Seminars

2011

GCOE Seminar
title
Superconductors and ferromagnets in contact: from thin films to nanostructures
author

Professor H. v. Lohneysen 
Karlsruhe Institute of Technology (KIT)

date
Date and Time: March. 29 (Thu), 2012, 10:00 -
place
Place: Room 401, Department of Physics
abstract
The interest in interfaces of metals with different groundstates has a long history. In recent years, the contact between a superconductor S and a ferromagnet F has received a lot of attention. Cooper pairs can penetrate from S into F, but experience the exchange field of F. The latter causes an oscillation of the pair amplitude leaking from S into F which leads to oscillations of the superconducting critical temperature Tc and of the critical current in S/F/S triple layers as a function of the F-layer thickness. The microscopic process of this “proximity effect”, i.e., the finite pair amplitude outside S - of course also present between S and a normal metal N - is Andreev reflection (AR) described as a coherent process of an electron from N (or F) incident on S and being reflected as a hole, thus generating a Cooper pair in S. In turn, Tc of an F/S/F trilayer depends on the relative magnetization direction of the two F layers. We have investigated this “spin switch effect” using F layers with perpendicular magnetic anisotropy [1,2]. ? Because of the spin structure of the Cooper pair (singlet for conventional superconductors) AR can be used as a tool to investigate the spin-dependent transport through an S/F interface. This however, requires the use of nanostructured contacts. We have investigated S/F contacts of typical diameters of 10-20 nm prepared by e-beam lithography with S = Al and F = Fe, Co, Ni, in order to determine the relation between the spin polarization PAR of the AR-induced current through the contact, and the spin polarization PB obtained for pure F materials by, e.g., spin-resolved photoemission [3]. We find a systematic dependence of PAR on the resistance of the contact which is attributed to spin-orbit scattering [4]. ? The coherent AR process occurs on a length scale of the coherence length ξS in S. Thus, the injection of an electron into S through one electrode and reflection of a hole into a second electrode is possible if both electrodes are placed within ξS. The use of F electrodes provides a means to detect this nonlocal AR, again by virtue of the spin structure of Cooper pairs. The observation [5] of nonlocal (or crossed) AR has opened the avenue to search for entangled, but spatially separated, Einstein-Podolski-Rosen pairs in solids. Nonlocal AR competes with another non-local process, i. e., electron cotunneling, leading to oscillations in the non-local conductance of injector and detector bias [6].
contact
Matsuda
( matsuda@scphys.kyoto-u.ac.jp)
note
GCOE Seminar
title
New Electron Microscope based on Coherent Diffraction Imaging
author
Dr. Tsumoru Shintake 
(OIST, Professor)
date
Date and Time: March. 2 (FRI), 2012, 15:00 - 17:00
place
Place: The 4th Lecture Hall [Rm525], Physics Department
abstract
Recently phase retrieve has been realized based on iterative fast FFTs in optics and X-ray FELs. We further advance this mathematic technique and apply on coherent electron beam, and develop following microscopes for biology: 
・We study basic interaction of low energy coherent electron and atoms.
・We develop new concept of atomic resolution SEM (scanning electron microscope) using digital holography technique on coherent diffraction.
・We perform electron crystallography on nano-crystals of membrane proteins.
・We also participate SACLA Free Electron Laser experiments.
With these atomic resolution microscopes, we will obtain 3D image of atomic structures in DNA, virus, and proteins, in few years.
contact
Nakaya
( t.nakaya@scphys.kyoto-u.ac.jp)
note
GCOE Seminar
title
Femto Second Physics based on Ultrafast Laser Experiments
author
Dr. Keshav Dani 
(OIST, Reseach Associate)
date
Date and Time: March. 2 (FRI), 2012, 15:00 - 17:00
place
Place: The 4th Lecture Hall [Rm525], Physics Department
abstract
In recent years, the ability to synthesize, engineer & observe materials on the nanometer length scale has led to novel phenomena and applications. On the other hand, modern lasers deliver powerful, ultra short pulses of light allowing us to observe the interaction of electrons and atoms on the femtosecond timescale. Together, these technologies allow us to study new paradigms in light-matter interaction - with femtosecond temporal resolution and nanometer spatial resolution. In the Femtosecond Spectroscopy Unit, we will direct these abilities towards two areas of study - (a) Metamaterials & Plasmonics, where artificially nano-engineered materials promise energy-efficient ultrafast photonic devices; and (b) Dirac Materials, where electrons in materials like graphene and topological insulators mimic those found in neutron stars and white dwarfs, leading to intriguing opto-electronic properties.
contact
Nakaya
( t.nakaya@scphys.kyoto-u.ac.jp)
note
GCOE/YITP seminar (Astrophysics)
title
Gravitational waves from extreme mass ratio inspirals to the 14th post-Newtonian order
author
Ryuichi Fujita
(Universitat de les Illes Balears, Spain)
date
January 25, 2012 (Wed.) 15:30-
place
Seminar Room K202, Yukawa Institute, Kyoto University
abstract
We derive gravitational waveforms needed to compute the 14th post-Newtonian (14PN) order energy flux, i.e. v28 beyond Newtonian approximation where v is the orbital velocity of a test particle, in a circular orbit around a Schwarzschild black hole. We exhibit clearly the convergence of the energy flux in the PN expansion and suggest the fitting formula which can be used for more general orbits around a Kerr black hole. The phase difference between the 14PN waveforms and numerical waveforms after two years inspiral becomes about 10-7for μ/M=10-4 and 10-3 for μ/M=10-5 where μ and M are the masses of a compact object and a supermassive black hole at the centers of galaxies respectively. The 14PN expressions will lead to the parameter estimation comparable to the ones resulting from high precision numerical waveforms for extreme mass ratio inspirals, which are one of the main targets of Laser Interferometer Space Antenna.
contact
note
GCOEセミナー
title
Feedback and teaching in reaction-diffusion information processing
author
Mr. Konrad Gizynski
(Institute of Physical Chemistry Polish Academy of Science)
date
Jan. 16 (Mon), 2012, 13:30 - 15:00
place
Kyoto Univ. Science Bldg V, North Bldg, #1 Lecture Room
abstract
Excitable chemical medium can be applied for information processing. All information processing executed by living organisms is based on chemistry. My PhD project is focused on increasing the flexibility of information processing with reaction-diffusion medium. We plan to design chemical computing systems that are able to modify their functions in the process of learning. In the project we will use Bielousov-Zhabotynski reaction as a computing medium. I am planning to design, build and program an experimental setup within which the state of computing medium can be analyzed. A set of cameras linked to a computer will process images of the medium in the real time. I will investigate different methods (local illumination, local change of electric field, local flows) of influencing the time evolution of the medium and write computer programs that control the applied stimuli.
This feedback will be used as a training tool to teach the medium to perform a selected function. The design of training strategy will be based on procedures similar to those used in genetic programming. It is expected that obtained results will help to determine the structure of the medium for which the process of training can be performed in the most efficient way.
contact
久保善嗣 ykubo@chem.scphys.kyoto-u.ac.jp(内線:3694)
note
       
GCOE seminar
title
Weyl gravity and Cosmology
author
Dr. Nathalie Deruelle
(APC, University Paris 7)
date
Jan. 10 (Tue.), 2012, 15:00-
place
Seminar Room K202, Yukawa Institute, Kyoto University
abstract

We consider the evolution of linear cosmological perturbations during
inflation when a Weyl term is added to the action. The presence of the
ghost degrees of freedom implies that vector perturbations can no longer
be ignored and that scalar modes diverge in the newtonian gauge but remain
bounded in the comoving slicing.

We then show that these ghost degrees of freedom can be eliminated by a
simple mechanism that invokes spontaneous Lorentz symmetry breaking.
As a result the kinetic term of the tensor perturbations is corrected at
short wave lengths. This leads to a redefinition of the quantum vacuum
state, which could be imprinted on the amplitude of the spectrum of
primordial gravitational waves.

contact
M, Sasaki, misao@yukawa.kyoto-u.ac.jp, Ext,7043
note
       
GCOE seminar
title
Space-charge physics design technique for linear accelertors
author
Dr. R.A. Jameson
(Inst. Angewandte Physik, Goethe University Frankfurt)
date
Nov. 28 (Mon.), 2011, 14:00 - 15:00)
place
ICR, Accelerator Laboratory 2F, Meeting Room
abstract
A general framework for the physics of high-intensity beam acceleration in linear accelerators has been developed. Its use in linac design and simulation, its relation to general nonlinear dynamics principles, and application to various contemporary projects such as Accelerator Driven Systems for radioactive waste transmutation, the International Fusion Materials Irradiation Facility, and small neutron sources will be discussed.
contact
Y.Iwashita, iwashita@kyticr.kuicr.kyoto-u.ac.jp, 17-3282
note
       
GCOE Seminar
title
The Sun as a laboratory for quantum physics
-Enigmatic scattering polarization of NaD1 observed in the Sun -
author
Dr. Jan Stenflo
(Eidgenossische Technische Hochschule Zurich)
date
OCT. 25 (TUE), 2011, 9:30 - 11:00
place
Building #4 Room 531[5F], Astrophysics Department
abstract
The Sun has often been referred to as a Rosetta stone for astrophysics, since its proximity allows us to explore in detail the fundamental processes that govern the physics of objects in distant parts of the universe. Among these fundamental processes there was little attention given to polarization phenomena until about a decade ago, apart from various applications of the standard Zeeman effect for magnetic field diagnostics. With the implementation of new, highly sensitive imaging Stokes polarimeters a new and previously unfamiliar face of the Sun has been revealed, in the form of the richly structured Second Solar Spectrum. Its spectral structures are exclusively due to coherent scattering processes, which are modified by the partial decoherence caused by magnetic fields via the Hanle effect. The observed polarization phenomena are signatures of a rich variety of quantum-state superpositions, which in a unique way reconnects astrophysics with fundamental aspects of quantum theory. Here I choose to address this topic from a personal perspective, starting with some biographical notes and ending with some ideas on how current quantum scattering theory may need to be extended to explain the enigmatic polarization observed in the D1 lines of sodium, barium, and potassium.
contact
Kiyoshi Ichimoto  ichimoto@kwasan.kyoto-u.ac.jp 0578-86-2311
note
       
GCOE Seminar
title
Vortex molecules in thin films of layered superconductors
author
Professor Alexandre Buzdin
(University of Bordeaux, France)
date
Wednesday, October 26, 2011, pm 3:30
place
Room 401, Department of Physics
abstract
Both the equilibrium and transport properties of the vortex matter are essentially affected by the behavior of the intervortex interaction potential. In isotropic bulk superconductors this potential is well known to be repulsive and screened at intervortex distances R greater than the London penetration depth λ. As a result, in perfect crystals quantized Abrikosov vortices form a triangular lattice. In thin films of anisotropic superconductors this standard interaction potential behavior appears to be strongly modified because of the interplay between the long-ranged repulsion predicted in the pioneering work by J. Pearl and the attraction caused by the tilt of the vortex lines with respect to the anisotropy axes. This interplay results in a new type of vortex arrangement formed by finite-size vortex chains, i.e., vortex molecules. Tilted vortices with such unusual interaction potential form clusters with the size depending on the field tilting angle and film thickness or/and can arrange into multiquanta flux lattice. The magnetic flux through the unit cells of the corresponding flux line lattices equals to an integer number N of flux quanta. Thus, the increase in the field tilting (or varying temperature) should be accompanied by the series of the phase transitions between the vortex lattices with different N. The similar scenario should be realized in strongly anisotropic BSCCO high Tc superconductors where in tilted field a crossing lattice of Abrikosov vortices and Josephson vortices appears.
contact
Yuji Matsuda (Ext. 3790)
note
       
GCOE seminar
title
Lack of inversion symmetry in heavy fermion and simple metal superconductors
author
Friedrich Kneidinger
(Technische Universitat Wien)
date
Oct. 31 (Mon), 2011, 17:15 - 18:45
place
Room 401 [4th Floor], Physics Department
abstract
Superconductors which do not have a center of inversion according to their space group are generally summarized as non-centrosymmetric (NCS) superconductors. The lack of inversion leads to an electrical field gradient which emerges in an antisymmetric spin-orbit-coupling of the so called Rashba type. Furthermore this triggers a splitting of the Fermi surface, thereby lifting the spin degeneracy. In theory this leads to a superposition of spin singlet as well as spin triplet state Cooper pairs. One material which shows NCS superconductivity as well as heavy fermion behavior is CePt3Si. This material shows various interesting features like a coexistence of AFM and superconductivity and an extraordinarily large upper critical field. The latter in combination with measurements of the Knight shift leads to the assumption of a mainly spin-triplet Cooper pairs in the SC condensate. Another class of materials are simple ternary intermetallics with a lack of inversion center. Promising candidates are BaPtSi3, SrPdSi3 and SrPtGe3. These candidates exhibit a conventional metallic behavior above Tc according to a Bloch-Gruneisen like resistivity. Measurements of the specific heat, which follows the Muhlschlegel model, and μSR- measurements which do not show time reversal symmetry breaking, strongly indicate a spin-singlet BCS-like Cooper pairing. Another interesting example is the ternary 111-type like LaPtSi which crystallizes in the I41md space group. This material shows SC at 3.3 K and a large upper critical field which refers to a non- vanishing contribution of spin triplet Cooper-pairs.
contact
Yoshi Maeno maeno@scphys.kyoto-u.ac.jp,ext. 3783
note
       
GCOE seminar
title
Implications of genuine gauge invariance and inflationary vacua
author
Dr. Yuko Urakawa
(University of Barcelona, Ochanomizu university)
date
October 17, 2011 (Mon), 16:30−17:30
place
Room K206, Yukawa Institute, Kyoto University
abstract
The conventional cosmological perturbation theory has been performed under an assumption that we can access the whole spatial region of the universe. This is, however, not the case in actual observations because observable region is a portion of the whole universe. To give a theoretical prediction to the observable fluctuations, gauge-invariant observables should be composed of information in our local observable universe with finite volume. In this talk, I will survey implications of the gauge invariance in the local universe, highlighting differences from results in the conventional perturbation theory. Interestingly, requesting the gauge invariance in the local universe may tell us about allowable initial states in inflationary universe.
contact
Takahiro Tanaka (tanaka@yukawa.kyoto-u.ac.jp)
note
       
GCOE seminar
title
Application of Wainwright’s Formalism to Anisotropic Inflation
author
Dr. Kei Yamamoto
(University of Cambridge)
date
October 18, 2011 (Tue) pm 13:30-15:30
place
K206 at YITP
abstract
Recently attempts have been made to extend the scope of inflationary model building from conventional scalar-dominating scenarios to including more general energy components such as vector fields. While isotropy of the background space is often taken for granted, it is necessary to abandon the FLRW model in order to fully incorporate the anisotropic nature of the fields. In this talk, I describe a systematic construction of dynamical systems for the anisotropic cosmological models, which was developed by John Wainwright. The use of vierbeins results in a unified treatment for all the different structures of spatial curvature. After normalizing the variables by Hubble expansion rate, to look for potential self-similar attractor solutions reduces to an algebraic problem. Then I apply this mathematical framework to a certain type of Lagrangian for Maxwell and Kalb-Ramond fields coupled to a dilaton and discuss “pseudo-no-hair” conjecture within this class of inflationary universes.
contact
Jiro Soda jiro@tap.scphys.kyoto-u.ac.jp
note
       
GCOE/YITP Seminar (particle physics)
title
Bulk-boundary resonance in one matrix model and Liouville gravity
author
Jean-Emile Bourgine
(CQUeST, Sogang University)
date
June 15 (Wed), 2011, 1:30 p.m.
place
Conference Room Y306, Yukawa Hall, Yukawa Institute, Kyoto University
abstract
The issue of relating discrete and continuous descriptions of a QFT will be discussed within the solvable example provided by the 2D Quantum Gravity. Here, a continuum limit for the discrete description, given by the hermitian matrix model, can be performed. Results should be compared with the Minimal Liouville Gravity, a minimal model matter coupled to the Liouville field theory. Effective comparison of the correlation functions requires the introduction of a finite renormalization of the couplings, known as the ’resonance transformation’. This transformation will be investigated at the level of boundary 2-pts and bulk-boundary correlators. In the process, the construction of matrix model boundaries will be reviewed.
contact
YITP, Naoki Sasakura (ext 7037)
note
http://www.yukawa.kyoto-u.ac.jp/contents/seminar/detail.php?SNUM=51215
GCOE/YITP Lecture (Astrophysics)
title
Effective Action in Non-trivial Background
author
Sang Pyo Kim
(Kunsan University)
date and time
May 24th, 2011 (Tue) 14:00-15:30, 15:40-17:10, May 25th(Wed) 10:30-12:00
place
Coference Room K206, Yukawa Institute, Kyoto University
abstract
The Schwinger variational principle has been known as one of two formalisms of quantum field theory, the other being the Feynman functional integral. The principle has been further developed by B. DeWitt such that it can be applied to systems with nonstationary backgrounds, external gauge fields and or curved spacetimes. In the first lecture, the covariant formulation of canonical quantum field theory will be introduced based on the Schwinger variational principle and the Peierls brackets and the principle will be employed in calculating the effective actions in terms of either Green's function or Bogoliubov coefficient. In the second lecture, the effective actions in terms of the Bogolioubov coefficient will be applied to fermions and bosons coupled to some configuration of electromagnetic fields and the physical aspects of the nonperturbative effective actions will be investigated. In the third lecture, the method will be applied to curved spacetimes such as a de Sitter space and a Schwarzschild black hole and physical interpretations and perspectives of the nonperturvtive effective action will be addressed.
contact
Misao Sasaki (YITP) (ext: 7043)
note
http://www.yukawa.kyoto-u.ac.jp/contents/seminar/detail.php?SNUM=51190
GCOE/YITP Seminar (Particle physics)
title
Brane Tilings and the mesonic moduli space of Ypq Theories
author
Rak-Kyeong Seong
(Imperial College London / YITP)
date and time
May 11th, 2011 (Wed) 13:30-
place
Coference Room Y306, Yukawa Institute, Kyoto University
abstract
Brane Tilings form a large class of superconformal field theories in 3+1d and 2+1d. In this talk, I will discuss a particular set of models known as Ypq theories in 3+1d. I discuss how the mesonic moduli space of these theories is characterized by a generating function of chiral gauge invariant operators known as the Hilbert series. I will illustrate how from the brane tiling construction certain limits in the parameter space lead from Ypq theories to abelian orbifold theories.
contact
Naoki Sasakura (YITP) (ext: 7037)
note
http://www.yukawa.kyoto-u.ac.jp/contents/seminar/detail.php?SNUM=51196

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