Quantum materials
ISIS's Quantum Sciences and Materials research focuses on novel properties due to quantum effects, including magnetism, superconductivity, ferroelectricity, topological order, quantum phase transitions, semiconductors, and quantum-information technology materials.
Why quantum materials research?
Neutrons and muons are ideal probes for studying quantum properties, as they interact with matter in a gentle and non-destructive way, and they are sensitive to both the nuclear and the electronic structure of materials. The way that they measure material properties is highly complementary, allowing researchers to form a deeper understanding of the materials they study. For example, to thoroughly explain fundamental phenomena like dynamics of hydrogen bonds, diffusion of atoms, and catalysis, one needs to consider quantum effects, such as nuclear quantum tunnelling and delocalisation. Nuclear quantum effects can be observed on Vesuvio, using the techniques of neutron Compton scattering.
Every experiment at ISIS could be considered a quantum beam experiment exploiting the quantum properties of neutrons and muons. There are also a few pure quantum beam science experiments that are performed at ISIS to reveal the behaviour and interactions of the smallest particles of matter. These experiments highlight the strange and often counterintuitive properties of the quantum world, such as superposition, entanglement, tunnelling, that challenge our classical understanding.
Quantum materials are materials that exhibit novel properties due to quantum effects such as superconductivity, magnetism, topological order, and quantum phase transitions, and quantum science provides theoretical and experimental tools for understanding and controlling these materials.
Some of the top areas in quantum materials research from the last 40 years at ISIS
Quantum research at ISIS
Semiconductors
Semiconductors are essential in modern electronics and optoelectronics, controlling electron flow in microscopic circuits. They are used in devices like computers, solar cells, lasers, and LEDs. ISIS has a long history of investigating the performance, stability, and defects of semiconductors like silicon, germanium, gallium arsenide, and perovskites, as well as their changes under various conditions like temperature, pressure, and electric field. For example, ISIS has been used to measure:
-how electronic charges move through in bulk silicon. The quasiparticle lifetime is an indicator of cleanliness in chip manufacturing and also determines the performance of solar cells.
-the assembly of conducing polymers for lightweight and low-cost organic solar cells. Understanding the structure at the nanoscale is necessary to produce reproducible cost-efficient large area solar cells that can be printed onto a surface.
ISIS provides a versatile suite of instruments for researchers to explore the properties and potential of materials and devices for semiconductor technology. For example, ChipIr is a beamline dedicated to irradiating electronic devices with neutrons to learn how they are affected by cosmic rays. A cosmic ray hitting a semiconductor device can change the information stored in a device’s memory or damage the electronics more permanently. By using the intense neutron beam available at ISIS, an hour of testing can simulate hundreds of years of flying time in an aircraft, leading to a better understanding of how different device designs mitigate against the natural cosmic radiation.
Superconductivity
Superconductivity is a phenomenon that occurs for certain materials, where the material conducts electricity without resistance and expels magnetic fields from their interior below a critical temperature. The goal is to find a superconductor that operates at room temperature, as this would revolutionize our energy systems. Electrons interact with the vibrations of the crystal lattice and form into pairs that can travel freely through the crystal lattice without scattering. Soon after ISIS opened, it was used to determine the structure of the new copper oxide superconductor YBCO.
The mechanism and the conditions for superconductivity are still not fully understood. This is especially true for the high-temperature superconductors that can operate above the boiling point of liquid nitrogen, such as cuprates, iron-based compounds, fullerides, pnictides, and organic superconductors. Neutron and muons are valuable tools to study the superconducting state and magnetic fluctuations in these materials. Understanding the mechanism that allows high-temperature superconductivity is a very active field of research.
Magnetism
Magnetism is one of the most familiar properties of materials that we come across in everyday life, but it is surprisingly complex. It arises from the spin and orbital motion of electrons in atoms, and how they interact. Most magnetic materials that are cooled below a certain temperature enter a state where their magnetic moments order into a pattern controlled by the symmetry of the material and the interactions between the atoms. Neutron diffraction allows this pattern to be determined, while neutron spectroscopy can measure the strength of these interactions within the material.
Magnetism can also couple to other properties of materials. Magnetostructural interactions can allow materials to display both magnetic and ferroelectric moments, allowing electric fields to control magnetism and vice versa in multiferroic compounds. The diffractometer SXD has been used to study the noncollinear magnetic order of new magnetoelectric materials.
The magnetic field strength, direction and order in a material in layers only a few nanometres thick can be determined on the reflectometer POLREF. The instrument has been used to measure the helical magnetic structure responsible for the topological Hall effect in epitaxial B20 thin films, and to investigate the magnetic field induced phase transition in FeRh thin films and the modifications of the magnetic phase transition after ion beam irradiation.
High-temperature superconductivity is a key research area, examining why certain compounds transition from magnetic insulators to superconductors. Muons are used at ISIS to study magnetic fields associated with such ordering. Magnetic moments within materials fluctuate due to thermal motion or quantum mechanical zero-point energy near absolute zero temperature. Inelastic neutron scattering measures these fluctuations, comparing them to theoretical predictions. Some materials avoid magnetic ordering at the lowest temperatures due to frustrated interactions between their magnetic moments. Even the smallest opportunity to satisfy interactions is seized by magnetic moments, leading to weakly magnetic states.
