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HomeScienceScientists identify quantum-based model system to better understand new materials

Scientists identify quantum-based model system to better understand new materials

Researchers have identified a model system of quantum critical points to better understand new materials. This model system can help understand unusual behaviors in materials close to a quantum critical point and can be used to understand entanglement and quantum computing.

Silicon and other well-studied materials are understood with the help of well-established frameworks, such as the widely used density functional theory. However, new materials such as transition metal oxides, manganates, rutinates and iridates are difficult to understand using these structures. The unique properties of these materials, such as sensitivity to small perturbations, make them promising for advanced applications in devices such as sensors, GPS and RAM memory.

Prof. NS Vidhyadhiraja of the Jawaharlal Nehru Center for Advanced Scientific Research (JNCASR), an autonomous unit of the Department of Science and Technology (DST), recently led a team of researchers to conduct a study focusing on a specific situation in quantum physics, called “local quantum criticality” that occurs in certain materials. His study, published in Physical examination B on May 1, 2023, was supported by the Science and Engineering Research Board (SERB), an institution attached to the Department of Science and Technology (DST). SERB has now been absorbed by ANRF.

Professor Vidhyadhiraja says his research in many-body quantum physics primarily focuses on the concept of emergence in condensed matter. He notes: “Drawing parallels with the organization of bees, birds and ants, we can say that the behavior of electrons in materials cannot be predicted by studying individual electrons, but depends on their collective interactions. “Environmental conditions, such as temperature, are important in determining the final order of the materials.”

Previous research focused on vanadium oxide, a material that undergoes a dramatic transition from insulator to metal and back again when subjected to small changes in pressure or temperature. Beyond its change in conductivity, vanadium oxide also alters its optical properties, becoming opaque or transparent, in response to small changes in temperature, pressure, doping and magnetic fields.

Specifically, the present study focuses on critical quantum transitions between metal and insulators that are local in nature and occur at zero kelvin. Imagine having a material where some electrons move around and are influenced by a critical point in its phase diagram. The quantum critical point, which is located at zero kelvin and cannot be accessed experimentally, has consequences on the properties of the system at finite temperatures and pressures. Thus, in this study, the researchers found a model system that contains a wide range of quantum critical points.

The theoretical model that studies this critical behavior is called the “modified periodic Anderson model (MPAM)”. It has been observed that in some cases, the way electronic energy levels are distributed changes dramatically at the critical point.

The researchers discovered a distinct energy distribution pattern called the “smooth gap spectrum” in MPAM, which is, in fact, a three-orbital lattice model. This unique energy distribution arises at a critical point when the material transitions from a metal to an insulator. A specific parameter, which describes the relationship between temperature and energy levels, changes in a peculiar way and becomes independent of temperature precisely at the critical point. This leads to the formation of the spectrum of soft gaps.

Professor Vidhyadhiraja concludes: “These findings can help characterize quantum criticality and understand unusual behaviors in materials close to a quantum critical point. The potential of this study lies in understanding entanglement and possibly quantum computing.”

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Illustration showing quantum computing and entanglement.

Image credit: Shutterstock

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