Manipulating the geometry of the ‘electron universe’ in magnets

Researchers at Tohoku University and the Japan Atomic Energy Agency develop fundamental experiments and theory to manipulate the geometry of the “electron universe,” which describes the structure of electron quantum states, environmental conditions within magnetic materials, in a way that mathematically resembles the actual universe .

The geometric properties under investigation (i.e. quantum measurements) are detected as electrical signals that differ from ordinary electrical conduction. This breakthrough reveals the fundamental quantum science of electrons and paves the way for designing innovative spintronic devices that exploit the unconventional conduction that occurs in quantum measurements.

Details of the study are published in the journal natural physics April 22, 2024.

Conducting electricity, which is critical to many devices, follows Ohm’s law: the current is directly proportional to the applied voltage. But in order to realize new devices, scientists must find a way to transcend this law.

This is where quantum mechanics comes in. This quantum metric is an intrinsic property of the material itself, showing that it is a fundamental feature of the material’s quantum structure.

The term “quantum metric” is inspired by the concept of “metric” in general relativity, which explains how the geometry of the universe distorts under the influence of strong gravity, such as that around a black hole. Likewise, understanding and utilizing quantum metrics becomes imperative when engineering non-ohmic conduction within materials.

This metric describes the geometry of the “electronic universe”, similar to the physical universe. Specifically, the challenge is to manipulate the quantum metrology structure within a single device and discern its impact on conduction at room temperature.

Research team reports successful manipulation of quantum metric structures in thin-film heterostructures composed of the exotic magnet Mn at room temperature₃Sn and heavy metal Pt.manganese₃When adjacent to Pt, Sn exhibits an important magnetic structure and is strongly modulated by the applied magnetic field.

The team detected and magnetically controlled a type of non-ohmic conduction called the second-order Hall effect, in which voltage responds quadrature and quadratically to an applied current. Through theoretical modeling, they confirmed that the observations can be fully described by quantum measurements.

“Our second-order Hall effect originates from the quantum metrology structure, which is combined with a specific magnetic texture at Mn₃Tin/platinum interface. Therefore, we can flexibly manipulate quantum metrics by changing the magnetic structure of materials through spintronic methods, and demonstrate this manipulation in the magnetic control of the second-order Hall effect.

Yasufumi Araki, a major contributor to the theoretical analysis, added: “Theoretical predictions treat quantum metrics as a fundamental concept that links material properties measured in experiments to geometric structures studied in mathematical physics. However, its confirmation in experiments The evidence remains and I hope that our experimental approach to obtaining quantum measurements will advance such theoretical research.

Lead researcher Shunsuke Fukami said: “So far, quantum measurements have been thought to be intrinsic and uncontrollable, like the universe, but we now need to change this view. Our discovery, in particular, of flexible control at room temperature , may provide new discoveries.