arXiv subjects

Y. Matsuda

Publications and source records attributed to Y. Matsuda.

At least 307 records · Page 17Linked to original sources

arXiv2004

A Subaru Search for Ly-alpha Blobs in and around the Proto-cluster Region at Redshift z=3.1

We report the properties of the 35 robust candidates of Ly-alpha blobs (LABs), which are larger than 16 arcsec^2 in isophotal area and brighter than 0.7 x 10^-16 ergs s^-1 cm^-2, searched in and around the proto-cluster region at redshift z=3.1 discovered by Steidel et al. in the SSA22 field, based on wide-field (31'x23') and deep narrow-band (NB497; 4977/77) and broad-band (B,V, and R) images taken with the prime-focus camera on the Subaru telescope. The two previously known giant LABs are the most luminous and the largest ones in our survey volume of 1.3 x 10^5 Mpc^3. We revealed the internal structures of the two giant LABs and discovered some bubble-like features, which suggest that intensive starburst and galactic superwind phenomena occurred in these objects in the past. The rest 33 LABs have isophotal area of about 16-78 arcsec^2 and flux of 0.7-7 x 10^-16 ergs s^-1 cm^-2. These 35 LABs show a continuous distribution of isophotal area and emission line flux. The distributions of average surface brightness and morphology are widespread from relatively compact high surface brightness objects to very diffuse low surface brightness ones. The physical origins of these LABs may be (i) photo-ionization by massive stars, or active galactic nuclei, or (ii) cooling radiation from gravitationally heated gas, or (iii) shock heating by starburst driven galactic superwind. One third of them are apparently not associated with ultra-violet continuum sources that are bright enough to produce Ly-alpha emission, assuming a Salpeter initial mass function. The 90% of these LABs are located inside the high surface density region of the 283 relatively compact and strong Ly-alpha emitters selected in our previous study. This suggests that these LABs may be the phenomena related to dense environment at high redshift.

astro-ph↗

arXiv2004

Superconducting Gap Function in Antiferromagnetic Heavy-Fermion UPd_2Al_3 Probed by Angle Resolved Magnetothermal Transport Measurements

The superconducting gap structure of heavy fermion UPd_2Al_3, in which unconventional superconductivity coexists with antiferromagnetic (AF) order with atomic size local moments, was investigated by the thermal conductivity measurements in a magnetic field rotating in various directions relative to the crystal axes. The results provide strong evidence that the gap function Δ(k) has a single line node orthogonal to the c-axis located at the AF Brillouin zone boundary, while Δ(k) is isotropic within the basal plane. The determined nodal structure is compatible with the resonance peak in the dynamical susceptibility observed in neutron inelastic scattering experiments. Based on these results, we conclude that the superconducting pairing function of UPd_2Al_3 is most likely to be d-wave with a form Δ(k)=Δ_0 cos(k_zc)

cond-mat.supr-con↗

arXiv2004

Vortex Solid-Liquid Transition in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ with a High Density of Strong Pins

The introduction of a large density of columnar defects in %underdoped Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ crystals does not, at sufficiently low vortex densities, increase the irreversibility line beyond the first order transition (FOT) field of pristine crystals. At such low fields, the flux line wandering length $r_{w}$ behaves as in pristine %Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ crystals. Next, vortex positional correlations along the $c$--axis in the vortex Bose glass at fields above the FOT are smaller than in the low--field vortex solid. Third, the Bose-glass-to-vortex liquid transition is signaled by a rapid decrease in c-axis phase correlations. These observations are understood in terms of the ``discrete superconductor'' model.

cond-mat.supr-con↗

arXiv2004

Large Cosmic Variance in the Clustering Properties of Lyman Alpha Emitters at z~5

We reported in a previous paper the discovery of large-scale structure of Lyman Alpha emitters (LAEs) at z=4.86+-0.03 with a projected size of 20 Mpc x 50 Mpc in narrow-band data of a 25' x 45' area of the Subaru Deep Field (Omega_0=0.3, lambda_0=0.7, H0=70 km/s/Mpc). However, the surveyed area, which corresponds to 55 Mpc x 100 Mpc, was not large enough that we can conclude that we are seeing a typical distribution of z~5 LAEs. In this Letter, we report the results of follow-up imaging of the same sky area using a new narrow-band filter (NB704, lambda_c=7046 A and FWHM=100 A) to detect LAEs at z=4.79, i.e., LAEs lying closer to us by 39 Mpc on average than the z=4.86 objects. We detect 51 LAEs at z=4.79+-0.04 down to NB704=25.7, and find that their sky distribution is quite different from the z=4.86 LAEs'. The clustering of z=4.79 LAEs is very weak on any scales and there is no large-scale high- contrast structure. The shape and the amplitude of the angular correlation function are thus largely different between the two samples. These results demonstrate a large cosmic variance in the clustering properties of LAEs on scales of ~ 50 Mpc.

astro-ph↗

arXiv2003

New High Field State of Flux Line Lattice in Unconventional Superconductor CeCoIn_5

Ultrasound velocity measurements of the unconventional superconductor CeCoIn_5 with extremely large Pauli paramagnetic susceptibility reveal an unusual structural transformation of the flux line lattice (FLL) in the vicinity of the upper critical field. The transition field coincides with that at which heat capacity measurements reveal a second order phase transition. The lowering of the sound velocity at the transition is consistent with the collapse of the FLL tilt modulus and a crossover to quasi two-dimensional FLL pinning. These results provide a strong evidence that the high field state is the Fulde-Ferrel-Larkin-Ovchinikov phase, in which the order parameter is spatially modulated and has planar nodes aligned perpendicular to the vortices.

cond-mat.supr-con↗

arXiv2003

Giant Nernst effect in a Kondo lattice close to a quantum critical point

We present a study of Nernst and Seebeck coefficients of the heavy-fermion superconductor CeCoIn$_{5}$. Below 18 K, concomitant with a field-dependent Seebeck coefficient, a large sub-linear Nernst signal emerges with a magnitude drastically exceeding what is expected for a multi-band Fermi-liquid metal. In the mixed state, in contrast with all other superconductors studied before, this signal overwhelms the one associated with the motion of superconducting vortices. The results point to a hitherto unknown source of transverse thermoelectricity in strongly interacting electrons.

cond-mat.str-el↗

arXiv2003

Tunneling Spectra of Skutterudite PrOs_4Sb_{12}

The tunnel conductance in normal-metal / insulator / PrOs$_4$Sb$_{12}$ junctions is theoretically studied, where skutterudite PrOs$_4$Sb$_{12}$ is considered to be an unconventional superconductor. The conductance are calculated for several pair potentials which have been proposed in recent works. The results show that the conductance is sensitive to the relation between the direction of electric currents and the position of point nodes. We also show that the conductance spectra often deviate from the shape of the bulk density of states and that the sub gap spectra have peak structures in the case of the spin-triplet pair potentials. The results indicate that the tunnel conductance is a useful tool to obtain an information of the pairing symmetry.

cond-mat.supr-con↗

arXiv2003

Multiphase Superconductivity in Skutterudite PrOs_4Sb_12

We propose a model of nodal order parameters for the superconducting A and B - phase of skutterudite PrOs_4Sb_{12} and discuss the associated angular dependent magnetothermal conductivity at low temperatures. The model for the hybrid gap functions \De(k) containing an s- and g- wave parts is consistent with recent thermal conductivity experiments in PrOs_4Sb_12. In particular the model accounts for the data on polar an azimuthal field angle dependence of κ_zz(θ,ϕ). The low temperature behaviour of thermodynamic properties in zero field is also presented. We show that the effect of impurity scattering on a nodal hybrid gap function immediately leads the opening of a gap and related exponential behaviour of low temperature specific heat and thermal conductivity which is very different from d- wave superconductors.

cond-mat.supr-con↗

arXiv2003

Anomalous Flux Flow Resistivity in Two Gap Superconductor MgB_2

The flux flow resistivity associated with purely viscous motion of vortices in high-quality MgB_2 was measured by microwave surface impedance. Flux flow resistivity exhibits unusual field dependence with strong enhancement at low field, which is markedly different to conventional s-wave superconductors. A crossover field which separates two distinct flux flow regimes having different flux flow resistivity slopes was clearly observed in H//ab-plane. The unusual H-dependence indicates that two very differently sized superconducting gaps in MgB_2 manifest in the vortex dynamics and almost equally contribute to energy dissipation. The carrier scattering rate in two different bands is also discussed with the present results, compared to heat capacity and thermal conductivity results.

cond-mat.supr-con↗

arXiv2003

Antiferromagnetic Vortex Core of Tl_2Ba_2CuO_{6+x} Studied by Nuclear Magnetic Resonance

Spatially-resolved NMR is used to probe the magnetism in and around vortex cores of nearly optimally-doped Tl_2Ba_2CuO_{6+x} (Tc=85 K). The NMR relaxation rate 1/T_1 at Tl site provides a direct evidence that the AF spin correlation is significantly enhanced in the vortex core region. In the core region Cu spins show a local AF ordering with moments parallel to the layers at T_N=20K. Above T_N the core region is in the paramagnetic state which is a reminiscence of the state above the pseudogap temperature (T*~120 K), indicating that the pseudogap disappears within cores.

cond-mat.supr-con↗

arXiv2003

Normal-state Hall Angle and Magnetoresistance in quasi-2D Heavy Fermion CeCoIn_5 near a Quantum Critical Point

The normal-state Hall effect and magnetoresisitance (MR) have been measured in the quasi-2D heavy fermion superconductor CeCoIn_5. In the non-Fermi liquid region where the reistivity rho_xx exhibits an almost perfect T-linear dependence, the Hall angle varies as cot theta_H propto T^2 and the MR displays a strong violation of Kohler's rule. We demonstrate a novel relation between the MR and the Hall conductivity, Delta rho_xx/rho_xx propto (sigma_xy rho_xx)^2. These results bear a striking resemblance to the normal-state properties of high-T_c cuprates, indicating universal transport properties in the presence of quasi-2D antiferromagnetic fluctuations near a quantum critical point.

cond-mat.supr-con↗

arXiv2003

Subaru Deep Survey. IV. Discovery of a Large-Scale Structure at Redshift \simeq 5

We report the discovery of a large-scale structure of Lyman alpha emitters (LAEs) at z=4.86 based on wide-field imaging with the prime-focus camera (Suprime-Cam) on the Subaru telescope. We observed a 25' x 45' area of the Subaru Deep Field in a narrow band (NB, lambdaC=7126 A and FWHM=73 A) together with R and i'. We isolate from these data 43 LAE candidates down to NB=25.5 mag using color criteria. Follow-up spectroscopy of five candidates suggests the contamination by low-z objects to be ~ 20%. We find that the LAE candidates are clustered in an elongated region on the sky of 20 Mpc in width and 50 Mpc in length at z=4.86, which is comparable in size to present-day large-scale structures (we adopt H0=70 km/s/Mpc, Omega0=0.3, lambda0=0.7). This elongated region includes a circular region of 12 Mpc radius of higher surface overdensity (delta=2), which may be the progenitor of a cluster of galaxies. Assuming this circular region to be a sphere with a spatial overdensity of 2, we compare our observation with predictions by Cold Dark Matter models. We find that an Omega0=0.3 flat model with sigma8=0.9 predicts the number of such spheres consistent with the observed number (one sphere in our survey volume) if the bias parameter of LAEs is b \simeq 6. This value suggests that the typical mass of dark haloes hosting LAEs at z \simeq 5 is of the order of 10^12 Msolar. Such a large mass poses an interesting question about the nature of LAEs.

astro-ph↗

arXiv2002

Multiple Superconducting Phases in New Heavy Fermion Superconductor PrOs4Sb12

The superconducting gap structure of recently discovered heavy fermion superconductor PrOs4Sb12 was investigated by using thermal transport measurements in magnetic field rotated relative to the crystal axes. We demonstrate that a novel change in the symmetry of the superconducting gap function occurs deep inside the superconducting state, giving a clear indication of the presence of two distinct superconducting phases with twofold and fourfold symmetries. We infer that the gap functions in both phases have a point node singularity, in contrast to the familiar line node singularity observed in almost all unconventional superconductors.

cond-mat.supr-con↗

arXiv2002

Vortex fluctuations in underdoped Bi2Sr2CaCu2O8+d crystals

Vortex thermal fluctuations in heavily underdoped Bi2Sr2CaCu2O8+d (Tc=69.4 K) are studied using Josephson plasma resonance (JPR). From the data in zero magnetic field, we obtain the penetration depth along the c-axis, lambda_{L,c}(0) = 229 micrometers and the anisotropy ratio gamma(0) = 600. The low plasma frequency allows us to study phase correlations over the whole vortex solid (Bragg-glass) state. The JPR results yield a wandering length r_{w} of vortex pancakes. The temperature dependence of r_{w} as well as its increase with applied dc magnetic field can only be explained by the renormalization of the tilt modulus by thermal fluctuations, and suggest the latter is responsible for the dissociation of the vortices at the first order transition.

cond-mat.supr-con↗

arXiv2002

Subaru Deep Survey II. Luminosity Functions and Clustering Properties of Lya Emitters at z=4.86 in the Subaru Deep Field

We report on early results from deep and wide-field narrow-band imaging on a 543 arcmin^2 area of the Subaru Deep Field. We find 87 Lya emitters (LAEs) at z=4.86(+/-0.03) which are photometrically selected by a combination of two broad bands (R and i') and one narrow band (NB711; 7126A FWHM=73A). We derive the luminosity functions (LFs) of the LAEs at Lya luminosity and at UV-continuum (1700A) luminosity. The LFs show little evolution between z=3.4 and z=4.86 either in Lya or UV-continuum emission. The amplitude of the LAE LF tends to decline at the bright magnitudes more rapidly than that of the LBG LF at similar redshifts. We calculate the angular correlation function of our LAEs up to ~15 arcmin separations. The angular correlation w(theta) is found to increase with decreasing angular separations, showing a clear signal of clustering. It is also found that the distribution of LAEs shows a large density gradient with a scale of >~15 arcmin, which would indicate the existence of a large-scale structure of LAEs on >~20h^(-1) Mpc scales.We fit the observed correlation function by Aw theta^(-0.8) to find Aw=29arcsec^(0.8). The estimated correlation length is r0=3.5(+/-0.3)h^(-1)Mpc in comoving units (Omega_m=0.3 and Omega_Lambda=0.7), which is slightly larger than the value for z~4 LBGs with i'<26. We calculate the angular correlation function for two sub-samples of the 87 LAEs divided by Lya luminosity, UV-continuum luminosity, and Lya equivalent width (EW). The Lya bright sub-sample shows a larger correlation amplitude than the Lya faint sub-sample, while no significant difference is found for the sub-samples divided by UV-continuum luminosity or EW.

astro-ph↗

arXiv2002

Antiferromagnetic ordering and disappearance of pseudogap within the vortex core of Tl_2Ba_2CuO_{6+δ}

Spatially-resolved NMR is used to probe the magnetism in and around the vortex core of nearly optimally-doped Tl_2Ba_2CuO_{6+δ} (T_c=85K). The NMR relaxation rate T_1^{-1} at ^{205}Tl site, at which antiferromagnetic (AF) fluctuation can be monitored sensitively, provides a direct evidence that the AF spin correlation is significantly enhanced in the vortex core region. In the core region Cu spins show a local AF ordering with moment ~ 0.1μ_B parallel to the layers at T_N=20K. Above T_N the core region is in the paramagnetic state which is a reminiscence of the state above the pseudogap temperature (T*=120K), indicating that the pseudogap disappears within the core.

cond-mat.supr-con↗

arXiv2002

Free flux flow resistivity in strongly overdoped high-T_c cuprate; purely viscous motion of the vortices in semiclassical d-wave superconductor

We report the free flux flow (FFF) resistivity associated with a purely viscous motion of the vortices in moderately clean d-wave superconductor Bi:2201 in the strongly overdoped regime (T_c=16K) for a wide range of the magnetic field in the vortex state. The FFF resistivity is obtained by measuring the microwave surface impedance at different microwave frequencies. It is found that the FFF resistivity is remarkably different from that of conventional s-wave superconductors. At low fields (H<0.2H_c2) the FFF resistivity increases linearly with H with a coefficient which is far larger than that found in conventional s-wave superconductors. At higher fields, the FFF resistivity increases in proportion to \sqrt H up to H_c2. Based on these results, the energy dissipation mechanism associated with the viscous vortex motion in "semiclassical" d-wave superconductors with gap nodes is discussed. Two possible scenarios are put forth for these field dependence; the enhancement of the quasiparticle relaxation rate and the reduction of the number of the quasiparticles participating the energy dissipation in d-wave vortex state.

cond-mat.supr-con↗

arXiv2002

Gap Function with Point Nodes in Borocarbide Superconductor YNi_2B_2C

To determine the superconducting gap function of a borocarbide superconductor YNi_2B_2C, the c-axis thermal conductivity kappa_zz was measured in a magnetic field rotated in various directions relative to the crystal axes. The angular variation of kappa_zz in H rotated within the ab-plane shows a peculiar fourfold oscillation with narrow cusps. The amplitude of this fourfold oscillation becomes very small when H is rotated conically around the c-axis with a tilt angle of 45 degrees. Based on these results, we provide the first compelling evidence that the gap function of YNi_2B_2C has POINT NODES, which are located along the [100] and [010]-directions. This unprecedented gap structure challenges the current view on the pairing mechanism and on the unusual superconducting properties of borocarbide superconductors.

cond-mat.supr-con↗