Forthcoming Seminars at F-1

Seminars Archive

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22 May 2018
Janez BončaCharge vs. Spin Disorder in a Correlated Electron System
In the first part [1] I will show that electron-magnon interaction delocalizes the particle in a system with strong charge disorder. The analysis is based on results obtained for a single hole in the one–dimensional t-J model. Unless there exists a mechanism that localizes spin excitations, the charge carrier remains delocalized even for a very strong charge disorder and shows subdiffusive motion up to the longest accessible times.
In the second part [2] I will present a study of dynamics of a single hole in one dimensional t-J model subject to a random magnetic field. Strong disorder that couples only to the spin sector localizes both spin and charge degrees of freedom. While we cannot precisely pinpoint the threshold disorder, we conjecture that there are two distinct transitions. Weaker disorder first causes localization in the spin sector. Carriers become localized for somewhat stronger disorder, when the spin localization length is of the order of a single lattice spacing. I will also discuss finite doping.

[1] J. Bonča and M. Mierzejewski, Phys. Rev. B 95, 214201 (2017)
[2] G. Lemut, M. Mierzejewski, and J. Bonča, Phys. Rev. Lett. 119, 246601 (2017)

Seminar room for physics (JSI main building)

18 May 2018
Peter PrelovšekMany-body localization in spin and Hubbard chains
I will describe concepts of many-body localization (MBL) on the example of the prototype MBL model - Heisenberg chain with random local magnetic fields. In particular, I will focus on the MBL criteria of nonergodic behavior of correlation functions and the absense of d.c. transport. On the other hand, analogous studies of the Hubbard chain with random potential show that even in the case of large disorder the charge degrees can be nonergodic, while spins behave as ergodic, but with subdiffusive dynamics. Results will be explained via an effective spin model, where subdiffusion emerges as the consequence of random distribution of exchange interactions.

Seminar room for physics (JSI main building)

11 May 2018
Jan ŠuntajsIntroduction to Anderson localization and MBL
Čajna soba F1

20 Apr 2018
Jan SkolimowskiJournal club: Bad metal physics with ultracold atoms

17 Apr 2018
Rok ŽitkoRevival of the physics of sub-gap states in superconductors: from Shiba to Majorana states
Recent advances in the fabrication of nanometer scale hybrid semiconductor-superconductor devices as well as in the scanning tunneling spectroscopy of adsorbate covered surfaces of superconductors have made possible very detailed experimental studies of the old problem of paramagnetic impurities in a superconducting host using local probes with very high energy and spatial resolution. At the same time, improved theoretical tools have been devised to reliably and accurately calculate the excitation spectra of the corresponding quantum impurity problems with gapped continuum electrons. These developments have enabled very stringent tests between experiment and theory. The results demonstrate the importance to describe the magnetic impurities as quantum objects with non-trivial internal dynamics due to the coupling to their environment. I will discuss the physics of bound states induced by the exchange interaction between the magnetic impurities and the Bogoliubov quasiparticles in superconductors. They are observable as spectroscopically sharp resonances in the tunneling spectra, located well inside the superconducting gap for sufficiently strong exchange coupling. They provide a new way to study the effects of strong correlations. Particularly interesting behaviour is found for cases of high-spin impurities in the presence of magnetic anisotropy, and when nearby impurities are coupled though exchange interaction. I will also briefly comment on the relation to recent experiments aimed at detecting fractional Majorana modes localized at the ends of chains of magnetic impurities, and on the non-Fermi-liquid features found in the two-channel Kondo model with superconducting channels.

10 Apr 2018
Mikhail KiselevThermoelectric Transport through SU(N) Kondo Impurity
We investigate thermoelectric transport through a SU(N) quantum impurity in the Kondo regime. The strong coupling fixed point theory is described by the local Fermi-liquid paradigm. Using Keldysh technique we analyze the electric current through the quantum impurity at both finite bias voltage and finite temperature drop across it. The theory of a steady state at zero-current provides a complete description of the Seebeck effect. We find pronounced non-linear effects in temperature drop at low temperatures. We illustrate the significance of the non-linearities for enhancement of thermopower by two examples of SU(4) symmetric regimes characterized by a filling factor m: i) particle-hole symmetric at m=2 and ii) particle-hole non-symmetric at m=1. We analyze the effects of potential scattering and coupling asymmetry on the transport coefficients. We discuss connections between the theory and transport experiments with coupled quantum dots and carbon nanotubes. D.B. Karki and M.N. Kiselev, Thermoelectric transport through SU(N) Kondo Impurity, Phys. Rev. B 96, 121403(R) (2017)

6 Apr 2018
Jernej MravljeIntroduction to bad metals
Čajna soba F1

16 Feb 2018
Bing-Sui LuVan der Waals interaction between anisotropic topological insulator slabs
Prof. Bing-­‐Sui Lu comes from the Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore. The lecture is based on recent paper Bing-Sui Lu, Phys. Rev. B 97, 045427 (2018).
Van der Waals interactions are prevalent in Nature and account for diverse natural phenomena, such as the flocculation of colloids and the adhesion of geckos to walls. Between similar dielectric materials such interactions are typically attractive and give rise to the problem of stiction and non-contact friction in micro and nano electro-mechanical systems, thus it is of importance to find possibilities of overcoming such stiction and friction. In the seminar we consider the van der Waals interaction between topological insulators, which are materials that exhibit axion electrodynamics, for which an electric field can give rise to magnetic polarization and a magnetic field can also give rise to electric polarization. For the case of dielectrically anisotropic topological insulators, we examine how such electrodynamics can give rise to the possibility of repulsive van der Waals forces and a reduction of frictional torque.

23 Jan 2018
Lev VidmarEmergent eigenstate solution to quantum dynamics
cajna soba f1

16 Jan 2018
Kazuhiro SekiElectron-hole doping asymmetry of Fermi surface reconstructed in a simple Mott insulator
Cajna soba f1

21 May, 2018 Seminar:
May 22: Charge vs. Spin...
Janez Bonča...
14 May, 2018 Seminar:
May 18: Many-body local...
Peter Prelovšek...
8 May, 2018 Seminar:
May 11: Introduction to...
Jan Šuntajs...
7 May, 2018 Abroad:
Invited Talk
Svjetlana Fajfer...
18 Apr, 2018 Seminar:
Apr 20: Journal club: B...
Jan Skolimowski...
13 Apr, 2018 Seminar:
Apr 17: Revival of the ...
Rok Žitko...
8 Apr, 2018 Seminar:
Apr 10: Thermoelectric ...
Mikhail Kiselev...
28 Mar, 2018 Abroad:
Invited Talk
Bosiljka Tadic...
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