The research shows the thinnest possible conductor steps, which consist of different electrical potentials

The research shows the thinnest possible conductor steps, which consist of different electrical potentials

Head of Ferroelectrics. Photo credit: Tel Aviv University

Research from Tel Aviv University shows two-dimensional crystals that exhibit unique control over different electric potential levels by shifting atomically thin layers against each other. The reported sequential, ultimately thin, electrical switches are a highly sought-after resource for information technology and novel electromechanical and optomechanical applications.

The study now published in Nature, was conducted by Dr. Swarup Deb, M.Sc. student Noam Raab, Prof. Moshe Goldstein and Dr. Moshe Ben Shalom, all from the Raymond & Beverly Sackler School of Physics & Astronomy at Tel Aviv University, and Dr. Wei Cao, Prof. Michael Urbach and Prof. Oded Hod from the Chemistry School of TAU and Prof. Leeor Kronik from the Weizmann Inst.

dr Moshe Ben Shalom, leader of the Quantum Layered Matter Group, says: “We are intrigued by how the atoms are ordered in a condensed matter, how electrons mix between the atoms, and whether or how external stimuli can manipulate the atomic order and the electrical one charge distribution.”

“Answering these questions is challenging because of the enormous number of atoms and electrons in even the smallest devices of our most advanced technologies. One of the tricks is to study crystals, which contain much smaller units, each made up of just a few atoms and electrons. While crystals are made up of many identical units that are periodically repeated in space, their properties are derived entirely from the symmetry of a unit cell and the details of the few atoms it traps.

“And yet it is difficult to understand and predict these details because the electrons propagate across all atoms simultaneously, which is determined by their shared quantum mechanical interactions.”

One way to study atomic order and electronic charge distribution is to break the symmetry of the cells to induce internal electric fields. Crystals with permanent internal electric fields are called polar crystals. In 2020, the same lab at TAU ​​reported a novel polar crystal by stacking two layers of a van der Waals crystal, with each layer just one atom thick.

dr Ben Shalom summarizes that the natural order in which “these crystals grow is symmetrical, with each successive layer rotated 180 degrees compared to the previous one. Here one type of atom is positioned just above the other. Conversely, the artificial crystals that are assembled in the laboratory are not rotated, resulting in a slight shift between the layers, thus deviating from the fully symmetrical configurations.

“This asymmetric crystal structure forces electrons to jump from one layer to another, creating a permanent electric field between them. Crucially, the group found that applying external electric fields causes the layers to slide back and forth to match the electron’s jumping direction with the external field orientation. They dubbed the phenomenon ‘interfacial ferroelectricity’ and pointed out the unique domain wall motion that controls the ‘slide tronics’ response.”

Israeli research shows the thinnest possible ladder steps made up of different electrical potentials

“Sliding and Climbing a Ladder-Ferroelectric”: The periodic crystal consists of two different atoms, which are repeated with constant spacing in each horizontal layer. If you shift the layers to the right or left to position the red atom over the blue (or vice versa), electrons jump up (or down) between the layers. Unlike ordinary polar crystals, the ferroelectric interface system exhibits distinct, evenly spaced electric potential steps that can serve as individual information units. Photo credit: Tel Aviv University

dr Ben Shalom states: “The ferroelectric reaction we have discovered takes place in a system two atoms thick, the thinnest possible, and is therefore extremely attractive for information technologies based on electronic quantum tunneling. We are now developing such tunneling devices in a stealth-phase company called Slide-Tro LTD, which was formed together with the university and an outside investor. We believe a wide range of devices, from low-power electronics to rugged non-volatile memory, can be realized with this technology.”

“From a basic scientific point of view, the discovery pointed us to new questions: How is the electrical charge arranged? And how does the electric potential grow as we stack additional layers to further break or restore the symmetry of the crystals? In other words, instead of thinning crystals, as has been extensively explored so far, we could now assemble new polar crystals layer by layer and study the electrical potential at each stage of the crystal ladder.

In the experiment, the researchers compared adjacent domains a few layers thick with different forward/backward shifts between the different layers, resulting in different polarization orientations. For example, in four layers (with three polar interfaces), there are four allowable configurations: all up ↑↑↑, one down and two up ↑↑↓, two down and one up ↑↓↓, and all down ↓ ↓↓ .

“We were excited to find a ladder with different electrical potentials separated by nearly equal steps, so each step can be used as an independent unit of information,” says Noam Rab, a student conducting the measurements. “This is very different from all previously known polar thin films, in which the polarization magnitude is very sensitive to many surface effects, and in which the polar alignment switches instantaneously between just two potentials.”

In addition, Dr. Swarup Deb, one of the lead authors of the paper, “we found that the internal electric fields remain significant even when we add external electrons to the system to make it both conductive and polar. Typically, the external charge shields the internal polarization, but in the current interface ferroelectrics, the extra electrons could just flow along the layers without bouncing too much between them to dampen the out-of-plane electric field.

dr Wei Cao, one of the other lead authors, adds: “Using theoretical calculations based on quantum mechanical principles, we have identified the precise distribution of polar charge and conductive charge. The former is strongly confined to the interfaces between the two layers and is thus protected from external disturbances.”

“The calculations allowed us to predict which crystals would best withstand the additional charge and how to design even better conductor ferroelectrics. The most likely direction of future research we envision is the manipulation of more electronic orders such as magnetism and superconductivity through differential sliding crystal symmetries to form novel ladder multiferroics.”

More information:
Swarup Deb et al, Cumulative polarization in conductive interface ferroelectrics, Nature (2022). DOI: 10.1038/s41586-022-05341-5

Provided by Tel Aviv University

Quote: Research Reveals Thinnest Ladder Steps From Different Electric Potentials (2022 November 21) Retrieved November 21, 2022 from https://phys.org/news/2022-11-reveals-thinnest-ladder-distinct-electric.html

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