Takanari Kashiwagi’s research while affiliated with University of Tsukuba and other places

What is this page?


This page lists works of an author who doesn't have a ResearchGate profile or hasn't added the works to their profile yet. It is automatically generated from public (personal) data to further our legitimate goal of comprehensive and accurate scientific recordkeeping. If you are this author and want this page removed, please let us know.

Publications (76)


Doping Dependence of Upper Critical Field of High- T c Cuprate Bi 2+ x Sr 2− x CaCu 2 O 8+ δ Estimated from Irreversibility Field at Zero Temperature
  • Article

October 2024

·

14 Reads

·

1 Citation

Journal of the Physical Society of Japan

Junichiro Kato

·

·

·

[...]

·

Taichiro Nishio

Doping Dependence of Upper Critical Field of High-Tc Cuprate Bi2+xSr2-xCaCu2O8+d Estimated from Irreversibility Field at Zero Temperature

September 2024

·

14 Reads

We investigated the temperature (T) dependence of the irreversibility field Hirr(T) in high-critical-temperature cuprate Bi2+xSr2-xCa1-yYyCu2O8+d (Bi-2212) single crystals over a wide range of hole doping level (p). Hirr(T) was evaluated by measuring the magnetization hysteresis loop. The value of Hirr(T) extrapolated to T = 0 K [Hirr(0)], is either equal to or sets the lower boundary for the upper critical field at T = 0 K [Hc2(0)]. Tc shows a parabolic p-dependence (peak at p = 0.16), whereas Hirr(0) increases monotonically with p by approximately one order of magnitude, from 19 T for the most underdoped sample (p = 0.065, Tc = 24 K) to 209 T for the most overdoped sample (p = 0.200, Tc = 75 K). The present results qualitatively agree with Hc2(0) values evaluated from the specific heat measurements. The observed p-dependence of Hirr(0) in Bi-2212 is distinct from those in YBa2Cu3O7-d and HgBa2CuO6+d, in which a pronounced dip structure appears in the underdoped region. Considering that the dip structures observed in these two systems are likely associated with the formation of competing orders (most likely field-induced charge orders), the present results indicate that the influence of the competing order in Bi-2212 is less prominent than that in the other two systems.


FIG. 2. Results of batch A. (a) The grown boule inside the quartz tube is shown. The color code represents the image of the Fe concentration [red means higher Fe concentration while blue means lower Fe concentration based on electron probe microanalyzer (EPMA) measurements]. In addition to the picture of the whole boule, the representative parts of the boule are shown: (b)-(d) are obtained from the upper part, (e)-(g) are obtained from the middle part, and (h)-(j) are obtained from the lower parts of the boule. As the Fe concentration decreases, the crystal habit becomes clearer due to the lower density of nucleation. The conglomeration growth (c) was often observed in the upper part of the boule, while crystals with clear shiny faces as seen in (e) and (h) in the rich AuPb flux part can be observed. Those crystals tend to precipitate to the surface as expected [40]. In the second column of the pictures, the EPMA composition images are shown, where the brighter parts correspond to AuPb flux, while the darker parts correspond to FeRh. The composition of FeRh is very close to the 1:1 ratio within the accuracy of ±1 at. %. In the far-right column, the extracted crystals are shown. The extraction of those crystals is relatively simple. The boule is immersed in diluted nitric acid (10%). Diluted nitric acid softens the AuPb flux from where, either mechanically or by vibration, the FeRh crystals can be separated.
FIG. 3. Many small single crystals grown together at the upper part of the boule that is shown in Fig. 2. (a) The congregation of FeRh crystals. (b) Clear edges, steps, and terraces of FeRh crystals can be observed. The composition investigated by electron probe microanalyzer (EPMA) was Fe : Rh = 1:1 within an experimental error of ±1 at. %.
FIG. 4. The results of batch B 2 . (a) The grown boule after the melting experiment. (b) One part of the surface of the boule. FeRh crystals with flat surfaces are clearly observed. Small shiny dots are found on the surface of FeRh crystals that have formed due to quenching. (c) Some of the FeRh crystals extracted from the surface of the boule. The surface of crystals is degraded if it is exposed to nitric acid for a longer time. (d) Needlelike crystals extracted from the inner part of the boule. (e) One of the hopper crystals of FeRh that usually forms at the bottom part of the boule. The underlying grid in the picture represents a 1 mm scale.
FIG. 5. The results of x-ray diffraction (XRD) analysis. (a) A typical photograph of the transmission Laue diffraction pattern obtained from the crystal shown in (b) using a W target (40 kV and 20 mA). The collimated x-ray beam was shone perpendicularly to the platelike single crystal of FeRh, and the imaging plate was put behind the single crystal ∼5 cm apart from the crystal. (c) The ω scan rocking curve of the 110 reflection.
FIG. 7. Temperature dependence of magnetization M(T) of FeRh in 1 T magnetic field applied to [1,0,0] direction between 10 and 400 K. The arrows denoted as FW and FC mean that the curves were obtained in the warming process and the cooling process, respectively.
Single crystal growth of FeRh from AuPb flux
  • Article
  • Full-text available

February 2024

·

111 Reads

Physical Review Materials

The FeRh compound has been known for a long time as an itinerant magnet with a peculiar first-order antiferromagnetic (AFM)-to-ferromagnetic (FM) transition near room temperature. Although a lot of work has been done, the origin of the physical properties associated with the AFM ↔ FM transition is still an ongoing debate and needs deeper investigation using good single crystals. Here, we report on the single-crystal growth of FeRh from the AuPb flux and confirm it by x-ray crystallographic methods such as Laue diffraction, four-circle diffractometer measurements, and electron probe microanalyzer elemental analysis. The temperature dependence of magnetization in our single crystals below the AFM ↔ FM transition shows an anomalous cascadelike multiple transition behavior, which is obviously very different from the reported results previously. It is only such high-quality single crystals grown here that will pave the way for a comprehensive understanding of the longstanding issues of the FeRh compound.

Download

Terahertz imaging system with on-chip superconducting Josephson plasma emitters for nondestructive testing

May 2023

·

32 Reads

·

1 Citation

Compared with adjacent microwaves and infrared frequencies, terahertz (THz) frequency offers numerous advantages for imaging applications. The unique THz spectral signatures of chemicals allow the development of THz imaging systems for nondestructive tests and the evaluation of biological objects, materials, components, circuits, and systems, which are especially useful in the security, medical, material, pharmaceutical, aeronautical, and electronics industries. However, technological advancements have been hindered owing to the lack of power-efficient and compact THz sources. Here, we use high-temperature superconducting monolithic sources known as Josephson plasma emitters (JPEs)-which are compact, chip-integrated coherent and monochromatic sources of broadly tunable THz waves-and report the art of non-destructive imaging of concealed metallic surgical blades, floppy disks, dandelion leaves, and slices of pork meat in the THz spectral range. The quality of the images, exhibiting high-contrast differentiation between metallic and non-metallic parts, making different features of objects visible, and targeting different powders, demonstrates the viability of this THz imaging system for nondestructive, contactless, quick, and accurate environmental monitoring, security, medicine, materials, and quantum science and technology applications.




Fig. 4 Schematic illustration showing a Bi2212 THz-emitter coupled with external triangular patch antennas. It is noted that the triangular patches are made on SiO 2 -film deposited on the Bi2212 crystal base.
Fig. 5 Schematic illustration showing a conventional mesa structure for considering the side wall effects.
Approaches to High Performance Terahertz-Waves Emitting Devices Utilizing Single Crystals of High Temperature Superconductor Bi2Sr2CaCu2O8+δ

December 2022

·

53 Reads

·

3 Citations

IEICE Transactions on Electronics

Our group has developed terahertz(THz)-waves emitting devices utilizing single crystals of high temperature superconductor Bi2Sr2CaCu2O8+δ (Bi2212). The working principle of the device is based on the AC Josephson effect which is originated in the intrinsic Josephson junctions (IJJs) constructed in Bi2212 single crystals. In principle, based on the superconducting gap of the compound and the AC Josephson effect, the emission frequency range from 0.1 to 15 THz can be generated by simply adjusting bias voltages to the IJJs. In order to improve the device performances, we have performed continuous improvement to the device structures. In this paper, we present our recent approaches to high performance Bi2212 THz-waves emitters. Firstly, approaches to the reduction of self Joule heating of the devices is described. In virtue of improved device structures using Bi2212 crystal chips, the device characteristics, such as the radiation frequency and the output power, become better than previous structures. Secondly, developments of THz-waves emitting devices using IJJs-mesas coupled with external structures are explained. The results clearly indicate that the external structures are very useful not only to obtain desired radiation frequencies higher than 1 THz but also to control radiation frequency characteristics. Finally, approaches to further understanding of the spontaneous synchronization of IJJs is presented. The device characteristics obtained through the approaches would play important roles in future developments of THz-waves emitting devices by use of Bi2212 single crystals.


Fig. 1 a Resistivity plot of Rh 0.993 Pb 2.007 up to 10 K. The residual resistance of ≈ 19 μΩ•cm is not so high while the room temperature resistivity is 142.4 μΩ cm. The transition width is ΔT c = 0.1 K. The photograph of the measured crystal is shown in SI. b The resistivity plot of Rh 0.993 Pb 2.007 up to 100 K. Linear dependence is obvious, indicating the metallic behavior of RhPb 2 . c The resistivity plot of sample Rh 0.963 Pb 2.037 up to 10 K. Three transitions can be observed. The transition width of 1.24 K transition is significantly narrower
Fig. 2 SEM photographs of Rh 0.993 Pb 2.007 , Rh 0.963 Pb 2.037 , and Rh 0.825 Pb 2.125 , respectively (from left to right), on which the EPMA measurements were done. The size of Rh 0.993 Pb 2.007 is
Crystal growth and characterization of RhPb2 and its related compounds

May 2022

·

28 Reads

·

2 Citations

MRS Advances

The physical properties of the intermetallic compound RhPb2 have been unexplored in detail and are controversial so far. Two values of superconducting transition temperatures have been reported experimentally in poly-crystal samples with the I4/mcm structure. Moreover, the recent report of band calculation results showed that RhPb2 with the I4/mmm structure (β-RhPb2) may be a topological superconductor candidate, having a higher Tc ≈ 9.7 K than that of the I4/mcm structure. Therefore, we grew single crystals of RhPb2 and performed X-ray diffraction study and the phase stability by EPMA, and resistivity measurements to clarify this intriguing compound. Surprisingly, the resistivity measurements showed three different values of Tc (1.24 K, 2.32 K, and 6.7 K) despite the same crystal structure (I4/mcm) but different levels of Rh vacancies up to 18%, inspiring that some sort of Rh vacancy ordering may occur.Graphic abstract


(a) The crystal structure of RhPb2 in a view along the b axis showing the atoms in the asymmetric unit with displacement ellipsoids at the 99.9%; (b) the crystal structure of RhPb2 in polyhedral representation in a view along the c axis; (c) details of the linkage of the [RhPb8] anti­prisms in the crystal structure of RhPb2.
(a) A photograph of two pieces of single crystals of RhPb2 taken under an optical microscope; (b) an enlarged optical photograph of one of the single-crystals of RhPb2.
Redetermination of the crystal structure of RhPb2 from single-crystal X-ray diffraction data, revealing a rhodium deficiency

November 2021

·

55 Reads

·

3 Citations

RhPb2 (rhodium dilead) is a superconductor crystallizing in the CuAl2 structure type (space group I4/mcm). The Rh and Pb atoms are located at the 4a (site symmetry 422) and 8h (m.2m) sites, respectively. The crystal structure is composed of [RhPb8] anti­prisms, which share their square faces along the c axis and the edges in the direction perpendicular to the c axis. We have succeeded in growing single crystals of RhPb2 and have re-determined the crystal structure on basis of single-crystal X-ray diffraction data. In comparison with the previous structure studies using powder X-ray diffraction data [Wallbaum (1943). Z. Metallkd. 35, 218–221; Havinga et al. (1972). J. Less-Common Met.27, 169–186], the current structure analysis of RhPb2 leads to more precise unit-cell parameters and fractional coordinates, together with anisotropic displacement parameters for the two atoms. In addition and likewise different from the previous studies, we have found a slight deficiency of Rh in RhPb2, leading to a refined formula of Rh0.950 (9)Pb2.



Citations (48)


... These findings are in qualitative agreement with the high-field measurements of the resistivity [3]. On the other hand, there is an apparent contradiction with experiments by Kato et al. [4], who estimate the upper critical field of Bi 2+x Sr 2−x CaCu 2 O 8+δ from the measured irre-versibility field. In this case, B c2 qualitatively follows a dome for small carrier concentrations, but then increases monotonically to high values in the overdoped regime. ...

Reference:

Magnetic phase diagram of cuprates and universal scaling laws
Doping Dependence of Upper Critical Field of High- T c Cuprate Bi 2+ x Sr 2− x CaCu 2 O 8+ δ Estimated from Irreversibility Field at Zero Temperature
  • Citing Article
  • October 2024

Journal of the Physical Society of Japan

... The mesa structure in IJJs closely resembles a patch antenna, especially since its radiation is governed by resonance conditions. 38,74,75) This similarity enables the application of antenna theory for the design and understanding of IJJ-based devices to control radiation properties, 40,41,[76][77][78] a topic that will be explored more later in this review. ...

External Resonators and Antennas for the High- T c Superconducting Terahertz Emitters
  • Citing Conference Paper
  • May 2023

... The Josephson plasma emitter (JPE), which utilizes intrinsic Josephson junctions included in a high-temperature cuprate superconductor Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212), is a promising candidate for continuous-wave terahertz sources [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. In this device, a DC voltage applied perpendicular to the junction layers induces an AC supercurrent, enabling effective spatial radiation controlled through device geometry [8]. ...

Approaches to High Performance Terahertz-Waves Emitting Devices Utilizing Single Crystals of High Temperature Superconductor Bi2Sr2CaCu2O8+δ

IEICE Transactions on Electronics

... An AuPb flux was chosen for the single-crystal growth of FeRh for several reasons. First, it was noted that, during the crystal growth of RhPb 2 [38,39], the Fe crucible reacts with the RhPb melt, making Pb a suitable choice as a flux. Second, from the rich Pb part at a higher temperature of the ternary phase diagram Au-Pb-Rh, AuPb 4 Rh 5 crystals tend to grow at the surface of the boule, making the extraction of the crystals easier [40]. ...

Crystal growth and characterization of RhPb2 and its related compounds

MRS Advances

... An AuPb flux was chosen for the single-crystal growth of FeRh for several reasons. First, it was noted that, during the crystal growth of RhPb 2 [38,39], the Fe crucible reacts with the RhPb melt, making Pb a suitable choice as a flux. Second, from the rich Pb part at a higher temperature of the ternary phase diagram Au-Pb-Rh, AuPb 4 Rh 5 crystals tend to grow at the surface of the boule, making the extraction of the crystals easier [40]. ...

Redetermination of the crystal structure of RhPb2 from single-crystal X-ray diffraction data, revealing a rhodium deficiency

... The crystals were then processed into rectangular chips using the wet-etching method. 51 Next, these chips were assembled into a sandwich structure developed by our group, serving as Bi2212 THz-wave emitters. 33 In this structure, a crystal chip was sandwiched between two sapphire substrates on which metallic thin films were deposited to serve as electrodes through which a DC bias voltage can be applied. ...

Investigation of wet etching solutions and method for thicker stand alone type of mesa structures of Bi2212 single crystals
  • Citing Article
  • October 2021

Japanese Journal of Applied Physics

... The mesa structure in IJJs closely resembles a patch antenna, especially since its radiation is governed by resonance conditions. 38,74,75) This similarity enables the application of antenna theory for the design and understanding of IJJ-based devices to control radiation properties, 40,41,[76][77][78] a topic that will be explored more later in this review. ...

Experimental validation of a microstrip antenna model for high- T c superconducting terahertz emitters
  • Citing Article
  • June 2021

... temperatures contrasts with the previously reported non-monotonous temperature dependence of the spectral intensity in an identically designed device 44 . It is plausible to consider that a slight difference in the device structure, such as the connection between the mesa and the triangular patches, improves the robustness of radiation polarization at low temperatures. ...

Design and characterization of microstrip patch antennas for high-T c superconducting terahertz emitters

... (1)- (6) with N > 321 becomes very time consuming. There are experimental evidences that the power of THz emission from Bi-2212 mesas increases for thicker Bi-2212 crystals [59]. ...

Study of Radiation Characteristics of Intrinsic Josephson Junction Terahertz Emitters with Different Thickness of Bi2Sr2CaCu2O8+δ Crystals

Materials

... We developed THz imaging systems for practical use based on JPE as the source, using both transmission and reflection modes [24][25][26][27]. Furthermore, the small size of the JPE THz camera, owing to the micrometer-sized superconducting cavity, facilitates the integration of cryogenic THz camera circuitry for imaging applications in quantum computing and processing, such as the imaging of superconducting microwave resonators [28,29]. ...

Liquid helium-free high- T c superconducting terahertz emission system and its applications
  • Citing Article
  • October 2020

Japanese Journal of Applied Physics