Faculty of Physics University of Warsaw > Events > Seminars > Leopold Infeld Colloquium (till 2017/18)

Leopold Infeld Colloquium

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Nowa A(425), Hoża 69 at 15:30

Prof. dr hab. Paweł Haensel (Centrum Astronomiczne im. Mikolaja Kopernika PAN)

The two-solar-mass pulsars and physics of dense matter

Existence of pulsars of mass close to two solar masses puts a strong constraint on the equation of state (EOS) of cold matter at the density significantly exceeding normal nuclear matter density (NNMD=3*10^14 g/cc). The maximum mass of neutron stars will be discussed. Theoretical EOSs involving nucleons, hyperons, and quark plasma consistent with two-solar-mass constraint will be reviewed; maximum densities reached in neutron stars will be shown to be from 7 to 10 NNMD. Then, structure of the EOS as given by the quantum chromodynamics and its approximations will be sketched. Four constraints on the EOS will be formulated and used to get an allowed strip in the pressure-density plane for the densities up 100*NNMD. Finally, prospects for the future determination of the EOS from the masses and radii of neutron stars extracted via analysing precise X-ray spectra obtained using orbital detectors planned for 2020s will be described

Nowa A(425), Hoża 69 at 15:30

Dr Bartłomiej Czech (Stanford University)

What is space? What is distance?

The notion of distance between two points is at best a semiclassical concept. What replaces it in the fundamental theory of gravity? Recent progress in the AdS/CFT correspondence suggests a radically new way of approaching this problem, which is related to the information-theoretic quantity called entanglement entropy. I will review this development and discuss what it teaches us about the emergence of space and distance. Roughly, space appears to be a geometric representation of correlations between abstract, delocalized quantum gravity degrees of freedom.

Nowa A(425), Hoża 69 at 15:30

Prof. dr hab. Tomasz Story (Instytut Fizyki PAN)

Topological crystalline insulators

Topological crystalline insulators (TCIs) constitute a new class of quantum topological materials with the Dirac-like metallic surface states that cross the bulk semiconductor band gap and are topologically protected by crystalline mirror plane symmetry. The TCIs offer new ways of controlling topological states by applying perturbations lowering crystalline symmetry. The TCI states have been experimentally observed in (Pb,Sn)Se, SnTe and (Pb,Sn)Te crystals for both (001) and (111) surfaces. These IV-VI semiconductors undergo (at a specific tin content, temperature, and pressure) a band structure inversion driven by strong relativistic effects. Using angle- and spin-resolved photoemission technique we experimentally observed a temperature-driven topological phase transition from a trivial insulator to a TCI state below the band inversion point as well as revealed a characteristic vortical electronic spin polarization texture at the Dirac points.

In the lecture, I will summarize the basic physical model of this class of materials, present the TCI crystals and the key experimental methods applied to study these new surface states (photoemission, scanning tunneling spectroscopy, magneto-transport) and discuss new topological device concepts.

T.H. Hsieh et al., Nat. Commun. 3, 982 (2012); P. Dziawa et al., Nat. Mat. 11, 1023 (2012).

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