Diamond anvil cells (DACs) have become indispensable tools for exploring the electrical properties of materials at extreme pressures. By compressing microscopic samples between two diamond anvils, pressures comparable to those found deep within planetary interiors can be achieved, while maintaining optical and electrical access to the sample. Resistivity measurements under these conditions provide valuable information on pressure-induced phase transitions, superconductivity, metallization, and changes in electronic structure.

Electrical resistivity measurements under pressure allows to explore:

• Superconducting materials : Rapidly map zero-resistance transitions in room-temperature hydride candidates and quantum materials;
• Electronic Phase Transitions: Track pressure-induced insulator-to-metal switching in real time;
• Geophysics & Deep-Earth Science: Measure electrical conductivity of minerals under simulated core-mantle conditions.

DAC resistivity measurements are frequently combined with temperature variation, magnetic fields, optical spectroscopy or X-ray diffraction to enable a full characterization of how materials behave under extreme conditions.

From our catalogue, the diamond anvil cells that are usually recommended for resistivity measurements, we can cite the Diacell ChicagoDAC or the Diacell® CryoDAC-PPMS which are listed under the Electrical category. The easyLab® easyCell 30 and the easyLab® Pcell15/30 are alternative clamp piston-cylinder cells that are more suitable for millimeter size samples and low pressures (P< 3 GPa).

In DAC experiments, resistivity is commonly measured using either two-probe or four-probe configurations.

Achieving reliable electrical contacts is often the most critical step in the experiment. This relies entirely on manual micro-wiring of the sample along with a custom gasket preparation.

Electrical contacts :

• Typically fabricated from thin metal foils or micro-wires such as gold, platinum, or tungsten;
• Positioning micron size wires and contact alignment onto a small sample requires steady hands, high-magnification optics, and micromanipulators;
• To significantly facilitate this step Almax easyLab offers diamond anvils with deposited gold patterns that enable electrical contact with the sample via  silver epoxy, silver paint or even soft solder.

Custom gasket preparation: 

• Gasket insulation is required for such measurements because standard metal gaskets (Rhenium, Steel and BeCu) short out the measurement wires upon contact;
• Insulating layers—including alumina, cubic boron nitride (cBN), or epoxy-based materials—prevent short circuits between the leads and the metallic gasket;
• Almax easyLab provides an effective solution to bypass the gasket insulation: the intelligent diamond anvils which feature metal probes protected by a CVD diamond layer.

Pressure Media and Environment: 

• To maintain hydrostatic or quasi-hydrostatic pressure conditions, a pressure-transmitting medium such as a noble gas, liquid, or soft solid is usually added.

Electrical resistivity measurements in diamond anvil cells are technically very demanding. There are a few other critical points to keep in mind, such as:

• Sample Geometry and Size: small dimensions (typically only a few micrometers thick and wide) introduce significant uncertainty in sample geometry, therefore many experiments focus on relative changes in resistivity rather than absolute values. An efficient solution from Almax easyLab is the new PulseCube – UV Laser that achieves clean cuts and high geometric accuracy when cutting small samples and fabricating masks for electrode deposition.
• Electrical Contact Stability : during compression, contacts can deform, lose connection to the sample, or short to the gasket;
• Non-Hydrostatic Stress Effects : at high pressures, pressure media may become less effective, resulting in non-uniform stress distributions;
• Measurement Sensitivity : the small sample volume often produces very low resistance signals, requiring low-noise electronics, careful shielding, and excellent thermal stability.

Success requires careful experimental design, precise micro-fabrication, and strong control over pressure and measurement conditions.

When properly implemented, these techniques provide unparalleled insight into how materials behave under extreme compression. Despite their complexity, DAC-based resistivity measurements offer unique advantages:

• Access to ultra-high pressures beyond the reach of large-volume presses;
• Compatibility with extreme temperatures and magnetic fields;
• Ability to correlate transport data with structural and spectroscopic probes in situ.

These capabilities make DACs indispensable for cutting-edge research in condensed matter physics, materials science, and geophysics.