Masashi Morishita

Magnetoresistance of RuO2-based resistance thermometers below 0.3 K

Abstract We have determined the magnetoresistance of RuO 2 -based resistors (Scientific Instruments (SI) RO-600) between 0.05 and 0.3 K in magnetic fields up to 8 T. The magnetoresistance is negative around 0.5 T and then becomes positive at larger fields. The magnitude of the negative magnetoresistance increases rapidly as the temperature is lowered, while that of the positive magnetoresistance has smaller temperature dependence. We have also examined the temperature dependence of the resistance below 50 mK in zero magnetic field. It is described in the context of variable-range hopping (VRH) conduction down to 15 mK. Hence, the resistors can be used as thermometers down to at least 15 mK.

Charge density waves and superconductivity in 2H-TaSe2

Charge density waves (CDW) in 2H-TaSe2 were studied by use of an ultra-low temperature STM over a wide temperature range between 90 mK and 300 K. The superlattice structure due to formation of the commensurate CDW was clearly seen below 90 K in atomically resolved STM images, which is consistent with a band calculation. Besides a known CDW energy gap of 80 meV a new small gap structure of a few meV width in the vicinity of the Fermi level was observed in tunneling spectroscopy data at low temperatures. Superconductivity in 2H-TaSe2 (Tc≈200 mK) studied by resistivity measurements is also discussed.

Construction of an ultra-low temperature scanning tunneling microscope

We describe designs and specifications of an ultra-low temperature scanning tunneling microscope developed at University of Tsukuba. It works over a wide temperature range between 90 mK and 300 K with atomic resolution as well as the capability of site specific tunneling spectroscopy. The microscope is now being used to study superconductivity and charge density waves in materials at millikelvin temperatures.

Low Temperature Heat-Capacities of Liquid 3He Thin Films

We have measured the heat capacity of3He thin films adsorbed on graphite at an areal density of 15.0 nm−2down to as low as 100 μK. The second-layer3He behaves as a degenerate 2D Fermi fluid in the whole temperature range we studied. We observed no anomalous behavior in the heat capacity near 3 mK in contradiction to the recent report by other workers. This indicates that possible superfluid transitions would be below 100 μK. Instead, a small and temperature-independent contribution to the heat capacity was observed, which we attribute to nuclear-spin degrees of freedom in glassy solid3He trapped in substrate heterogeneities.

Low Temperature Heat Capacities of Submonolayer Solid 3He

AbstractHeat capacities (C) of3He submonolayer solids adsorbed on a graphite surface are measured down to 100 μK, a factor of twenty lower temperatures than previous work. At a real densities near the commensurate

Heat capacity of kagome 3He monolayer film on graphite

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Heat Capacities of Monolayer 3He Fluids Floated on A Superfluid 4He Thin Film

solid (6.4 nm−2), an anomalous temperature dependence, C ∝ 1/T, is observed in a wide temperature range over two orders of magnitude (0.1 ≤ T ≤ 20mK). Similar behavior was observed for the commensurate