Category: Meeting Scene

Talk by Prof. Anil P S KUMAR (MRS India)

Granularity controlled topological phase

Prof. Anil P S KUMAR from Department of Physics, Indian Institute of Science, Bangalore, India, delivered a review talk for granular topological insulators. In this symposium, a focused session for topological materials was arranged inside and Prof. Xi Dai from Institute of Physics, Chinese Academy of Science shortly reviewed the progress of research of topological materials, followed by several invited talks for theoretical and experimental studies. The topological material is expected to be useful in technologies especially for quantum computing and highly sensitive magnetic sensors, although it has not been practical for many years. However, recent progress of materials development of topological insulator makes the situation changed. In the early generation of topological materials nearly massless and very fast electrons run only on the surfaces and edges of materials; however, recent topological materials show unique and useful transport properties of bulk, suggesting increasing possibilities for applications. In this session, audiences reviewed recent progress of theoretical and experimental studies of topological materials.

Prof. Chunlei Wan (Tsinghua University, China) presented high-performance inorganic / organic superlattices for flexible thermoelectric energy harvesting.

The authors showed thermoelectric properties of organic molecule cation intercalated TiS2 (electrochemically), which looks like superlattice (layered structure). They successfully reduced the thermal conductivity while maintain its rather high electrical conductivity. Positively charged organic cations play several important roles such as good donor (strong positive electric field), enhancement of two-dimensionality, and reducing agent of thermal conductivity.

Prof. Kyu Hyoung Lee (Kangwon National University, Korea) presented design and preparation of high performance thermoelectric materials with defect structures.

The authors showed interesting way to enhance thermoelectric figure of merit of several materials such as BiSbTe, BiTeSe, and half-Heusler. They successfully reduced the thermal conductivity by introducing dislocation arrays at around the grain boundaries. They achieved 30-50% enhancement of their zT.

Prof. Wei Liu (Wuhan University of Technology) presented an invited talk on “Growth and transport properties of tetradymite thin films”.

The authors discussed their interesting results for MBE grown Bi2Te3/Sb2Te3 superlattice and solid-solution thin films; for the film characterization used techniques such as STS to investigate topological insulator properties. For the solid-solution thin films the doping was controlled from n-type to p-type depending on the Bi/Sb ratio.

Dr. Jihui Yang ? (instead of Yonggao Yan; Wuhan University of Technology) presented a contributed talk on “Rapid fabrication of thermoelectric SnTe via non-equilibrium lased 3D printing and the finite element simulation”.

The authors were able to fabricate high-quality 25 µm-thick SnTe films with selective laser melting (SLM). By controlling the power of the laser and thereby decreasing the melting temperature used the quality of the films could be improved.

Chairpersons: Akiyasu YAMAMOTO and Valeria BRACCINI 

A3-K30-001 Keynote
Vortex Pinning in iron based superconductors
Kees VAN DER BEEK

Jc and Hc2 in IBS look very interesting but way lower than in HTS (in particular in YBCO): the phase 1111 is the better performing in this respect. Flux pinning mechanisms look similar in all IBS, and have been extensively studied and presented in this talk.

Pinning centers can be nm-size inclusions, dislocations or Fe vacancies (in particular in FeSe single crystals, see very recent work by Sprau et al., 357 (2017) 65).

Jc vs field has been extensively investigated, and presents a similar behaviour in various materials. After a plateau where Jc is constant, it decreases proportionally to B^-0.5, then again it smoothest down. At low field it is predominant the contribution from big grains, isolated vortices (strong pinning on a nm scale), at intermediate fields we have collective pinning due to charged dopants / vacancies.

The depairing current density has been investigated: it presents a dome as a function of the doping, as it happens for the Tc vs x.

Vortex pinning has been correlated to the behaviour of l.

The multiple band character of superconductivity has a strong influence on Jc and on its anisotropy, which in particular in the ab direction is strongly related to the anisotropy of x.

 A3-I30-003 Invited 

Arsenic Chemistry of Iron-based Superconductors and Strategy for New Superconducting Materials
Minoru NOHARA

Prof. Nohara reported the progress of iron-based superconducting materials with the emphasis on the valence states and chemical bonds of arsenic. They demonstrated that in the novel 112-type CaFeAs2, monovalent arsenic produced As zigzag chains of CaAs intermediary layers, while trivalent arsenic produced FeAs layers. The superconducting transition temperature of this materials was enhanced up to 47 K when La and Sb were simultaneously substituted for Ca and As, respectively. Sb is preferably substituted for the As of the zigzag chains. On the other hand, in the 10-4-8-type Ca10(Pt4As8)(Fe2−xPtxAs2)5 with the highest Tc of 38 K, he emphasized that divalent arsenic produced As2 dimers in Pt4As8 layers. Finally, he discussed the structural phase transition in 122-type CaFe2As2 that is characterized by the formation of As2 dimers between the adjacent FeAs layers, which resulted in the loss of magnetism and disappearance of superconductivity. This transition can be viewed as an As2-/As3- valence transition.

  

A3-I30-002 Invited 

Doping dependent critical current properties in K, Co, and P-doped BaFe2As2 single crystals
Hiroshi EISAKI

Dr. Eisaki reported the in-plane critical current density (Jc) of BaFe2As2-based superconductors, Ba1-xKxFe2As2 (K-Ba122), Ba(Fe1-xCox)2As2 (Co-Ba122), and BaFe2(As1-xPx)2 (P-Ba122) in a wide range of doping concentration (x) by means of magnetization hysteresis loop (MHL) measurements on single crystal samples. Depending on the dopant elements and their concentration, Jc exhibits a variety of magnetic-field (H)- and temperature (T)- dependences. In the case of K-Ba122, the MHL of the under-doped samples (x < 0.33) exhibits the second magnetization peak (SMP), which sustains high Jc at high H and high T, exceeding 105 A/cm2 at T = 25 K and μ0H = 6 T for x = 0.30. On the other hand, the SMP is missing in the optimally- (x ~ 0.36-0.40) and overdoped (x ~ 0.50) samples, and consequently Jc rapidly decreases by more than one order of magnitude, although the change in Tc is within a few K. He pointed out that the T-dependent Jc indicates that the two pinning mechanisms, namely, the spatial variations in Tc (referred to as delta-Tc pinning) and the fluctuations in the mean free path (delta-l pinning), are enhanced for the under-doped samples, which results in the enhancement of Jc. Possible origins for the different pinning mechanism are discussed in connection with the x-dependence of Tc, the residual resistivity, AFO domain boundaries, a possible quantum critical point, etc.

 

A3-K30-004 Invited

Pressure Effects of FeSe by Novel DAC using metallic Diamond Electrodes
Yoshihiko TAKANO

A deep work published very recently (Matsumoto et al., JJAP 56 (2017)) has been presented, regarding the pressure effects induced in FeSe single crystals by a novel Diamond Anvil Cell.

Superconducting properties of many different materials under high pressure have recently received great attention, especially after the discovery with great surprise of superconductivity in H2S at ∼200 K under 150 GPa which was reported by resistivity measurements using a diamond anvil cell (DAC) in 2015. In fact, if one can measure the resistivity under extremely higher pressure above 300 GPa, superconductivity at room temperature in light elements such as hydrogen would be observed.

The resistivity measurement though is difficult because the sample space is very small (<100 μm) and the electrodes are deformed by compression. A novel diamond anvil cell specialized for resistivity measurements under high pressure has been developed at NIMS, Tsukuba. Once metallic diamond is heavily boron-doped, it shows metallicity and superconductivity at low temperature. Boron-doped metallic diamond electrodes were deposited onto a diamond anvil using a electron beam lithograph: in this way, resistivity measurements can be performed up to 10 GPa.

In particular, results obtained through this technique on FeSe single crystals have been reported. FeSe shows a Tc of 8 K, which can increase up to 37 K with the application of idrostatic pressure (8 GPa). When uniaxial pressure is applied, at NIMS they were able to reach Tc as high as 44 K, similarly to what happens in FeSe phase after K intercalation. This Tc increase depends on the anion height from the Fe layer which can be changed through the intercalation or through the application of the uniaxial pressure.

Chairs: Petre BADICA and Tomoya HORIDE, 13.45-15.25

4 presentations:
1 keynote (A3-K30-018 – J H Durell) – 35 min
2 invited (A3-130-019 – X Yao; A3-130-020 J Gazquez) – 25 min
1 oral (A3-O30-021- S Horii) – 15 min

Presentations introduced by P. Badica

Keynote presentation: The challenge of high filed bulk superconductors, J. H. Durell discussed the problems associated with melt textured HTS bulk superconductors especially regarding poor mechanical strength of HTS. It was emphasized the necessity to improve the mechanical properties of the materials (e.g. by metal fibers additives such as Ta) or by innovative engineering solutions using compressing metal rings to help keeping the integrity of the magnetically loaded bulk. Questions were about different possibilities of clamping and about the limitations imposed by size.

Invited presentation 1: The artificial control of film microstructures in LPE-processes YBCO by tuning solute supersaturation state, X. Yao introduced different aspects of the crystal growth of REBa2Cu3O7 superconductors (especially by liquid phase epitaxy method). The possibilities to control growth and quality of materials were discussed (e.g. by using non-stroichiometric compositions, or the appropriate conditions of cooling based on thermodynamic aspects of the supersaturation). Questions were about film thickness and spiral growth mechanism.

Attendance: good – about 20 persons

Schedule: according to the program

Atmosphere: relaxed, friendly, collaborative

A Challenge for Future Carbon Devices by Advanced Plasma Nano-Processes

Masaru Hori of Nagoya University, Japan, gave a fantastic keynote lecture in the oral session of Symposium C-5 in the morning session on August 30. He has investigated advanced plasmas as a synthesis method, the growth mechanism, control of structure, and applications for nano-carbons. First, he presented fabrication of the tough fuel cell devices with carbon nanowalls (CNWs), where Pt nanoparticles were supported on CNWs by super critical CVD after the growth of CNWs. Second, he explained that the triple phase plasma employing the ethanol alcohol showed the high speed and high quality nano graphene synthesis for a high performance of fuel cell device. Then, he concluded that nano carbons, especially CNWs, had a great potential as a key material for future industrial and medical applications.

Fabrication of High-Mobility Amorphous In₂O₃:Sn Films by RF Magnetron Sputtering with Impurity-Mediated Amorphization Method

Naho Itagaki of Kyushu University, Japan, gave an excellent keynote lecture in the oral session of Symposium C-5 in the afternoon session on August 30. She proposed an impurity mediated amorphization (IMA) method, where the impurity was introduced to the conventional control parameters (temperature and pressure) for crystal growth. She explained that high mobility (> 50 cm²/Vs) and nanocrystal-free a-ITO films have been obtained, and the a-ITO films were grown even at higher temperature than the crystallization temperature (150°C) of In₂O₃. In addition, the a-ITO films fabricated via IMA showed high thermal stability, which means that the amorphous structure was maintained even after they were annealed at 300°C.

 

Keynote lecture scene by Prof. Hori.

Keynote lecture scene by Prof. Itagaki.

A3-I29-016

Invited talk given by Alexey V Pan from Institute for Superconducting and Electronic Materials, University of Wollongong.

The first part of the talk was about magnetic measurements performed with a VSM system where it could be observed that the Jc performance of a superconducting sample was strongly dependent on the measurement frequency.
The second part talk was about the design of different microstructures (with many different shape, distribution and sizes) patterned on superconducting films. Samples were mainly characterized by means of magnetic measurements and magneto-optical imaging. Nice correlation of superconducting properties could be obtained depending on the patterning performed. Ratchet effects were studied in samples with asymmetric patterns. Both theoretical calculations and measurements show differences in the critical current density when inverting the direction of the current.

A3-I29-017

Invited talk given by Petriina Paturi from Wihuri Physical Laboratory, University of Turku.
The talk was about theoretical calculation of flux pinning effects in YBCO thin films with artificial pinning sites (nano-rods, nano-particles).
The first part of the talk was about simulations of angular Jc measurements performed on samples with different artificial pinning centre landscape. The samples were grown alternating layers of different thicknesses with rods and plane YBCO in order to change the length of nanorods. Experimental angular Jc measurements show that long nano-rods produce strong c-axis peak while short nano-rods could not. The simulations performed could nicely explain the experimental data.
The second part of the talk was about the analysis of alpha values and pinning force curves in YBCO samples with different nano-structures, correlating the experimental results with simulations.

A3-O29-018

Oral talk given by Gianluca de Marzi from ENEA C. R. Frascati, Technical Unit for Nuclear Fusion-FSN (Rome), Italy
The talk was about ac measurements on YBCO thin films with BNTO and BNTO+YO nanoparticles. The activation energy of different samples was evaluated from ac susceptibility measurements performed at different frequency and different conditions of ac and dc magnetic field. From those measurements the activation energy as a function of the magnetic field and critical current density could be obtained and correlated with the critical current density performance of different samples.

* The session finished 15 minutes late since we had some technical problems with the projection of the last talk and we had to change the computer.

-Talk 1 A3-129-005 by G. Celentano (invited)

PLD YBCO thin films with improved pinning by doping tamtalates and niobates (BaYTaO6 and BYNnO6) in extended temperature and high H field via double perovskite (sponsored  by Euro tapes and Euro fusion programs)

Several doping schemes of single and double APCs were explored and the superconducting properties, especially Jc were compared.

For example, three specific schemes were compared:

1. BYTO at 5 at%, d=8nm), 1D(5nm, H*~5.2 T) +2D(stacking faults?)
2. 5at%+BYTO2.5at% (d=8nm), 1D(5nm, H*~5.2 T) +2D(stacking faults?)-best Jc-H in few-10T, still see both Jc peaks at both H//c, and ab
3. 5at%+BYTO2.5at%+3.75at% Y2O3, 1D(10 nm, H*~1.9 T), many 3D

Also, varied the PLD repetition rates were explored: from 1Hz (12 nm, 1.1T) to 5Hz (7nm, H*~2T), to 10 Hz (5nm, 5.2 T)

-Talk 2 A3-129-006 by L. Civale for B. Bairov (invited)

Talk’s primary focus was on the Rho and Jc measurements in pulsed H field at LANL, which has facility that  can reach 65T up to 100 T ( as a part of the Nat. High Mag. Field Lab) in few to tens of ms time frame  in He4 and He3.  Measurement can be operated at fixed theta, pulsed H at different Ts, or fixed T, pulsed field at different theta’s

Measurement on iron-based supercond, two band model SUST 2014, 27 by Maiorov. Mele, et al and on the YBCO with DD (similar to the N Mat. Paper in 2011), BZO NPs in CSD film increases the B_irr significantly

-Talk 3 A3-129-007 by T. Izumi (invited)

Control in-field performance by modifying microstructure in cc, 1D, 2D and 3D APCs, morphologies depending on the process (PLD, MOD, MOCVD), conditions (T, PO2, composition)and materials of APCs.

In situ method PLD-1D APCs, while ex situ one CSD, 3D APCs of the same dopants (BZO)

Super saturation at the synthesis temperature leads to formation of  BZO NPs in CSD process. PLD multilayer growth to generate layered (2D) APCs in ab-plane (BHO) in BHO/GdBCO (Yoshida), by spinning thinner precursor (30 nm) vs old 170 nm, found smaller BZO NPs ~ 10-12nm, in contrast to 16 nm, radius of NP lambda=2D/V, V-growth velocity, D-diffusion speed.

 

In our symposium, active researchers in soft matter science have gotten together from all over the world (more than 10 countries) and have made active discussion of the up-to-date results on soft matter science. “Langmuir Award” and “Soft Matter Award” were provided to our symposium by courtesy of the ACS publications and Royal Society for Chemistry. The presentations made by young researchers were judged by the aid of invited speakers of our symposium and the symposium organizers have elected the five award winners. The winners are listed as below:

Langmuir Award

B4-P29-009 Yuki OHARA (University of Hyogo, Japan)

“Incorporation of and release behavior of guest molecules by pH-responsive polyion complex vesicles”

B4-P29-021 Ko MATSUKAWA (The University of Tokyo, Japan)

“Preparation of hydrogel which has comb-type polymer network only in the surface region”

Soft Matter Award

B4-O29-012 NienTing HSIEH (Chung Yuan Christian University, Taiwan)

“Molecular design of a dual-functional quaternary amine copolymer for bacterial reversible self-cleaning control via zwitterionic counterion activation”

B4-P29-003 Nozomi ARAI (Kyoto University, Japan)

“Direct observation and modeling of attachment behavior of colloid particles on a bubble surface”

B4-P29-005 Yoji YAMASHITA (Osaka City University, Japan)

“Synthesis of curable hyperbranched polymers containing dense degradable groups and their application to degradable cured materials”

Congratulations!!

Group photo of the B-4 Symposium.

Mr. Nozomi ARAI (Kyoto University), the winner of the Soft Matter Award

 

A3-I29-014
Kenji Ishida reported in his invited talk on NMR and NQR studies on U-based ferromagnetic superconductors. He showed that in UCoGe a spin triplett superconducting state is induced by fluctuations. This is a new mechanism to suppress superconductivity.

A3-O29-015
A collaboration of groups from Japan and a group of Vietnam develops a scanning LTS-SQUID vector microscope with three orthogonal pick-up loops on a tip cooled by a commercial GM cryocooler. The sensors were tested and high spatial resolution demonstrated.

The figure shows the pick-up loops (left) and a trapped vortex structure measured by the new SQUID vector sensors within a commercial SSM (right).

Matsumoto: Interesting TDGL simulations of Jc and comparison to experiment. It is reported experimental Jc measurements on BHO doped GdBCO with different level of doping. Best pinning force density Fp at 10 K was achieved on 20:1 volume fraction. The analysis of temperature behavior Jc(T) with Griessen’s model is reported.

Questions: Is the simulation 3D? No. How many pinning sites can be added to the simulation? What is the meaning of the background pins at high field? Difference of delta-l and delta-Tc pinning? How is Jc determined in the simulation?

Yoshida: SmBCO + BaHfO3 coated conductors. Low-T growth technique (750 C vs 960 C) with seed layer (150 C less than without). Rods are thinner (7 nm vs 13.5 nm), B_phi is larger. High rate leads to small pinning sites (similarly as in previous presentations).

High speed growth technique in a reel-to-reel deposition systems up to 100 Hz. No degradation of Jc reported. No clear which is the actual film growth rate.

Questions: How are the inclination angles defined? What is the effect of strain in growth of nanocolumns? What is the Ic of the sample? (from patterned sample) What is the growth rate in “high growth rate”-films?

How is the substrate temp measured? 960 C is a lot! (didn’t ask this, because of lack of time)

Erbe: ReBCO + BHO on TFA-MOD on STO and CeO2-buffered CC. Re = Gd, higher Tc, should have wider deposition parameters. Result: Narrow process parameters, otherwise impurities (on STO). On STO optimal deposition conditions are: T = 810 °C and P(O2) 100 – 50 ppm. On metal optimal t_sub is 20 C lower (we’ve seen this also on PLD films) due to the reaction with CeO2 seed layer (BaCeO3 forms). Pores in films on meta.

Questions: What about the in-plane texture? Good in-plane texture. Optimal temperature difference STO / CC. Thickness of the films: 250-300 nm.

Jha: Surface modified target approach to enhance Jc, Y211 dopant as segment of target. Nano dots formed into YBCO matrix. Jc measurements carried out at 77 and 65 K. Dip in the Jc(theta) near ab-plane. Otherwise almost isotropic. Theory from Mishec SUSt 28. Planar defects cause a dip in ab-planes. For further work doping with other rare earths RE211 phases will be studied.

Questions: Could this promote substitution of rare earth ion of dopant on superconductor? A: yes, but the final effect of this cannot be predicted in advance.

van der Beek: edge disorder and rough flux front. Flux noise in rf antennas. MO-visualization. Seen also in Nb. And in other elastic media (paper, ink on paper etc). Calculate correlations in space and time. Universality classes vary between different superconducting materials. Controlled disorder, irradiated with heavy ions.

Questions: How do the flux avalanches in MgB2 relate to this? Not really definite yet.