


Forthcoming Seminars at F1
Seminars Archive
2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 22 May 2018 15:00  Janez Bonča  Charge vs. Spin Disorder in a Correlated Electron System 

In the first part [1] I will show that electronmagnon 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 tJ 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 tJ 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 13:00  Peter Prelovšek  Manybody localization in spin and Hubbard chains 

I will describe concepts of manybody 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 13:00  Jan Šuntajs  Introduction to Anderson localization and MBL 

Čajna soba F1 
20 Apr 2018 13:00  Jan Skolimowski  Journal club: Bad metal physics with ultracold atoms 


17 Apr 2018 12:00  Rok Žitko  Revival of the physics of subgap states in superconductors: from Shiba to Majorana states 

Recent advances in the fabrication of nanometer scale hybrid semiconductorsuperconductor 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 nontrivial 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 highspin 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 nonFermiliquid features found in the twochannel Kondo model with superconducting channels. 
10 Apr 2018 11:00  Mikhail Kiselev  Thermoelectric 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 Fermiliquid 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 zerocurrent provides a complete description of the Seebeck effect. We find pronounced nonlinear effects in temperature drop at low temperatures. We illustrate the significance of the nonlinearities for enhancement of thermopower by two examples of SU(4) symmetric regimes characterized by a filling factor m: i) particlehole symmetric at m=2 and ii) particlehole nonsymmetric 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 13:00  Jernej Mravlje  Introduction to bad metals 

Čajna soba F1 
16 Feb 2018 11:00  BingSui Lu  Van 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 BingSui 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 noncontact friction in micro and nano electromechanical 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 15:00  Lev Vidmar  Emergent eigenstate solution to quantum dynamics 

cajna soba f1 
16 Jan 2018 11:00  Kazuhiro Seki  Electronhole doping asymmetry of Fermi surface reconstructed in a simple Mott insulator 

Cajna soba f1 





