Precise low temperature and high pressure apparatus using herium on an experimental basis

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High pressure techniques at low temperatures have been proved to be very powerful tools in studies of recent topics related to the fundamental problems in strong correlated electron systems such as high-Tc superconductors, heavy fermion compounds and organic conductors. One of the main difficulties in high pressure techniques at low temperatures is to obtain uniform pressures at which reliable results are given, In, order to generate hydrostatic pressures at low temperatures we try to make a high pressure apparatus using herium on a experimental basis.In the first step, in order to measure the superfluid fraction of the A phase of ^3He we made a high pressure equipment combined with a superconducting magnet using ^3He as a pressure transmitting medium. It works at high pressures up to 29 bar and at temperatures down to 34mK.Next, we tried to make an apparatus by which the unidirectional pressure can bbe applied on a fragile single crystal at low temperatures. Using this apparatus we made resistivity measurements of alpha -( BEDT-TTF )_2 KHg(SCN)_4 in the conducting plane under uniaxial stress below 1K.We used the cold bellows in which a pressure is variable by changing _4He gas at room temperature because of no solidification of liquid _4He up to 25 bar. The effective diameter of the bellows is about 70mm and the pressure amplification is about 100-200.Similar bellows are adapted to high pressure generation up to 3OGPa using a diamond anvils combined with a dilution refrigerator and a superconducting magnet. This system is expected tobe a powerful tool in studies of recent and future topics related to the fundamental problems.