Participant Seminar Abstracts
15/10/2014
Mr. Tomas Bzdusek
Institute for Theoretical Physics, ETH Zürich, Zürich
Weyl semimetal from spontaneous inversion symmetry breaking in pyrochlore oxides
Abstract: Topological semimetals became a topic of intense research in recent years. Their electronic structure is gapped everywhere except for a discrete set of $\mathbf{k}$-points, the so-called Weyl nodes. These points constitute the bulk Fermi surface and their.
09/10/2014
Mr. Giacomo Dolcetto
Dipartimento di Fisica, Università degli Studi di Genova, Genova
Transport and spin properties in two-dimensional topological insulators
Abstract: The discovery of topological insulators has recently attracted a lot of interest. In two spatial dimensions they realize the quantum spin Hall effect, characterized by the presence of a gap in the bulk and gapless edge states protected by time-reversal.
17/10/2014
Dr. Paola Gentile
CNR-SPIN Salerno
Spin-triplet superconductors: interface to ferromagnets and magnetic edge states
Abstract: In the last decades the study of spin-triplet superconductivity has raised a lot of interest, due to the increasing number of theoretical predictions and experimental evidences about its possible realization in bulk materials and at the interface of hybrid systems. One of the most studied spin-triplet superconductor (TSC) is Sr2RuO4 [1], where the emergent consensus indicates triplet chiral pairing. This material has been so far investigated in form of single-crystals, but recently high-quality Sr2RuO4 thin films have been synthesized [2], which provide a key milestone to the experimental realization of Sr2RuO4 based epitaxial heterostructures, where a great variety of novel phenomena are expected. With this context we have found two remarkable effects: i) a spin-orbital coupling at the interface between a TSC and a ferromagnet (FM) [3], ii) magnetic Andreev states and anomalous spin/charge currents induced at TSC's edge in the presence of a subdominant singlet pairing [4]. In a TSC-FM heterostructure, the orientation of the FM moment relative to the TSC vector order parameter is a crucial variable that controls the physical behavior. In addition to the pair breaking, spin-flip reflection processes at the interface with the FM scatter the triplet Cooper pairs between the spin up and down condensates, setting up an effective Josephson-like coupling between them [5]. The pair-breaking and spin Josephson coupling both make significant contributions to the free energy of a TSC-FM junction but, although both depending upon the direction of the FM's exchange field, they do not necessarily act constructively. For a single-component p-wave TSC, we find that the gap variation controls the orientation of the FM's moment and stabilizes the FM magnetization direction either parallel or perpendicular to the TSC vector order parameter, depending on the alignment of the TSC gap with respect to the interface, thus evidencing a unique form of spin-orbital coupling. The competing orbital components of the chiral px ipy state generate a non unique behavior and a first-order transition from the perpendicular to the parallel configuration as the FM exchange field is increased [3]. Concerning the TSC surface states, novel magnetic effects can occur if triplet and singlet pairing get mixed and have a non-uniform spatial profile close to the edge. We show that a) a subdominant in-phase s-wave order can exist near the edge of the sample; b) the in-phase s-wave component gives a non-unitary superconducting state at the boundary; c) the bound states are spin-polarized, leading to a finite surface magnetization; d) spin current flows along the interface; e) surface charge currents exhibit anomalous dependence on the magnetization [4].
[1] Y. Maeno et al., J. Phys. Soc. Jpn. 81, 011009 (2012).
[2] Krockenberger et al., Appl. Phys. Lett. 97, 082502 (2010).
[3] P. Gentile, M. Cuoco, A. Romano, C. Noce, D. Manske, P. M. R. Brydon, Phys. Rev. Lett. 111, 097003 (2013).
[4] A. Romano, P. Gentile, C. Noce, I. Vekhter, M. Cuoco, Phys. Rev. Lett. 110, 267002 (2013).
[5] P. M. R. Brydon, Phys. Rev. B 80, 224520 (2009); P. M. R. Brydon, Y. Asano, and C. Timm, Phys. Rev. B 83, 180504(R) (2011).
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10/10/2014
Miss. Dorota Gotfryd
Marian Smoluchowski Institute of Physics, Jagellonian University, Kraków,
Spin correlations for frustrated Kitaev--Heisenberg interactions on a hexagon
Abstract: Recently spin-orbital systems with entangled interactions attract a lot of attention [1].Strong spin-orbit interactions in iridates result in on-site entangled states [2].The goal of this seminar is to present detailed analysis of the Kitaev--Heisenbe.
10/10/2014
Mr. Johannes Stephan Hofmann
Institute of theoretical physics and Astrophysics,Julius-Maximilians-University, Wuerzburg
Interaction effects along the edge of a topological superconductor
Abstract: Topological nodal superconductors, such as $d_{xy}$-wave and nodal non-centrosymmetric superconductors, exhibit protected zero-energy flat-band edge states. These zero-energy edge modes are protected by time-reversal and translation symmetry.
13/10/2014
Mr. Thomas Köhler
Institute for theoretical physics, Georg-August - University Göttingen,Göttingen
Recent progress with MPS based methods for finite temperature dynamics
Abstract: Matrix Product State (MPS) approaches are very powerful tools for treating a multitude of different systems. In this talk, I will summarize recent progress with the real time and frequency space dynamics of spin systems at finite temperatures.
14/10/2014
Mr. John David Malcolm
Guelph-Waterloo Physics Institute, University of Guelph,Guelph
Magneto-optics of general-pseudospin Dirac-Weyl fermions in two dimensions
Abstract: The popularity of graphene--a pseudospin-1/2 two-dimensional Dirac-Weyl material--has prompted the search for related materials and the characterization of their properties. The magneto-optical conductivity is calculated for systems that obey the general.
08/10/2014
Mr. Pasquale Marra
CNR-SPIN Salerno
Fractionally quantized charge pumping in a one-dimensional superlattice
Abstract: A one-dimensional quantum charge pump transfers a quantized charge in each pumping cycle. This quantization is topologically robust being analogous to the quantum Hall effect. The charge transferred in a fraction of the pumping period is instead generally not quantized. We show, however, that with specific symmetries in parameter space constraining the pumping protocol, the charge transferred at well-defined fractions of the pumping period is quantized as integer fractions of the Chern number. We discuss the relevance of this fractionally quantized charge pumping for cold atomic gases in one-dimensional optical superlattices with closed as well as open geometries.
16/10/2014
Mr. Shuo Mi
Instituut-Lorentz, Leiden University, Leiden
From Fake Majorana states to Real Majorana shooting gun
Abstract: The quasi-bound states of a superconducting quantum dot that is weakly coupled to a normal metal appear as resonances in the Andreev reflection probability, measured via the differential conductance.
We study the evolution of these Andreev resonances when an external parameter (such as magnetic field or gate voltage) is varied, using a random-matrix model for the N×N scattering matrix.
We contrast the two ensembles with broken time-reversal symmetry, in the presence or absence of spin-rotation symmetry (class C or D).
The poles of the scattering matrix in the complex plane, encoding the center and width of the resonance, are repelled from the imaginary axis in class C. In class D, in contrast, a number ∝N−−√ of the poles has zero real part. The corresponding Andreev resonances are pinned to the middle of the gap and produce a zero-bias conductance peak that does not split over a range of parameter values (Y-shaped profile), unlike the usual conductance peaks that merge and then immediately split (X-shaped profile).
17/10/2014
Dr. Tomoki Ozawa
Department of Physics and INO-CNR BEC Center, University of Trento, Trento
Quantum mechanics with momentum-space artificial magnetic field
Abstract: Berry curvature is known to act as an effective magnetic field in the momentum space. We exploit this perspective to investigate momentum-space counterpart of models which we are more familiar in the real space. The kinetic energy in the momentum space is provided by the external harmonic trap in the real space. As specific examples, we consider the Landau levels in the momentum space and the momentum-space Hofstadter model. These models are experimentally relevant in ultracold gases and photonics.
17/10/2014
Dr. Vladislav Pokorný
Center for Electronic Correlations and Magnetism, University of Augsburg, Augsburg
Diagrammatic perturbation theory of a zero-pi transition in a superconducting quantum dot system
Abstract: We study phase transitions in a quantum dot with local Coulomb interaction embedded between two superconductors showing a phase difference. The system is described by a single-impurity Anderson model coupled to BCS superconducting leads. We utilize diagrammatic.
17/10/2014
Mr. Thomas Scaffidi
University of Oxford,UK
Exact Solutions of Fractional Chern Insulators: Interacting Particles in the Hofstadter Model at Finite Size
Abstract: We show that all the bands of the Hofstadter model on the torus have an exactly flat dispersion and Berry curvature when a special system size is chosen. This result holds for any hopping and Chern number.
17/10/2014
Rafal Jaroslaw Skolasinski
Kavli Institute of NanoScience, Delft University of Technology, Delft
Quantum spin Hall effect in InAs/GaSb quantum wells
Abstract: InAs/GaSb quantum have been predicted, depending on the thicknesses of the quantum well layers, to be in a topological phase. Recently, experiments have found a very promising signatures of the quantum spin Hall effect in this system.
