{"id":4883,"date":"2019-12-14T14:41:33","date_gmt":"2019-12-14T05:41:33","guid":{"rendered":"http:\/\/163.180.4.222\/lab\/?p=4883"},"modified":"2019-12-14T14:41:33","modified_gmt":"2019-12-14T05:41:33","slug":"heat-transferred-in-a-previously-unknown-way","status":"publish","type":"post","link":"https:\/\/biochemistry.khu.ac.kr\/lab\/?p=4883","title":{"rendered":"Heat transferred in a previously unknown way"},"content":{"rendered":"<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>Experiments show that quantum fluctuations can allow heat to be transported between two objects separated by a vacuum gap. This effect could be harnessed to exploit and control heat transfer in nanoscale devices.<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<div class=\"article__body serif cleared\">\n<p>Acoustic waves and electromagnetic waves can transport heat between objects through their respective energy carriers: phonons and photons. At or near room temperature, the heat transfer between objects separated by a material medium occurs at a much higher rate when facilitated by phonons than by photons. However, phonons are generally thought to be ineffective at transporting heat between objects separated by a vacuum gap, because these energy carriers are vibrations in an atomic lattice and thus would require a material medium to propagate.\u00a0<a href=\"https:\/\/www.nature.com\/articles\/s41586-019-1800-4\" data-track=\"click\" data-label=\"https:\/\/www.nature.com\/articles\/s41586-019-1800-4\" data-track-category=\"body text link\">Writing in\u00a0<i>Nature<\/i><\/a>, Fong\u00a0<i>et al.<\/i><sup><a href=\"https:\/\/www.nature.com\/articles\/d41586-019-03729-4?utm_source=feedburner&amp;utm_medium=feed&amp;utm_campaign=Feed%3A+nature%2Frss%2Fcurrent+%28Nature+-+Issue%29#ref-CR1\" data-track=\"click\" data-action=\"anchor-link\" data-track-label=\"go to reference\" data-track-category=\"references\">1<\/a><\/sup>\u00a0report experimental evidence that phonons can travel across a vacuum gap and therefore induce heat transfer between vacuum-separated objects because of the effect of quantum fluctuations.<\/p>\n<p>&nbsp;<\/p>\n<aside class=\"recommended pull pull--left sans-serif\" data-label=\"Related\"><a href=\"https:\/\/www.nature.com\/articles\/s41586-019-1800-4\" data-track=\"click\" data-track-label=\"recommended article\"><img decoding=\"async\" class=\"recommended__image\" src=\"https:\/\/media.nature.com\/w400\/magazine-assets\/d41586-019-03729-4\/d41586-019-03729-4_17485414.jpg\" \/><\/a><\/p>\n<p class=\"recommended__title serif\">Read the paper: Phonon heat transfer across a vacuum through quantum fluctuations<\/p>\n<\/aside>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>In simple terms, quantum fluctuations can be understood as being the source of an electromagnetic signal that a perfectly sensitive detector would detect in a vacuum, even when this vacuum is shielded from all possible internal and external sources of electromagnetic waves, such as charges and currents<sup><a href=\"https:\/\/www.nature.com\/articles\/d41586-019-03729-4?utm_source=feedburner&amp;utm_medium=feed&amp;utm_campaign=Feed%3A+nature%2Frss%2Fcurrent+%28Nature+-+Issue%29#ref-CR2\" data-track=\"click\" data-action=\"anchor-link\" data-track-label=\"go to reference\" data-track-category=\"references\">2<\/a><\/sup>. The fluctuations are a consequence of a law in quantum mechanics known as Heisenberg\u2019s uncertainty principle<sup><a href=\"https:\/\/www.nature.com\/articles\/d41586-019-03729-4?utm_source=feedburner&amp;utm_medium=feed&amp;utm_campaign=Feed%3A+nature%2Frss%2Fcurrent+%28Nature+-+Issue%29#ref-CR3\" data-track=\"click\" data-action=\"anchor-link\" data-track-label=\"go to reference\" data-track-category=\"references\">3<\/a><\/sup>, which states that certain pairs of physical quantities cannot be determined at the same time with absolute precision. The presence of quantum fluctuations subtly influences surrounding matter, leading to several observable effects.<\/p>\n<p>One of these effects, relevant to Fong and colleagues\u2019 work, is the Casimir force<sup><a href=\"https:\/\/www.nature.com\/articles\/d41586-019-03729-4?utm_source=feedburner&amp;utm_medium=feed&amp;utm_campaign=Feed%3A+nature%2Frss%2Fcurrent+%28Nature+-+Issue%29#ref-CR4\" data-track=\"click\" data-action=\"anchor-link\" data-track-label=\"go to reference\" data-track-category=\"references\">4<\/a><\/sup>\u00a0\u2014 the force that two neutral atoms separated by a vacuum gap exert on each other. The Casimir force results when quantum fluctuations induce fluctuating charge densities in these atoms; the charge densities then interact through their electric fields. The force that sticks a gecko\u2019s foot to a wall is an example of a macroscopic manifestation of the Casimir force. It arises from the combined interactions between fluctuating charge densities in all the atomic constituents of the two objects.<\/p>\n<p>To understand how the Casimir force can induce phonon transfer between vacuum-separated objects, consider an object that is maintained at a particular temperature by being kept in contact with a heat source (Fig. 1). Thermal agitation of the object\u2019s atoms, which can be thought of as being interconnected by elastic springs, gives rise to phonons. In the presence of these phonons, the surface of the object undulates over time. When a second object is brought close to the first one, it is subjected to a time-varying Casimir force owing to its interaction with the undulations of the first object\u2019s surface. The second object\u2019s surface is thus subjected to tugging that then gives rise to phonons in the object\u2019s interior. Phonons are therefore transmitted from the first object to the second one.<\/p>\n<p>&nbsp;<\/p>\n<figure class=\"figure\">\n<div class=\"embed intensity--high\">\n<div class=\"embed intensity--high\"><img decoding=\"async\" class=\"figure__image\" src=\"https:\/\/media.nature.com\/lw800\/magazine-assets\/d41586-019-03729-4\/d41586-019-03729-4_17485464.gif\" alt=\"\" data-src=\"\/\/media.nature.com\/lw800\/magazine-assets\/d41586-019-03729-4\/d41586-019-03729-4_17485464.gif\" \/><\/div>\n<\/div><figcaption>\n<p class=\"figure__caption sans-serif\"><span class=\"mr10\"><b>Figure 1 | Phonon transmission across a vacuum.<\/b>\u00a0Fong\u00a0<i>et al.<\/i><sup><a href=\"https:\/\/www.nature.com\/articles\/d41586-019-03729-4?utm_source=feedburner&amp;utm_medium=feed&amp;utm_campaign=Feed%3A+nature%2Frss%2Fcurrent+%28Nature+-+Issue%29#ref-CR1\" data-track=\"click\" data-action=\"anchor-link\" data-track-label=\"go to reference\" data-track-category=\"references\">1<\/a><\/sup>\u00a0show that phonons \u2014 vibrations in an atomic lattice \u2014 can be transported between objects that are separated by a vacuum gap. To understand how this process occurs, consider an object at a fixed temperature\u00a0<i>T<\/i><sub>1<\/sub>. Thermal agitation of the object\u2019s atoms produces phonons that propagate as acoustic waves and cause the object\u2019s surface to exhibit time-varying undulations (the amplitudes of the undulations shown are exaggerated for clarity). A second object, at a fixed temperature\u00a0<i>T<\/i><sub>2<\/sub>\u2009&lt;\u2009<i>T<\/i><sub>1<\/sub>, is brought close to the first object, with a vacuum gap between the objects. The undulations of the first object\u2019s surface exert a time-varying \u2018Casimir\u2019 force (caused by quantum fluctuations) on the second object\u2019s surface, which gives rise to phonons in the second object. Because phonons are heat carriers, heat is transferred from the first object to the second one.<\/span><\/p>\n<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>Because phonons are heat carriers, when they are transported from one object to another across a vacuum gap, as a result of the Casimir force, they induce heat transfer if the second object is maintained at a lower temperature than that of the first one. This phenomenon of heat transport facilitated by the Casimir force has been predicted previously using theoretical models<sup><a href=\"https:\/\/www.nature.com\/articles\/d41586-019-03729-4?utm_source=feedburner&amp;utm_medium=feed&amp;utm_campaign=Feed%3A+nature%2Frss%2Fcurrent+%28Nature+-+Issue%29#ref-CR5\" data-track=\"click\" data-action=\"anchor-link\" data-track-label=\"go to reference\" data-track-category=\"references\">5<\/a><\/sup><sup>\u2013<\/sup><sup><a href=\"https:\/\/www.nature.com\/articles\/d41586-019-03729-4?utm_source=feedburner&amp;utm_medium=feed&amp;utm_campaign=Feed%3A+nature%2Frss%2Fcurrent+%28Nature+-+Issue%29#ref-CR7\" data-track=\"click\" data-action=\"anchor-link\" data-track-label=\"go to reference\" data-track-category=\"references\">7<\/a><\/sup>. Fong\u00a0<i>et al.<\/i>\u00a0have now measured such a heat-transfer mode experimentally.<\/p>\n<p>The authors used a technique called optical interferometry to observe the thermal agitation of atoms (Brownian motion) at the surface of a membrane. This membrane was kept in contact with a heat source held at a constant temperature. Measurements of thermal agitation can be related to, and therefore used as a gauge for, the temperature of the atoms at the membrane\u2019s surface. Moreover, the difference in this temperature with and without Casimir interaction with another, closely juxtaposed membrane is directly proportional to the resulting heat transfer between the two interacting membranes. The authors used these features to estimate the amount of heat transmitted between the membranes for vacuum gaps of different sizes. They found that their measurements accurately conform to theoretical estimates of such heat transport.<\/p>\n<p>&nbsp;<\/p>\n<aside class=\"recommended pull pull--left sans-serif\" data-label=\"Related\"><a href=\"https:\/\/www.nature.com\/articles\/d41586-019-00974-5\" data-track=\"click\" data-track-label=\"recommended article\"><img decoding=\"async\" class=\"recommended__image\" src=\"https:\/\/media.nature.com\/w400\/magazine-assets\/d41586-019-03729-4\/d41586-019-03729-4_17485416.jpg\" \/><\/a><\/p>\n<p class=\"recommended__title serif\">Refrigeration based on plastic crystals<\/p>\n<\/aside>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>Fong and colleagues\u2019 work provides conclusive evidence that the Casimir force can induce heat transfer. However, the use of this method to transport heat between two objects is limited, because the Casimir force decreases rapidly in strength as the space between the objects is increased. It is only when the gap between two objects is of the order of a few nanometres that the Casimir force is strong enough for this heat-transfer mode to dominate over competing modes, such as photon tunnelling<sup><a href=\"https:\/\/www.nature.com\/articles\/d41586-019-03729-4?utm_source=feedburner&amp;utm_medium=feed&amp;utm_campaign=Feed%3A+nature%2Frss%2Fcurrent+%28Nature+-+Issue%29#ref-CR8\" data-track=\"click\" data-action=\"anchor-link\" data-track-label=\"go to reference\" data-track-category=\"references\">8<\/a><\/sup>.<\/p>\n<p>The authors discovered a way to amplify the Casimir mode of heat transfer so that it remains dominant even when the gap between the membranes is in the range of hundreds of nanometres. The membranes were carefully designed in such a way that their dimensions and the temperatures at which they were maintained allowed them to vibrate with their maximum possible displacements \u2014 in other words, at their natural frequencies. Thus, applications that are devised to exploit this heat-transfer mode to dissipate heat (such as in a hard-disk drive, where the distance between the writing head and the storage disk is a few nanometres) would require such careful design to ensure that the mode is amplified. Achieving this would be a challenge for the future.<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<\/div>\n<p><span class=\"emphasis\">Nature<\/span>\u00a0<strong>576<\/strong>, 216-217 (2019)<\/p>\n<p>&nbsp;<\/p>\n<div class=\"emphasis\">doi: 10.1038\/d41586-019-03729-4<\/div>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>(\uc6d0\ubb38: <a href=\"https:\/\/www.nature.com\/articles\/d41586-019-03729-4?utm_source=feedburner&amp;utm_medium=feed&amp;utm_campaign=Feed%3A+nature%2Frss%2Fcurrent+%28Nature+-+Issue%29\">\uc5ec\uae30<\/a>\ub97c \ud074\ub9ad\ud558\uc138\uc694~)<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>&nbsp; &nbsp; Experiments show that quantum fluctuations can allow heat to be transported between two objects separated by a vacuum gap. This effect could be<a href=\"https:\/\/biochemistry.khu.ac.kr\/lab\/?p=4883\" class=\"more-link\">(more&#8230;)<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[42,38,34,36,29],"tags":[],"class_list":["post-4883","post","type-post","status-publish","format-standard","hentry","category-06---07---","category-38","category-lets-do-chemistry","category-lets-do-physics","category-lets-do-science"],"aioseo_notices":[],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack-related-posts":[{"id":3805,"url":"https:\/\/biochemistry.khu.ac.kr\/lab\/?p=3805","url_meta":{"origin":4883,"position":0},"title":"The changing phase of data storage","author":"biochemistry","date":"June 19, 2019","format":false,"excerpt":"\u00a0 \u00a0 The combination of ferroelectrics and phase-change materials provides a route towards phase-change data storage at room temperature, without heating. \u00a0 \u00a0 The current pace of data creation is truly staggering; in 2018 alone, it amounted to 33 zettabytes1. The relentless growth of data generation is likely to continue\u2026","rel":"","context":"In &quot;Let's Do Chemistry!&quot;","block_context":{"text":"Let's Do Chemistry!","link":"https:\/\/biochemistry.khu.ac.kr\/lab\/?cat=34"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":4909,"url":"https:\/\/biochemistry.khu.ac.kr\/lab\/?p=4909","url_meta":{"origin":4883,"position":1},"title":"The physics of ice skating","author":"biochemistry","date":"December 19, 2019","format":false,"excerpt":"\u00a0 \u00a0 The slipperiness of ice is poorly understood at a microscopic level. Experiments that probe how the surface of ice melts and flows in response to wear help to explain the exceptionally low friction that underpins winter sports. \u00a0 \u00a0 It is widely thought that ice skating is enabled\u2026","rel":"","context":"In &quot;'05. \ubb3c\uc9c8\uc758 \uc9c4\ud654' \uad00\ub828&quot;","block_context":{"text":"'05. \ubb3c\uc9c8\uc758 \uc9c4\ud654' \uad00\ub828","link":"https:\/\/biochemistry.khu.ac.kr\/lab\/?cat=41"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":3485,"url":"https:\/\/biochemistry.khu.ac.kr\/lab\/?p=3485","url_meta":{"origin":4883,"position":2},"title":"A role for optics in AI hardware","author":"biochemistry","date":"May 9, 2019","format":false,"excerpt":"\u00a0 \u00a0 Experiments show how an all-optical version of an artificial neural network \u2014 a type of artificial-intelligence system \u2014 could potentially deliver better energy efficiency can conventional computing approaches. \u00a0 Optical fibres transmit data across the world in the form of light and are the backbone of modern telecommunications1.\u2026","rel":"","context":"In &quot;Let's Do Biology!&quot;","block_context":{"text":"Let's Do Biology!","link":"https:\/\/biochemistry.khu.ac.kr\/lab\/?cat=33"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":3255,"url":"https:\/\/biochemistry.khu.ac.kr\/lab\/?p=3255","url_meta":{"origin":4883,"position":3},"title":"All for one and one for all (QUANTUM OPTICS)","author":"biochemistry","date":"April 8, 2019","format":false,"excerpt":"\u00a0 \u00a0 Quantum information (QI) has become a focus of research during the past two decades, with the goal of exploiting the potentialities offered by superposition and entanglement of quantum states (1). The first hardware implementations of QI relied on quantum systems hosting clean, well-isolated two-level systems such as atoms\u2026","rel":"","context":"In &quot;Essays on Science&quot;","block_context":{"text":"Essays on Science","link":"https:\/\/biochemistry.khu.ac.kr\/lab\/?cat=32"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":4564,"url":"https:\/\/biochemistry.khu.ac.kr\/lab\/?p=4564","url_meta":{"origin":4883,"position":4},"title":"Light trapping gets a boost","author":"biochemistry","date":"October 24, 2019","format":false,"excerpt":"\u00a0 \u00a0 The ability of structures called optical resonators to trap light is often limited by scattering of light off fabrication defects. 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