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Pitt researchers create nanoscale slalom course for electrons: Professors from the Department of Physics and Astronomy have created a serpentine path for electrons

Published

2 months ago

November 28, 2020

Home > Press > Pitt researchers create nanoscale slalom course for electrons: Professors from the Department of Physics and Astronomy have created a serpentine path for electrons

Illustration of sketched serpentine nanowires created from lanthanum aluminate and strontium titanate. The side-to-side motion of the electrons as they travel gives them additional properties that can be used to make quantum devices CREDIT
Jeremy Levy

Abstract:
A research team led by professors from the Department of Physics and Astronomy have created a serpentine path for electrons, imbuing them with new properties that could be useful in future quantum devices.

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Pitt researchers create nanoscale slalom course for electrons: Professors from the Department of Physics and Astronomy have created a serpentine path for electrons

Pittsburgh, PA | Posted on November 27th, 2020

Jeremy Levy, a distinguished professor of condensed matter physics, and Patrick Irvin, research professor, are coauthors of the paper “Engineered spin-orbit interactions in LaAlO3/SrTiO3-based 1D serpentine electron waveguides,” published in Science Advances on November 25.

“We already know how to shoot electrons ballistically through one-dimensional nanowires made from these oxide materials,” explains Levy. “What is different here is that we have changed the environment for the electrons, forcing them to weave left and right as they travel. This motion changes the properties of the electrons, giving rise to new behavior.”

The work is led by a recent PhD recipient, Dr. Megan Briggeman, whose thesis was devoted to the development of a platform for “quantum simulation” in one dimension. Briggeman is also the lead author on a related work published earlier this year in Science, where a new family of electronic phases was discovered in which electrons travel in packets of 2, 3, and more at a time.

Electrons behave very differently when forced to exist along a straight line (i.e., in one dimension). It is known, for example, that the spin and charge components of electrons can split apart and travel at different speeds through a 1D wire. These bizarre effects are fascinating and also important for the development of advanced quantum technologies such as quantum computers. Motion along a straight line is just one of a multitude of possibilities that can be created using this quantum simulation approach. This publication explores the consequences of making electrons weave side to side while they are racing down and otherwise linear path.

One recent proposal for topologically-protected quantum computation takes advantage of so-called “Majorana fermions”, particles which can exist in 1D quantum wires when certain ingredients are present. The LaAlO3/SrTiO3 system, it turns out, has most but not all of the required interactions. Missing is a sufficiently strong “spin-orbit interaction” that can produce the conditions for Majorana fermions. One of the main findings of this latest work from Levy is that spin-orbit interactions can in fact be engineered through the serpentine motion that electrons are forced to undertake.

In addition to identifying new engineered spin-orbit couplings, the periodic repetition of the serpentine path creates new ways for electrons to interact with one another. The experimental result of this is the existence of fractional conductances that deviate from those expected for single electrons.

These slalom paths are created using a nanoscale sketching technique analogous to an Etch A Sketch toy, but with a point size that is a trillion times smaller in area. These paths can be sketched and erased over and over, each time creating a new type of path for electrons to traverse. This approach can be thought of as a way of creating quantum materials with re-programmable properties. Materials scientists synthesize materials in a similar fashion, drawing atoms from the periodic table and forcing them to arrange in periodic arrays. Here the lattice is artificial–one zig-zag of the motion takes place in a ten nanometer of space rather than a sub-nanometer atomic distance.

Levy, who is also director of the Pittsburgh Quantum Institute, stated that this work contributes to one of the main goals of the Second Quantum Revolution, which is to explore, understand, and exploit the full nature of quantum matter. An improved understanding, and the ability to simulate the behavior of a wide range of quantum materials, will have wide-ranging consequences. “This research falls within a larger effort here in Pittsburgh to develop new science and technologies related to the second quantum revolution,” he said.

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In addition to Levy, Irvin, and Briggeman, Pitt research team members include Physics and Astronomy graduate students Jianan Li, and Mengchen Huang. Other team members include Hyungwoo Lee, now at Pusan National University in South Korea, and Jung-Woo Lee, Ki-Tae Eom, and Chang-Beom Eom, from the University of Wisconsin-Madison.

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Scientists synthetize new material for high-performance supercapacitors

Published

3 days ago

January 20, 2021

Republished by Plato

Home > Press > Scientists synthetize new material for high-performance supercapacitors

Photo: modified rGO supercapacitor electrodes

Abstract:
Scientists of Tomsk Polytechnic University jointly with colleagues from the University of Lille (Lille, France) synthetized a new material based on reduced graphene oxide (rGO) for supercapacitors, energy storage devices. The rGO modification method with the use of organic molecules, derivatives of hypervalent iodine, allowed obtaining a material that stores 1.7 times more electrical energy. The research findings are published in Electrochimica Acta academic journal (IF: 6,215; Q1).

Scientists synthetize new material for high-performance supercapacitors

Tomsk, Russia | Posted on January 19th, 2021

A supercapacitor is an electrochemical device for storage and release of electric charge. Unlike batteries, they store and release energy several times faster and do not contain lithium.

A supercapacitor is an element with two electrodes separated by an organic or inorganic electrolyte. The electrodes are coated with an electric charge accumulating material. The modern trend in science is to use various materials based on graphene, one of the thinnest and most durable materials known to man. The researchers of TPU and the University of Lille used reduced graphene oxide (rGO), a cheap and available material.

“Despite their potential, supercapacitors are not wide-spread yet. For further development of the technology, it is required to enhance the efficiency of supercapacitors. One of the key challenges here is to increase the energy capacity.

It can be achieved by expanding the surface area of an energy storage material, rGO in this particular case. We found a simple and quite fast method. We used exceptionally organic molecules under mild conditions and did not use expensive and toxic metals,” Pavel Postnikov, Associate Professor of TPU Research School of Chemistry and Applied Biomedical Science and the research supervisor says.

Reduced graphene oxide in a powder form is deposited on electrodes. As a result, the electrode becomes coated with hundreds of nanoscale layers of the substance. The layers tend to agglomerate, in other words, to sinter. To expand the surface area of a material, the interlayer spacing should be increased.

“For this purpose, we modified rGO with organic molecules, which resulted in the interlayer spacing increase. Insignificant differences in interlayer spacing allowed increasing energy capacity of the material by 1.7 times. That is, 1 g of the new material can store 1.7 times more energy in comparison with a pristine reduced graphene oxide,” Elizaveta Sviridova, Junior Research Fellow of TPU Research School of Chemistry and Applied Biomedical Sciences and one of the authors of the article explains.

The reaction proceeded through the formation of active arynes from iodonium salts. They kindle scientists` interest due to their property to form a single layer of new organic groups on material surfaces. The TPU researchers have been developing the chemistry of iodonium salts for many years.

“The modification reaction proceeds under mild conditions by simply mixing the solution of iodonium salt with reduced graphene oxide. If we compare it with other methods of reduced graphene oxide functionalization, we have achieved the highest indicators of material energy capacity increase,” Elizaveta Sviridova says.

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The research work was conducted with the support of the Russian Science Foundation.

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Alina Borovskaia
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Researchers guide a single ion through a Bose Einstein condensate

Published

4 days ago

January 20, 2021

Republished by Plato

Jan 20, 2021 (Nanowerk News) Transport processes are ubiquitous in nature but still raise many questions. The research team around Florian Meinert from the 5th Institute of Physics at the University of Stuttgart has now developed a new method that allows them to observe a single charged particle on its path through a dense cloud of ultracold atoms. The results were published in Physical Review Letters (“Transport of a single cold ion immersed in a Bose-Einstein condensate”) and are subject in a Viewpoint of the accompanying popular science journal Physics (“Tracking a Single Ion in an Ultracold Gas”).

Artistical visualization of the trajectory of a positively charged ion (yellow) through the BEC (green). (Image: Celina Brandes, University of Stuttgart) Meinert‘s team uses a so called Bose Einstein condensate (BEC) for their experiments. This exotic state of matter consists of a dense cloud of ultracold atoms. By means of sophisticated laser excitation, the researchers create a single Rydberg atom within the gas. In this giant atom the electron is a thousand times further away from the nucleus than in the ground state and thus only very weakly bound to the core. With a specially designed sequence of electric field pulses, the researchers snatch the electron away from the atom. The formerly neutral atom turns into a positively charged ion that remains nearly at rest despite the process of detaching the electron. In a next step, the researchers use precise electric fields to pull the ion in a controlled way through the dense cloud of atoms in the BEC. The ion picks up speed in the electric field, collides on its way with other atoms, slows down and is accelerated again by the electric field. The interplay between acceleration and deceleration by collisions leads to a constant motion of the ion through the BEC. “This new approach allows us to measure the mobility of a single ion in a Bose Einstein condensate for the very first time,” Thomas Dieterle, PhD student on the experiment, is pleased. The researchers’ next goal is to observe collisions between a single ion and atoms at even lower temperatures, where quantum mechanics instead of classical mechanics dictates the processes. “In future, our newly created model system – the transport of a single ion – will allow for a better understanding of more complex transport processes that are relevant in many-body systems, e.g. in certain solids or in superconductors,” Meinert is sure. These measurements are also an important step on the way to investigate exotic quasi-particles, so-called polarons, which can arise through interaction between atoms and ions. The neighboring lab at the institute already works on an ion microscope that will allow to directly observe collisions between atoms and ions. While an electron microscope uses negatively charged particles to create an image, this is what happens in an ion microscope with positively charged ions. Electrostatic lenses deflect ions similar to light rays in a classical optical microscope. The work was created in the Center for Integrated Quantum Science and Technology IQST, a consortium of the universities of Stuttgart and Ulm and the Max Planck Institute for Solid State Research in Stuttgart. The aim of the center is to promote synergies between physics and related natural and engineering sciences and to represent quantum science from the basics to technological applications. Researchers and practitioners from the fields of physics, chemistry, biology, mathematics, and engineering science at IQST investigate the world of quanta in its entirety and in some cases cooperate directly with the industry.

Source: https://www.nanowerk.com/nanotechnology-news2/newsid=57061.php

Nano Technology

Storing information with light: photo-ferroelectric materials

Published

4 days ago

January 20, 2021

Republished by Plato

Jan 20, 2021 (Nanowerk News) Can you imagine controlling the properties of a material by just shining light on it? We are used to see that the temperature of materials increases when exposed to the sun. But light may also have subtler effects. Indeed, light photons can create pairs of free charge carriers in otherwise insulating materials. This is the basic principle of the photovoltaic panels we use to harvest electrical energy from sun. In a new twist, a light-induced change of materials’ properties could be used in memory devices, allowing more efficient storage of information and faster access and computing. This, in fact, is one of our society’s current challenge: being able to develop high-performance commercially available electronic devices which are, at the same time, energy efficient. Smaller electronic devices having lower energy consumption and high performance and versatility. Now, researchers from the Institute of Materials Science of Barcelona (ICMAB, CSIC) have studied photoresponsive ferroelectric materials integrated in devices exploiting nanotechnologies and quantum effects. Memory elements have been engineered to store non-volatile information in distinct resistance states (ON/OFF). It has been discovered that, when properly designed, their electrical resistance can be modulated by pulsed light. This means that they can switch from a low-resistance to a high-resistance state just by the application of light pulses. “Materials that show changes of resistance under illumination are abundant, although the effect is typically volatile and the material recovers its initial state after some dwell time” says ICMAB researcher Ignasi Fina, co-author of the study (Nature Communications, “Non-volatile optical switch of resistance in photoferroelectric tunnel junctions”). “For devices to be used in computing and data storage, non-volatile optical control of electrical resistance is of potential interest” and adds “for non-volatile, we mean that the information can be retained stored in the device, even when the power is off”.

A photon reverses the binary 0/1 state of a memory device. (Image: ICMAB) Currently two different devices are required to use optical signals for non-volatile data storage: optoelectronic sensors and memory devices. The ICMAB study features these properties in one single material able to modulate its resistance by pulsed light: a photo-ferroelectric material. Ferroelectric materials have electrically switchable spontaneous non-volatile electric polarization. In ferroelectric ultrathin films of such material sandwiched between appropriate metals, a quantum mechanical phenomenon effect appears called the tunneling current. This effect allows a charge current flow across the ferroelectric layer, which is genuinely insulating, in an amount that depends on the direction of its polarization. In the explored devices, first an electric field is used once to write the ON/OFF states, and it is combined with the optical stimulus to promote the ON/OFF change of states, and reversibly modulate the resistance (from high to low, and vice versa). These devices are energy efficient for two main reasons: firstly, the energy consumption is reduced when the memory state is written, as it does not need any charge current flow. Secondly, as the information is stored in a non-volatile manner, the state is preserved and there is no need to refresh the information (re-writing) as continuously done in current RAMs memories of all computers, for example. The observed optical switch is not restricted to the studied materials and, thus, opens a path towards further investigations on this phenomenon. As for future applications, Ignasi Fina envisions the following: “The studied devices combine light sensor and memory functions. In addition, as shown in the study, the device behaves like a memristor. A memristor is a device that can display multiple resistance states according to the stimulus it has received, and is one of the basic devices for the development of neuromorphic computing systems. Therefore, the developed device opens a path to be explored in relation to its integration into neuromorphic vision systems, where the system learns to recognize images.”

Source: https://www.nanowerk.com/nanotechnology-news2/newsid=57060.php

Nano Technology

Do simulations represent the real world at the atomic scale?

Published

4 days ago

January 20, 2021

Republished by Plato

Jan 20, 2021 (Nanowerk News) Computer simulations hold tremendous promise to accelerate the molecular engineering of green energy technologies, such as new systems for electrical energy storage and solar energy usage, as well as carbon dioxide capture from the environment. However, the predictive power of these simulations depends on having a means to confirm that they do indeed describe the real world. Such confirmation is no simple task. Many assumptions enter the setup of these simulations. As a result, the simulations must be carefully checked by using an appropriate “validation protocol” involving experimental measurements. To address this challenge, a team of scientists at the U.S. Department of Energy’s (DOE) Argonne National Laboratory, the University of Chicago and the University of California, Davis, developed a groundbreaking validation protocol for simulations of the atomic structure of the interface between a solid (a metal oxide) and liquid water (Physical Review Materials, “Validating first-principles molecular dynamics calculations of oxide/water interfaces with x-ray reflectivity data”). The team was led by Giulia Galli, a theorist with a joint appointment at Argonne and the University of Chicago, and Paul Fenter, an Argonne experimentalist. Computer simulation at the atomic scale

Pictorial representation of joint experimental and computational study of materials. The study utilized the Advanced Photon Source (upper panel) and Argonne Leadership Computing Facility (lower panel). The team addressed the atomistic structure of interfaces, which are ubiquitous in materials. (Image: Emmanuel Gygi, University of California, San Diego) “We focused on a solid/liquid interface because interfaces are ubiquitous in materials, and those between oxides and water are key in many energy applications,” said Galli. “To date, most validation protocols have been designed for bulk materials, ignoring interfaces,” added Fenter. “We felt that the atomic-scale structure of surfaces and interfaces in realistic environments would present a particularly sensitive, and therefore challenging, validation approach.” The validation procedure they designed uses high-resolution X-ray reflectivity (XR) measurements as the experimental pillar of the protocol. The team compared XR measurements for an aluminum oxide/water interface, conducted at beamline 33-ID-D at Argonne’s Advanced Photon Source (APS), with results obtained by running high-performance computer simulations at the Argonne Leadership Computing Facility (ALCF). Both the APS and ALCF are DOE Office of Science User Facilities. “These measurements detect the reflection of very high energy X-ray beams from an oxide/water interface,” said Zhan Zhang, a physicist in Argonne’s X-ray Science division. At the beam energies generated at the APS, the X-ray wavelengths are similar to interatomic distances. This allows the researchers to directly probe the molecular-scale structure of the interface. “This makes XR an ideal probe to obtain experimental results directly comparable to simulations,” added Katherine Harmon, a graduate student at Northwestern University, an Argonne visiting student and the first author of the paper. The team ran the simulations at the ALCF using the Qbox code, which is designed to study finite temperature properties of materials and molecules using simulations based on quantum mechanics. “We were able to test several approximations of the theory,” said Francois Gygi from the University of California, Davis, part of the team and lead developer of the Qbox code. The team compared measured XR intensities with those calculated from several simulated structures. They also investigated how X-rays scattered from the electrons in different parts of the sample would interfere to produce the experimentally observed signal. The endeavor of the team turned out to be more challenging than anticipated. “Admittedly, it was a bit of a trial and error at the beginning when we were trying to understand the right geometry to adopt and the right theory that would give us accurate results,” said Maria Chan, a co-author of the study and scientist at Argonne’s Center for Nanoscale Materials, a DOE Office of Science User Facility. “However, our back and forth between theory and experiment paid off, and we were able to set up a robust validation protocol that can now be deployed for other interfaces as well.” “The validation protocol helped quantify the strengths and weaknesses of the simulations, providing a pathway toward building more accurate models of solid/liquid interfaces in the future,” said Kendra Letchworth-Weaver. An assistant professor at James Madison University, she developed software to predict XR signals from simulations during a postdoctoral fellowship at Argonne. The simulations also shed new insight on the XR measurements themselves. In particular, they showed that the data are sensitive not only to the atomic positions, but also to the electron distribution surrounding each atom in subtle and complex ways. These insights will prove beneficial to future experiments on oxide/liquid interfaces.

Source: https://www.nanowerk.com/nanotechnology-news2/newsid=57058.php