CMP/CNMD

COLLOQUIA 2017

 

2017年度
ナノ機能予測分野
計算機ナノマテリアルデザイン
コロキューム

目的

研究室のメンバーの研究発表の場であると同時に、 外部の方にも積極的に依頼して講演していただき、 産研における物性関係の研究の活性化を図るというものです。

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2017年度 前期

4月20日
13:30
Uemura Prediction of hydrogenated α-tetragonl boron by first-principles calculation
4月27日
13:30
Takahashi
Hayashi
My Self-Introduction
My self-introduction
5月4日
13:30
National holiday
5月11日
13:30
Fukuichi First-principles calculations on mechanical properties using HiLAPW
5月18日
13:30
Katsumoto
Hamaguchi
Huyen
Optical Activity in X-ray region and First-principle Calculation
First-Principles Study on Li2MnTiO4 Based and their Related Cathode Compounds for Li-Ion Batteries
Calculating the exchange interactions and Dzyaloshinskii-Moriya interaction in MnSi helical spin
5月25日
13:30
Thao
Kuroda
Perpendicular magnetocrystalline anisotropy in 3d transition-metal thin films.
Materials exploration of multifunctional Heusler alloys
6月1日
13:30
Hung
Kumakura
X-ray magnetic circular dichroism for rare-earth compound
The structural stability and magnetism of Heusler alloys Mn2YZ
6月8日
13:30
Kosaka
Izumi
First-principles calculation of Bismuth thin films
Introduction of investigations on phonon mode and spin states of LaCoO3
6月15日
13:30
Kanehira
Kanda
Statistical modeling on structural stability of full-Heusler alloys
Study of electronic structure and magnetism of Co-based Heusler alloys by first-principles calculations
6月22日
13:30
Tahara
Hiraiwa
First-principles calculation of perpendicular magnetic anisotropy of tetragonal MMn3N (M= V, Cr, Fe, Co, Ni, Cu)
Measurement of temperature dependence on the lattice constant of α-YbAlB4 by hard x-ray
6月29日
13:30
Hiraoka
Yamashita Shogo
Kou(Yoshida lab.)
Self-introduction and Analysis of tunneling probability by using wave packet
Self introduction and my graduate study
Calculation of Temperature Dependent Electrical Resistivity
7月6日
13:30
Fujii
Yamashita Tomoki
Masago(Osaka Univ.)
Regression Analysis of Slater-Pauling curve
Development of Crystal Structure Prediction Method for Magnet Materials
Simulation Methods for Spintronics Devices
7月13日
13:30
Kotaka
Yamauchi
Funashima(Kobe Univ.)
Discharge reaction mechanism in Tin sulfide anode for Na-ion battery
Magneto-electric quadrupole order in Ba(TiO)Cu4(PO4)4 with square cupolas
Thermoelectric chalcogenide thermoelectric mineral
7月20日
13:30
Oguchi
Shirai
Hamada
Phonon Calculations on HiLAPW
Excitons observed in photoluminescence spectra
Ferromagnetic instability in 2D electride Y2C
7月27日
13:30
Fukushima
Fujimura
Calculations of anisotropic exchange interaction and atomic force by Korringa-Kohn-Rostoker Green’s function method
Cu4 reactions with H impurities in Si

2017年度 後期


Title : Prediction of hydrogenated α-tetragonl boron by first-principles calculation

Speaker : Naoki Uemura

Abstract:

I would like to talk about recent works of my studies. My research subjects on a doctoral program are to study boron crystal theoretically, especially α-tetragonl (α-T) boron phase, which is supposedly one of pure boron crystals. We already indicated that α-T boron has a non-stoichiometric composition(B52.1~52.2) at finite temperature but it is stoichiometric at ground state, B52, and a geometrical frustration is caused by conflictions between crystal symmetries, partial occupancies sites of boron atom, and a covalency of boron on α-T boron at T=0[1]. Recently, a new boron allotrope with orthorhombic symmetry(B51.5~52) have been synthesized at high pressures by pyrolysis of decaborane, B10H14[2]. A structure of this phase is almost similar to that of α-T phase. The difference between two phases is only a slight lattice distortion. Before getting this pure orthorhombic phase, parent crystals have a tetragonal symmetry and are released some amount of hydrogen twice on an annealing experiment with gradually increasing temperature. The symmetry of samples changed from tetragonal to orthorhombic due to the twice dehydrogenation process. However on the experience, there are no information of the number of hydrogen, sites of hydrogen, and the reason why the dehydrogenations are happened twice. Our simulations make it clear that the most stable site for hydrogen is 8j-site, the number of hydrogen atom per unit cell is 7(8j-site:5, 4g-site:2) if the number of boron is 51, this hydrogenated boron phases have two stoichiometric compositions, which consist of B and H, and the two emitting hydrogen are caused by the stabilities of hydrogen sites.
[1]N. Uemura, K. Shirai, H. Eckert, and J. Kunstmann, PRB 93, 104101 (2016)
[2]E. A. Ekimov, Yu. B. Lebed’, N. Uemura, K, Shirai, T. B. Shatalova, V. P. Sirotinkin, J. Mater. Res., 31 2773 (2016).


Title : My self-introduction

Speaker : Takafumi Hayashi

Abstract:

I will talk about my profile, hometown, and hobby.

Title : My Self-Introduction

Speaker : Tatsuya Takahashi

Abstract:

I would like to talk about myself: my profile, hometown and hobby.


Title : First-principles calculations on mechanical properties using HiLAPW

Speaker : Masayuki Fukuichi

Abstract:

In this talk, we would like to discuss, using HiLAPW, the origin of mechanical properties from the viewpoint of elastic properties. Metal carbides attract attention as superhard materials. However, much is not known yet about a relation in the materials between mechanical properties and the electron theory of solids. We will, therefore, consider the case of infinitesimal deformation, comparing mechanical properties with a theoretical model. The aim of our discussion is to understand the origin of mechanical properties.


Title : Optical Activity in X-ray region and First-principle Calculation

Speaker : Hiroshi Katsumoto

Abstract:

Nowadays, investigating physical properties of magnetic/non-magnetic materials is widely spread by using x-ray; XAS, XMCD and XNCD. I would like to focus on XNCD in theoretical way. It stands for X-ray Natural Circular Dichroism. In X-ray range, The phenomena requires pretty mixing and non-magnetic. NCD come up from a cross term of electric dipole(E1) and electric quadrupole(E2) transition. The origin of XNCD is different from origin of it in optical range which is E1 and magnetic dipole transition(M1). This research gives analytic expression of angular dependence of XNCD and numerical results. It supply deep insight to E1.E2 cross term. Moreover, it is fundamental study of Non-reciprocal Optical Activity in X-ray range, because E1.E2 cross term give rise to it in magnetic materials.

Title : First-Principles Study on Li2MnTiO4 Based and their Related Cathode Compounds for Li-Ion Batteries

Speaker : Motoyuki Hamaguchi

Abstract:

Li-ion batteries have attracted much interest because of their high energy densities, voltage, and capacities compared to conventional secondary batteries such as lead-acid batteries, and there are many applications such as electric power sources in portable electric devices and stationary energy storage systems of natural power stations. Cation-disordered rock-salt type LixMTiO4 (M=V, Mn, Fe, Co, and Ni) have received much attention because of high-voltage, high-capacity cathode compounds originated from two-electron reaction. However, measured capacities are less than those of two-electron reaction, and the reaction mechanism is not yet clarified. In this presentation, I will report electronic structure analyses and discuss about the guideline for the improvement of battery characteristics.

Title : Calculating the exchange interactions and Dzyaloshinskii-Moriya interaction in MnSi helical spin

Speaker : Vu Thi Ngoc Huyen

Abstract:

Recently, chiral-lattice magnets have been extensively studied for their nontrivial spin textures. Among them, skyrmion found in the B20-type helical-magnets with the chiral space group of P213 have been of current interest also for their intriguing topological transport properties. As a consequence of B20 distortion phase, several interesting features can be observed in the band dispersions. The important origin of the transforms form helical spin MnSi structure to skyrmion state in a magnetic field is the antisymmetric spin exchange interaction, termed the Dzyaloshinskii- Moriya interaction (DMI). In order to find out the magnetic structure and other characteristic in the helical spin states, the first-principles calculations were constructed for the helical spin structures to obtain their exchange interactions and also their DMIs.


Title : Perpendicular magnetocrystalline anisotropy in 3d transition-metal thin films.

Speaker : Nguyen Thi Phuong Thao

Abstract:

The search of magnetic thin films with perpendicular magnetocrystalline anisotropy (PMA) for magnetic tunnel junctions has raised interest in transition-metal systems where the spin-orbit coupling (SOC) could play a key role. In order to search for promising PMA materials, the microscopic mechanisms of magnetocrystalline anisotropy in Co-based 3d transitions-metal (Mn, Fe, Co, Ni) thin films are systematically investigated by first-principles calculations. The results predict that large PMA can be achieved by tuning the atomic-layer alignments in Co-Ni films. Furthermore, we discuss the mechanism of the PMA in Co-Ni films with SOC taken into account.

Title : Materials exploration of multifunctional Heusler alloys

Speaker : Fumiaki Kuroda

Abstract:

Heusler alloys have attracted much attention for many years because of highly desired properties for spintronic, thermoelectric, and shape-memory device applications. Some of Heusler alloys are topological materials. Recently, spin-gapless semiconductors or semimetals (SGS) with Heusler structures have been proposed [1,2] and realized [3]. The electronic structure of Heusler based SGS is quite peculiar in the sense that semiconducting or semimetallic electronic nature takes place in one spin channel while the other spin bands are gapped.
To begin with, I talk a summary of multifunctionality in Heusler alloys. Then, I report that we found SGS materials in equiatomic quaternary Heusler alloys by using first-principles calculations. The electronic structure, structural stability and magnetic properties of newly found Heusler based SGS as well as previously proposed and realized systems are discussed. Finally, I show my ideas for future works.
[1] X. L. Wang, Phys. Rev. Lett. 100, 156404 (2008).
[2] K. Ozdogan, et al., J. Appl. Phys. 113, 193903 (2013).
[3] S. Ouardi, et al., Phys. Rev. Lett. 110, 100401 (2013).


Title : X-ray magnetic circular dichroism for rare-earth compound

Speaker : Tran Ba Hung

Abstract:

X-ray magnetic circular dichroism (Xmcd) is a difference spectrum of two X-ray absorption spectra (Xas) taken in a magnetic field, one taken with left circularly polarized light, and one with right circularly polarized light. By closely analyzing the difference in the Xmcd spectrum, information can be obtained on the magnetic properties of the atom, such as spin and orbiter magnetic moment. In my calculation, i use HiLAPW program package for calculation and i have included Spin-Orbit coupling, plusU in second variation. I start calculated band structure and Xmcd of rare-earth nitride( GdN, EuN and DyN) to compare with previous paper[1]. Recently, experiment show that GaN dope Gd with low concentration (diluted magnetic semiconductor) have colossal magnetic moment[2]. So i have calculated GaN-R( Gd, Dy) with high and low concentration to compare with experiment results. And in future work, i will calculate BaR2NiO5, perovskite RTiO5 and Bi2Se3-R( R: Gd, Eu and Dy).
[1]:PHYSICAL REVIEW B 75, 045114 2007
[2]:PRL 94, 037205 (2005)

Title : The structural stability and magnetism of Heusler alloys Mn2YZ

Speaker : Masahito Kumakura

Abstract:

Heusler alloys (X2YZ , X and Y are transition elements , Z is typical elements .) have a variety of properties including half-metal, spin-gapless semiconductor, and so on , and Heusler alloys are expected for application in many fields.In this talk, we report about our calculations of Mn2YZ( Mn2YZ, Y is transition elements , Z is Al, Ga, and In) alloys by using HiLAPW. We talk about structural stability and magnetic properties of these alloys.


Title : First-principles calculation of Bismuth thin films

Speaker : Takao Kosaka

Abstract:

Bismuth has attracted particular attention because of its unique electric properties. Bismuth posses spin-split Rashba surface states, resulting from the strong spin-orbit coupling with the broken space-inversion symmetry [1]. And in bismuth thin films, the one-dimensional topological edge state, that is, quantum spin hall states, appears [2]. These physical properties have attracted increasing study interest, in that application in spintronics. So, it is required that to elucidate the detailed electric structure of bismuth. Recently, it has been observed by angle-resolved photoelectron spectroscopy that the surface band of bismuth thin films changes with temperature. In this research, using a first-principles calculation, I examined for changes in energy change and surface state band by the surface atomic displacements to illustrate the temperature dependence of the surface band.
[1] S. Murakami, Phys. Rev. Lett. 97, 236805 (2006).
[2] Yu. M. Koroteev et al., Phys. Rev. Lett. 93, 046403 (2001).

Title : Introduction of investigations on phonon mode and spin states of LaCoO3

Speaker : Kei Izumi

Abstract:

LaCoO3 is one of the typical perovskite Co oxides, and well investigated because of its various physical properties. And it is known that spin state of LaCoO3 is changed by the external fields, these phenomena are called ‘spin-crossover’. We focus on the relations between structure symmetry and spin states of LaCoO3. On the other hand, when crystal structure is distorted, we can consider various types of distortion. Crystals are distorted according to irreducible representations in the point group of crystals. In this presentation, I would like talk some explanation about phonon mode and group theory, and give introduction about investigations on spin states of LaCoO3.


Title : Statistical modeling on structural stability of full-Heusler alloys

Speaker : Shinichi Kanehira

Abstract:

There are more 10000 patterns of full Heusler alloys X2YZ (X and Y: transition metals, Z: sp elements). The structures of full-Heusler alloys exist L21 type and Xa type. Full Heusler alloys have interesting properties, for example half-metal and shape memory alloys. However, these properties depend on structure. Therefore, the discussion of the structural stability of the full Heusler alloy is important. In this study, the structural stability of full Heusler alloys was discussed by using statistical modeling. We discuss about the result of statistical modeling.

Title : Study of electronic structure and magnetism of Co-based Heusler alloys by first-principles calculations

Speaker : Yosuke Kanda

Abstract:

Co-based full Heusler alloys (Co 2 YZ, Y: transition element, Z: sp element) have attracted much attention as spintronics materials for a long time because of interesting physical properties. For example, the very large tunnel magnetoresistance effect is expected and researched in magnetic tunnel junction devices using the Co-based full Heusler alloys [1, 2] because Co-based full Heusler alloys have high spin polarizations and high Curie temperatures. However, no systematic studies on Co-based full Heusler alloys are done. Therefore, in order to contribute to the search of new spintronics materials, we investigated the electronic structures and magnetism of various Co-based full Heusler alloys by using first-principles calculations. In this talk, we show and discuss the results.
[1] H. Liu et al., Appl. Phys. Lett. 101, 132418 (2012)
[2] T. Scheike et al., Appl. Phys. Express. 9, 053004 (2016)


Title : First-principles calculation of perpendicular magnetic anisotropy of tetragonal MMn3N (M= V, Cr, Fe, Co, Ni, Cu)

Speaker : Masaki Tahara

Abstract:

Materials with perpendicular magnetic anisotropy (PMA) have gathered considerable attention because of high-performance magnetic recording devices and spintronics devices. While CoPt-based alloy thin films are widely used as perpendicular magnetic recording media, development of noble metal-free PMA materials is strongly desired from the viewpoint of element strategy. In this study, we focused on antiperovskite-type manganese nitrides Mn4N, which are reported for PMA [1-3]. We performed first-principles calculation by using the all-electron FLAPW method. Firstly, we optimized MMn3N (M= V, Cr, Fe, Co, Ni, Cu) and calculated Magneto-crystalline anisotropy (MCA) energy. Then, we investigated electronic structure and magnetic property. From the results of calculation, Fe atoms in FeMn3N were clarified to contribute to perpendicular MCA.
[1]Y. Yasutomi, K. Ito, T. Suemasu., J. Appl. Phys. 115, 17A935 (2014).
[2]K. Kabara and M. Tsunoda, J. Appl. Phys. 117, 17B512 (2015).
[3]K. Ito et al., AIP Advances 6, 056201 (2016)

Title : Measurement of temperature dependence on the lattice constant of α-YbAlB4 by hard x-ray

Speaker : Takuro Hiraiwa

Abstract:

β-YbAlB4 is a superconducting material (Tc = 80 mK) of the heavy electron system first discovered in the Yb sys em and has non-fermi liquid behavior.[1] α-YbAlB4 is a polymorph of β-YbAlB4 having the same structure locally. the previous study, the temperature dependence on the lattice constant of α-YbAl(1-x)Mn(x)B4 (x = 0.34) was invest\ igated, and large anisotropy was found in the a,b-axis and the c-axis.[2]This anisotropy is expected to be due to th e anisotropy of 4f electrons of Yb. In this study, I attempted to obtain information on the electronic state of Yb i n α-YbAlB4 by investigating the temperature dependence on α-YbAlB4 and α-LuAlB4 lattice constants by hard x-ray.
[1]S.Nakatsuji et al. Nature Physics 4, 603 - 607 (2008)
[2]後藤駿斗 2016年 卒業論文


Title : Self-introduction and Analysis of tunneling probability by using wave packet

Speaker : Keiya Hiraoka

Abstract:

In this presentation, I would like to introduce myself briefly and talk about my previous research in Wakayama University. My previous research is about Analysis of tunneling probability by using wave packet. Tunneling effect is an important phenomenon because it is used for tunnel diode and STM and so on. So, it is desirable to know the exact tunneling probability. Conventional way for calculating tunneling probability is using plane wave. However, plane wave doesn’t express a real particle exactly. So, we should use a wave packet which expresses it exactly. In this research, I constructed wave packet by superposing plane wave and calculated exact tunneling probability by simulating its time development. In this way, I got different tunneling probability in comparison to conventional method.

Title : Self introduction and my graduate study

Speaker : Shogo Yamashita

Abstract:

Recently, a two dimensional material (nanosheet) which have specific properties such as graphene have attracted attention of many researchers. I calculated electronic structure of two nanosheets (Graphene and MnO2) using tight binding approximation in order to revel the origin of those properties. In this talk, I show the results of calculation.

Title : Calculation of Temperature Dependent Electrical Resistivity

Speaker : Kou(Yoshida lab.)

Abstract:

The KKR-CPA method is a powerful tool for calculating the single-particle properties of disordered alloys. This technique is extended to transport properties. [1,2] Although this formalism is based on the one electron Kubo formula, its calculation is not take account electron-phonon scattering and electron-magnon scattering effect in finite temperature. The main objective of this study is to develop a practical first principles method that can calculate the conductivity of metallic crystal in finite temperature including electron-phonon and electron-magnon scattering. Our approach is in accordance with: 1) the KKR method with linear response theory, 2) the local phonon and local magnon approach, and 3) the alloy analogy model.
References:
[1] H. Ebert, S. Mankovsky, et al., Phys. Rev. B 91, 165132 (2015).
[2] W. H. Butler, Phys. Rev. B 31, 3260 (1985)


Title : Regression Analysis of Slater-Pauling curve

Speaker : Hitoshi Fujii

Abstract:

In the field of material science, “informatics” is a new and powerful tool not only to accelerate finding new materials with target properties but also to understand the origin of the properties. We have applied this informatics technique to the magnetic moment of Fe-based 3d transition metal alloys, i.e., the Slater-Pauling (SP) curve, by using the AkaiKKR code which is based on the Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) method within the local density approximation. Our calculations successfully reproduced the experimental SP curve. We also performed a regression analysis of the SP curve with the linearly independent descriptor generation (LIDG) method and show that the LIDG allows us to extract a very good regression model, i.e., accurate, simple, physically reasonable model from the calculated data.

Title : Development of Crystal Structure Prediction Method for Magnet Materials

Speaker : Tomoki Yamashita

Abstract:

Random search algorithm in combination with structure optimization technique using first-principles calculations was developed for crystal structure prediction. Furthermore, Bayesian optimization method was added to accelerate crystal searches. We started with simple systems to test the random search algorithm. Crystal structure prediction simulations were carried out for Y2Co17. Our predicted structures were in complete agreement with structures in experiments. We further tried a Bayesian optimization method to search the of Y2Co17 efficiently. The structure prediction was succeeded with fewer trials. We could show the high efficiency of the Bayesian optimization.

Title : Simulation Methods for Spintronics Devices

Speaker : Akira Masago

Abstract:

I would like to discuss simulation methods for measurement and operation of spintronics materials, devices, and systems by combination of methods that my current coworkers and I have developed so far. For the aim, in the beginning, I introduce my recent works: "the tight-binding simulation for scanning probe microscopy" and "magnetization of Eu-doped GaN". In the former topic, I would like to talk about the simulation method for systems including not only a sample but also a probe, and then talk about fabrication method and magnetic properties of nanoscale samples. After these, I consider how these simulation methods will be applied to spintronics systems.
References:
[1] "Computational nano-materials design of self-organized nanostructures by spinodal nano-decomposition in Eu-doped GaN", A. Masago, T. Fukushima, K. Sato, and H. Katayama-Yoshida, Jpn. J. Appl. Phys. Rapid Commun. 55 (2016) 070302.
[2] "Noncontact Atomic Force Microscopy Line-profiling of Irregular Dimers on the Monohydride Si(001) Surface: Tight-binding Simulation", A. Masago, e-J. Surf. Sci. Nanotech. 11 (2013) 80.
[3] "Simulation method of Kelvin probe force microscopy at nanometer range and its application", A. Masago, M. Tsukada, and M. Shimizu, Phys. Rev. B 82 (2010) 195433.


Title : Discharge reaction mechanism in Tin sulfide anode for Na-ion battery

Speaker : Hiroki Kotaka

Abstract:

Li-ion batteries have been widely used as power sources in portable electronics devices because of its high energy densities and high voltages. However typical Li-ion batteries are relatively expensive, because electrode materials contain rare-metals such as Li and Co. To solve the cost problem, Na-ion batteries have been expected as a next-generation rechargeable battery. We focus tin sulfide (SnS) as the cathode of Na-ion battery. In this study, we focus attention on tin sulfide (SnS) as a candidate anode material for Na-ion batteries.
We perform the structural search and appear the dis-charge process in Na-SnS half-cell using first-principles calculation. We calculate the electro-chemical properties and compare our calculation results with experiments. We also show calculation results of x-ray absorption spectra, and discuss the experimentally reported spectral changes.

Title : Magneto-electric quadrupole order in Ba(TiO)Cu4(PO4)4 with square cupolas

Speaker : Kunihiko Yamauchi

Abstract:

I will introduce my recent research activity on multiferroic oxides as collaborating with Dr. Toyoda and Prof. Kimura’s group. It has been theoretically proposed that spin-vortex and magnetic multipole may exhibit magneto-electric (ME) effect. However, such ME effect has been experimentally found only with toroidal moment while monopole or quadrupole orders have not been focused so far. In a recent work by Kimura et al. [1], it was newly found that a square-cupola Cu cluster is responsible for the magnetic quadrupole moment, which indeed activates ME effect. In this talk, I will discuss the magnetism, mechanism of the ME effect, and the symmetry analysis by using Landau theory.

[1] K. Kimura, P. Babkevich, M. Sera, M. Toyoda, K. Yamauchi, G.S. Tucker, J. Martius, T. Fennell, P. Manuel, D.D. Khalyavin, R.D. Johnson, T. Nakano, Y. Nozue, H.M. Ronnnow, and T. Kimura, Nature Communications vol 7 13039/1-7 (2016).

Title : Thermoelectric chalcogenide thermoelectric mineral

Speaker : Hiroki FUNASHIMA

Abstract:

In this colloquia, I will introduce the thermoelectrics and recent my work in which I collaborate with Prof. Tou’s group(Kobe Univ). Recently, ``Thermoelectric sulphide( or chalcogenide mineral)’’ , e.g, ``tetrahedrite:Cu12Sb4S13’’, ``collusite:Cu26A2E6S32’’ has attracted the attention in thermoelectrics. In this talk, I’ll introduce the concept these material and recent my activity. If I could find an time, I will also introduce my recent work in J-Physics project, about f2 Quadrupole-Kondo System collaborating with Prof. Kuramoto(KEK)

ref) K. Suekuni et al, J. Appl. Phys. 113, 043712 (2013)


Title : Phonon Calculations on HiLAPW

Speaker : Tamio Oguchi

Abstract:

Phonons play a major role in many of the physical phenomena and properties, of which the study is an important chapter in condensed matter physics. With the progress in first-principles total energy and atomic force calculation methods within the framework of density functional theory, phonon band structure and related properties can be easily and precisely computed together with the electronic band structure. Recently, phonon calculation techniques using a supercell approximation have been implemented in our HiLAPW code and tested for several kinds of condensed matter systems. In this Colloquium, I shall introduce the fundamentals of phonon calculation methods and demonstrate their accuracy and validity for your future usage. This work was done in collaboration with T. Shishidou (U of Wisconsin, Milwaukee).

Title : Excitons observed in photoluminescence spectra

Speaker : Koun SHIRAI

Abstract:

For years, we have been studying the behavior of Cu4 complex in silicon. This complex is supposed to be the cause of the sharp and intense emission at 1014 cm-1 in photoluminescence spectra of Cu-doped Si. This emission line has been identified as the zero-phonon (ZP) line of a bound exciton of Cu complex. I will give a general account for the exciton appearing in optical spectra. What is exciton all about? That is a bound exciton? Why so narrow? Why so intense? What is the meaning of zero phonon? I will describe how to interpret experimental spectra and how to identify the above attributions.

Title : Ferromagnetic instability in 2D electride Y2C

Speaker : Noriaki Hamada

Abstract:

I talk about the feature of the electronic states in the two-dimensional electrides. Among them, Y2C has a unique electronic band structure, in which two interlayer-electron bands crosses the Fermi enregy and causes the ferromagnetic instability. The origin of the instability is explained by three key words, two-dimesional, semimetallic and interlayer bands.
ref.)
[1] T. Inoshita, N. Hamada, and H. Hosono, Phys. Rev. B 92, 201109 (2015).
[2] K. Horiba, R. Yukawa, T. Mitsuhashi, M. Kitamura, T. Inoshita, N. Hamada, S. Otani, N. Ohashi, S. Maki, J. Yamaura, H. Hosono, Y. Murakami, and H. Kumigashira,Phys. Rev. B 96, 045101 (2017).


Title : Calculations of anisotropic exchange interaction and atomic force by Korringa-Kohn-Rostoker Green's function method

Speaker : Tetsuya Fukushima

Abstract:

We give a brief summary of the Korringa-Kohn-Rostoker (KKR) Green's function method, in which the one electron Green's function for the Kohn-Sham equation is directly calculated. The KKR Green's function method can access various physical quantities, using the one-electron Green's functin. In particular, we focus on the exchange tensor (magnetic exchange interaction and Dzyaloshinski-Moriya interaction) and atomic force in this seminar.

Title : Cu4 reactions with H impurities in Si

Speaker : Takayoshi Fujimura

Abstract:

The copper complex defect in Si emitting light of photoluminescence in 1014meV exists. This defect generally called Cu_PL. This is so stable at room temperature that Cu_PL is expected as luminous element. The structure of Cu_PL is four copper complex which consists of one substitutional site and of three interstitial site copper atom in Si. Yarykin[1] report the experiment which this defect is hydrogenated at 380K by reverse bias annealing, then DLTS measurement was performed. The reaction mechanism when this defect is hydrogenized, doesn't become clear. I talk about coppre-hydrogen complex in Si.
[1] Nikolai Yarykin and Jorg Weber, Appl. Phys. Lett. 105, 012109 (2014)