Invited Article: High-pressure techniques for condensed matter physics at low temperature

Abstract

Determination of the variation of the fluorescence line positions of ruby, strontium tetraborate, alexandrite, and samarium-doped yttrium aluminum garnet with pressure and temperature J. Appl. Phys. 110, 023521 (2011) Condensed matter experiments at high pressure accentuate the need for accurate pressure scales over a broad range of temperatures, as well as placing a premium on a homogeneous pressure environment. However, challenges remain in diamond anvil cell technology, including both the quality of various pressure transmitting media and the accuracy of secondary pressure scales at low temperature. We directly calibrate the ruby fluorescence R1 line shift with pressure at T = 4.5 K using high-resolution x-ray powder diffraction measurements of the silver lattice constant and its known equation of state up to P = 16 GPa. Our results reveal a ruby pressure scale at low temperatures that differs by 6% from the best available ruby scale at room T. We also use ruby fluorescence to characterize the pressure inhomogeneity and anisotropy in two representative and commonly used pressure media, helium and methanol:ethanol 4:1, under the same preparation conditions for pressures up to 20 GPa at T = 5 K. Contrary to the accepted wisdom, both media show equal levels of pressure inhomogeneity measured over the same area, with a consistent ⌬P / P per unit area of Ϯ1.8 % / ͑10 4 m 2 ͒ from 0 to 20 GPa. The helium medium shows an essentially constant deviatoric stress of 0.021Ϯ 0.011 GPa up to 16 GPa, while the methanol:ethanol mixture shows a similar level of anisotropy up to 10 GPa, above which the anisotropy increases. The quality of both pressure media is further examined under the more stringent requirements of single crystal x-ray diffraction at cryogenic temperature. For such experiments we conclude that the ratio of sample-to-pressure chamber volume is a critical parameter in maintaining sample quality at high pressure, and may affect the choice of pressure medium.

Hidden one-dimensional spin modulation in a three-dimensional metal

“…At 16.1 GPa, the highest pressure that antiferromagnetism was directly observed, the monoclinic splitting of the (0, 1, 1) order remains clear (Fig. 1f), although the longitudinal line shapes are slightly broadened above the instrument resolution 21 . Here, both the spontaneously twinned single crystals and near-resolutionlimited diffraction profiles testify to the quasi-hydrostatic pressure condition in the sample environment.…”

“…At 16.1 GPa, the pressure inhomogeneity across our sample is estimated to be either 0.30 GPa FWHM using a comparison of the FWHM of lattice diffraction with that of the instrument resolution (Fig. 1), accounting for the sample-specific bulk moduli 28 , or a full range of ± 0.19 GPa from previous pressure chamber studies under similar conditions 21 . The pressure inhomogeneity is typically linearly proportional to the absolute pressure in our assembly 21 .…”

“…A NaI detector was used for measuring X-ray intensity, but no polarization analyser was used for magnetically diffracted X-rays. Using a six-circle Huber c-diffractometer in the vertical diffraction geometry, a high resolution in momentum space better than 1 Â 10 À 3 Å À 1 FWHM is achieved for longitudinal scans 11,20,21 . All measurements were made at the base temperature of the cryostat, which varied between 3.5 and 5.5 K for various cooldowns.…”

“…1), accounting for the sample-specific bulk moduli 28 , or a full range of ± 0.19 GPa from previous pressure chamber studies under similar conditions 21 . The pressure inhomogeneity is typically linearly proportional to the absolute pressure in our assembly 21 .…”

“…By comparison with the typical total diamond thickness of 3.2-4.5 mm with normal anvils, this wide-angle partial perforation design significantly reduces the elastic X-ray scattering background, while still reaching at least 17 GPa for 800 mm culet-sized anvils. The pressure medium was a 4:1 methanol:ethanol solution, and the cells were equipped with a helium-membrane controlled in situ pressure tuning mechanism at low temperature 21 . At 16.1 GPa, the pressure inhomogeneity across our sample is estimated to be either 0.30 GPa FWHM using a comparison of the FWHM of lattice diffraction with that of the instrument resolution (Fig.…”