Quantum Probes for High-Pressure Superconductivity

Introduction

Materials under high pressure exhibit exciting topics such as the superconductivity (SC) of hydrogen-rich molecular compounds (super-hydrides) in the long-standing search for room-temperature SC. While pressures above 100 GPa can be routinely created in a diamond anvil cell (DAC), the tiny sample volume almost precludes the use of non-optical detection schemes to probe the sample properties.

Project Idea

The project idea is to integrate nitrogen-vacancy (NV) centers in the DAC and use the optically detected magnetic resonance (ODMR) of the NV electronic spin to image the Meissner effect. The project relies on our first results where we engineered NV centers on the tip of a diamond anvil and adapted quantum sensing methods to detect pressure-induced magnetic and SC transitions under tens of GPa.

Methodology

By controlling the stress distribution to achieve hydrostatic conditions that preserve the NV symmetry, we have extended this method above 100 GPa, reaching the pressure range of existence of SC in super-hydrides. These materials need to be synthesized at high pressure by laser heating, which induces strong inhomogeneities on a micron scale.

Imaging Techniques

We will use widefield NV magnetometry to locally image the Meissner effect and the flux trapping in the SC grains, whereas conventional measurements average over the entire DAC geometry and therefore discard all local information.

Crystal Structure Determination

By operating NV sensing on a synchrotron beamline, we will determine the crystal structure of the super-hydrides after the synthesis in the DAC. We will finally couple the spatial detection with noise spectroscopy to measure the temporal current fluctuations in the SC. These methods will be implemented in parallel on Hg-doped cuprates as testbed systems.

Complementary Task

In a complementary task, we will investigate the implementation of NV-based microscale nuclear magnetic resonance in the DAC. Our goal will be to exploit the sensitivity of a dense ensemble of NV centers to detect the chemical shift of the nuclear spins in the sample.