{"id":42813,"date":"2023-03-03T09:10:48","date_gmt":"2023-03-03T10:10:48","guid":{"rendered":"https:\/\/peymantaeidi.net\/stem-cell\/?p=42813"},"modified":"2023-03-03T10:36:38","modified_gmt":"2023-03-03T10:36:38","slug":"scanning-probe-with-a-twist-observes-electrons-wavelike-behaviour","status":"publish","type":"post","link":"https:\/\/peymantaeidi.net\/stem-cell\/2023\/03\/03\/scanning-probe-with-a-twist-observes-electrons-wavelike-behaviour\/","title":{"rendered":"Scanning probe with a twist observes electron\u2019s wavelike behaviour"},"content":{"rendered":"
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\n\t\t\t\t\t\t\t\t\t\t\t\t\"Scanning
\n\t\t\t\t\t\t\t\t\t\t<\/a>
How it works: illustration of the quantum twisting microscope in action. Electrons tunnel from the probe (inverted pyramid at the top) to the sample (bottom) in several places at once (green vertical lines), in a quantum coherent manner. (Courtesy: Weizmann Institute of Science)<\/figcaption><\/figure>\n

When the scanning tunnelling microscope<\/a> made its debut in the 1980s the result was an explosion in nanotechnology and quantum-device research. Since then, other types of scanning probe microscopes have been developed and together they have helped researchers flesh out theories of electron transport. But these techniques probe electrons at a single point, thereby observing them as particles and only seeing their wave nature indirectly. Now researchers at the Weizmann Institute of Science in Israel have built a new scanning probe \u2013 the quantum twisting microscope \u2013 that detects the quantum wave characteristics of electrons directly.<\/p>\n

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\u201cIt\u2019s effectively a scanning probe tip with an interferometer at its apex,\u201d says Shahal Ilani<\/a>, the team leader. The researchers overlay a scanning probe tip with ultrathin graphite, hexagonal boron nitride and a van der Waals crystal such as graphene, which conveniently flop over the tip like a tent with a flat top about 200 nm across. The flat end is key to the device\u2019s interferometer function.  Instead of an electron tunnelling between one point in the sample and the tip, the electron wave function can tunnel across at multiple points simultaneously.<\/p>\n

\u201cQuite surprisingly we found that the flat end naturally pivots so that it is always parallel with the sample,\u201d says John Birkbeck<\/a>, the corresponding author of a paper describing this work. This is fortunate because any tilt would alter the tunnelling distance and hence strength from one side of the plateau to the other. \u201cIt is the interference of these tunnelling paths, as identified in the measured current, that gives the device its unique quantum wave probing function,\u201d says Birkbeck.<\/p>\n

Double slit experiment<\/h3>\n

This interference is analogous to the effects of firing electrons at a screen with two slits in it, like the famous Young\u2019s double slit experiment, as Erez Berg<\/a> explains. Berg, together with Ady Stern<\/a>, Binghai Yan<\/a> and Yuval Oreg<\/a> led the theoretical understanding of the new instrument.<\/p>\n

If you measure which slit the particle passes through \u2013 like what happens with the measurements of other scanning probe techniques \u2013 the wave behaviour is lost and all you see is the particle. However, if you leave the particle to pass with its crossing position undetected, the two available paths produce a pattern of constructive and destructive interference like the waves that ripple out from two pebbles dropped in a pond side by side.<\/p>\n

\u201cSince the electron can only tunnel where its momentum matches between the probe and sample, the device directly measures this parameter, which is key for theories explaining collective electron behaviour,\u201d says Berg.<\/p>\n

In fact the idea of measuring the momentum of an electron using the interference of its available tunnelling routes dates back to the work of Jim Eisenstein at Caltech in the 1990s<\/a>. However, the Weizmann researchers move things up several gears with some key innovations thanks to two explosive developments since. These are the the isolation of graphene<\/a> prompting research into similar atomically thin van der Waals crystals; and the subsequent experimentally observed effects of a twist<\/a> in the orientation of layered van der Waals materials.<\/p>\n

When layered with a twist, materials like graphene form a moir\u00e9 lattice, so named after textiles where the mesh of the fabric is slightly out of register and has funny effects on your eyes. The electrons in these moir\u00e9 2D materials are subjected to the potential of this additional artificial moir\u00e9 lattice, which has a period determined by the twist angle. Hence twisting through the relative angles between two layers of van der Waals crystal using a piezoelectric rotator on the quantum twisting microscope, makes it possible to measure a much wider range in momentum than was possible with the magnetic fields used previously, as well as exploring many other electronic phenomena too. The natty device also makes it easy to study a range of different van der Waals crystals and other quantum materials.<\/p>\n

From problem to solution<\/h3>\n

Following the discovery of twist effects, people were keen to experiment with materials at different twist angles. However they had to go through the painstaking process of producing each device afresh for each twist angle. Although it had been possible to twist through angles is a single device, the twist tends to get locked at certain angles where, it\u2019s basically game over for the experiment. In the quantum twisting microscope the atomically thin material on the tip has strong adhesion along the tip sides as well as the end, so that the net forces easily outweigh the attraction between the two van der Waal crystal layers of probe and sample, even for these most attractive twist angles. It was fabrication challenges like these that the Weizmann researchers had originally set out to tackle.<\/p>\n

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\t\t\t\t\t\"Twistronics\"\n\t\t\t\t<\/div>\n

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Discovery of \u2018magic-angle graphene\u2019 that behaves like a high-temperature superconductor is Physics World<\/i> 2018 Breakthrough of the Year<\/p>\n<\/h4>\n

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Twisted graphene pioneer Cory Dean<\/a>, who was not involved with this research, describes how some of the most detailed understanding of twisted layer systems is coming from scanning probes over them. This way each region with its unique albeit uncontrolled twist can be identified and treated as its own device. \u201cIn the Weizmann approach, they have taken this step to a really creative new direction where the twist angle control and spectroscopic analysis are integrated into the same platform,\u201d says Dean, who is at Columbia University. \u201cThis idea, that the device is also the instrument, is a rare and exciting combination in condensed matter systems.\u201d He also highlights that the device is not limited to twisted layer systems.<\/p>\n

Ilani says of his team\u2019s invention, \u201cTo be honest every week we discover a new type of measurement that you can do with the quantum twisting microscope \u2013 it\u2019s a very versatile tool\u201d. For example,  the researchers can also press the tip down to explore the effects of pressure, which decreases the distance between van der Waals layers. \u201cThere are experiments on 2D materials done with pressure, also in the context of magic angle graphene,\u201d says Birkbeck, as he refers to experiments with pistons in oil chambers plunged to low temperatures that need to be reset from scratch for each pressure value. \u201cWe\u2019ve reached comparable pressures with the quantum twisting microscope but now with the ability to quickly and continuously tune it in situ<\/em>.\u201d<\/p>\n

The results are reported in Nature<\/em><\/a>.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

How it works: illustration of the quantum twisting microscope in action. Electrons tunnel from the<\/p>\n","protected":false},"author":1,"featured_media":42815,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"_links":{"self":[{"href":"https:\/\/peymantaeidi.net\/stem-cell\/wp-json\/wp\/v2\/posts\/42813"}],"collection":[{"href":"https:\/\/peymantaeidi.net\/stem-cell\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/peymantaeidi.net\/stem-cell\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/peymantaeidi.net\/stem-cell\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/peymantaeidi.net\/stem-cell\/wp-json\/wp\/v2\/comments?post=42813"}],"version-history":[{"count":3,"href":"https:\/\/peymantaeidi.net\/stem-cell\/wp-json\/wp\/v2\/posts\/42813\/revisions"}],"predecessor-version":[{"id":42832,"href":"https:\/\/peymantaeidi.net\/stem-cell\/wp-json\/wp\/v2\/posts\/42813\/revisions\/42832"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/peymantaeidi.net\/stem-cell\/wp-json\/wp\/v2\/media\/42815"}],"wp:attachment":[{"href":"https:\/\/peymantaeidi.net\/stem-cell\/wp-json\/wp\/v2\/media?parent=42813"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/peymantaeidi.net\/stem-cell\/wp-json\/wp\/v2\/categories?post=42813"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/peymantaeidi.net\/stem-cell\/wp-json\/wp\/v2\/tags?post=42813"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}