Future science and research: few ideas to a boiler plate.
High pressure group at the Geophysical Laboratory has several important contributions to
the expanding field of materials research at high pressure. Emerging access to the most
fundamental properties of materials at high-pressure, such as phonon and electron quasiparticle excitations, and understanding of their interactions, will eventually promote the
field of high-pressure research to the status of the most advanced experimental method in
materials science, and in condensed matter research. The future of the high-pressure
science will be determined to a large extent by the successful application of the existing
and emerging techniques to a multitude of unsolved problems in condensed matter
physics, geosciences, and materials sciences.
Superconductivity
Over the years we have introduced many critical improvements enabling high
pressure experiments on superconductors. The field of possible research is enormous, and
I have concentrated on only a few important areas, mostly superconductivity in elements
and high-Tc materials, and related properties of strongly correlated materials (MottHubbard insulators). The research has brought to our attention many instances when
superconducting temperature is at its maximum close to structural instabilities in a
material, being most prominent at the conditions when covalent bonds become unstable,
e.g., at insulator-metal transitions, at crossover from 2-dimensional to 3-dimensional
solid, etc. As such, this research is at the forefront of current quest for mechanisms and
highest possible critical temperature of superconductivity. The lab’s infrastructure allows
now in-depth research in many directions, and future developments in the technique will
make it more accessible for less experienced user – students, freshly hired fellows,
postdocs. Continuing support in experimental developments and manpower will help to
keep the GL’s competitive edge.
Hydrogen and hydrogen-rich materials
Hydrogen is predicted to be a high temperature superconductor, with a Tc close to
room temperature. Needless to say, the experimental challenges in achieving this goal are
tremendous. Even the metallization of hydrogen is yet to be discovered and pressures as
high as 400-500 GPa may be required for that. However, we are now approaching this
goal. First, the magnetic susceptibility technique has become very sensitive and with
further ongoing improvements of the technique, is suitable for measurements of very
small samples typical for 300 GPa experiments. With the emerging new micro- and
nanofabrication capabilities (see below), the experimental challenges of achieving
metallization of hydrogen and measuring its properties in the predicted superconducting
state may be addressed in coming few years.
Developments of the high-pressure techniques.
Recent advances in diamond-anvil cell methods have expanded the domain of static pressure
experiments well into the megabar pressure range. Despite the array of new techniques, probing
the magnetic properties of materials under the most extreme conditions reached in the laboratory
had not been possible because of the small sample sizes involved and the low sensitivity of
conventional methods. Such magnetic measurements are widely considered the most reliable for
identifying and characterizing superconductivity and are crucial for tracking the superconducting
states of metals, including novel metals that form only at very high pressures. These obstacles
have been overcome recently with the development of ultra-sensitive induction techniques for
magnetic measurements in the diamond cell. Using these techniques, we completed the first
magnetic measurements of superconductivity into the megabar pressure range and proceeded
further to 230 GPa. These techniques should be further improved with the micro/nanofabrication
technologies. Critical aspects of the new technology require FIB facility (available now at GL),
nano-photolithography tools (not available), and few other components of a typical clean-room
facilities routinely used at universities for nano- and micro-fabrication work.
One possible extension of the available techniques would be to manufacture coils for
magnetic measurements and also to use a protective CVD diamond layer, similar to “designer
anvil”. Another approach would allow building a “designer” gasket, with embedded electrodes
and sample (or sample volume for loading gases and fluids, e.g. hydrogen). The FIB technology
combined with photolithography and other clean-room facility tools provides a manifold of
functional approaches to manipulate, prepare, and attach samples of very small sizes (down to
nano-scale) to the electrodes.
The clean room facility would be also of great potential value for CVD diamond growth
projects involving fabrication of novel electronic and optical devices, which could be applied not
only in the high-pressure environment, but also at normal conditions, or in hot and chemically
aggressive conditions.
The estimated cost of new facilities may be in the range from few to tens of millions of
dollars, depending on the availability of experimental labs and the set of tools we may need (CVD
growth, TEM, nanolithography, and similar equipment).
Summary
What could win next prize?
1. Room temperature superconductivity
2. Metallic/superconducting hydrogen
3. Novel states of matter (fluid superconducting hydrogen or hydrides,
etc..)
4. Going beyond LDA to calculate electronic structure of strongly
correlated materials from first principles
We are working in these directions using pressure variable, but we need
a better infrastructure.
What is missing? few experimental needs listed below
1)
typical clean-room facility items ( clean room environment, FIB,
photolithography, plasma etching/deposition, ion implantation, etc..) – some of
these are already available
2)
tailored growth (CVD and high-pressure synthesis) ) of diamond anvils with
desired properties
3)
TEM and other analytical tools at the nanoscale
4)
Low temperature environment – dilution refrigerator
5)
High temperature environment - pulsed laser heating infrastructure (lasers,
detectors)
6)
Laser processing of samples, diamonds, gaskets – femtosecond lasers, UV
lasers