arXiv subjects

Jumpei G. Nakamura

Publications and source records attributed to Jumpei G. Nakamura.

4 recordsLinked to original sources

arXiv2026

Incommensurate Magnetic Ordered Phase with Enhanced Low-Temperature Magnetic Specific Heat in SmAu$_3$Al$_7$

Neutron scattering and muon spin rotation ($μ$SR) measurements on single-crystal SmAu$_3$Al$_7$ reveal magnetically ordered states associated with successive transitions at $T_{\rm N}$ = 2.8 K and $T^*$ = 0.9 K. Magnetic Bragg peaks appear below $T_{\rm N}$ with an incommensurate (IC) propagation vector ${\bf q}$ = (0.30, 0, 1.33). $μ$SR detects spontaneous internal fields below $T_{\rm N}$, and the spectral shape is consistent with the IC magnetic ordering. No anomalies are observed at $T^*$, indicating that the magnetic structure remains essentially unchanged below and above $T^*$. The magnetic order is revealed to be a spatially homogeneous long-range ordered state, rather than a partially disordered state proposed in earlier studies. The possible connection between the IC magnetic order and the enhanced low-temperature magnetic specific heat is discussed.

cond-mat.str-el↗

arXiv2024

Investigation of superconducting gap of high-entropy telluride AgInSnPbBiTe5

We performed transverse-field muon spin relaxation/rotation (TF-μSR) on a high-entropy-type (HE-type) superconductor AgInSnPbBiTe5. The emergence of bulk superconducting states was confirmed from magnetic susceptibility, specific heat, and μSR. The superconducting gap 2Δ(0) estimated from μSR was clearly larger than that expected from conventional weak-coupling phonon-mediated model, suggesting the strong-coupling nature of superconductivity. In addition, a long penetration depth of 3.21(7) μm was obtained. The strong-coupling nature of superconductivity and the long penetration depth are similar to the trends observed in the other HE-type superconductors (HE alloys and transition-metal zirconides), which may be universal feature of HE-type superconductors.

cond-mat.supr-con↗

arXiv2024

Muon spin relaxation in mixed perovskite (LaAlO$_3$)$_{x}$(SrAl$_{0.5}$Ta$_{0.5}$O$_3$)$_{1-x}$ with $x\simeq 0.3$

We report on muon spin relaxation ($μ^+$SR) measurements in a mixed perovskite compound, (LaAlO$_3$)$_{x}$(SrAl$_{0.5}$Ta$_{0.5}$O$_3$)$_{1-x}$ with $x\simeq 0.3$ (LSAT), which is widely used as a single-crystalline substrate for thin film deposition. In zero applied field (ZF), muon depolarization due to the distribution of nuclear dipole fields was observed in the temperature range from 4 K to 270 K. Interestingly, $μ^+$SR time spectra in ZF maintained a Gaussian-like feature over the entire range, while the depolarization rate exhibited a monotonic decrease with increasing temperature. This behavior may be attributed to the thermally activated diffusion of muons between a few adjacent sites within a confined space of the angstrom scale, where the motionally averaged local field that each muon experiences can remain non-zero and result in maintaining the Gaussian-like line shape. The spatial distribution of electrostatic potential at lattice interstices evaluated via density functional theory calculations suggests that such a restriction of muon diffusion paths can be caused by the random distribution of cations with different nominal valences in the mixed perovskite lattice.

cond-mat.mtrl-sci↗

arXiv2023

Magnetic Instability of Pr3Ru4Sn13

We report on the quantum criticality of Pr$_3$Ru$_4$Sn$_{13}$ revealed by our new material research. Pr$_3$Ru$_4$Sn$_{13}$ has been synthesized by flux growth and characterized by single X-ray, powder X-ray, and powder neutron diffraction measurements. The compound adopts a Yb$_3$Rh$_4$Sn$_{13}$-type structure with a cubic Pm$\bar{3}$n. From the magnetization at 1 T, the effective magnetic moment was estimated to be 3.58 $μ_B$ per Pr$^{3+}$, suggesting that the magnetism is mainly contributed by Pr$^{3+}$ ions. The specific heat and magnetization show an anomaly at $T_{N} = 7.5$ ~ K owing to the phase transition. The muon spin rotation and relaxation ($μ$SR) time spectra exhibit clear oscillations below $T_N$. This suggests that the phase is magnetically ordered. The volume fraction of the magnetic phase estimated from the initial asymmetry is around ten percent. In addition, spin fluctuations were observed at low temperatures. These results provide microscopic evidence that the material is closest to the antiferromagnetically quantum critical point with a partial order among Pr$_3$$T_4$Sn$_{13}$ ($T= $ Co, Ru, Rh).

cond-mat.str-el↗