Physics theory seminar

– Spring 2016

Division of Theoretical Physics at the Department of Physics organizes a series of theory seminars. Physics theory seminars are open.

Time: Monday 14:15 - 15:00

Location: Realfagbygget E5-103


Theory seminars for the Spring 2016

February 15

Yukio Tanaka, Nagoya University, Japan
«Surface Andreev-Bound States and Unconventional Superconductivity»

February 15

Yukio Tanaka, Nagoya University, Japan
«Surface Andreev-Bound States and Unconventional Superconductivity»

Abstract

Surface Andreev-Bound States and Unconventional Superconductivity

It is known that surface Andreev bound state (SABS) is an important ingredient to identify unconventional superconductors. Up to now, there have been several types of SABSs stemming from their topological origins. They can be classified into:

  1. dispersionless flat band type realized in cuprate
  2. linear dispersion type realized in chiral superconductor like Sr2RuO4
  3. helical dispersion type realized in non-centrosymmetric superconductor in quasi two-dimensional superconductors

In three-dimensional superconductor, we can consider chiral superconductor where both line and point nodes exist.

Based on the topological nature of nodes, it is shown that the surface flat bands are fragile against (i) the surface misorientation and (ii) the surface Rashba spin-orbit interaction. We demonstrate that these flat-band instabilities vanish or suppress a zero-bias conductance peak in a tunneling spectroscopy, which behavior is clearly different from high-Tc cuprates and noncentrosymmetric superconductors.

We have predicted new types of SABS in doped topological insulators (TI) and Weyl semimetals which will be discussed in this talk. We have also studied charge conductance in anomalous Rashba metal (ARM) /superconductor junctions for various types of pairing symmetries in a superconductor.

March 17

Haakon Andresen, Max-Planck-Institut für Astrophysik, Garching, Germany
«Can Gravitational Waves provid»

March 17

Haakon Andresen, Max-Planck-Institut für Astrophysik, Garching, Germany
«Can Gravitational Waves provid»

Abstract

Can Gravitational Waves provid

April 8

Hans Skarsvåg, Eirik Fjærbu, Stefan Rex, Vetle Risinggård, Jabir Ali Ouassou (PhD candidates at the Department of Physics)
«Highlights of the APS March Meeting»

April 8

– Extraordinary Physics Theory Seminar

Hans Skarsvåg, Eirik Fjærbu, Stefan Rex, Vetle Risinggård, Jabir Ali Ouassou (PhD candidates at the Department of Physics)
«Highlights of the APS March Meeting»

Extraordinary seminar on Friday 8. April, 14:15-15:00 in D4-132

Highlights of the APS March Meeting

The seminar will be presented by the PhD students from the section who attended the meeting: Hans Skarsvåg, Eirik Fjærbu, Stefan Rex, Vetle Risinggård and Jabir Ali Ouassou

Mon, 18 Apr 2016 11:45:45 +0200

April 11

Jeroen Danon - Onsager Fellowship in Theoretical Condensed Matter Physics at the Department of Physics
«Multi-level interference resonances in strongly-driven three-level systems»

April 11

Jeroen Danon - Onsager Fellowship in Theoretical Condensed Matter Physics at the Department of Physics
«Multi-level interference resonances in strongly-driven three-level systems»

Abstract

Multi-level interference resonances in strongly-driven three-level systems

I will talk about multi-photon resonances in a strongly-driven three-level quantum system, where one level is periodically swept through a pair of levels with a constant energy separation.  Near the n-photon resonance condition (where the splitting of the pair matches n times the driving frequency) we find qualitatively different behavior for n being even or odd.  We can explain this phenomenon in terms of families of interfering trajectories of the multi-level system.  Remarkably, the behavior is insensitive to fluctuations of the energy of the driven level, and also survives deep into the strong dephasing regime.  The setup can be relevant for a variety of solid state and atomic or molecular systems.  In particular, I will show that it provides a clear mechanism to explain recent puzzling experimental observations in strongly-driven double quantum dots.

Fri, 08 Apr 2016 11:46:54 +0200

April 18

Øyvind Almelid, Higgs Centre for Theoretical Physics, The University of Edinburgh
«Soft singularities in general field theories»

April 18

Øyvind Almelid, Higgs Centre for Theoretical Physics, The University of Edinburgh
«Soft singularities in general field theories»

Abstract

Soft singularities in general field theories

Infrared singularities are a salient feature of any field theory containing massless particles, including QED, QCD and theories beyond the standard model. Their proper description and treatment involve an intricate cancellation between virtual and real emissions, which yield logarithmic corrections to scattering amplitudes. At energies relevant to scattering experiments, these corrections can grow large and threaten perturbativity. Thankfully, IR singularities also have a number of properties which enable their computation and treatment to all orders in perturbation theory. Chiefly: they factorise from the high-energy scattering, they are process-independent, and they do not depend on the spin of the emitting particle.

In this talk I will show how we may categorise and understand soft singularities (IR singularities which arise due to a small loop momentum) in a simplified, general gauge theory. I will then show how we may obtain a direct, diagrammatic all-order description of exponentiated soft singularities, ultimately allowing us to resum soft singularities to all orders. I will then discuss current results and the general understanding of the structure of soft singularities at two and three loops.

Mon, 18 Apr 2016 10:51:31 +0200