Broadly Tunable CW Terahertz Sources Using Intrinsic Josephson Junction Stacks in High‐Temperature Superconductors

Electromagnetic waves in the 0.3–3.0 THz frequency range are considered to have great potential in research and industry; thus, compact, solid‐state and continuous‐wave (CW) terahertz sources have been developed throughout the vast field of science and technology. Since the first demonstration of terahertz emission from intrinsic Josephson junctions (IJJs) in the high‐temperature (high‐Tc ) superconductor Bi2Sr2CaCu2O8+δ , terahertz generation utilizing stacks of IJJs has become a major topic of research, both experimentally and theoretically. In this chapter, we describe recent progress on the development of high‐Tc superconducting terahertz sources. We demonstrate that these superconducting terahertz sources emit continuous terahertz radiation and generate power in the microwatt range at broadly tunable frequencies in the range of 0.5–2.4 THz. The solid‐state source is extremely small in size and its output power is sufficiently stable during operation. In addition, we also established a transmission imaging system using high‐Tc sources to promote effective use in various applications

Local SiC photoluminescence evidence of non-mutualistic hot spot formation and sub-THz coherent emission from a rectangular Bi2_2Sr2_2CaCu2_2O8+δ_{8+\delta} mesa

From the photoluminescence of SiC microcrystals uniformly covering a rectangular mesa of the high transition temperature $T_c$ superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$, the local surface temperature $T({\bm r})$ was directly measured during simultaneous sub-THz emission from the $N\sim10^3$ intrinsic Josephson junctions (IJJs) in the mesa. At high bias currents $I$ and low bath temperatures $T_{\rm bath}\lesssim~35$ K, the center of a large elliptical hot spot with $T({\bm r})> T_c$ jumps dramatically with little current-voltage characteristic changes. The hot spot doesn't alter the ubiquitous primary and secondary emission conditions: the ac Josephson relation and the electromagnetic cavity resonance excitation, respectively. Since the intense sub-THz emission was observed for high $T_{\rm bath}\gtrsim~50$ K in the low $I$ bias regime where hot spots are absent, hot spots can not provide the primary mechanisms for increasing the output power, the tunability, or for promoting the synchronization of the $N$ IJJs for the sub-THz emission, but can at best coexist non-mutualistically with the emission. No $T({\bm r})$ standing waves were observed

Local SiC photoluminescence evidence of hot spot formation and sub-THz coherent emission from a rectangular Bi2Sr2CaCu2O8+delta mesa

From the photoluminescence of SiC microcrystals uniformly covering a rectangular mesa of the high transition temperature T-c superconductor Bi2Sr2CaCu2O8+delta, the local surface temperature T(r) was directly measured during simultaneous sub-THz emission from the N similar to 10(3) intrinsic Josephson junctions (IJJs) in the mesa. At high bias currents I and low bath temperatures T-bath less than or similar to 35 K, the center of a large elliptical hot spot with T(r) \u3e T-c jumps dramatically with little current-voltage characteristic changes. The hot spot does not alter the ubiquitous primary and secondary emission conditions: the ac-Josephson relation and the electromagnetic cavity resonance excitation, respectively. Since the most intense sub-THz emission was observed for high T-bath greater than or similar to 50 K in the low I bias regime where hot spots are absent, hot spots cannot provide the primary mechanisms for increasing the output power, the tunability, or promoting the synchronization of the N IJJs for the sub-THz emission, but can at best coexist nonmutualistically with the emission. No T(r) standing waves were observed

Terahertz Radiation Emitted from Intrinsic Josephson Junctions in High-Tc Superconductor Bi2Sr2CaCu2O8+δ

The present status of superconducting terahertz emitter using the intrinsic Josephson junctions in high-Tc superconductor Bi2Sr2CaCu2O8+δ is reviewed. Fabrication methods of the emitting device, electrical and optical characteristics of them, synchronizing operation of two emitters and an example of applications to the terahertz imaging will be discussed. After the description of fabrication techniques by an Argon ion milling with photolithography or metal masks and by a focused ion beam, optical properties of radiation spectra, the line width, polarization and the spatial distribution of emission are presented with some discussion on the operation mechanism. For electrical properties, reversible and irreversible operations at high and low electrical currents, respectively, and electrical modulation of the radiation intensity for terahertz imaging are presented

Parental legacy and regulatory novelty in Brachypodium diurnal transcriptomes accompanying their polyploidy

Polyploidy is a widespread phenomenon in eukaryotes that can lead to phenotypic novelty and has important implications for evolution and diversification. The modification of phenotypes in polyploids relative to their diploid progenitors may be associated with altered gene expression. However, it is largely unknown how interactions between duplicated genes affect their diurnal expression in allopolyploid species. In this study, we explored parental legacy and hybrid novelty in the transcriptomes of an allopolyploid species and its diploid progenitors. We compared the diurnal transcriptomes of representative Brachypodium cytotypes, including the allotetraploid Brachypodium hybridum and its diploid progenitors Brachypodium distachyon and Brachypodium stacei. We also artificially induced an autotetraploid B. distachyon. We identified patterns of homoeolog expression bias (HEB) across Brachypodium cytotypes and time-dependent gain and loss of HEB in B. hybridum. Furthermore, we established that many genes with diurnal expression experienced HEB, while their expression patterns and peak times were correlated between homoeologs in B. hybridum relative to B. distachyon and B. stacei, suggesting diurnal synchronization of homoeolog expression in B. hybridum. Our findings provide insight into the parental legacy and hybrid novelty associated with polyploidy in Brachypodium, and highlight the evolutionary consequences of diurnal transcriptional regulation that accompanied allopolyploidy

Broadly Tunable Sub-terahertz Emission from Internal Branches of the Current-voltage Characteristics of Superconducting Bi2Sr2CaCu2O8+d Single Crystals

Continuous, coherent sub-terahertz radiation arises when a dc voltage is applied across a stack of the many intrinsic Josephson junctions in a Bi2Sr2CaCu2O8+d single crystal. The active junctions produce an equal number of I-V characteristic branches. Each branch radiates at a slightly tunable frequency obeying the ac Josephson relation. The overall output is broadly tunable and nearly independent of heating effects and internal cavity frequencies. Amplification by a surrounding external cavity to allow for the development of a useful high-power source is proposed.Comment: 4 pages, 4 figures, accepted for publication in PR

RB1CC1 Together with RB1 and p53 Predicts Long-Term Survival in Japanese Breast Cancer Patients

RB1-inducible coiled-coil 1 (RB1CC1) plays a significant role in the enhancement of the retinoblastoma tumor suppressor (RB1) pathway and is involved in breast cancer development. However, RB1CC1's role in clinical progression of breast cancer has not yet been evaluated, so, as a first step, it is necessary to establish its usefulness as a tool to evaluate breast cancer patients. In this report, we have analyzed the correlation between abnormalities in the RB1CC1 pathway and long-term prognosis, because disease-specific death in later periods (>5 years) of the disease is a serious problem in breast cancer. Breast cancer tissues from a large cohort in Japan were evaluated by conventional immunohistochemical methods for the presence of the molecules involved in the RB1CC1 pathway, including RB1CC1, RB1, p53, and other well-known prognostic markers for breast cancer, such as estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2. The correlation between the immunohistochemical results and clinical outcomes of 323 breast cancer patients was analyzed using a Kaplan-Meier log-rank test and a multivariate Cox proportional hazards regression analysis. Absence of nuclear RB1CC1 expression was associated with the worst prognosis (Log-rank test, Chi-Square value = 17.462, p<0.0001). Dysfunction of either one of RB1CC1, RB1, or p53 was associated with the highest risk for cancer-specific death, especially related to survival lasting more than 5 years (multivariate Cox proportional hazard ratio = 3.951, 95% Confidence Interval = 1.566–9.967, p = 0.0036). Our present data demonstrate that the combined evaluation of RB1CC1, RB1 and p53 by conventional immunohistochemical analysis provides an accurate prediction of the long-term prognoses of breast cancer patients, which can be carried out as a routine clinical examination