arXiv subjects

Katsuya Shimizu

Publications and source records attributed to Katsuya Shimizu.

24 records · Page 2Linked to original sources

arXiv2014

Collapse of CuO Double Chains and Suppression of Superconductivity in High-Pressure Phase of YBa$_2$Cu$_4$O$_8$

The crystal structure and electrical resistivity of YBa$_2$Cu$_4$O$_8$ (Y124) were studied under high pressure up to 18 GPa using diamond-anvil cells, respectively, in order to clarify its conduction mechanism. Y124 causes the first-order phase-transition into the orthorhombic Immm at pressure around 11 GPa. The high-pressure phase (HPP) also shows the superconductivity, while the manner of temperature dependence of electrical resistance and the pressure dependence of transition temperature, Tc, drastically change above 11 GPa. The CuO$_2$ plane persists in HPP but the CuO double chains collapse with the phase transition and transform into three-dimensional Cu-O network, resulting in the renewal of conduction system.

cond-mat.supr-con↗

arXiv2013

Interplay between Charge and Magnetic Ordering in YbPd

The pressure-temperature phase diagram of an intermediate-valence compound YbPd was revealed via simultaneous ac-calorimetry and electrical resistivity measurements. Two successive structural phase transition temperatures, $T_1$ = 125 K and $T_2$ = 110 K, are found to decrease with increasing pressure. The magnetic ordering transition at $T_{\rm N} ~sim$ 1.9 K decreases monotonically up to 1.7 GPa and disappears discontinuously at $P_{\rm c} sim$ 1.9 GPa, where the structural phase transition at $T_2$ is also suppressed. At $P_{\rm c}$, enhancement of the effective mass and residual resistivity are observed. Another probable magnetic phase transition, however, is found to take place at $T_{\rm ML} sim$0.3 K and smoothly varies even when crossing $P_{\rm c}$. Structural phase transitions at ambient pressure were also studied by a single crystal X-ray diffraction measurement. Below $T_2$, a tetragonal lattice distortion with doubling of the unit cell along the c-axis is observed, and thus there are two inequivalent Yb-sites below $P_{\rm c}$. These results indicate that one Yb-site, having larger valence configuration and thus smaller Kondo temperature, orders at $T_{\rm N}$. The other phase transition at $T_{\rm ML}$ seems to couple to the crystal structure for $T_2 < T < T_1$. YbPd is a unique system exhibiting magnetic orderings in metallic charge-ordered Yb systems.

cond-mat.str-el↗

arXiv2013

Charge ordering in the intermediate valence magnet YbPd

An x-ray diffraction study reveals the charge ordering structure in an intermediate valence magnet YbPd with a CsCl-structure. The valence of the Yb ions forms an incommensurate structure, characterized by the wavevector (+-0.07 +-0.07 1/2) below 130 K. At 105 K, the incommensurate structure turns into a commensurate structure, characterized by the wavevector (0 0 1/2). Based on the resonant x-ray diffraction spectra of the superlattice reflections, the valences of the Yb ions below 105 K are found to be 3+ and 2.6+. The origin of the long wavelength modulation is discussed with the aid of an Ising model having the second nearest neighbor interaction.

cond-mat.str-el↗

arXiv2011

Experimental and theoretical evidence for pressure-induced metallization in FeO with the rock-salt type structure

Electrical conductivity of FeO was measured up to 141 GPa and 2480 K in a laserheated diamond-anvil cell. The results show that rock-salt (B1) type structured FeO metallizes at around 70 GPa and 1900 K without any structural phase transition. We computed fully self-consistently the electronic structure and the electrical conductivity of B1 FeO as a function of pressure and temperature, and found that although insulating as expected at ambient condition, B1 FeO metallizes at high temperatures, consistent with experiments. The observed metallization is related to spin crossover.

cond-mat.mtrl-sci↗

arXiv2009

Pressure-induced Superconductivity in Crystalline Boron Nanowires

We report high-pressure induced superconductivity in boron nanowires (BNWs) with rhombohedral crystal structure. Obviously different from bulk rhombohedral boron, these BNWs show a semiconductor-metal transition at much lower pressure than bulk boron. Also, we found these BNWs become superconductors with Tc=1.5 K at 84 GPa, at the pressure of which bulk boron is still a semiconductor, via in-situ resistance measurements in a diamond anvil cell. With increasing pressure, Tc of the BNWs increases. The occurrence of superconductivity in the BNWs at a pressure as low as 84 GPa probably arises from the size effect.

cond-mat.supr-con↗

arXiv2007

Pressure induced magnetic ordering in Yb2Pd2Sn with two quantum critical points

Pressure induced long range antiferromagnetic order is discovered in Yb2Pd2Sn by measuring the electrical resistivity under pressure up to 5.0 GPa. Magnetic ordering is observed above about 1.0 GPa, being the lowest pressure in Yb-intermetallics showing pressure induced magnetic ordering, Unexpectedly, ordering disappears above about 4.0 GPa, giving rise to the first observation of the appearance of two quantum critical points persisting in a broad range of pressure within a single material.

cond-mat.str-el↗