Quantum materials offer many benefits to the future of electronic devices — from batteries to sensors and even our smartphones. Thanks to quantum behaviors like entanglement, these materials exhibit unusual electronic, optical and magnetic properties, making them more energy efficient.
“Being superior to conventional materials for certain electronic processes, quantum materials open vast application opportunities,” says Carmine Ortix, an associate professor of physics at the University of Salerno in Italy.
Electronic Properties of Quantum Materials
Ortix is part of an international research team, led by the University of Geneva, that studied how the electronic properties of quantum materials can be controlled. Their recent research shows that we can create tighter electronic control by curving the fabric of space within these materials.
The researchers wrapped their quantum material in insulators, trapping electrons — which control energy output — within a sandwich layer and limiting their free space. Then, using specific laser pulses, the team stacked each atom of their material on top of one another.
The results, published in Nature Materials, suggest this new material could boost the future of energy-efficient electronics.
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What Are Berry Phases?
In understanding how to control electrons’ movements, Ortix and the rest of his team relied on a concept in quantum physics known as the Berry phase. Named after English physicist Sir Michael Berry, this phase happens when a wave-like particle (such as an electron) moves in a closed loop through a magnetic field or another force field.
As the particle moves through the loop, part of its wave function — a “map” of where the particle might be in a general area of the quantum realm — changes, affecting how it behaves around other particles.
The Berry phase is quite complicated, so it can help to imagine the process like an eye exam: The giant metal headpiece (a lensometer) that an ophthalmologist uses to test your near- and far-sightedness contains two focus wheels for either lens.
As the eye doctor spins these wheels, asking, “Is one or two better?,” the lenses change in quality. When you get back to the beginning of the wheel, the difference between the first and last lens is quite different.
This looping process is similar to what happens during the Berry phase, where the electron evolves as the object moves through a loop (or wheel). But Ortix and his colleagues took the Berry phase one step further in their experiment, by studying the Berry curve of the electrons in their material.
Two Types of Berry Curvature
“You can think of the Berry curvature as an effective magnetic field generated by the electrons when they have some peculiar properties,” Ortix says.
Previous studies have shown that these electron curves were either spin-sourced or orbital-sourced. A spin-sourced Berry curve can be graphed to show how an electron’s momentum changes as it moves through a material in the presence of a magnetic field.
The curve is called “spin-sourced” because it considers the electron’s spin, or the quantum property that gives the electron magnetic moment, magnetizing it. The magnetic field’s presence causes the electron to rotate in the same direction as the field.
In contrast, the orbital-sourced Berry curve shows the changes in the electron’s wave function without a magnetic field.
This curve considers the electron’s orbital properties, which describe its spatial distribution around the nucleus of an atom. The electron’s orbitals can affect the phase of its wave function, influencing its behavior within the material.
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In their new study, the researchers found that by curving the space where the electrons were housed and simultaneously changing the magnetic fields of the material, the electrons could exhibit both spin- and orbital-sourced Berry curves.
“The curvature of quantum materials is an intrinsic property of elementary electrons,” Ortix says. “In practice, the large number of electrons inside the material form a ‘quantum geometric space’ that can possess curvature.”
This means that by trapping the electrons within the designated space, scientists can more easily control when and how the electrons curve the fabric of space within the material. The two curves working in tandem allow the material to be more tightly controlled, suggesting a more energy-efficient future for our devices as it exhibits less energy loss.
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Energy Efficient Technology
“This potential needs to be explored with further experimentation,” says Andrea Caviglia, a professor at the University of Geneva and a co-author of the study. This new quantum material could also prove key for the future of nanotechnology and in sensing electromagnetic signals.
Ortix explains that “the significance of these results lies in the fact that the measured quantum transport properties might be exploited in future optoelectronic nanodevices.” Examples of these types of devices, not on a nanoscale, include solar cells or LED lights.
“The nonlinear electrical responses discussed in our study might be relevant to creat[ing] microscale devices that convert electromagnetic energy into usable electrical energy,” Ortix adds.
Converting electromagnetic energy into electrical energy could be especially useful in the telecommunications industry, where electromagnetic signals are transmitted and received constantly by phones, laptops or TV satellites.
As the telecommunications industry advances, having quantum materials like the one studied by Ortix and Caviglia could become vital in creating more powerful satellites and other devices.
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