Department of Applied Physics, Tokyo University of Science

Japanese version

  • Tokyo University of Science
  • Faculty of Science
  • Department of Applied Physics, Faculty of Science, Tokyo University of Science
    apperance (laboratory)8F, (secreatry)3F
    6-3-1 Niijuku, Katsushika, Tokyo, 125-8585 Japan
Chair:Prof. Osamu Araki

About us

The Department of Applied Physics was established in 1960 at the instigation of the then President, Dr. Masaichi Majima, to engage in applied research based on basic sciences. It maintains this tradition to this day, providing unique learning and research opportunities as one of Japan’s few such departments to be found within science faculty.

Applied Physics Seminar

Semianr organized by applied physics department of TUS.
Please Join freely.
Time #38,11/8(Wed.) 16:10-17:40NEW
Place 1st semianr room at 8F Research building
Speaker Prof. Ilya Eremin
Affiliation Ruhr-Universität Bochum(Germany), invited instructor of Tokyo University of Science
Title Cooper-pairing with small Fermi energies in multiband superconductors: BCS-BEC crossover and time-reversal symmetry broken state
Abstract In my talk I will consider the interplay between superconductivity and formation of bound pairs of fermions in multi-band 2D fermionic systems (BCS-BEC crossover). In two spatial dimensions a bound state develops already at weak coupling, and BCS-BEC crossover can be analyzed already at weak coupling, when calculations are fully under control. We found that the behavior of the compensated metal with one electron and one hole bands is different in several aspects from that in the one-band model. There is again a crossover from BCS-like behavior at EF>>E0 (E0 being the bound state energy formation in a vacuum) to BEC-like behavior at EF < < E0 with Tins > Tc. However, in distinction to the one-band case, the actual Tc, below which long-range superconducting order develops, remains finite and of order Tins even when EF = 0 on both bands. The reason for a finite Tc is that the filled hole band acts as a reservoir of fermions. The pairing reconstructs fermionic dispersion and transforms some spectral weight into the newly created hole band below the original electron band and electron band above the original hole band. A finite density of fermions in these two bands gives rise to a finite Tc even when the bare Fermi level is exactly at the bottom of the electron band and at the top of the hole band. I also analyze the formation of the s+is state in a four-band model across the Lifshitz transition including BCS-BEC crossover effects on the shallow bands. Similar to the BCS case, we find that with hole doping the phase difference between superconducting order parameters of the hole bands change from 0 to π through an intermediate s+is state, breaking time-reversal symmetry (TRS).

  •  Past seminar and abstracts
  • Time #37, 7/10(Mon.) 14:50-15:50
    Place Room #301, Lecture Building
    Speaker Prof. Oliver Steinbock
    Affiliation Department of Chemistry and Biochemistry, Florida State University
    Title Self-organization and complexity: The origin of macroscopic order from microscopic processes
    Abstract Simple rules can create complex patterns and dynamics. This connection is routinely used by living systems to create complex rhythms, spatio-temporal structures, and high-performance materials with design features at meso- and macroscopic length scales that seem to defy their molecular origins. In my lecture, I will present several examples that illustrate this point and demonstrate that many phenomena that appear to be unique to life processes actually occur in non-biological, often simple chemical systems. Specifically, I will discuss nonlinear wave patterns in reaction-diffusion media and examples of life-like structures in chemical reactions that form polycrystalline or amorphous solids. The unexpectedness of some of these universalities has profound consequences in a wide range of scientific disciplines ranging from the misidentification of early microfossils to deadly cardiac arrhythmias.

    * O. Steinbock, J. H. E. Cartwright and L. M. Barge “The Fertile Physics of Chemical Gardens” Physics Today 69, March 2016.
    * Z. Zhang and O. Steinbock “Local Heterogeneities in Cardiac Systems Suppress Turbulence by Generating Multi-armed Rotors” New Journal of Physics 18, 053018, 2016.
    * E. Nakouzi and O. Steinbock “Self-organization in Precipitation Reactions Far From the Equilibrium” Science Advances 2, e1601144, 2016.
    * J. M. García-Ruiz, E. Nakouzi, E. Kotopoulou, L. Tamborrino and O. Steinbock "Biomimetic Mineral Self-organization From Silica-rich Spring Waters" Science Advances 3, e1602285, 1-7, 2017.

    Time #36, 6/28(Wed.) 16:10-17:40
    Place 1st semianr room at 8F Research building
    Speaker Prof. Konrad Matho
    Affiliation Institut Néel(Grenoble, FRANCE)
    Title "Heavy Fermions“ as observed by photoemission and interpreted by the "PAM"
    Abstract The general context of this seminar is the experimental and theoretical study of "Heavy Fermion“ systems: Metallic compounds containing rare earth (RE) ions such as Ce and Yb. The experimental method considered is photoemission, as carried out either in angle integrated ("PES") or angle resolved ("ARPES") mode. The Periodic Anderson Model ("PAM") has frequently been employed to interpret the spectra. The subject, started half a century ago, is still surprisingly lively and full of new challenges.
    I have collaborated with Clemens Laubschat's group at the TU Dresden in Germany. My theoretical contribution was to consult a PhD student in the group, Alla Chikina, in the development of a computer code for the PAM that uses our phenomenological Continued Fraction Method (CFM) [1]. The CFM was generalized from the Hubbard model to the PAM and the code was tested in comparison with results from Dynamical Mean Field Theory [2]. The benchmarking was carried out in the "Kondo Lattice“ regime of the PAM, which is characterized by the presence of a "large“ Fermi surface (FS). The physical meaning of this concept is explained in terms of Luttinger's counting principle [3].
    The PAM englobes other scenarios, beyond the Kondo Lattice, such as charge transfer and mixed valence regimes. An overview of possible spectra is presented, as calculated with our code [4]. The PAM predicts damped van Hove singularities in the quasiparticle density of states. One of the new challenges is to demonstrate their presence in the PES data.
    A detailed discussion of ARPES and PES results on YbRh2Si2 [5] and YbNiSn [6] uses an "asymmetric KL“ scenario. We conclude that Doniach's KL model, based on a single Kramers doublet per RE ion, is not applicable. The excited 4f levels under the crystalline electric field exert a strong influence in stabilizing the large FS at temperatures well beyond the Kondo temperature of a Kramers doublet.
    [1] R. Hayn, P. Lombardo, and K. Matho, Phys. Rev. B 74, 205124 (2006).
    [2] A. Benlagra, T. Pruschke, and M. Vojta, Phys. Rev. B 84, 195141 (2011).
    [3] R. M. Martin, Phys. Rev. Lett. 48, 362 (1982); J. Appl. Phys. 53, 2134 (1982).
    [4] A. Chikina, PhD Thesis, Dresden (2016) and t.b.p.
    [5] K. Kummer et al., Phys. Rev. X 5, 011028 (2015).
    [6] A. Generalov et al., Phys. Rev. B (accepted May 2017).

    Time #32:2/13(Mon.) 16:00-17:30
    Place 2nd semianr room at 8F Research building
    Speaker Prof. Denis ARČON
    Affiliation Jozef Stefan Institute and University of Ljubljana, Slovenia
    Title Unconventional magnetic and superconducting states emerging in strongly correlated orbitally-degenerate light-element molecular solids
    Time #28:10/27(Thu.) 16:10-17:10
    Place 2nd semianr room at 8F Research building.
    Speaker Prof. Dragan Mihailovic
    Affiliation Jozef Stefan Institute, Slovenia
    Title Electronic phase transitions through time – on a femtosecond timescale

    Time #27:10/25(Tue.) 16:10-17:40
    Place 1st semianr room at 8F Research building
    Speaker Prof. William Sacks
    Affiliation Sorbonne Universities, Paris
    Title Pair-pair interactions in high-Tc superconductivity : evidence from tunneling experiments
    Time #11:April 8th, Wed. 16:00-17:00
    Place 2nd semianr room at 8F Research building.
    Speaker Prof. Dr. Dirk Manske
    Affiliation Max Planck Institute for Solid State Research (Stuttgart, Germany)
    Title Novel proximity and Josephson effect with triplet superconductors
    Abstract Josephson junctions with magnetic tunneling barriers provide an excellent opportunity to observe the interplay of ferromagnetism and superconductivity in a controlled setting. Using a tunneling Hamiltonian approach, we predict a universal 0-π transition (sign reversal) of the charge current as the orientation of the barrier magnetic moment is varied. Furthermore, in the theoretical study of Josephson junctions, it is usually assumed that the properties of the tunneling barrier are fixed. This assumption breaks down when considering tunneling between two triplet superconductors with misaligned d-vectors in a TFT-junction (triplet–ferromagnet–triplet). Such a situation breaks time-reversal symmetry, which radically alters the behaviour of the junction, stabilizing it in a fractional state, i.e. the free energy minimum lies at a phase difference intermediate between 0 and π. Fractional flux quanta are then permitted at the junction. A further consequence of the d-vector misalignment is the appearance of a Josephson spin current. Finally, we contrast the prototype TFT-junction with both a TFS (triplet–ferromagnet–singlet) and NCS-I-S (noncentrosymmetric-insulator-singlet) Josephson junction in which the d-vector misalignment is absent. Recent experimental progress allows to fabricate interfaces with the triplet superconductor Sr2RuO4 which opens the route for these devices.

    Time #10:January 8th, Thu. 16:10-17:10
    Place 2nd semianr room at 8F Research building.
    Speaker Prof. Seyed Akbar Jafari
    Affiliation Department of Physics, Sharif University of Technology
    Title Collective excitations of strongly correlated Dirac fermions
    Abstract Dirac electrons have began to appear repeatedly in the solid state physics, a remarkable example of which is graphene. Other examples include Silicene that compared to graphene has a longer bond length and hence much more enhanced ratio of the Hubbard U to the kinetic energy scale “t”. This motivates us to study the Dirac fermions subject to strong on-site Coulomb repulsion. In this talk we report on an Einstein-like branch of bosonic excitations in strongly correlated Dirac fermions that is formed as a bound state of two spinons when the underlying Dirac cone is doped away from the Driac node. We find a peculiar doping dependence for the energy scale of this branch of collective excitations. We discuss implications in ARPES data of graphene.

    Time #6:October 23rd,Thu. 14:30-16:00
    Place 2nd semianr room at 8F Research building.
    Speaker Prof. Sergei P. Kruchinin
    Affiliation Bogolyubov Institute for Theoretical Physics, Ukraine
    Title Hybrid ferromagnetic-superconductor nanosystems
    Abstract Recent advances in nanoscience have demonstrated that fundamentally new physical phenomena are found, when systems are reduced in size to dimensions that become comparable to the fundamental microscopic length scales of a material under study. Superconductivity is a macroscopic quantum phenomenon, and therefore it is of particular interest to see how this quantum state is influenced when the samples are reduced to nanometer sizes. Nowadays, developments in nanotechnologies and measurement techniques allow the experimental investigation of the magnetic and thermodynamic superconducting properties of mesoscopic samples in this regime. In this lecture, we will present theoretical models to describe such nanoscale superconducting systems and discuss possible new experimental phenomena we can predict within these theoretical models.
    We will consider the theory of interactions between two nanoscale ferromagnetic particles embedded in a superconductor. In the London limit approximation, we show that the interactions between ferromagnetic particles can lead to either parallel or antiparallel spin alignment. The crossover between those is dependent on the ratio of the interparticle spacing and the London penetration depth. We will show that a phase transition between spin orientations can occur as the temperature is varied. Finally, we comment on the extension of these results to arrays of nanoparticles in different geometries.
    In view of modern experimental data, we consider also composite nanowires made from both superconducting and ferromagnetic metals in the case of cylindrical geometry, where one metal forms the core of a nanowire, and the second forms an outer cylindrical sheath. Moreover, we analyze also the inverse situation, in which a normal or ferromagnetic core is surrounded by a superconducting sheath. In this case, it is interesting to examine the spectrum of Andreev bound states in the normal or ferromagnetic core.

    Time #5:July 31st Thu. 16:10-17:40
    Place 2nd semianr room at 8F Research building.
    Speaker Prof. Janez Bonca
    Affiliation Department of Mathematics and Physics, University of Ljubljana, Slovenia
    Title Relaxation dynamics of a charge carrier in correlated electron systems
    Abstract I will present the relaxation dynamics of an charge carrier in the spin background described by the two dimensional t-J model using a full quantum mechanical picture. Besides numerical simulations I will also discuss a simple analytical argument for the unusual scaling of the relaxation time with the exchange interaction. In the second part I will present the formation of a spin-lattice polaron in one spatial dimension after a quantum quench that simulates absorption of the pump pulse in the time resolved experiments. A two-stage relaxation is found where spin and lattice degrees of freedom represent an integral part of the relaxation mechanism. In the first stage the kinetic energy of the spin-lattice polaron relaxes towards its ground state. In the second, typically much longer stage, a subsequent energy transfer between lattice and spin degrees of freedom via the charge carrier emerges. The excess local spin energy radiates away via magnon excitations. Finally, I will present optical properties of the system in a non-equilibrium setup.

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