image acquisition results in time-averaging of molecular occurrence under the STM tip. We prove by the KMC simulations that in the proximity of fixed molecules STM images represent the PCF. We demonstrate that STM is capable of visualizing directly the pair correlation function in real space.

 

Más información: http://www.ifimac.uam.es/category/seminars/

 

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Generales

Total 100 eventos
Agenda de eventos
FechaEvento
03/11/2017 - 03/11/2017From Loving Viruses, to being Amazed by Cancer, to Admiring the Immune Response

 

 

 

 

 

 

27/10/2017 - 27/10/2017Evolution of Coronaviruses

 

 

09/10/2017 - 09/10/2017Computational study of the collective motion of micro-swimmers

 

Abstract:  

Micro-swimmers are active matter (AM), where AM can be seen as systems

composed of self-driven units, active particles, each capable of converting stored

or ambient free energy into systematic movement. Active materials are

intrinsically out of equilibrium and their collective behavior emerges from their

dynamic self-organization. Examples of active systems are found in all length

scales and could be classified in living and nonliving systems like individual living

cells, tissues and organisms, animal groups, self-propelled colloids and artificial

nanoswimmers. Particularly, in the micro and nano scale we find an enormous

range of interesting systems either biological or artificial, the spermatozoa that

fuse with the ovum during fertilization, the bacteria that inhabit our guts, the

protozoa in our ponds, the algae in the ocean; these are but a few examples of a

wide biological spectrum. Whereas in the artificial world we have self-healing

colloidal crystals and membranes to self-assembled microswimmers and robots.

Experiments in this field are now developing at a very rapid pace and new theoretical ideas are needed to bring unity to the field and identify “universal” behavior in these internally driven systems.

With numerical simulations we are able to find the fundamental role that the hydrodynamic coupling through the embedding solvent has in the collective behaviour in model systems of self-propelled microswimmers.

Such a fundamental understanding will help us to identify new routes to design micro-robots that can imitate micro-organisms and it might become possible to design materials that assemble and repair themselves from their microscopic components.

 

Más información: http://www.ifimac.uam.es/category/seminars/

22/09/2017 - 22/09/2017Polymer-theory insights into biomolecular systems

 

Abstract:  

Biomolecular systems are nowadays being the focus of a massive amount of research, both theoretical and experimental. The advancement of techniques has enabled the exploration of single-molecule properties, thus posing new challenges at the theoretical level. In this talk I will present two recent works inspired by such findings.

- The first part will be focused on a constitutive model for amyloid fibrils based on the minimization of the total energy per fibril. The constitutive model quantitatively recapitulates the main mesoscopic topological features of amyloid fibrils, that is, the evolution of fibril periodicity as a function of the ionic strength of the solution and of the fibril width.

A universal mesoscopic structural signature of the fibrils emerges from this picture, predicting a general, parameter-free law for the periodicity of the fibrils, that depends solely on the number of protofilaments per fibril. These predictions are validated experimentally and conclusively highlight the role of competing electrostatic and elastic contributions as the main players in the establishment of amyloid fibrils structure.

- The second work is focused on the shape and the orientational properties of a polymer chain under tension in a good solvent, a physical condition that is often realized both in single-molecule experiments and in vivo. Our findings reveal the existence of hitherto unobserved universal laws encompassing polymers with different rigidities and including the possible presence of excluded-volume effects, showing that both shape and orientation are solely determined by the force contribution to the free energy. In doing so, they also provide a simple way to retrieve these quantities from the knowledge of the force-versus-extension curve.

 

Más información: http://www.ifimac.uam.es/category/seminars/

 

18/09/2017 - 18/09/2017Fabrication of Gold Nano-Crystal Arrays for Molecular Electronics: High Frequency Molecular Rectifiers and π-π Inter Molecular Interaction Energy

 

Abstract:  

E-beam lithography was used for versatile fabrication of sub-15 nm single-crystal gold nanoarrays at wafer-scale by the so-called dot on the fly (DOTF) technique [1]. Here DOTF and other methods are compared evidencing the limiting factors for the writing speed. Wafer-scale fabrication of such arrays with 50 nm pitch allowed XPS analysis of a ferrocenylalkyl thiol self- assembled monolayer coated gold nanoarray. We exploit these arrays as a suitable test bed for Molecular Electronics (ME) [2] and propose two studies on high frequency molecular rectifiers [3] and inter molecular Interactions [4].

 

In a first study, we demonstrate molecular diodes operating up to 17.8 GHz. Direct current and radio frequency (RF) properties were simultaneously measured with the tip of an interferometric scanning microwave microscope and S11 parameters show a diode rectification ratio of 12 dB. In a second investigation, we explore the π-π intermolecular interactions. This factor is one of the most important to optimize the transport and optical properties of organic transistors, light-emitting diodes or (bio-) molecular devices. Electrochemical measurements indicate two different phases localized on top and facets of the nanocrystals with clear intermolecular interactions and electrical current statistics on ~3000 molecular junctions confirm the theoretical prediction [5] of asymmetrical histograms due to cooperative effects.

 

References:

 

[1] J. Trasobares, F. Vaurette, M. François, H. Romijn, J-L. Codron, D. Vuillaume, D. Théron and N.

Clément. High speed e-beam lithography for gold nanoarray fabrication and use in nanotechnology. Beilstein J. Nanotechnol. 5, 1918–1925 (2014).

[2] N. Clement, G. Patriarche, K, Smaali, F. Vaurette, K. Nishiguchi, D. Troadec, A. Fujiwara, D. Vuillaume. Large array of sub-10-nm single-grain Au nanodots for use in nanotechnology. Small, 7, 2607 (2011).

[3] J. Trasobares, D. Vuillaume, D. Théron, N. Clement, A 17 GHz Molecular Rectifier, Nat.Commun. 7, 12850 (2016).

[4] J. Trasobares, J. Rech, T. Jonckeere, T. Martin, O. Aleveque, E. Levillain, V. Diez-Cabanes, Y. Olivier, J. Cornil, J.P. Nys, R. Sivakumarasamy, K. Smaali, Ph. Leclère, A. Fujiwara, D. Théron, D. Vuillaume, N. Clément. Estimation of π-π Electronic Couplings from Current Measurements. Nano Letters, 17, 3215-3224 (2017).

[5] M.G. Reuter, M.C. Hersam, T. Seideman, M.A. Ratner. Signatures of cooperative effects and transport mechanisms in conductance histograms. Nano Letters, 12, 2243-2248 (2012).

 

Más información: http://www.ifimac.uam.es/category/seminars/

 

 

 

 

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#InnoAlimentación: La nutrición del futuro. Tecnologías, tendencias y networking
El profesor Jeff Errington imparte la 12ª Lección Conmemorativa David Vázquez
XXIV Lección Conmemorativa en honor de Severo Ochoa, a cargo del Profesor Fred Gage

Agentes y colaboradores

  • Universidad Autónoma de Madrid
  • CSIC
  • ASEYACOVI
  • ACENOMA
  • AICA
  • Centro de Microanálisis de Materiales (CMAM)
  • Centro de Investigación en Física de la Materia Condensada (IFIMAC)
  • CBMSO - Centro de Biología Molecular Severo Ochoa
  • CIAL - Centro de Investigación en Ciencias de la Alimentación
  • CNB - Centro Nacional de Biotecnología 
  • Centro de Iniciativas Emprendedoras (CIADE)
  • Cámara de Madrid
  • FEMAN
  • Fundación Universitaria Autónoma de Madrid
  • ICMAT - Instituto de Ciencias Matemáticas
  • ICMM - Instituto de Ciencia de Materiales de Madrid
  • ICP - Instituto de Catálisis y Petroquímica
  • ICV - Instituto de Cerámica y Vidrio
  • IFT - Instituto de FísicaTeórica
  • IIBM - Instituto de Investigaciones Biomédicas Alberto Sols
  • IMDEA - Alimentación
  • IMDEA - Nanociencia
  • IMM - Instituto de Microelectrónica de Madrid
  • InNorMadrid
  • Parque Científico de Madrid
  • Oficina de Transferencia de Resultados de la Investigación (OTRI) de la UAM
  • Facultad de Ciencias
  • Facultad de Ciencias Económicas y Empresariales
  • Facultad de Derecho
  • Facultad de Filosofía y Letras
  • Facultad de Medicina
  • Facultad de Formación de Profesorado y Educación
  • Facultad de Psicología
  • Escuela Politécnica Superior
Proyecto realizado con ayudas concedidas por el Ministerio de Economía y Competitividad / EXPEDIENTE: CEI10-1-0009 CEI UAM+CSIC: INNOCAMPUS 2010 Proyecto financiado por el Ministerio de Educación, Cultura y Deporte, y el Ministerio de Economía y Competitividad en el marco del Programa Campus de Excelencia Internacional/ EXPEDIENTE: CEI10-1-0009 CEI UAM+CSIC: INNOCAMPUS 2010