arXiv subjects

Yoshichika Ōnuki

Publications and source records attributed to Yoshichika Ōnuki.

23 records · Page 2Linked to original sources

arXiv2016

Magnetic structure of divalent europium compound EuGa$_4$ studied by single crystal time-of-flight neutron diffraction

The magnetic structure of the intermetallic compound EuGa$_4$ was investigated using single-crystal neutron diffraction with the time-of-flight (TOF) Laue technique on the new diffractometer SENJU at MLF of J-PARC. In spite of high neutron absorption of Eu, a vast number of diffraction spots were observed without isotope enrichment. The magnetic reflections were appeared at the positions with the diffraction indices of $h+k+l{\neq}2n$ below 16 K, indicating that the ordering vector is ${\bf q}=(0~0~0)$. Continuous evolution of magnetic reflection intensity below $T_{\rm N}$ follows a squared Brillouin function for $S$=7/2. By adopting a wavelength-dependent absorption collection, the magnetic structure of EuGa$_4$ was revealed that a nearly full magnetic moment of 6.4$~μ_{\rm B}$ of Eu lies within the basal plane of the lattice. The present study reveals a well-localized divalent Eu magnetism in EuGa$_4$ and demonstrates a high ability of SENJU to investigate materials with high neutron absorption.

cond-mat.str-el↗

arXiv2015

Effect of Geomagnetism on 101Ru Nuclear Quadrupole Resonance Measurements of CeRu2

We performed 101Ru nuclear quadrupole resonance (NQR) measurements on the s-wave superconductor CeRu2 and found oscillatory behavior in the spin-echo amplitude at the +-1/2 <-> +-3/2 transitions but not at the +-3/2 <-> +-5/2 transitions. The modulation disappears in the superconducting state or in a magnetic shield, which implies a geomagnetic field effect. Our results indicate that the NQR spin-echo decay curve at the +-1/2 <-> +-3/2 transitions is sensitive to a weak magnetic field.

cond-mat.supr-con↗

arXiv2012

Strong Correlation between Anomalous Quasiparticle Scattering and Unconventional Superconductivity in Hidden Order Phase of URu$_2$Si$_2$

The pressure dependent electrical resistivity of URu$_2$Si$_2$ has been studied at high pressure across the first order phase boundary of $P_x$ where the ground state switches under pressure from "hidden order" (HO) to large moment antiferromagnetic (LAFM) states. The electrical transport in URu$_2$Si$_2$ at low temperatures shows a strong sample dependence. We have measured an ultra-clean single crystal whose quality is the highest among those used in previous studies. The generalized power law $ρ{\,}={\,}{ρ_0}+{\,}{A_n}T{^n}$ analysis finds that the electric transport property deviates from Fermi liquid theory in the HO phase but obeys the theory well above $P_x$. The analysis using the polynomial in $T$ expression $ρ{\,}={\,}{ρ_0}+{\,}{α_1}T+{\,}{α_2}T{^2}$ reveals the relation ${α_1}/{α_2}$ $\propto$ $T_{sc}$ in the HO phase. While the pressure dependence of ${α_2}$ is very weak, ${α_1}$ is roughly proportional to $T_{sc}$. This suggests a strong correlation between the anomalous quasiparticle scattering and the superconductivity and that both have a common origin. The present study clarifies a universality of the HO phase inherent in strongly correlated electron superconductors near quantum criticality.

cond-mat.supr-con↗

arXiv2004

Enhancing the Superconducting Transition Temperature in the Absence of Spin Correlations in Heavy Fermion Compound CeIrIn$_5$

We report on a pressure($P$)-induced evolution of superconductivity and spin correlations in CeIrIn$_5$ via the $^{115}$In nuclear-spin-lattice-relaxation rate measurements. We find that applying pressure suppresses dramatically the antiferromagnetic fluctuations that are strong at ambient pressure. At $P$ = 2.1 GPa, $T_{\rm c}$ increases to $T_{\rm c}$ = 0.8 K that is twice $T_{\rm c}$($P$ = 0 GPa), in the background of Fermi liquid state. This is in sharp contrast with the previous case in which negative, chemical pressure (replacing Ir with Rh) enhances magnetic interaction and increases $T_{\rm c}$. Our results suggest that multiple mechanisms work to produce superconductivity in the same compound CeIrIn$_5$.

cond-mat.supr-con↗

arXiv2004

New Superconducting and Magnetic Phases Emerge on the Verge of Antiferromagnetism in CeIn$_3$

We report the discovery of new superconducting and novel magnetic phases in CeIn$_3$ on the verge of antiferromagnetism (AFM) under pressure ($P$) through the In-nuclear quadrupole resonance (NQR) measurements. We have found a $P$-induced phase separation of AFM and paramagnetism (PM) without any trace for a quantum phase transition in CeIn$_3$. A new type of superconductivity (SC) was found in $P=2.28-2.5$ GPa to coexist with AFM that is magnetically separated from PM where the heavy fermion SC takes place. We propose that the magnetic excitations such as spin-density fluctuations induced by the first-order magnetic phase transition might mediate attractive interaction to form Cooper pairs.

cond-mat.str-el↗