2016

11/1 Dr. Akihiko Ikeda(Research Associate)
    Quantum spin-crossover of correlated electrons

Spin state is a characteristic degree of freedom in a multi-electron and multi-orbital system (e.g. magnetic ion under crystal field) where crystal field splitting (Δ) and Hund's coupling (J ) are delicately competitive. Low spin [LS] (or high spin [HS]) state emerges when Δ (or J ) overwhelms the other. Recently, we found a low entropy phase in a spin crossover cobaltite LaCoO3 at ultrahigh magnetic fields of above 100 T by means of magnetization measurement up to 140 T [1]. Various exotic orders are claimed as its origin such as LS/HS order and excitonic order. They are considered to be stabilized by the correlation effects based on analysis of the two-orbital Hubbard model [2, 3]. The excitonic phase is characterized with the spontaneous and quantum-mechanical mixing of the wave functions of LS and HS states. Whereas, the LS/HS ordered phase is the spatial alternation of the LS and HS states.
In the talk we briefly review our experimental results on LaCoO3 [1] and Y-doped Pr0.7Ca0.3CoO3 [4]. Then we discuss the physical origin of the possible stabilization of exotic phases [2] and their field effects [3]. We also mention our future plan.
[1] A. Ikeda et al., Phys. Rev. B 93, 220401(R) (2016).
[2] J. Nasu et al., Phys. Rev. B 93, 205136 (2016)
[3] T. Tatsuno, et al., J. Phys. Soc. Jpn. 85, 083706 (2016)
[4] A. Ikeda et al., Phys. Rev. B 94, 115129 (2016).



2015

9/25 Prof. Kenichi Asano (Osaka University)
    グラフェンのサイクロトロン共鳴における多体効果

放物線形のエネルギー分散を持つ電子系に対するサイクロトロン共鳴には相互作用効果が現れない。この事実は Kohn の定理として知られている。 しかし、グラフェンに代表される Dirac 電子系(線形のエネルギー分散を持つ二次元電子系)には、この Kohn の定理を適用できないので、サイ クロトロン共鳴に電子間相互作用の効果が現れる。 本講演では、グラフェン系のサイクロトロン共鳴に現れる多体効果を、少数電子系の数値的対角化で調べた結果について説明する。まず、単層グラ フェン系については、N=0 のランダウ準位から N=1 のランダウ準位への遷移に対応するサイクロトロン共鳴にほとんど多体効果が現れず、Kohn の 定理が近似的に成立しているとみなせることが分かった。その一方で、N=-1 からN=2 への遷移に対応するサイクロトロン共鳴には相互作用効果が 現れる。時間に余裕があれば、二層グラフェン系に対する結果についても述べたい。



4/8 Dr. Atsuhiko Miyata (Laboratoire National des Champs Magnetiques Intenses, Toulouse, France)
    Direct measurements of the exciton binding energy and effective masses for charge carriers in organic-inorganic perovskites

Solar cells based on the organic-inorganic perovskite family of materials have made a dramatic impact on emerging photovoltatic (PV) research with efficiencies of around 20% [1], which offers a new route to low-cost solar energy devices with simple fabrication processes. However, the fundamental electronic properties of the perovskites such as the electron and hole effective masses and the exciton binding energy are poorly known. We have measured both properties for methyl ammonium lead tri-iodide (CH3NH3PbI3) using magneto absorption in very high magnetic fields up to 150 T showing that the exciton binding energy at low temperatures is only 16 meV, a value three times smaller than previously assumed [2]. Landau level spectroscopy shows that the reduced effective mass of 0.104 me is also smaller than previously assumed [2], but in good agreement with recent calculations [3]. We also observe Landau levels in the room temperature phase (350 K > T > 140 K) in which PV devices actually perform, showing an evidence that the binding energy falls to a few milli-electron volts in the room temperature. This result indicates the performance of PV devices using this material is attributed to the spontaneous generation of free carriers following photo-absorption.
[1] NREL Best research cell efficiencies: http://www.nrel.gov/ncpv/images/efficiency_chart.jpg
[2] K. Tanaka et al., Solid State Commun, 127, 619 (2003).
[3] E. Menendez-Proupin et al., Phys. Rev. B, 90, 045207 (2014).



4/3 Dr. Sergei Zherlitsyn (HLD-EMFL, Germany)
    Spin-lattice effects in high magnetic fields

The Dresden High Magnetic Field Laboratory (HLD) is a pulsed-field user facility which currently operates ten experimental chambers equipped with a variety of pulsed magnets energized by two capacitor banks with maximum stored energies of 50 and 14 MJ at 24 kV maximum operational voltage. The magnets support a broad range of experiments in pulsed magnetic fields for user and in-house research. In the first part of my talk I will present some recent developments at the HLD. Spin-lattice effects play an important role in many magnetic materials, frequently leading to novel phases and phase transformations. In this presentation, I give some examples of such effects studied in frustrated magnets characterized by competing interactions. The delicate balance between these interactions can be easily disturbed by the application of strong magnetic fields leading to field-induced phase transitions. The phase transformations and the related critical phenomena in magnetic systems are fruitful grounds for ultrasound experiments which provide valuable information on the spin-strain coupling. I discuss the sound-velocity and sound-attenuation results obtained in magnetic fields up to 87 T for some selected materials with a magnetic pyrochlore lattice, such as CdCr2O4 and CoCr2O4 which exhibit unusual phase transitions and extended metastable magnetostructural states. I will show that the spin-strain coupling is crucial and determines the underlying physics of the frustrated magnetic materials.



1/28 Prof. Hirohiko Sato (Chuo University)
    水熱合成法を用いた新物質探索と単結晶作成

高温、高圧の水溶液中での化学反応を利用した水熱合成法は、宝石などの良質な単結晶の育成法として古くから知られている。我々は水熱合成法を利用し、新物質を含む興味深い磁性体の単結晶の作成に成功してきた。本セミナーでは得られた幾つかの物質について、その構造と磁性を紹介する。



1/23 Ms. Suyeon Lee (IMGSL)
    Magnetic field-induced insulator-metal transition in transition metal oxides at ultrahigh magnetic fields


1/19 Prof. Kim Yongmin (Department of Applied Physics Dankook University, Yongin si, Korea)
    Negative Diamagnetic Shift in InP-GaP Lateral Nanowires under Pulsed Magnetic Fields and a Progress Report on Developing Pulsed Magnetic Field Facility at Dankook University

While growing a short period superlattice (SPS), due to an in-plane strain field along [110] direction, depositing atoms cross penetrate, which spontaneously generates potential modulation along the lateral [110] direction. In such growth condition, lateral superlattice can be achieved. Limiting the thickness of the SPS layer, similarly, one can grow a lateral nanowire. We measured photoluminescence (PL) of an InP-GaP lateral nanowire under pulsed magnetic fields to 50 T. We observed strong negative diamagnetic shift in a certain magnetic field direction due may to a variation of exciton center of mass potential. We will also discuss the current achievement of pulsed magnetic field facility at Dankook University. We successfully developed 1.6 MJ (9 kV) capacitor bank for the generation of pulsed magnetic fields. We obtained ~47 T at 6 KV charging voltage with the 22 ms total transient time of the magnetic pulse. We plan to develop higher and longer magnetic field facility in future.



1/14 Prof. Hsiang-Lin Liu (Department of Physics, National Taiwan Normal University)
    THz response of graphene-based materials

We present the results of THz absorption measurements of monolayer graphene with molecular doping and four-layer graphene. There are several important findings in this study. First, the THz conductivity of the triazine-doped film consists of free carrier absorption at zero frequency and a disorder-induced finite frequency peak around 4.65 THz. As the temperature is lowered, the Drude plasma frequency (30 THz) decreases, whereas the carrier relaxation time (54 fs) does not show much temperature variation. These scenarios show the semiconducting behavior of the triazine-doped film. Second, a comparison of our measured conductance spectra and the theoretical predictions in turn illuminates the importance of the several scattering mechanisms present in these materials. Third, in a magnetic field, the Drude oscillator strength of four-layer graphene is suppressed and transferred to various finite frequency transitions between the Landau levels. The dramatic increase of the low-frequency transmission is a THz counterpart of the positive magnetoresistance effect. The 300 K magnetodielectric contrast is as large as 60% near 1 THz at 10 Tesla. The results are potentially useful for magnetic memory applications away from the dc limit.



2014

12/11 Dr. Gael Bastien (CEA-Grenoble)
    Fermi surface and upper critical field study of UCoGe under hydrostatic pressure

UCoGe is a ferromagnetic superconductor with a Curie temperature of T_C ~ 2.8 K and a superconducting transition at T_sc ~ 0.6 K. The Curie temperature decreseases with pressure and vanishes at a critical pressure p_c~ 1 GPa [1]. Superconductivity was observed both below and above p_c. At ambient pressure in the ferromagnetic phase the upper critical field as a function of temperature shows an unusual upward curvature [2]. We report magnetoresistance and Hall effect measurements on UCoGe for field along the easy magnetization axis c. We focused mainly on Shubnikov-de Haas oscillations and on the temperature dependence of the upper critical field as function of pressure in the ferromagnetic and paramagnetic states. At ambient pressure an anomaly around 9T and a Fermi surface reconstruction around 17 T were observed both in the quantum oscillations and in the Hall effect. Quantum oscillations evolve continuously with pressure between ambient pressure and 2.3 GPa, no Fermi surface reconstruction was observed around the critical pressure p_c. Finally it was shown that the upper critical field of UCoGe for field along the easy magnetization axis c increases with pressure through the critical pressure p_c and the upward curvature of the upper critical field is also enhanced above the critical pressure.
[1] E. Hassinger, D. Aoki, G. Knebel, J. Flouquet, J. Phys. Soc. Jpn. 77, 7, 073703 (2008)
[2] N. T. Huy, D. E. de Nijs, Y. K. Huang, and A. de Visser, Phys. Rev. Lett. 100, 077002 (2008)



10/17 Mr. Ayumu Iwasa (IMGSL)
    Experimetal search for a new high-field phase of the semimetals Bi and BiSb

7/25 Mr. Kazuto Akiba (IMGSL)
    Research of semimetals under pulsed high magnetic fields

5/30 Dr. Zhou Weihang (IMGSL)
    High-field Magneto-optical Study on the Excitonic and Phononic Transitions in Single-walled Carbon Nanotubes

4/30 Dr. Atsushi Miyake (IMGSL)
    Current status of solid state physics reseach in Tokunaga laboratory

3/30 Dr. Akihiko Ikeda (IMGSL)
    Current status of solid state physics reseach in Matsuda laboratory

2/21 Dr. Akihiro Kondo (IMGSL)
    Current status of solid state physics reseach in Kindo laboratory

1/30 Dr. Daisuke Nakamura (IMGSL)
    Current status of solid state physics reseach in Takeyama laboratory

2013

8/16 Prof. Alexander T. Holmes (School of Physics and Astronomy, University of Birmingham, UK)
    Neutrons and X-rays at high field, from superconductors to viruses

2012

9/4 Dr. S. Zherlitsyn(Hochfeld-Magnetlabor Dresden, Helmholtz-Zentrum Dresden-Rossendorf, Germany)
    High Magnetic Fields for Science

Magnetic fields are powerful tools for studying the state of matter. Under extreme conditions, such as high-magnetic fields, new interesting properties of matter can appear and an understanding of materials behavior can be gained. Access to high magnetic fields could provide new insight into various fundamental physical phenomena. Currently the only ways to reach magnetic fields beyond 50 T are pulsed magnets. The Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden, HLD) has achieved the strongest non-destructive magnetic fields in Europe. Last year the HLD held the world record for some time. Typical pulse durations of the available magnets are from 0.01 to 1 s that is long enough for many experiments which are usually performed in static magnetic fields. Magnetic fields up to about 90 T are available for user experiments such as electrical transport, magnetization, ultrasound, magnetostriction, electron spin resonance, and high-field infrared spectroscopy. Several less typical pulsed-field experiments, for instance, nuclear magnetic resonance or specific heat are also emerging at the HLD now. In my talk I explain how the pulsed fields are generated and applied for various scientific experiments. I will show you recent results obtained on some magnetic systems in high magnetic fields. Results of high-field ultrasound investigations will be analyzed in more details. I acknowledge support from the "JSPS Invitation Fellowship Program for Research in Japan (Short-term)".



8/7 Mr. Mitsuru Inagaki (Toyota Technological Institute)
    GaAsNにおける支配的な電子散乱機構に関する研究


5/30 Mr. Raju Kati (Department of Physics, Osmania University, India)
    Elastic and anelastic behaviour of some charge ordered manganites

The Physics of these manganite materials is dominated by complex interplay between charge, spin and lattice degrees of freedom. The correlation between charge and spin has been well studied and explained. But, there is limited knowledge on how the lattice interact with the charge and spin in these materials, because the lattice related properties are to be studied with care by making use of non destructive techniques. Therefore, systematic studies of elastic longitudinal modulus and internal friction behaviour along with magnetic and electrical properties of the samples have been studied. In doped manganites, the charge-ordered phases are novel manifestations arising from the interaction between the charge carriers and phonons where in the Jahn-Teller distortions play a significant role. Charge ordering (CO) arises because the carriers are localized into specific sites below a certain temperature known as charge ordering temperature, TCO, giving rise to long- range order throughout the crystal structure. Although, charge ordering would be expected to be favored when doping level x = 0. 5, due to the presence of equal concentrations of Mn3+ and Mn4+ states, the phenomenon is found be present in the doping range, 0.3 < x < 0.75. The physical properties in CO manganites arise from the strong competition between ferromagnetic double-exchange and antiferromagnetic superexchange interactions. Under high magnetic fields, the charge ordered state melts leading to the formation of CMR state. At Charge Ordered transition temperature, a jump in resistivity, a peak in magnetization and structural phase transitions etc., may be observed. Although a few studies on these charge ordered materials were reported earlier, several other aspects of these materials including electron phonon and spin phonon interactions have not been understood clearly. Therefore, the present investigation is aimed at understanding the electron phonon and spin phonon interactions in these materials. The motivation for undertaking the electrical and magnetic property investigation along with the elastic and anelastic studies has also been explained. One of the most important characteristic properties of CMR materials is the exhibition of metal-insulator transition (TP). The electronic properties of these materials are known to change with doping at A-site. Depending on the concentration of Mn3+/ Mn4+ ions and mean ionic A-site ionic radius, these materials also show charge-ordering transitions (TCO). Therefore, in order to determine their TP and TCO values and to investigate their variation with doping material concentration, resistivity measurements were undertaken over a temperature range, 2 - 300K using four - probe method on a superconducting magnetic system (Oxford Spectromag). The variation of TP and TCO with dopant concentration has been discussed. The resistivity data of all the samples has been thoroughly studied in the presence of magnetic fields and the results demonstrate a clear decrease of resistivity in the magnetic field. The resistivity below TCO drastically reduced, exhibiting a large CMR effect. The large decrease of the resistivity and the downward shift of TCO upon the application of a field manifest the unstable nature of the CO state. Thus melting of CO state in a magnetic field and the unusual resistivity behavior in magnetic field may be explained within the framework of the phase separation. The fundamental property of mixed-valence manganites is the close relationship between electronic transport and magnetism. A key feature of these materials is the simultaneous occurrence of metal-insulator (TP) and ferro-paramagnetic transitions (TC). Depending on the composition of samples, they exhibit different magnetic transitions viz., Curie transition (TC), Charge ordering transition (TCO) and Neel transitions (TN). The magnetic transition temperatures were obtained by measuring magnetization values as a function of temperature using Vibrating Sample Magnetometer (VSM) over a temperature range, 80-300K and their variation with compositions is explained in detail. The materials characterization is a serious challenge in many fields of technology. The ability of the technique to explore the structural and mechanical properties of materials is essentially required for many applications of the materials. Therefore, the determination of elastic and anelastic behaviour is vital for the discovery of newer materials. The measurement of ultrasonic velocities (longitudinal) and attenuation in materials directly relates the elastic properties of materials. The structural changes in the materials are well reflected in density/velocity and hence, the modulus. The phenomenon such as fatigue, creep and materials strength can be explained through change in ultrasonic velocities. Thus, the measurement of ultrasonic velocity, attenuation and elastic constants is an important ultrasonic non-destructive testing (NDT) for quality assessment of materials. The data on newer materials such as CMR materials, composites, and ceramics as a function of temperature and frequency are required for the selection of right material for a particular application. Therefore, to measure the elastic properties of these charge ordered manganites in the temperature range 100 300 K, composite oscillator technique has been used. The low temperature elastic and anelastic behaviours of magnetic materials in general and CMR materials in particular are very much useful in understanding the electron phonon and spin phonon couplings. All the samples of present investigation are found to exhibit a minimum in the longitudinal velocity in the vicinity of their respective TC's and TCO's. In recent times, although several theoretical models were proposed, mean field theory incorporating the ideas relating to the Jahn-Teller effect seems to be better one in explaining the anomalous behaviour of magnetic oxides in general and manganites in particular in the vicinity of their transition temperatures. Therefore, an attempt has been made to explain the anomalous elastic behaviour in the vicinity of magnetic transitions observed in the present investigation using the mean field theory. The important criterion based on which the mean field theory was developed, is the existence of an interaction between a lattice distortion (i. e elastic strain) and wave function of degenerate ground state, which lifts the degeneracy causing the molecule to seek a distorted configuration of lower energy.



5/21 Prof. Giti A. Khodaparast (KEK)
    Magneto-Optical Spectroscopy of MOVPE Grown Narrow Gap III-Mn-V Ferromagnetic Semiconductors

Narrow gap ferromagnetic semiconductors (NGFS) have significant potential for applications in both infrared spin photonics and spin transport devices due to their lighter holes, smaller energy gaps, and much higher carrier mobilities compared to other III-Mn-V ferromagnetic semiconductors. A Rudermann- Kittel-Kasuya-Yosida (RKKY) mechanism, where free holes mediate the ferromagnetism, is favored in NGFS and a small hole effective mass results in a long interaction distance and effective exchange coupling. The calculated hole effective Bohr radius in NGFS indicates sufficient overlap of the hole wave functions to stabilize ferromagnetism for hole concentrations greater than 1018 cm-3. In this work, several time resolved differential transmission and magneto-optical spectroscopy techniques were employed to provide insight into both the time scales and the nature of microscopic interactions in MOVPE grown ferromagnetic InMnAs and InMnSb with the Curie temperatures above room temperature.



4/16 Prof. Eiji Nakamura (KEK)
    Proposal of applications of the MegaGauss techniques for higher-energy charged particle handling

The MagaGauss techniques are attractive to explore a frontier of physics study for high-energy particles. The following three articles are discussed for examples of the applications: (1) Beam handling of GeV ~ PeV hadrons at high-energy particle accelerators, (2) Compact fusion reactor, (3) Improvement of light source for short wavelength of 1 fm, which is equivalent to the core size of nucleon, produced by the synchrotron radiation method. It is difficult to apply the MegaGauss technique because severe stability and homogeneity are required for such high- energy charged particle handling now. I would like to solve the problems, and realize a new energy field.



2/13 Dr. Zhou Weihang (IMGSL)
    The Quantum Chaotic Dynamics of Hydrogen-like Shallow Impurities in Solid State Environment

In this work, we report the first experimental study on the quantum chaotic dynamics of hydrogen analogues in solid state environment. We realized the hydrogen analogue in anisotropic crystal field by introducing an isolated phosphorus donor in Si and study its quantum chaotic dynamics by means of photo- thermal ionization spectroscopy technique. The interference of electron wave packets which leads to quasi-Landau resonances were observed. By analyzing the magnetic field dependence of the statistical energy level distributions, we observed smooth transitions between the Poisson limit and the Wigner limit for the impurity energy level distributions, demonstrating the magnetic field control of the quantum chaotic dynamics of hydrogen analogues in an anisotropic crystal field. Effects of the crystal field anisotropy on the quantum chaotic dynamics have been studied and good agreements between theoretical calculations and the experimental data were found.



2/3 Prof. Tung-Ming Pan(Chang Gung University)
    High-k Rare-Earth Oxide for Thin-Film Transistors, Nonvolatile Memories, pH Sensors, and Biosensors Applications

We have developed high-k rare-earth oxide films for TFTs, nonvolatile memories, pH sensors, and biosensors applications. High-k Pr2O3 and Tb2O3 dielectrics deposited on poly-Si film using a N2O and CF4 plasma treatment exhibited excellent electrical characteristics, respectively. Consequently, the concentration of nitrogen and fluorine in the oxide/poly-Si interface has to be optimized in terms of the reliability reduction due to hot carrier and positive-bias temperature instability. The stacked Pr2O3/SiOxNy film and Tb2O3 are very attractive as gate dielectric materials for high performance low-temperature poly-Si TFTs. High-k Y2O3 memory device annealed 700oC in N2 ambient exhibited excellent electrical characteristics, such as memory window, gate disturb, data retention, and endurance. This is due to the formation of Y-silicate layer after annealing in N2 ambient. Furthermore, our group explored Nd2O3, Er2O3, and Sm2TiO5 films to replace a traditional SiO2 film as the sensing membrane in pH-ISFET devices. These metal oxides deposited on Si by reactive sputtering exhibit a high detection sensitivity, small hysteresis voltage, and low drift rate. EIS devices incorporating high-k rare-earth sensing membranes appear to be very promising SOC systems for use in biomedical engineering application.



1/30 Dr. Moaz Altarawneh (Department of Physics, Mu'tah University)
    Radio Frequency Contactless Methods in Pulsed Magnetic Field

Radio frequency (rf) contactless methods are useful to study a wide range of physical properties in materials. In metals, skin depth and sheet resistance are accessible, in superconductors upper critical fields and penetration depths can be determined, and in magnetic materials dynamical susceptibility and magnetic transitions can be measured. Advantages of rf measurements include the high sensitivity, high stability oscillator circuits and the contactless nature of the measurement. The tunnel diode oscillator is one of the common rf methods that is proved to be very powerful method in different experimental environments.
In this talk, I will describe the setup of the traditional tunnel diode oscillator in pulsed magnetic field. In addition, a radio frequency oscillator circuit based on a proximity detector integrated circuit will be described as an alternative for the traditional tunnel diode oscillator used for pulsed magnetic field measurements at low temperatures.



1/23 Prof. John Singleton (National High Magnetic Field Laboratory, Los Alamos National Laboratory)
    Magnetic quantum oscillations in underdoped cuprate superconductors observed using the Los Alamos 100 T Multi-Shot Magnet

Magnetic quantum oscillations in single crystals of several underdoped cuprates YBa2Cu3O6+x have been observed using the Los Alamos 100 T Multi-Shot Magnet. Typical data for x = 0. 61, measured using a MHz contactless conductivity technique, are shown in the figure; the frequency shift is proportional to the change in conductivity. The quantum oscillation frequencies and effective masses obtained suggest that the Fermi energy in the cuprates has a maximum at a hole doping of p ~ 0.11-0.12. On either side, the effective mass may diverge, possibly due to quantum-critical phase transitions associated with the T = 0 limit of the metal-insulator crossover (low-p side), and the topological transition from small to large Fermi surface close to optimal doping (high p side). These results will be compared with other data for the cuprates and recent models in order to build up a picture of the probable Fermi surface and its dependence on doping.



2011

11/18 Dr. Xuan Luo (Pohang University of Science and Technology)
    Orbital physics and magnetocaloric effect in spinel vanadates

The orbital physics of spinel vanadates (ZnV2O4 and MnV2O4) are most investigated prototypical systems to study the different couplings between spin, orbital and lattice degrees of freedom. I will talk about the phase diagram of the Zn-doped MnV2O4 system. The ferromagnetic orbital order appears in the parent compound MnV2O4 and low Zn-doped compounds. Additionally, I will talk about the large magnetocaloric effect is observed in this spinel vanadate. It might be due to the change of the orbital state of V3+ induced by an applied magnetic field around the phase transition temperature.



11/18 Dr. Bosen Wang (Institute of Solid State Physics, Chinese Academy of Sciences)
    Chemical composition-dependent magnetocaloric effect and giant magnetoresistance in antiperovskite GaCMn3

In this presentitation, manganese-based antiperovskite compound GaCMn3 is selected to study the physical properties of the parent compound and the physical mechanisms of the magnetic transitions systematically. Our results indicate that GaCMn3 are electron-correlated itinerant ferromagnetisms commonly due to strong hybridizations of C2p-Mn3d and that the physical mechanisms could be attribute to the reconsitution of Fermi surface around the first-order magnetic transition. Based on systemic chemical substitutions, we optimize the functional parameters (GMR and MCE) and analysis the chemical doping phase diagram. For GaCMn3, partial substitutions of Ni for Mn or Zn for Ga enhance the antiferromagnetic metastability, resulting in the occurrences of GMR( 80%, at 50kOe) and adjustable MCE.



4/25 Dr. Daisuke Nakamura (IMGSL)
    Terahertz electrical conductivity measurement of the cuprate superconductor thin films


2/15 Dr. William Knafo (LNCMI, Toulouse France)
    Study of heavy-fermion systems in pulsed magnetic field

In this talk, I will present recent studies of heavy-fermion systems performed at the LNCMI-Toulouse (France) in pulsed magnetic fields up to 60 T. Heavy fermions are characterized by relatively small energy scales which can be easily tuned by pressure or doping, leading generally to a quantum instability between a paramagnetic and an antiferromagnetic ground states. The application of a magnetic field is an alternative to induce a quantum phase transition on these systems, which are driven in high fields to a polarized paramagnetic state. An investigation of the magnetic field - temperature phase diagram of CeRh2Si2 by resistivity, torque, magnetostriction, and thermal expansion measurements will be presented. CeRh2Si2 is an antiferromagnet which becomes superconducting in the neighbouring of its pressure-induced quantum phase transition to a paramagnetic regime, at around 11 kbar. High fields applied along the easy-axis c permit to tune the system to a polarized paramagnetic regime above 26 T . The magnetic field- temperature phase diagram is found to be composed of (at least) three different antiferromagnetic phases. The magnetic-field and pressure-dependences of the quadratic exponent A of the resistivity indicate a similar enhancement of the effective mass at the pressure- and field-tuned quantum instabilities in CeRh2Si2 , which suggests that both kinds of criticality are controlled by common features.
In a second part, I will summarize recent works performed on the "hidden-order" system URu2Si2. High fields applied along the easy-axis c drive the system to a polarized paramagnetic state via a cascade (at very low temperatures) of first-order transitions, at magnetic fields between 35 and 39 T. The magnetoresistance of new high-quality single crystals has been studied for several field-directions, at temperatures between 100 mK and 150 K and in high magnetic fields up to 60 T. Our data confirm the well-established low-temperature magnetic phase diagram of URu2Si2, but also permit to evidence that quantum criticality at the field-induced polarization is initially controlled by the field-induced vanishing of a crossover temperature, which equals approximately 40 K at zero-field. This energy scale might be related to the development of antiferromagnetic correlations, as suggested by the maximum of the susceptibility also observed at around 40-50 K. A comparison of the characteristic energy scales determined by transport and inelastic neutron scattering will be made. Finally, quantum oscillations observed above 30 T in our magnetoresistivity data and their analysis will be presented.



2010

9/28 Prof. Yan Chen (Fudan University)
    Exploring FFLO states of polarized fermions in cold atoms and condensed matter systems

The BCS theory explains conventional superconductivity in terms of electrons with opposite spin and momentum that condense into pairs. A sufficiently large magnetic field destroys superconductivity by coupling to the orbital motion of the electrons. In 1964, Fulde & Ferrell and Larkin & Ovchinnikov (FFLO) showed that this coupling would give rise to a state different to the conventional BCS-state. In particular, this state may exhibit a spatially modulated order parameters as well as finite momentum of Cooper pairs. Up to now, the FFLO state is still elusive to experimental observation. In the talk, I will discuss our theoretical studies on the FFLO states of polarized fermions in cold atoms and condensed matter systems. First we investigate the superfluidity with imbalanced populations of harmonically trapped ultracold fermions in a 2D optical lattice. In the high- density regime, a novel FFLO state with gap oscillation along the angular direction shows up and the accompanying ferromagnetic order modulates accordingly. Next we study the electronic properties of a heterostructure consisting of ferromagnetic metallic layer and s-wave superconductor layer. We demonstrate that a novel stripe FFLO state as well as a 2D FFLO state may show up due to the proximity effect.
Dr. Yan Chen is now a professor at Fudan University. He received his BS and Ph.D. in theoretical physics from Nanjing University in China. Thereafter he conducted postdoctoral research at the University of Houston (1998-2003). Between 2003 and 2007, he was employed as research assistant professor at the University of Hong Kong. Since then he moved to Fudan University as an endowed Dongfang Professor of special appointment. His current research interests include high temperature superconductivity, exotic superfluidity in ultracold atoms, quantum entanglement and quantum phase transitions. He has published more than 40 papers in peer reviewed journals.



9/17 Prof. Jochen Wosnitza (Hochfeld-Magnetlabor Dresden (HLD))
    Research at the Dresden High Magnetic Field Laboratory

High magnetic fields are one of the most powerful tools available to scientists for the study, modification, and control of the state of matter. The application of magnetic fields, therefore, has become a commonly used instrument in condensed-matter physics. For the observation of many phenomena very high magnetic fields are essential. Consequently, the demand for the highest possible magnetic-field strengths is increasing. At the Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden, HLD), that in 2007 has opened its doors for external users, pulsed magnetic fields up to 70 T are available and a European record field of 87.2 T has been reached. The laboratory has set the ambitious goal of reaching 100 T on a 10 ms timescale. As a unique feature, a free-electron-laser facility next door allows high-brilliance radiation to be fed into the pulsed field cells of the HLD, thus making possible high-field magneto-optical experiments in the range 3-250 um. Cryotechniques and different sample probes for a broad range of experimental techniques custom designed for the pulsed magnets are readily available for users. In-house research of the HLD focuses on electronic properties of strongly correlated materials at high magnetic fields. Besides introducing some highlights of the HLD experimental infrastructure, some recent scientific research results will be presented.



3/30 Prof. Oliver Portugall(Laboratoire National des Champs Magnetiques Intenses CNRS)
    The LNCMI - technical installations, recent scientific highlights and future plans

In the first part of the talk I will present the installations and technical activities of the French national high magnetic field laboratory (LNCMI). The LNCMI features two sites at Grenoble and Toulouse respectively dedicated to the generation and application of static and pulsed magnetic fields. Both sites are subject of specific upgrade plans that will be explained.
The second part will be dedicated to selected scientific highlights of the pulsed field installation in Toulouse. In particular I will comment on the study of quantum oscillations in high-Tc superconductors, investigations on low-dimensional carbon allotropes and a unique experiment to verify the magnetic birefringence of the quantum vacuum.
I will close the talk with an overview over collaborations and future plans of the LNCMI on the European level.



2/4 Prof. YUDSON, Vladimir(Russian Academy of Sciences, Russia / ISSP)
    Conductivity of Layered Systems: Localization vs Delocalization by Disorder

Conductivity of many layered materials is more anisotropic than it is predicted by theband theory and Drude model. To understand this anomaly, we consider a model wherethere are two kinds of the disordrr a "planar" disorder due to the presence of randomly spaced "wrong" planes, and a weak "bulk" disorder caused by isotropic impurities located randomly in the bulk of the material. This model has been solved numerically and analytically, with the use of an exact solution for the conductivity of a strictly onedimensional (1D) disordered system. Bulk disorder destroys 1D localization along the c-axis (perpendicular to the layers) which would be in the absence of the bulk disorder. Hence, the conductivity along the c-axis is finite and is proportional to the weak scattering rate by bulk impurities The out-of-plane conductivity turns out to be of a non-Drude form, and this may result in a much stronger anisotropy of the conductivity than it follows from the band theory for systems with only a bulk disorder.



1/26 Prof. Yuping Sun(Chinese Academy of Sciences Hefei, China)
    Introduction to Steady High Magnetic Field Facilities in China


2009

10/6 Prof. Hark Hoe Tan(The Australian National University)
    Semiconductor Quantum Dots and Nanowires for Optoelectronic Applications

Quantum confined structures are utilised in a variety of applications due to the quantum confinement effect that leads to device improvement. The mature epitaxy technology has allowed us to grow quantum dot (QD) structures with unique electronic and optical properties. These QDs have found applications in optoelectronic devices such as lasers and photodetectors and show superior performance in comparison their quantum well counterparts. In this part of the talk, I will present the results of metal-organic chemical vapour deposition-grown QDs and discuss how the various growth parameters affect the properties of the QDs. The results of QD lasers and infrared photodetectors will be briefly presented. Selective area epitaxy is used as a way of controlling the nucleation of QDs to achieve device integration. By patterning the wafers, local growth rates can be varied depending on the dimensions of the masks and hence the density, size and composition of the QDs could be finely tuned. By using this technique, I will present the results of our integrated QD devices.
Nanowires grown by the so-called vapour-liquid-solid mechanism have recently gain significant interests. This growth mechanism relies on the use of a nm-sized liquid droplet which acts as an ideal sink for reaction species supplied from the surrounding vapour and is readily supersaturated with reaction species. The precipitation of reaction species predominantly occurs at the liquid/solid interface and leads to highly anisotropic growth. Axial and radial heterostructure nanowires have been proposed as nano- building blocks for future optoelectronic devices with properties superior to those of conventional layered heterostructures.
For this part of the talk, the optical and structural properties of binary and ternary III-V nanowires including GaAs, InGaAs, InP and GaSb nanowires grown by metal-organic chemical vapour deposition will be presented. Various issues with such as tapering of the nanowires, compositional non- uniformity along nanowires and the crystal structure will be discussed. I will also present our results of III-V nanowires grown on Si substrate which are of great interests for the integration of nano-optoelectronic devices on Si platform.



8/17 Prof. Yongmin Kim (Dancock University, Korea)
    Magnetic field induced softening of the tunneling gap in modulation-doped GaAs/AlGaAs asymmetric coupled double quantum wells

We present optical transitions performed on a series of GaAs/AlGaAs asymmetric coupled double quantum well structures (ACDQW, Fig. (a)) in magnetic field (~45 T). The conduction band in such ACDQW structures has symmetric (E1) and antisymmetric (E2) subbands located energetically in close proximity through a tunneling gap ( Δsas). The valence band on the other hand has only one heavy hole level because the valence band quantum well on the substrate side is unbound.



7/17 Prof. Shojiro Takeyama (IMGSL)
    破壊型パルス磁場発生と計測環境のアールアンドデー


7/17 Prof. Masashi Tokunaga (IMGSL)
    新規鉄系超伝導体に対する強磁場物性研究の現状


7/3 Prof. Jan J. Dubowski(University of Sherbooke, Canada)
    Quantum Dot Template Biosensor

 The conventional schemes for detection of viruses, bacteria, fungi and toxins include cell culture, immunological methods and molecular methods such as polymerase chain reaction [1]. These techniques, however, require much time and expertise in both sample preparation and data analysis. Development of alternative methods of detection that would be easy (automated), fast and specific for targeted biomolecules would be advantageous for medical diagnostics, clinical analysis or field tests.
Optical and electronic properties of III-V and II-VI semiconductor quantum well (QW) and quantum dot (QD)microstructures are potentially attractive for building biosensing devices where miniscule perturbation of the semiconductor surface, induced by selectively trapped biomolecules, could be monitored rapidly and in-situ by measuring some of these properties. For instance, bright photoluminescence (PL) of colloidal CdSe QD has been investigated to develop fluorescent probes in sensing, imaging, immunoassay, and some other diagnostics applications [2]. We have proposed that templates of epitaxial QD, such as InAs QD in a GaAs matrix, offer significant advantage in designing a biosensor for rapid detection of numerous pathogens in parallel [3,4]. Biofunctionalization and stabilization (passivation) of the GaAs (001) surface is one of the key elements of this approach [5,6]. I will discuss the results of our research addressing both fundamental and practical aspects of thiolation of GaAs, specific immobilization of selected antibodies on the surface of this semiconductor and optical detection of the Influenza A virus.
[1] Y.X. Chen et al., J. Virol. Meth. 154, 213 (2008).
[2] H. Mattoussi et al., J. Am. Chem. Soc. 122 (49), 12142 (2000).
[3] J.J. Dubowski, Lasers and Electro-Optics Society, LEOS 2006, 19th Annual Meeting IEEE: Montreal,Vol. 0-7803-9556-7, pp 302-3 (2006).
[4] X. Ding et al., Appl. Phys. A83, 357 (2006).
[5] O. Voznyy, J.J. Dubowski, J. Phys. Chem. C112, 3726 (2008).
[6] O. Voznyy, J.J. Dubowski, Langmuir 24(23), 13299 (2008).



6/26 Prof. Yasuhiro H. Matsuda (IMGSL)
    放射光を用いた強磁場X線スペクトロスコピー


6/19 Dr. Eiji Kojima (IMGSL)
    Cuライニングコイルを用いた電磁濃縮法磁場発生の現状


5/29 Prof. Koichi Kindo (IMGSL)
    非破壊パルスマグネット開発の考え方と現状


5/8 Prof. Fritz Herlach(Katholieke Universiteit Leuven)
    Milestones and highlights in the design and use of pulsed magnets

The development and use of pulsed magnets reviewed, beginning with the groundbreaking work of P. Kapitsa around 1925 up to the development of big dedicated pulsed field laboratories. For fields exceeding 100 T, the range goes from flux compression driven by high explosives and by electromagnetic forces to the exploding single turn coil that has been the workhorse for experiments for more than a decade.



3/25 Dr. Yoshimitu Kohama (NHMFL)
    鉄系超伝導体およびセメント超伝導体の熱的性質と上部臨界磁場


3/18 Mr. Ryo Sakakura (IMGSL)
    縦一巻きコイル法を用いた100 T領域での超強磁場下磁化測定装置の開発


2/24 Mr. Hiroya Suzuki (IMGSL)
    ミセル化単層カーボンナノチューブのパルス強磁場下における近赤外磁気光吸収


2/17 Mr. Kenichi Takeda (IMGSL)
    Yb1-xLuxB12の強磁場下ホール抵抗


1/27 Ms. Ineko Katakura (IMGSL)
    強磁場下におけるMn酸化物の電荷軌道秩序融解高速イメージング


1/13 Dr. Her Jim-Long (IMGSL)
    Observation of Magneto-Dielectric Coupling on Spinel Compound, CdCr2S4

 We observe new interesting behavior and phase transition in this cubic spinel system from dielectric and magnetic measurements. Two types of dipolar ordering states are clearly identified. First, a glassy type dipolar ordering near the fluctuating region of the Curie temperature TC ~ 85 K was observed, which was stimulated by the onset of ferromagnetic ordering. Second, a new ferroelectric ordering was arisen at near Tp~ 56 K by applied external electric field. The magnitude and step-up temperature of dielectric constant () near TC are suppressed by electric field while increased by magnetic field. However, both electric and magnetic fields colossally enhance the magnitude of dielectric constant () near Tp. Attempt has been made to analyze these field dependent properties by considering strong spin-lattice coupling and exchangestriction effect in this crystal.



2008

12/16 Mr. Atsuhiko Miyata (IMGSL)
    Cr系スピネル酸化物の超強磁場磁化過程


12/9 Mr. Tadahiro Hosoya (IMGSL)
    マルチフェロイック物質TbMnO3の強磁場磁化と分極


12/2 Mr. Masahiro Iwaki (IMGSL)
    強磁場中X線回折測定によるGd5Ge3の構造と磁性の研究


11/28 Prof. Tatsuo Kobayashi (Okayama University)
    固体酸素における磁場誘起分子再配列の提案


11/25 Prof. Liang Li (Wuhan University, China)
    The Progress at Wuhan Pulsed High Magnetic Field Center

Wuhan Pulsed High Magnetic Field Facility is under development. Magnets of bore sizes from 12 to 34 mm with the peak field in the range of 50 to 80 T have been designed. The pulsed power supplies are a 12 MJ, 25 kV capacitor bank and a 100 MVA/100 MJ flywheel pulse generator. A prototype 1 MJ, 25 kV capacitor bank are under construction. Five magnets wound with CuNb wire, copper wire and the combination of them have been developed to be tested to verify the design. The design and analysis of the pulsed magnets and the power supply are presented.



11/17 Mr. Yuki Otsubo (IMGSL)
    超強磁場下における単層カーボンナノチューブの励起子アハラノフ・ボーム効果


11/11 Mr. Yasuhiro Hirayama (IMGSL)
    (Cd,Mn)Te/(Cd,Mg)Teにおける二次元荷電励起子の磁気光学測定


10/21 Dr. Akira Matsuo (IMGSL)
    ロスアラモス国立強磁場研究所を訪ねて -大型発電機を使った60テスラ準定常磁場発生の現状-



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