October 2024
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14 Reads
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1 Citation
Journal of the Physical Society of Japan
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October 2024
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14 Reads
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1 Citation
Journal of the Physical Society of Japan
September 2024
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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.
February 2024
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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.
May 2023
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32 Reads
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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.
May 2023
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17 Reads
May 2023
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8 Reads
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1 Citation
December 2022
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53 Reads
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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.
May 2022
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28 Reads
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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
November 2021
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55 Reads
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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.
October 2021
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20 Reads
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5 Citations
Japanese Journal of Applied Physics
... 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. ...
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. ...
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]. ...
December 2022
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]. ...
May 2022
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]. ...
November 2021
... 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. ...
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. ...
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. ...
May 2021
... (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]. ...
February 2021
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]. ...
October 2020
Japanese Journal of Applied Physics