# Physics theory seminar

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

- Time: Monday 14:15
- Location: E5-103, Realfagbygget NTNU. Natural Science Building

Coordinator: Jacob Linder

## Theory seminars for the Autumn 2014

### September 1

Daniele Toniolo (NTNU)

«From the Bogoliubov theory of Superfluidity to the present spin-orbit coupled Bose-Einstein condensates confined in an optical lattice: a theoretical surveys»

# September 1

Daniele Toniolo (NTNU)

«From the Bogoliubov theory of Superfluidity to the present spin-orbit coupled Bose-Einstein condensates confined in an optical lattice: a theoretical surveys»

*Abstract*

### From the Bogoliubov theory of Superfluidity to the present spin-orbit coupled Bose-Einstein condensates confined in an optical lattice: a theoretical survey

This talk consists of two parts: in the first one I briefly present the Landau criterium and the Bogoliubov theory of superfluidity; in the second one I illustrate the presently realized spin-orbit coupling in a weakly interacting Bose-Einstein condensate confined on a lattice and describe the features of its superfluid phase by an analogy with the standard bulk superfluidity.

Mon, 01 Sep 2014 09:15:32 +0200

### September 17

Enrique Lomba, Instituto de Química Física Rocasolano, CSIC, Spain

«Self-consistency and critical behavior in D-dimensional spin systems»

# September 17

Enrique Lomba, Instituto de Química Física Rocasolano, CSIC, Spain

«Self-consistency and critical behavior in D-dimensional spin systems»

*Abstract*

### Self-consistency and critical behavior in D-dimensional spin systems

We present an analysis of the critical properties of the solution of an accurate approximation for the study of the thermodynamics of fluids: the Hierarchical Reference Theory (HRT). The analysis focus on the behavior of D-dimensional spin systems in a three dimensional lattice. When the spin dimension D=1, we are back to the well known Ising model, D=3 corresponds to Heisenberg spins, and for infinite D we have the spherical model. We will show in our general analysis that the HRT theory yields non-classical critical exponents which happen to be simple rational numbers for all finite D, and we show the importance of subleading contributions when spin dimensionality increases all the way up the the spherical model limit D=∞.

Wed, 17 Sep 2014 17:26:12 +0200

### October 6

Peter Lange and Camilla Espedal (NTNU)

«Extrinsic Spin-Orbit Induced Transport Properties in Diffusive Superconductors»

# October 6

Peter Lange and Camilla Espedal (NTNU)

«Extrinsic Spin-Orbit Induced Transport Properties in Diffusive Superconductors»

*Abstract*

### Extrinsic Spin-Orbit Induced Transport Properties in Diffusive Superconductors

We study the effects of elastic impurity scattering on transport of spin and charge in a diffusive superconductor. By employing the nonequilibrium Keldysh Green's function technique, we aim to derive transport equations that include scattering from magnetic and nonmagnetic impurities, as well as from spin-orbit coupling. The spin-orbit interaction gives rise to the spin and inverse spin Hall effects, as well as the spin swapping effect, and in our studies we will investigate these effects below the critical superconducting temperature.

Mon, 06 Oct 2014 11:40:53 +0200

### October 27

Alexander Balatsky, Nordic Institute for Theoretical Physics (Nordita), Sweden

«Odd frequency pairing in hybrid structures and multiband superconductors»

# October 27

Alexander Balatsky, Nordic Institute for Theoretical Physics (Nordita), Sweden

«Odd frequency pairing in hybrid structures and multiband superconductors»

*Abstract*

### Odd frequency pairing in hybrid structures and multiband superconductors

Odd frequency superconductivity proved to be an elusive state that is yet to be observed as a primary pairing state. On the other hand the list of systems and structures where odd frequency can be present as an induced component is growing.

I will review various scenarios pointing to emergence of odd frequency pairing due to modifications of the primary conventional pairing. Recently we find that odd frequency component is ubiquitously present in multiband superconductors. We show that odd-frequency superconducting pairing requires only a finite band hybridization, or scattering, and non-identical intraband order parameters, of which only one band needs to be superconducting. From a symmetry analysis we establish a complete reciprocity between parity in band-index and frequency. I will also discuss extensions of the odd frequency superconductivity to the spin and boson systems.

Mon, 29 Sep 2014 13:49:58 +0200

### November 10

Sinéad Majella Griffin (ETH Zürich)

«Cosmic Strings meet Multiferroics: Understanding Topological Defect Formation in Crystals»

# November 10

Sinéad Majella Griffin (ETH Zürich)

«Cosmic Strings meet Multiferroics: Understanding Topological Defect Formation in Crystals»

*Abstract*

### Cosmic Strings meet Multiferroics: Understanding Topological Defect Formation in Crystals

Jumping from the expanse of galactic scales to land in the laboratory might seem a gargantuan task. Common to both, however, is the the concept of symmetry breaking and in particular the formation of topological defects. Here I discuss the formation of topological defects in multiferroic hexagonal manganites whose ferroelectric behavior enables the direct imaging of these defects. I also show how this material can be used to study the Kibble-Zurek model of topological defect formation in the early universe and give quantitative insights on the number of domains formed during the spontaneous symmetry breaking phase transition. We also uncover a surprising 'beyond Kibble-Zurek' behaviour, and discuss this in the context of the material's properties

Tue, 09 Sep 2014 14:02:37 +0200

### November 17

Sol Jacobsen (NTNU)

«A brief introduction to topics in quantum entanglement, integrable systems and error correction»

# November 17

Sol Jacobsen (NTNU)

«A brief introduction to topics in quantum entanglement, integrable systems and error correction»

*Abstract*

### A brief introduction to topics in quantum entanglement, integrable systems and error correction

I introduce myself and my background by reviewing three interesting questions from different subdisciplines of fundamental quantum theory in a manner accessible to non-experts. Specifically, we will look at an extension of the famous Einstein-Podolsky-Rosen paradox and its implementation in quantum optics, we will examine a new exactly solvable three-level model analogous to the Kondo model for spins on a lattice, and we will consider the design of optimal quantum codes for information fidelity in complete, realistic noisy channels. Something for everyone!

Tue, 11 Nov 2014 11:15:42 +0100

### December 15

Alireza Qaiumzadeh, Radboud University, Netherlands

«Spin-orbit torques in 2D ferromagnetic metals»

# December 15

Alireza Qaiumzadeh, Radboud University, Netherlands

«Spin-orbit torques in 2D ferromagnetic metals»

*Abstract*

### Spin-orbit torques in 2D ferromagnetic metals

Recent advantages in magnetization dynamics and ultrafast magnetization switching promise a new era of data storage and information processing. There exist various ways to manipulate magnetisation direction, e.g. by varying external magnetic field or injecting a spin-polarised current via a spin-valve. Interestingly, it has been demonstrated recently, both theoretically and experimentally, that even unpolarised currents can trigger magnetisation dynamics in 2D ferromagnets due to the presence of spin-orbit interaction. So far the existing theory of the effect has been based on phenomenological models.

Here we utilise a non-equilibrium microscopic approach to analyse a variety of spin-orbit torques in a 2D system at zero temperature.

Irene Aspli

## Contact information

## Open Lectures and Seminars

Physics Friday Colloquia

Friday 14:15

Physics theory seminar

Monday 14:15