arXiv subjects

Itsuhiro Kakeya

Publications and source records attributed to Itsuhiro Kakeya.

7 recordsLinked to original sources

arXiv2026

Discriminating superconducting fluctuations from the pseudogap in Bi$_2$Sr$_2$Ca$_{n-1}$Cu$_n$O$_{2n+4+\delta} (n = 2,3)$: A magnetotransport study

Understanding the normal state is essential for uncovering the mechanism of high-$T_c$ superconductivity. We investigate magnetotransport in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ and Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+\delta}$ single crystals over a wide doping range. While the in-plane resistivity and Hall coefficient show strong pseudogap-induced temperature dependence, the $T^2$ Hall-angle behavior and the modified Kohler's rule remain robust across all dopings. The onset temperatures of the pseudogap are clearly distinct from superconducting fluctuations, although they scale with the pseudogap magnitudes with a factor consistent with a $d$-wave superconductor. These results demonstrate that the pseudogap does not arise from superconducting fluctuations and instead suggest that it may originate from preformed Cooper pairing in the BCS-BEC crossover regime.

cond-mat.supr-con↗

arXiv2026

Time-resolved synchronization analysis of stacked intrinsic Josephson junctions of a cuprate superconductor with frequency-modulated terahertz radiation spectra

Terahertz radiation from $\text{Bi}_2\text{Sr}_2\text{CaCu}_2\text{O}_{8+\delta}$ intrinsic Josephson junctions (IJJs) provides an ideal platform to study the synchronization of a macroscopic quantum system. Here, we present a spectral analysis of a frequency-modulated Josephson plasma emitter coupled with patch antennas. In the unmodulated intensity distribution as a function of radiation frequency $I_{\mathrm{UM}}(\omega)$, we observe a double Gaussian peak structure. Crucially, double-peak spectra obtained at a constant bias voltage imply either a rapid temporal distribution of resonances or their simultaneous excitation, driven by the mutual electromagnetic coupling between the IJJ mesa and the antennas. At low modulation frequencies $f_m$, the spectra are well reproduced by the products of $I_{\mathrm{UM}}(\omega)$ and frequency combs, yielding a synchronized relaxation time $\tau_s \simeq 0.28\text{ ns}$. Incorporating $\tau_s$ quantitatively reproduces a drastic spectral transformation observed around $f_m \sim 1\text{ GHz}$, unveiling the sub-nanosecond non-equilibrium dynamics of coupled Josephson plasma.

cond-mat.supr-con↗

arXiv2024

Effects of vortex and antivortex excitations in underdoped Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+\delta}$ bulk single crystals

The observance of vortex and anti-vortex effects in bulk crystals can prove the existence of phase-disordered superconductivity in the bulk. To gain insights into the mechanisms that govern superconducting transition in copper oxide high-transition temperature ($T_c$) superconductors, this study investigated the transport properties of underdoped Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+\delta}$ (Bi-2223) bulk single crystals.The $I$-$V$ characteristics results and the typical tailing behavior owing to the temperature dependence of in-plane resistivity ($\rho_{ab}$) were consistent with the Kosterlitz-Thouless (KT) transition characteristics. Thus, with increasing temperature, copper oxide high-$T_c$ superconductors transitioned to their normal state owing to destruction of their phase correlations, although a finite Cooper pair density was prevalent at $T_c$. Further, magnetization measurements were performed to determine the temperature dependence of the irreversible magnetic field $B_{irr}$. Consequently, the mechanism governing the KT transition-like superconducting transition in this bulk system was elucidated. These results support the extreme strong-coupling models for high-$T_c$ superconductivity in cuprates.

cond-mat.supr-con↗

arXiv2020

THz emission from a Bi2Sr2CaCu2O8+{\delta} cross-whisker junction

Cuprate superconductor Bi2Sr2CaCu2O8+{\delta} (BSCCO) has been a promising candidate of a coherent, continuous, and compact THz light source owing to its intrinsic Josephson junction inside the crystal structure. In this paper, we utilized BSCCO cross-whisker junctions to produce THz emitter device using the whisker crystals which can be easily obtained compared with single crystals. As a result, we have successfully observed the emission from the cross-whisker intrinsic Josephson junction, with frequency of ~0.7 THz. Our findings might enlarge the applicability of BSCCO superconductors for the THz emission source.

cond-mat.supr-con↗

arXiv2016

Origin of positive out-of-plane magnetoconductivity in overdoped Bi$_{1.6}$Pb$_{0.4}$Sr$_{2}$CaCu$_{1.96}$Fe$_{0.04}$O$_{8+δ}$

To elucidate the pseudogap phase diagram including the overdoped state of high transition temperature (high-$T_c$) cuprates, we must understand the origin of the positive out-of-plane magnetoconductivity (MC) observed in these compounds. For this purpose, the out-of-plane resistivity $ρ_c(T,H)$ of an overdoped Bi$_{1.6}$Pb$_{0.4}$Sr$_{2}$CaCu$_{1.96}$Fe$_{0.04}$O$_{8+δ}$ (Bi-2212) single crystal is measured under pulsed magnetic fields up to 60 T. We show that the superconductive density-of-states (DOS) depletion effect, in addition to the pseudogap effect, clearly appears below the superconductive fluctuation regime, and the contribution becomes dominant in the superconducting state.

cond-mat.supr-con↗

arXiv2014

Epitaxial growth and superconducting anisotropy of PbSr$_{2}$Y$_{1-x}$Ca$_{x}$Cu$_{2}$O$_{7+δ}$ thin films

Thin films of single-crystal Pb$_{1-y}$Bi$_{y}$Sr$_{2}$Y$_{1-x}$Ca$_{x}$Cu$_{2}$O$_{7+δ}$ (PbBi1212) were grown on SrTiO$_{3}$ (100) substrates by a two-step growth technique in which an amorphous film is annealed at 970 $^\circ$C in a closed ceramic container prepared using the same material as the film. We find that PbBi1212 exhibits superconductivity when the Ca concentration $x$ exceeds 0.3. The effective number of holes per Cu atom $n_{\rm eff}$ is well described as $n_{\rm eff}=0.34x$. The highest onset temperature for the superconducting transition attained in the present study is 65 K. The resistivity measurement in a magnetic field reveals that the coherence lengths of Pb1212 ($y=0$) are approximately 25 and 2.7 Å, along the $ab$ plane and the $c$ axis, respectively.

cond-mat.supr-con↗

arXiv2012

Effect of thermal inhomogeneity for THz radiation from intrinsic Josephson junction stacks of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$

Terahertz radiation from the mesa structures of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ is detected in samples with thin electrodes $< 100$ nm. In samples with thick electrodes $\simeq$ 400 nm, neither radiations nor voltage jumps in current-voltage characteristics are detected. This suggests that the thin electrode helps excite the Josephson plasma oscillation as a result of the poor heat flow through the electrode. The shielding effect by the electrode is not essential. We consider that the local temperature rise is the origin of the synchronization of the phase kink for terahertz radiation.

cond-mat.supr-con↗