Chieko Terakura

Manometer extension for high pressure measurement: Nuclear quadrupole resonance study of Cu2O with a modified Bridgman anvil cell up to 10 GPa

We report (63)Cu nuclear quadrupole resonance (NQR) measurement of Cu(2)O under pressure up to about 10 GPa at low temperatures. Because the lattice parameter of Cu(2)O changes with increasing pressure, the electric field gradient at the Cu site also changes correspondingly with pressure. This enables us to use the Cu(2)O as an in situ manometer for high pressure nuclear magnetic resonance/NQR up to about 9 GPa.

High pressure effects revisited for the cuprate superconductor family with highest critical temperature

How to enhance the superconducting critical temperature (Tc) has been a primary issue since the discovery of superconductivity. The highest Tc reported so far is 166 K in HgBa2Ca2Cu3O8+δ (Hg1223) at high pressure of 23 GPa, as determined with the reduction onset, but not zero, of resistivity. To clarify the possible condition of the real maximum Tc, it is worth revisiting the effects of pressure on Tc in the highest Tc family. Here we report a systematic study of the pressure dependence of Tc in HgBa2CaCu2O6+δ (Hg1212) and Hg1223 with the doping level from underdoped to overdoped. The Tc with zero resistivity is probed with a cubic-anvil-type apparatus that can produce hydrostatic pressures. Variation, not only increase but also decrease, of Tc in Hg1212 and Hg1223 with pressure strongly depends on the initial doping levels. In particular, we confirm a maximum Tc of 153 K at 22 GPa in slightly underdoped Hg1223.

Pressure-induced transition from a spin glass to an itinerant ferromagnet in the half-doped manganite L0.5Ba0.5MnO3 (L=Sm and Nd) with quenched disorder

The effect of quenched disorder on the multiphase competition has been investigated by examining the pressure phase diagram of half doped manganite Ln0.5B0.5MnO3 (Ln = Sm and Nd) with A-site disorders. Sm0.5Ba0.5MnO3, a spin glass insulator at ambient pressure, switches to a ferromagnetic metal with increasing pressure, followed by a rapid increase of the ferromagnetic transition temperature Tc. The rapid increase of Tc was confirmed also for Nd0.5Ba0.5MnO3. These observations indicate that the unusual suppression of the multicritical phase boundary in the A-site disordered system, previously observed as a function of the averaged A-site ionic radius, is essentially controlled by the pressure and hence the band width. The effect of quenched disorder is therefore much enhanced with approaching the multicritical region.

Pressure-Induced Transition from a Correlated Insulator to a Fermi Liquid Observed in Geometrically Frustrated Hg2Ru2O7 Pyrochlore

Recently discovered pyrochlore oxide, Hg 2 Ru 2 O 7 , shows a first order metal–insulator transition at T ∼107 K. The effect of hydrostatic pressure on the M–I transition was studied by measuring the temperature dependent resistivity ρ( T ) up to 12 GPa. The application of pressure suppressed the low temperature insulating state and eventually induced a transition from a correlated insulator to a metal at around 5 GPa. With decreasing temperature, ρ( T ) in the metallic phase showed a rapid decrease at around T * ∼40 K, likely representing the onset of a coherent–incoherent crossover, and eventually a well defined T 2 -dependence at low temperatures, indicative of the presence of coherent quasi-particles. All these results point the formation of a Fermi liquid with an enhanced mass in the metallic state of this geometrically frustrated system, located close proximity to the correlation driven metal–insulator transition.

High Pressure 63Cu Nuclear Quadrupole Resonance Measurements in Cu2O up to 10 GPa Using Modified Bridgman Anvil Cell

63 Cu Nuclear Quadrupole Resonance (NQR) measurements in Cu 2 O have been performed under high pressures ( P ) up to 10 GPa at 1.6 K. The pressure cell, based on a technique using modified Bridgman anvils with a liquid pressure medium in Teflon capsule, generates nearly hydrostatic pressure with a volume of 1 ×10 -3 ml, which is sufficiently large for the detection of NMR/NQR signals. The narrow 63 Cu NQR was observed at 26.82 MHz ( P = 0), and the resonance frequency varies linearly with P up to 9 GPa. This result shows that Cu NQR line in Cu 2 O becomes a convenient and precise P manometer.