arXiv subjects

Y. Hirose

Publications and source records attributed to Y. Hirose.

9 recordsLinked to original sources

arXiv2023

Unusually strong electronic correlation and field-induced ordered phase in YbCo$_2$

We report the first study of electrical resistivity, magnetization, and specific heat on YbCo$_2$. The measurements on a single-phased sample of YbCo$_2$ bring no evidence of magnetic ordering down to 0.3 K in a zero magnetic field. The manifestations of low Kondo temperature are observed. The specific heat value divided by temperature, C/T, keeps increasing logarithmically beyond 7 J/mol.K2 with decreasing temperature down to 0.3 K without no sign of magnetic ordering, suggesting a very large electronic specific heat. Analysis of the magnetic specific heat indicates that the large portion of the low-temperature specific heat is not explained simply by the low Kondo temperature but is due to the strong intersite magnetic correlation in both the 3d and 4f electrons. Temperature-dependent measurements under static magnetic fields up to 7 T are carried out, which show the evolution of field-induced transition above 2 T. The transition temperature increases with increasing field, pointing to a ferromagnetic character. The extrapolation of the transition temperature to zero field suggests that YbCo$_2$ is in the very proximity of the quantum critical point. These results indicate that in the unique case of YbCo$_2$, the itinerant electron magnetism of Co 3d-electrons and the Kondo effect within the vicinity of quantum criticality of Yb 4f-local moments can both play a role.

cond-mat.str-el↗

arXiv2020

Two-Gap Time Reversal Symmetry Breaking Superconductivity in Non-Centrosymmetric LaNiC2

We report a $μ$SR investigation of a non-centrosymmetric superconductor (LaNiC$_2$) in single crystal form. Compared to previous $μ$SR studies of non-centrosymmetric superconducting polycrystalline and powder samples, the unambiguous orientation of single crystals enables a simultaneous determination of the absolute value of the magnetic penetration depth and the vortex core size from measurements that probe the magnetic field distribution in the vortex state. The magnetic field dependence of these quantities unambiguously demonstrates the presence of two nodeless superconducting energy gaps. In addition, we detect weak internal magnetic fields in the superconducting phase, confirming earlier $μ$SR evidence for a time-reversal symmetry breaking superconducting state. Our results suggest that Cooper pairing in LaNiC$_2$ is characterized by the same interorbital equal-spin pairing model introduced to describe the pairing state in the centrosymmetric superconductor LaNiGa$_2$.

cond-mat.supr-con↗

arXiv2020

Magnetic structure of Cd-doped CeIrIn$_5$

We report the magnetic structure of nominally 10% Cd-doped CeIrIn$_5$, CeIr(In$_{0.9}$Cd$_{0.1}$)$_5$, determined by elastic neutron scattering. Magnetic intensity was observed only at the ordering wave vector $Q_{AF} = (1/2,1/2,1/2)$, commensurate with the crystal lattice. A staggered moment of 0.47(3)$μ_B$ at 1.8 K resides on the Ce ion. The magnetic moments are found to be aligned along the crystallographic $c$ axis. This is further confirmed by magnetic susceptibility data, which suggest the $c$ axis to be the easy magnetic axis. The determined magnetic structure is strikingly different from the incommensurate antiferromagnetic ordering of the closely related compound CeRhIn$_5$, in which the magnetic moments are antiferromagnetically aligned within the tetragonal basal plane.

cond-mat.str-el↗

arXiv2020

High-Field Ultrasonic Study of Quadrupole Ordering and Crystal Symmetry Breaking in CeRhIn5

We performed an ultrasonic measurement for the heavy-fermion compound CeRhIn$_5$ to investigate the origin of the field-induced anisotropic phase in high magnetic fields. The transverse elastic constant $C_\mathrm{T} = (C_{11} - C_{12})/2$ and the ultrasonic attenuation coefficient $α_\mathrm{T}$ show clear anomaly at $B^\star = 28.5$ T, which was discussed as the electronic nematic transition point. In addition, $C_\mathrm{T}$ exhibits acoustic de Haas-van Alphen oscillation below 28.5 T. These elastic anomalies around $B^\star$ indicate an electric quadrupole ordering of $O_{x^2-y^2}$ accompanied by $B_\mathrm{1g}$ crystal symmetry breaking and Fermi surface reconstruction due to the quadrupole-strain coupling, which results from itinerant $4f$ electrons and the $p$-$f$ hybridized state.

cond-mat.str-el↗

arXiv2017

Quasi-two-dimensional Fermi surfaces with localized $f$ electrons in the layered heavy-fermion compound CePt$_2$In$_7$

We report measurements of the de Haas-van Alphen effect in the layered heavy-fermion compound CePt$_2$In$_7$ in high magnetic fields up to 35 T. Above an angle-dependent threshold field, we observed several de Haas-van Alphen frequencies originating from almost ideally two-dimensional Fermi surfaces. The frequencies are similar to those previously observed to develop only above a much higher field of 45 T, where a clear anomaly was detected and proposed to originate from a change in the electronic structure [M. M. Altarawneh et al., Phys. Rev. B 83, 081103 (2011)]. Our experimental results are compared with band structure calculations performed for both CePt$_2$In$_7$ and LaPt$_2$In$_7$, and the comparison suggests localized $f$ electrons in CePt$_2$In$_7$. This conclusion is further supported by comparing experimentally observed Fermi surfaces in CePt$_2$In$_7$ and PrPt$_2$In$_7$, which are found to be almost identical. The measured effective masses in CePt$_2$In$_7$ are only moderately enhanced above the bare electron mass $m_0$, from 2$m_0$ to 6$m_0$.

cond-mat.str-el↗

arXiv2017

Determination of the magnetic structure of CePt$_2$In$_7$ by means of neutron diffraction

The magnetic structure of the heavy fermion antiferromagnet CePt$_2$In$_7$ is determined using neutron diffraction. We find a magnetic wave vector $\mathbf{q}_M = (1/2,1/2,1/2)$, which is temperature independent up to $T_N =$ 5.5 K. A staggered moment of 0.45(1)$μ_B$ at 2 K resides on the Ce ion. The nearest-neighbor moments in the tetragonal basal plane are aligned antiferromagnetically. The moments rotate by 90$^\circ$ from one CeIn$_3$ plane to another along the $c$ axis. A much weaker satellite peak with an incommensurate magnetic wave vector $\mathbf{q}_M = (1/2,1/2,0.47)$ seems to develop at low temperature. However, the experimental data available so far are not sufficient to draw a definitive conclusion about the possible co-existence of commensurate and incommensurate magnetic structures in this material.

cond-mat.str-el↗

arXiv2016

Specific heat in high magnetic fields and magnetic phase diagram of CePt$_2$In$_7$

We report specific heat measurements on a high quality single crystal of the heavy-fermion compound CePt$_2$In$_7$ in magnetic fields up to 27 T. The zero-field specific heat data above the Néel temperature, $T_N$, suggest a moderately enhanced value of the electronic specific heat coefficient $γ= 180 \; \rm{mJ/K^2mol}$. For $T<T_N$, the data at zero applied magnetic field are consistent with the existence of an anisotropic spin-density wave opening a gap on almost entire Fermi surface, suggesting extreme two-dimensional electronic and magnetic structures for CePt$_2$In$_7$. $T_N$ is monotonically suppressed by magnetic field applied along the $c$-axis. When field is applied parallel to the $a$-axis, $T_N$ first increases at low field up to about 10 T and then decreases monotonically at higher field. Magnetic phase diagram based on specific heat measurements suggests that a field-induced quantum critical point is likely to occur slightly below 60 T for both principal orientations of the magnetic field.

cond-mat.str-el↗

arXiv2006

Imprint of Gravitational Lensing by Population III Stars in Gamma Ray Burst Light Curves

We propose a novel method to extract the imprint of gravitational lensing by Pop III stars in the light curves of Gamma Ray Bursts (GRBs). Significant portions of GRBs can originate in hypernovae of Pop III stars and be gravitationally lensed by foreground Pop III stars or their remnants. If the lens mass is on the order of $10^2-10^3M_\odot$ and the lens redshift is greater than 10, the time delay between two lensed images of a GRB is $\approx 1$s and the image separation is $\approx 10 μ$as. Although it is difficult to resolve the two lensed images spatially with current facilities, the light curves of two images are superimposed with a delay of $\approx 1$ s. GRB light curves usually exhibit noticeable variability, where each spike is less than 1s. If a GRB is lensed, all spikes are superimposed with the same time delay. Hence, if the autocorrelation of light curve with changing time interval is calculated, it should show the resonance at the time delay of lensed images. Applying this autocorrelation method to GRB light curves which are archived as the {\it BATSE} catalogue, we demonstrate that more than half light curves can show the recognizable resonance, if they are lensed. Furthermore, in 1821 GRBs we actually find one candidate of GRB lensed by a Pop III star, which may be located at redshift 20-200. The present method is quite straightforward and therefore provides an effective tool to search for Pop III stars at redshift greater than 10. Using this method, we may find more candidates of GRBs lensed by Pop III stars in the data by the {\it Swift} satellite.

astro-ph↗

arXiv2002

Step Repulsion Mediates Wandering on a Si(001) Vicinal Face

With a Si(001) vicinal surface in mind, we study step wandering instability on a vicinal surface with an anisotropic surface diffusion whose orientation dependence alternates on each consecutive terrace. In a conserved system step wandering takes place with step-up adatom drift. Repulsive interaction between steps is found indispensable for the instability. Monte Carlo simulation with a strong repulsive step interaction confirms the result of linear stability analysis, and further shows that in-phase step wandering produces straight grooves. Grooves widen as their amplitudes increase in proportion to the square root of time.

cond-mat.mtrl-sci↗