Critical Behavior and Spectrum of Holographic Superconductors

Hyo Chul AHN,홍덕기,박천수 한국물리학회 2017 New Physics: Sae Mulli Vol.67 No.1

We study a minimal gravity dual of planar superconductivity at finite temperature to estimate the Meissner and Debye masses of photons in a planar superconductor, which are the characteristic properties of superconductors. We also study the temperature dependences of those masses to find their critical behavior near the critical temperature to see if the behaviors of holographic superconductors deviate from those of the usual conventional BCS superconductors because high-temperature superconductors exhibit properties very different from those of the usual BCS superconductors, as they are strongly correlated. We find that the critical exponents to be 0.49 and 0.92 for the Debye mass and the Meissner mass, respectively. Finally, we study the critical behavior of the radial excitations of the order parameter.

Fundamental characteristic analysis on 6 T-class high-temperature superconducting no-insulation magnet using turn-distributed equivalent circuit model

Q. Liu,J. Choi,K. Sim,김석호 한국초전도저온학회 2021 한국초전도저온공학회논문지 Vol.23 No.4

In order to obtain ultra-high resolution MRI images, research and development of 11 T or higher superconducting magnets havebeen actively conducted in the world, recently. The high-temperature superconductor (HTS), first discovered in 1986, was verylimited in industrial application until mid-2010, despite its high critical current characteristics in the high magnetic field comparedto the low-temperature superconductor. This is because HTS magnets were unable to operate stably due to the thermal damagewhen a quench occurred. With the introduction of no-insulation (NI) HTS magnet winding technology that does not burnelectrically, it could be expected that the HTS magnets are dramatically reduced in weight, volume, and cost. In this paper, a 6 T-class NI HTS magnet for basic characteristic analysis was designed, and a distributed equivalent circuitmodel of the NI coils was configured to analyze the charging current characteristics caused by excitation current, and the chargedelay phenomenon and loss were predicted through the development of a simulation model. Additionally, the critical current of theNI HTS magnets was estimated, considering the magnetic field, its angle and temperature with a given current. The loss due tocharging delay characteristics was analyzed and the result was shown. It is meaningful to obtain detailed operation technology tosecure a stable operation protocol for a 6T NI HTS magnet which is actually manufactured.

Fundamental characteristic analysis on 6 T-class high-temperature superconducting no-insulation magnet using turn-distributed equivalent circuit model

Q. Liu,J. Choi,K. Sim,S. Kim 한국초전도저온공학회 2021 초전도와 저온공학 Vol.23 No.4

In order to obtain ultra-high resolution MRI images, research and development of 11 T or higher superconducting magnets have been actively conducted in the world, recently. The high-temperature superconductor (HTS), first discovered in 1986, was very limited in industrial application until mid-2010, despite its high critical current characteristics in the high magnetic field compared to the low-temperature superconductor. This is because HTS magnets were unable to operate stably due to the thermal damage when a quench occurred. With the introduction of no-insulation (NI) HTS magnet winding technology that does not burn electrically, it could be expected that the HTS magnets are dramatically reduced in weight, volume, and cost. In this paper, a 6 T-class NI HTS magnet for basic characteristic analysis was designed, and a distributed equivalent circuit model of the NI coils was configured to analyze the charging current characteristics caused by excitation current, and the charge delay phenomenon and loss were predicted through the development of a simulation model. Additionally, the critical current of the NI HTS magnets was estimated, considering the magnetic field, its angle and temperature with a given current. The loss due to charging delay characteristics was analyzed and the result was shown. It is meaningful to obtain detailed operation technology to secure a stable operation protocol for a 6T NI HTS magnet which is actually manufactured.

Study of damping in 5kWh superconductor flywheel energy storage system using a piezoelectric actuator

Jang, H.K.,Song, D.,Kim, S.B.,Han, S.C.,Sung, T.H. North-Holland 2012 Physica. C, Superconductivity Vol.475 No.-

A 5kWh superconductor flywheel energy storage system (SFES) has advantages in terms of high electrical energy density, environmental affinity and long life. However, the SFES has disadvantage that electromagnetic damper is needed because superconducting bearings do not have enough damping coefficient. The purpose of this experiment is to develop a method of damping the vibration of the SFES. A piezoelectric actuator was attached to a superconducting bearing system for feasibility test in order to make it as a damper of the SFES. For this experiment, a cylindrical permanent magnet (PM) 40mm in diameter and 10mm height was used as a rotor, a high-temperature superconductor bulk (HTS bulk) with dimensions 40mmx40mmx15mm was used as a stator, and two vibration exciters (an upper and a lower vibration exciter) and a piezoelectric actuator were used. The PM was fixed on the upper vibration exciter. The HTS bulk was fixed on either the lower vibration exciter to test for damping in the feasibility test, or on the piezoelectric actuator for the actual SFES. The conditions of this experiment included various voltage outputs of a power amplifier to the lower vibration exciter, moving distances of the piezoelectric actuator which are displacements of the HTS bulk, and phase differences between the upper and lower vibration exciter or the piezoelectric actuator. The damping feasibility test was conducted with a 300μm gap between the PM and HTS bulk with a PM vibration of 30μm. For the actual SFES test, the gap between the PM and HTS bulk was 1.6mm and the PM vibration was 25μm. The following conditions were conducted to optimize: an appropriate voltage input to the lower vibration exciter or a displacement of piezoelectric actuator and an appropriate phase difference. When the piezoelectric actuator was used, the damping effect was greatly improved up to 92.32% which a displacement of damped PM was 1.92μm.

High Temperature Superconducting Pseudo-Lumped Element Bandpass Filter

Min, Byoung-Chul,Choi, Young-Hwan,Kim, Hong-Teuk,Moon, Seung-Hyun,Lee, Seung-Min,Oh, Byung-Du The Korean Superconductivity Society 1999 Progress in superconductivity Vol.1 No.1

A high-temperature superconducting 1.78 GHz bandpass filter, designed for PCS applications, is presented. The structure consists of microstrip pseudo-lumped elements, which enables miniaturization of the filter. A 5-pole microstrip filter could be realized on a 37 mm $\times$ 9 mm $LaAlO_3$ substrate, using double-sided high-temperature superconducting $YBa_2Cu_3O{7-\delta}$ thin film. This filter showed 0.7 % fractional bandwidth, 0.3 dB insertion loss, and 12 dB return loss in the passband at 60 K.

초전도체 YBCO/NiFe/CoFe/Cu/CoFe/IrMn 다층박막에서의 스핀밸브 효과에 의한 반전된 자기저항비 특성 연구

양우일(Woo-Il Yang),최종구(Jong-Gu Choi),이상석(Sang-Suk Lee) 한국자기학회 2018 韓國磁氣學會誌 Vol.28 No.1

The antiferromagnetic IrMn based GMR-SV (giant magnetoresistance-spin valve) multilayer on the high-Tc superconductor YBCO film fabricated by using ion beam deposition and dc magnetron sputtering systems. The hybrid multilayer structure performed with the typical GMR-SV film and the superconducting YBCO film was compared two different magnetoresistance curves, which are measured at a room and a liquid nitrogen temperatures below the critical temperature. The exchange biased coupling field (H<SUB>ex</SUB>), coercivity (H<SUB>c</SUB>), magnetoresistance ratio (MR (%)) for the pure GMR-SV multilayer measured at 77 K are enhanced to the increment values of 80 Oe, 43 Oe, and 6.6% more than those measured at room temperature, respectively. In case of YBCO/GMR-SV mulitlayer, the H<SUB>ex</SUB>, H<SUB>c</SUB>, and MR (%) are 410 Oe, 240 Oe, −4.6% more than those measured at 77 K, respectively. The phenomenon having a negative MR (%) below the critical temperature is explained the current in plane tunneling (CIPT) effect when the resistance of the middle G layer between the high-temperature superconductor YBCO and the GMR-SV multilayer reaches a level comparable to the plane resistance of the upper metal layer.

High-Tc superconductivity from an atomic point of view via tunneling

유정훈,이진호 한국물리학회 2017 Current Applied Physics Vol.17 No.6

Even after 30 years of discovery of the high temperature superconductivity (HTSC) from the cuprate compounds by Bednorz and Müller, the mechanism of the formation of Cooper pairs well above the liquid nitrogen boiling temperature is still remained to be elucidated. The discovery of a yet another HTSC family of the iron-based superconductors seemed to add more complexity to this puzzle, but also seems to render a prospect of finding a universal principle shared by the entire HTSC family. The tunneling experiments, on the other hand, also witnessed remarkable breakthroughs ever since Giaever succeeded the first tunneling experiment on a superconducting aluminum. The scanning tunneling microscopy (STM) invented by Binnig and Rohrer began to be heavily applied to the research of the condensed matter and became one of the most versatile spectroscopic tools as well as the most powerful microscope available also in the HTSC research field as of today. In this review, we would like to convey a snapshot of the current application of the STM in the research of HTSC, mainly focusing on the studies using the spectroscopic imaging scanning tunneling microscopy (SI-STM) which eventually led to the scanning Josephson tunneling microscopy (SJTM) by which we can visualize the superconducting Cooper pairs in an atomic scale.

High-T_c superconductivity from an atomic point of view via tunneling

Yoo, J.H.,Lee, J. ELSEVIER 2017 Current Applied Physics Vol.17 No.6

<P>Even after 30 years of discovery of the high temperature superconductivity (HTSC) from the cuprate compounds by Bednorz and Muller, the mechanism of the formation of Cooper pairs well above the liquid nitrogen boiling temperature is still remained to be elucidated. The discovery of a yet another HTSC family of the iron-based superconductors seemed to add more complexity to this puzzle, but also seems to render a prospect of finding a universal principle shared by the entire HTSC family. The tunneling experiments, on the other hand, also witnessed remarkable breakthroughs ever since Giaever succeeded the first tunneling experiment on a superconducting aluminum. The scanning tunneling microscopy (STM) invented by Binnig and Rohrer began to be heavily applied to the research of the condensed matter and became one of the most versatile spectroscopic tools as well as the most powerful microscope available also in the HTSC research field as of today. In this review, we would like to convey a snapshot of the current application of the STM in the research of HTSC, mainly focusing on the studies using the spectroscopic imaging scanning tunneling microscopy (SI-STM) which eventually led to the scanning Josephson tunneling microscopy (SJTM) by which we can visualize the superconducting Cooper pairs in an atomic scale. (C) 2017 Elsevier B.V. All rights reserved.</P>

110K급 Bi계 고온 초전도체의 성장에 대한 연구

주유환,손보견,고영제,손인호 경남대학교 환경문제연구소 2003 환경연구 Vol.26 No.-

High temperature superconductor Bi₂Sr₂Ca₂Cu₃O_(x) compound has been grown by improved directional solidification method at various temperatures. It is found that the superconducting transition temperature(T_(c)) of Bi-2223 sample grown at 855℃ is 110K. The transition temperature of the samples grown at the higher and lower than 855℃ is 80K and 55K, respectively.

Electrical Characteristics of Second Generation High Temperature Superconducting Wires for Power Device Application

Jae-Ho Kim 한국조명·전기설비학회 2017 조명·전기설비학회논문지 Vol.31 No.9

Three kinds of second generation (2G), high temperature superconducting(HTS) wires were characterized for critical current density and over-current behavior under over-current conditions cooled by liquid nitrogen. The critical current density and over-current behavior were measured as a function of increasing temperature and current ramping rate, respectively. The critical current density of HTS wire proportionally decreased with increasing temperature. The critical temperature of the GdBCO HTS wires was higher than that of the YBCO HTS wires. An instantaneous breakdown was observed after 30A/sec of the current ramping rate. Stabilizers were delaminated after the over-current test. Over-current behavior is particularly important in HTS power device applications because the short circuit current can be much larger than the steady state value. These results are in the context of important design and fabrication considerations of HTS power devices application.