Insider Brief<\/p>\n
Berkeley Lab researchers observed a tunable Bose-Einstein condensate of excitons in an atomically thin semiconductor, creating a controllable platform for studying quantum fluids in solid materials. <\/p>\n
The exciton condensate persisted up to about 2 Kelvin and could be tuned electrically, overcoming key limitations of short-lived, optically generated excitons. <\/p>\n
Researchers found the condensate has multiple internal spin-valley structures that can be switched with a magnetic field, with potential applications in quantum simulation, optoelectronics and future superfluid-based devices.<\/p>\n
Image: Schematic of a bilayer 2D semiconducting device.\u00a0(Ruishi Qi\/Berkeley Lab)<\/p>\n
PRESS RELEASE \u2014 Bose-Einstein Condensates (BECs) are often described as a \u201cfifth state of matter\u201d: a quantum state in which many particles lose their individual identities and behave as one collective object. For more than 60 years, researchers have sought to create such condensates from excitons \u2014 electron-hole pairs \u2014 as a solid-state route to macroscopic quantum coherence, which is useful for quantum technologies. This has been difficult to realize in controllable semiconductor devices because optically generated excitons have very short lifespans of around a billionth of a second, and BECs are normally attained with supercold gasses in a vacuum.\u00a0<\/p>\n
But now, a team led by Lawrence Berkeley National Laboratory<\/a> (Berkeley Lab) has observed a tunable BEC of excitons at high temperature in an atomically thin semiconductor. The findings, published in\u00a0Nature<\/a>, reveal not only that the excitons form a BEC, but also that the condensate has an internal structure that can be switched by a magnetic field.\u00a0<\/p>\n The work enables a new platform for studying quantum fluids in solid materials. (A quantum fluid is\u00a0an exotic state of matter in which gasses of electrons or other particles behave collectively like a fluid.) It also has implications for future quantum simulations, coherent optoelectronics in next-generation telecommunications and computing, and exciton-based devices enabling faster, more efficient computing.\u00a0<\/p>\n \u201cWhile previous studies have shown that electrons and holes can bind into excitons, there wasn\u2019t an easy way to determine whether those excitons formed a condensate, nor could they ascertain what kind of internal quantum order that condensate has. Our work provides a way to access that hidden structure directly,\u201d said principal investigator Feng Wang. He is a faculty senior scientist in Berkeley Lab\u2019s Materials Sciences Division and a professor in UC Berkeley\u2019s Department of Physics.\u00a0\u00a0<\/p>\n In many experiments, excitons are created by light and exist only as short-lived excited states. In the new study, Wang and team counter this transience by engineering a 2D semiconducting device with excitons in the ground state rather than an excited state. The researchers predicted that such a system would enable the excitons to reach equilibrium and persist as a BEC.<\/p>\n Using a technique called magneto-optical spectroscopy under cryogenic conditions, the researchers cooled the device down to a temperature near absolute zero and measured how the electron and hole components responded to small magnetic fields. Electrical gates above and below the device allow researchers to tune the density of these excitons.<\/p>\n The excitons performed collectively as predicted, but the researchers were surprised to find that the condensate signatures persisted up to about 2 Kelvin \u2014 still very cold but millions of times warmer than previous BEC demonstrations in ultracold atomic gases.\u00a0<\/p>\n \u201cWhat is unusual here is that the excitons are not just short-lived particles created by light. They form an equilibrium quantum fluid in a device that we can tune electrically and magnetically,\u201d explained Ruishi Qi, a co-first author on the paper and a former doctoral researcher in Berkeley Lab\u2019s Materials Sciences Division.\u00a0\u00a0<\/p>\n In the atomically thin semiconductors, electrons and holes carry not only charge and spin, but also a quantum property known as \u201cvalley,\u201d which is tied to their motion \u2014 or degrees of freedom \u2014 inside the crystalline material. These spin\u2013valley degrees of freedom give excitons multiple possible \u201cflavors\u201d or spin patterns, such as up-up, down-down, up-down, or down-up. In the current study, the Berkeley Lab-led team found that the BEC is not a simple one-flavor quantum state: It has two components, each with different flavors of internal spin\u2013valley structure. This gives rise to multiple distinct condensate phases that can be switched by a magnetic field.<\/p>\n \u201cThe exciting part is that this is not just a simple condensate,\u201d Qi said. \u201cIt has internal structures that we can control. By simply applying a small magnetic field, we can switch the same exciton fluid between different quantum states.\u201d\u00a0 \u00a0<\/p>\n In future work, the researchers hope to demonstrate superfluid-based quantum devices and circuits building on the exciton BEC.\u00a0<\/p>\n Researchers from UC Berkeley; the University of Texas at Austin; and the National Institute for Materials Science, Japan, contributed to the study.\u00a0\u00a0<\/p>\n This work was supported by the DOE Office of Science.\u00a0<\/p>\n","protected":false},"excerpt":{"rendered":"Insider Brief Berkeley Lab researchers observed a tunable Bose-Einstein condensate of excitons in an atomically thin semiconductor, creating…\n","protected":false},"author":2,"featured_media":810067,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[49],"tags":[199,79],"class_list":["post-810066","post","type-post","status-publish","format-standard","has-post-thumbnail","category-physics","tag-physics","tag-science"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts\/810066","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/comments?post=810066"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts\/810066\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/media\/810067"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/media?parent=810066"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/categories?post=810066"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/tags?post=810066"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}