Seminars

2012

GCOE/YITP Seminar
title
The equilibrium dynamics of the Dean-Kawasaki model for colloids: the standard MCT and beyond
author
Bongsoo Kim
Changwon National University
date
March 21, 2013 (Thu) 16:00〜
place
Seminar room K202, Yukawa Institute, Kyoto University
abstract
This talk aims to communicate our recent results on the dynamics of equilibrium density fluctuations of colloids. The Dean-Kawasakiequation, a stochastic model equation for the density fluctuations of colloidal dispersions, poses a theoretical challenge of developing a systematic perturbation theory which preserves the fluctuation-dissipation relation order by order, mainly due to its multiplicative noise nature. A beautiful idea of time-reversal symmetry of the corresponding action offers a solution to the challenge: a loop expansion method applied to the new dynamic action incorporating a new set of auxiliary variables is guaranteed to preserve the fluctuation-dissipation relation (FDR) order by order. Our previous work along this line made an error of overlooking a delta function in one of the FDRs between the response and correlation functions. Restoring this missing contribution cries out for the distinct scenario from that in previous work. Instead of obtaining a single closed equation for the density-density correlation function, we now face with the simultaneous equations of the three independent correlation functions. The standard MCT equation is retrieved from this coupled set of equations after a further approximation to get an equation for the density-density correlation alone. The full one-loop theory is analytically shown to remove the ergodic-nonergodic transition via dynamic coupling to the auxiliary variable, making the dynamics always ergodic.
contact
Hisao Hayakawa (7024)
note
URL: http://www.yukawa.kyoto-u.ac.jp/contents/seminar/detail.php?SNUM=51506
GCOE/YITP Seminar (Particle Physics)
title
Matrix models for irregular conformal blocks
author
Chaiho Rim
Sogang University
date
15th Fubruary (Fri), 2013, pm16:00
place
Conference Room Y306, Yukawa Hall, Yukawa Institute, Kyoto University
abstract
Irregular conformal block is a new tool to study Argyres-Douglas theory, whose irregular vector is represented as a simultaneous eigenstate of a set of positive Virasoro generators. We describe how to find the irregular conformal block using the partition function of the beta-ensemble of hermitian matrix model.
contact
Kazuo Hosomichi, Yukawa Institute (Ex. 7077)
note
HP:http://www.yukawa.kyoto-u.ac.jp/contents/seminar/detail.php?SNUM=51483
GCOE seminar
title
New features of broken time reversal symmetry in unconventional superconductors
author
Professor Manfred Sigrist
(ETH Zurich)
date
Feb. 15 (Fri), 2013, 10:00 - 11:30
place
Room 525[5F], Physics Department
abstract
Spontaneously broken time reversal symmetry (TRS) has been a fascinating feature of unconventional superconductivity every its discovery. In this talk I will discuss two phenomena in unconventional superconductors, one motived by recent experiments on the 3-Kelvin phase of Sr2RuO4 and the other representing a prediction of a novel state in non-centrosymmetric superconductors.
(1) The Josephson effect coupling Pb to Sr2RuO4 through Ru-metal inclusions shows a pronounced anomaly in the Josephson critical current at the transition to bulk superconductivity in Sr2RuO4. We will argue that this behavior may result from the TRS breaking chiral p-wave phase introducing topologically frustrated Josephson junction with a new limiting effect on the Josephson current.
(2) It was shown a few years ago that non-centrosymmetric superconductors could produce a TRS breaking phase locally at twin boundaries. However, this phase does not produce any magnetic features unlike other TRS breaking superconducting phases. We will show that in combination with spin magnetism the twin boundary state can undergo a secondary transition to a phase producing spin and orbital magnetism. This phase may be considered as spontaneous spin Hall effect.
contact
Y. Maeno(3783)
note
GCOE/YITP Seminar, Condensed Matter Physics
title
Nonequilibrium thermodynamics theory describing heat working at maxmum power
author
Yuki Izumida
Ochanomizu University
date
6th February, 2013, 16:00
place
Room K202, Yukawa Institute
abstract
In recent years, there have been renewed interests in the efficiency at the maximum power (EMP) of heat engines among theoretical physicists since the so-called Curzon-Ahlborn (CA) efficiency [1] has been generally proved to be the upper bound of EMP for the linear irreversible systems in 2005 [2]. In this talk, I would like to introduce some recent theoretical advances on this new and old problem, especially focusing on our work. First I study a molecular kinetic model of a finite-time Carnot cycle working in the linear irreversible regime in detail [3, 4]. I show that the model satisfies a special condition to attain the bound (CA efficiency) by analyzing its transport coefficients explicitly. Then I propose a minimal model of general nonlinear irreversible heat engines [5], extending the results of the linear irreversible systems [2]. I derive an upper bound of EMP for these systems, which turns out be higher than the CA efficiency. If time permitted, I would also like to discuss physical significance of the size dependence of EMP by a molecular dynamics computer simulation of a heat engine model [6].

[1] F. Curzon and B. Ahlborn, Am. J. Phys. 43, 22 (1975).
[2] C. Van den Broeck, Phys. Rev. Lett. 95, 190602 (2005).
[3] Y. Izumida and K. Okuda, EPL. 83, 60003 (2008).
[4] Y. Izumida and K. Okuda, Phys. Rev. E 80, 021121 (2009).
[5] Y. Izumida and K. Okuda, EPL. 97, 10004 (2012).
[6] Y. Izumida and N. Ito, submitted
contact
Hisao Hayakawa, Yukawa Institute(ext:7024)
note
HP:http://www.yukawa.kyoto-u.ac.jp/contents/seminar/detail.php?SNUM=51478
GCOE/YITP Seminar, Condensed Matter Physics
title
Nonequilibrium Equation of States for a Confined Quantum Gas: Effects due to a Moving Piston
author
Katsuhiko Nakamura 
(ウズベキスタン国立大学(タシケント))
date
4th February, 2013 (Mon) 16:00
place
Room K202, Yukawa Institute
abstract
We study a nonequilibrium equation of states for an ideal quantum gas confined in the cavity under a moving piston with a small but finite velocity [1], [2]. Confining to the thermally-isolated process, the quantum nonadiabatic (QNA) contribution to Poisson’s adiabatic equation and to Bernoulli’s formula which bridges the pressure and internal energy is elucidated. We carry out a statistical mean of the pressure operator in both the low-temperature quantum-mechanical and high temperature quasi-classical regimes. The QNA contributions are quadratic in the piston’s velocity and therefore time-reversal symmetric, in marked contrast to the conventional belief, and they are positive, which means that the moving piston gives rise to the apparently repulsive interaction among non-interacting Fermi particles, for both expansion and contraction of the cavity. The QNA contributions are inversely proportional to the longitudinal size of the cavity, and thereby play a nontrivial role in nano-scale heat engines based on quantum dots. The investigation is done for a unidirectionally-expanding 3-d rectangular parallelepiped cavity as well as its 1-d version. Its relevance in a realistic nano-scale heat engine is discussed.
[1] K. Nakamura, et al: Phys. Rev. E 83, 041133 (2011);
[2] K. Nakamura, et al: Phys. Rev. E 86, 061128 (2012).
contact
Hisao Hayakawa, Yukawa Institute (ext7024)
note
http://www.yukawa.kyoto-u.ac.jp/contents/seminar/detail.php?SNUM=51477
GCOE Seminar, Condensed Matter Physics
title
High Field NMR in Cuprates and Quantum Spin Systems
author
Prof. Claude Berthier 
(LNCMI, CNRS (UPR 3228) UJF, UPS, INSA,
CNRS, BP 166, 38042 Grenoble Cedex, France)
date
Nov. 8th (Thu), 2012, 16:00 - 17:00)
place
Room 401 [4F], Physics Department
abstract
After a short presentation of the Grenoble High Field magnetic facility, I’ll first describe recent experimental results on detwinned ultra-pure single crystals of underdoped YBaCuO6+x. In the ortho II and the ortho VIII phases, it is shown that above threshold field and below some threshold temperature, the magnetic field H induces a charge ordering which is compatible with stripe order of period 4a [1], providing a natural explanation for a reconstruction of the Fermi surface and the quantum oscillations observed in these sample. I’ll also discuss the particular case of YBaCuO6.45 on which neutron experiments have shown an increase “magnetic ordering” with the magnetic field [2]. NMR experiments show that this corresponds to a progressive freezing of AF fluctuations, with a huge increase of their average amplitude of the with H. The underdoped part of the phase diagram of the cuprate is re-discussed on this basis [3].
In the second part, I’ll illustrate the physics of weakly coupled dimers by NMR experiments in two quasi 2D systems, SrCu2(BO3) [4] and BaCuSi2O6 [5] . The first one is a frustrated system which is the archetype of the physics of magnetization plateaus. The second one undergoes a Bose Einstein Condensation triplet of excitations[6], but presents very unconventional properties[7] , namely an apparent 2D BEC due to the frustration between adjacent planes and different spin-gaps every second plane [5].
[1] T. Wu et al., Nature 477 191 (2011)
[2] D. Haug et al., Phys. Rev. Lett. 103 017001 (2009) ; New. J. Phys. 12 105006 (2010)
[3] T. Wu et al., submitted to PRL.
[4] K. Kodama et al., Science 202 (2000) ; M. Takigawa et al, arXiv : 1209.0069
[5] S. Kramer et al., Phys. Rev. B 76 100406 (2007) and unpublished
[6] M. Jaime et al., Phys. Rev. Lett. 93 087203 (2004)
[7] S.E. Sebastian et al., Nature 441 617 (2006)
contact
Kenji Ishida (kishida@scphys.kyoto-u.ac.jp), 内線3752
note
GCOE Lecture, Condensed Matter Physics
title
Quantum Spin Systems under high magnetic field
author
Prof. Claude Berthier 
(LNCMI, CNRS (UPR 3228) UJF, UPS, INSA,
CNRS, BP 166, 38042 Grenoble Cedex, France)
date
I: 26th October, 2012 (Fri), 16:00-17:30
II: 2nd November, 2012 (Fri) 10:00−12:30
place
I: No. 363 [3F], North Building, Phys. Depart.
II: No. 525 [5F], Main Building, Phys. Depart.
abstract
Lecture 1
・Introduction to general concepts
1. Quasi-1D systems:
Introduction to Jordan Wigner transformation, and Tomonaga-Luttinger Liquid
・The XXZ spin chain
・Alternated spin chains, J1-J2 Frustrated spin chains, spin-Peierls case.
・Spin-ladders
・Others

Lecture 2
2. Quasi-2D systems
・Bipartite systems
(square lattice, J1-J2 frustrated square lattice and geometrically)
・Frustrated systems (Triangular, Kagome lattice)
・Weakly coupled dimers
・Bose Einstein Condensation
・Magnetization plateaus

Purpose of The Lectures
Although a spin is by essence a quantum object, the denomination quantum spin system is usually dedicated to low-dimensional systems including localized electronic spins of small values (1/2, 1..), dominantly coupled by anti-ferromagnetic (AF) exchange interaction. These conditions enhance thermal and quantum fluctuations, and can destabilize the “semi-classical” long range order ground states, of Neel type. The interest for quantum spin systems has appeared very early from the theoretical point of view with the introduction of the Ising model, the Heisenberg model, the Jordan Wigner transformation, and the Bethe ansatz for spin 1/2 chains, all of them between 1925 and 1931. The excitations of the Heisenberg spin 1/2 chains were calculated in 1962, and notions like fractional excitations (the spinons), predictions in the framework of the Luttinger-Tomonaga paradigm, the Haldane conjecture that spin chains of integer spin should have gaped excitations have appeared well before any experimental support. For example, the first experimental evidence of spinons came only in 1995.
The purpose of these two lectures is not to review that enormous field, but simply to present an experimentalist point of view the general concepts used in the study of quantum spin systems, the development of this area in the last few decade, as well as unanswered questions. I’ll focus on the important role the magnetic field in the physics of quantum systems which has the capability to induce quantum critical points and new exotic ground states, like for example Bose-Einstein condensate or Wigner crystals of triplet excitations. This will be illustrated by examples based on experiments using NMR technique, which is presently (with EPR) the only technique allowing microscopic investigation above 17 T.
contact
Kenji Ishida (kishida@scphys.kyoto-u.ac.jp), 内線3752
note
GCOE seminar
title
Stochastic differential equations and a review of their applications
author
Professor Petr Lansky 
(Academy of Sciences of the Czech Republic)
date
Nov. 1 (Thursday), 2012, 13:30 - 14:30
place
Physics Department, Faculty of Science Bldg #5
abstract
Differential equations played a unique role in physics over centuries and later on this also held for other branches of research as engineering, biology, chemistry and recently economics. In the first part of this lecture, the concept of stochastic differential equations will be introduced and illustrated on the simplest stochastic functions, namely Poisson and Wiener stochastic processes. In the next part, several applications to the real world problems will be mentioned, including population modeling and mathematical finance applications. Further, questions about the identification of the parameters of the stochastic differential equations will be shortly reviewed. Finally, a summary of our own results, including numerical techniques and search for the first passage time as a functional of random functions will be given. These results will be presented together with their implications for neuronal coding.
contact
Shigeru Shinomoto, shinomoto@scphys.kyoto-u.ac.jp)
note
GCOE seminar
title
Fate of long wavelength fluctuations and initial states of inflationary universe
author
Dr. Yuko Urakawa 
(University of Barcelona)
date
Oct. 26 (Fri), 2012, 17:30 - 18:30
place
Conference Room K206, Yukawa Institute
abstract
The infrared(IR) behavior of fluctuations in (a quasi) de Sitter spacetime has been an issue of debate for more than decade. A key to the IR issue is to remove influences from an unobservable region in the universe, which can be interpreted also as gauge artifacts in the local observable universe. In this talk, we will adress the regularity of IR contributions in a general single field mode of inflation without employing the slow-roll approximation. We will show that the IR regularity of primordial perturbations strictly constrains the allowed quantum state. We will also reveal the connection between the IR regularity and the gauge invariance in the local universe.
contact
Takahiro Tanaka, tanaka@yukawa.kyoto-u.ac.jp・宇治 7018)
note
GCOE Seminar
title
Trapped Anti-hydrogen : A new frontier in fundamental physics
author
Prof. Dr. Niels Madsen 
(Swansea University, Department of Physics)
(Institute for Chemical Research, Kyoto University: Invited Foreign Scholoar)
date
Oct. 4 (Thu), 2012, 15:00 - 16:30
place
The 2nd Lecture Hall [2F], North Building, Physics Department
abstract
Detailed comparisons of anti-hydrogen with hydrogen promise to be a fruitful test bed of fundamental symmetries such as the CPT Theorem for quantum field theory or studies of gravitational influence on antimatter. With a string of recent successes, starting with the first trapped anti-hydrogen and recently resulting in the first measurement of a quantum transition in anti-hydrogen, the ALPHA collaboration is well on its way to perform such precision comparisons. The presentation will discuss the key innovative steps that has made these feats possible and in particular focus on the detailed work on positron and antiproton preparation to achieve anti-hydrogen cold enough to trap as well as the unique features of the ALPHA apparatus that has allowed the first quantum transitions in anti-hydrogen to be measured with only a single trapped anti-hydrogen atom per experiment. We will also look at how ALPHA plans to step from here towards more precise comparisons of matter and antimatter and what we could possibly learn from such comparisons.
contact
Akira Noda、noda@kyticr.kuicr.kyoto-u.ac.jp・ext (17)3281
note
GCOE Seminar
title
Dissipation through dispersion
author
Professor Avraham Soffer 
(Rutgers University)
date
June 27th (Wed), 2012, 16:30 -
place
Bldg5 North 2F[room 265], Physics Department)
abstract
We consider systems coupled to a dispersive medium, in particular, Hamiltonian systems, both linear and nonlinear. The prime examples are the Nonlinear Klein-Gordon equation, the NLS with multibound state linear part, and the resonance problem in Quantum Mechanics. We show how the coupled modulation equations to the internal degrees of freedom of the localized system, leads to dissipation, through the dispersion of waves to infinity, and to, in general, non linear Master quations. In particular, this approach was used to derive rigorously the phenomena of “Selection of the Ground State” for NLS, which was later observed experimentally.
contact
Takao Ohta, ext 3740
note
GCOE Seminar
title
Asymptotic Stability of Solutions-Modulation Equations
author
Professor Avraham Soffer 
(Rutgers University)
date
June 20th (Wed), 2012, 16:30 -
place
Bldg5 North 2F[room 265], Physics Department
abstract
I will describe a general theory to study the dynamics of soliton type solutions of Dispersive equations, under small perturbations. The solution equations are nonintegrebale in general, and the dynamics for large times of such systems is very rich and complicated. The approach I will use allows the control of the dynamics for all times, the scattering theory included, for small perturbations of such solitons.
contact
Takao Ohta, ext 3740
note
GCOE/YITP Seminar
title
Particle Acceleration in Relativistic Shocks
author
Dr. Donald Ellison 
(North Carolina State University)
date
Date and Time: April. 26 (Thu), 2012, 15:00 -
place
Place: Conference Room K206, Yukawa Institute, Kyoto University
abstract
The first-order Fermi mechanism for particle acceleration in collisionless shocks has been studied extensively for over 30 years. Nevertheless, important problems remain, particularly when the shock speed approaches the speed of light. Nonrelativistic shock acceleration has been applied in many astrophysical environments, and relativistic shocks may be important for pulsar winds and for gamma-ray bursts, two of the most exotic of all phenomena. I will discuss the Fermi mechanism in general, and show new Monte Carlo results for relativistic shocks both in the test-particle limit and when accelerated particles make up a sizable fraction of the total energy. I will emphasize trans-relativistic shocks, a regime that is particularly difficult to address analytically but one that may be important for gamma-ray burst afterglows.
contact
note
GCOE Seminar
title
The Surprising Story of Collisionless Shocks in Astrophysics
author
Dr. Donald Ellison 
(North Carolina State University)
date
Date and Time: April. 12 (Thu), 2012, 11:00 -
place
Place: Conference Room K206, Yukawa Institute, Kyoto University
abstract
For more than 30 years, first-order Fermi particle acceleration in collisionless shocks (i.e., diffusive shock acceleration, DSA) has remained the mechanism of choice for producing cosmic rays and other superthermal particle populations in various astrophysical environments. The nonlinear nature of the mechanism, a result of the intrinsic high acceleration efficiency, has presented challenges and surprises for modelers over the years. I will briefly describe some of the surprising aspects of DSA and, in particular, focus on magnetic field amplification and particle escape; two phenomena that highlight the difficult plasma physics involved and which are undergoing active current research. While collisionless shocks, with associated particle acceleration, are believed to exist on scales from the Earth bow shock to galaxy clusters, supernova remnants (SNRs) offer our best chance to study the mechanism.
This is the case because SNRs occur in varying environments including dense molecular clouds and several SNRs show extremely broadband continuum emission from radio to TeV gamma rays, sometimes accompanied with thermal X-ray emission. Other aspects, such as the morphology of some young remnants, offer unique clues to fundamental properties of the underlying plasma physics of both the remnant and the coupled acceleration mechanism.
contact
Nagataki
(nagataki@yukawa.kyoto-u.ac.jp)
note
 

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