Khalidwe la mikwingwirima ya Mohr ndi malamba athyathyathya mu sayansi ya sayansi ndi fizikisi ya quantum yotchedwa "Magic Angle" twisted bilayer graphene (TBLG) lakopa chidwi chachikulu kuchokera kwa asayansi, ngakhale kuti zinthu zambiri zikukumana ndi mkangano waukulu. Mu kafukufuku watsopano wofalitsidwa mu magazini ya Science Progress, Emilio Colledo ndi asayansi mu Dipatimenti ya Fizikisi ndi Sayansi ya Zinthu ku United States ndi Japan adawona superconductivity ndi kufanana mu twisted bilayer graphene. Mott insulator state ili ndi twist angle ya pafupifupi madigiri 0.93. Ngodya iyi ndi yocheperako ndi 15% kuposa ngodya ya "magic angle" (1.1°) yomwe idawerengedwa mu kafukufuku wapitawu. Kafukufukuyu akuwonetsa kuti "magic angle" ya twisted bilayer graphene ndi yayikulu kuposa momwe amayembekezera kale.
Kafukufukuyu akupereka chidziwitso chatsopano chochuluka chothandizira kumvetsetsa zochitika zamphamvu za quantum mu twisted bilayer graphene kuti zigwiritsidwe ntchito mu quantum physics. Akatswiri a fizikisi amatanthauzira "Twistronics" ngati ngodya yozungulira pakati pa zigawo za van der Waals zomwe zili pafupi kuti apange moiré ndi flat bands mu graphene. Lingaliro ili lakhala njira yatsopano komanso yapadera yosinthira kwambiri ndikusintha mawonekedwe a chipangizocho kutengera zida ziwiri kuti zikwaniritse kuyenda kwa magetsi. Zotsatira zodabwitsa za "Twistronics" zidawonetsedwa mu ntchito yoyambirira ya ofufuza, zomwe zikuwonetsa kuti pamene zigawo ziwiri za single-layer graphene zimayikidwa pa "magic angle" twist angle ya θ=1.1±0.1°, gulu losalala kwambiri limawonekera.
Mu kafukufukuyu, mu twisted bilayer graphene (TBLG), gawo loteteza kutentha la microstrip yoyamba (kapangidwe kake) ya superlattice pa "ngodya yamatsenga" linali lodzaza theka. Gulu lofufuza linapeza kuti iyi ndi Mott insulator (insulator yokhala ndi mphamvu zowongolera mphamvu) yomwe imawonetsa superconductivity pamlingo wapamwamba pang'ono komanso wotsika wa doping. Chithunzi cha gawo chikuwonetsa superconductor yotenthetsera kutentha kwambiri pakati pa kutentha kwa superconducting transition (Tc) ndi kutentha kwa Fermi (Tf). Kafukufukuyu adabweretsa chidwi chachikulu komanso mkangano wokhudza chiphunzitso cha kapangidwe ka gulu la graphene, topology ndi machitidwe ena a semiconductor a "Magic Angle". Poyerekeza ndi lipoti loyambirira la chiphunzitso, kafukufuku woyesera ndi wosowa ndipo wangoyamba kumene. Mu kafukufukuyu, gululi lidachita miyeso yotumizira pa "ngodya yamatsenga" twisted bilayer graphene yowonetsa momwe zinthu zotetezera kutentha ndi superconducting zimakhalira.
Ngodya yosokonezeka mosayembekezereka ya 0.93 ± 0.01, yomwe ndi yocheperako ndi 15% kuposa "Magic Angle" yokhazikitsidwa, ndiyonso yaying'ono kwambiri yomwe yanenedwa mpaka pano ndipo ikuwonetsa mphamvu zowongolera kwambiri. Zotsatirazi zikusonyeza kuti mkhalidwe watsopano wa ubale ukhoza kuwonekera mu "Magic Angle" twisted bilayer graphene, yotsika kuposa "magic angle" yoyamba, kupitirira microstrip yoyamba ya graphene. Kuti apange zida izi za "magic horn" twisted bilayer graphene, gululi linagwiritsa ntchito njira ya "kung'amba ndi kuyika". Kapangidwe ka pakati pa zigawo za hexagonal boron nitride (BN) kamayikidwa mkati; kamapangidwa kukhala mawonekedwe a Hall rod geometry yokhala ndi mawaya angapo olumikizidwa ku ma contacts a Cr/Au (chromium/gold). Chipangizo chonse cha "Magic Angle" twisted bilayer graphene chinapangidwa pamwamba pa graphene layer yomwe imagwiritsidwa ntchito ngati chipata chakumbuyo.
Asayansi amagwiritsa ntchito njira zomangira magetsi mwachindunji (DC) ndi alternating current (AC) poyesa zipangizo mu HE4 ndi HE3 cryostats zopompedwa. Gululi linalemba ubale pakati pa longitudinal resistance (Rxx) ya chipangizochi ndi extended gate voltage (VG) range ndipo linawerengera mphamvu ya maginito B pa kutentha kwa 1.7K. Kusagwirizana kwa ma electron-hole pang'ono kunawonedwa kuti ndi chinthu chodziwika bwino cha chipangizo cha "Magic Angle" chopotoka bilayer graphene. Monga taonera m'malipoti am'mbuyomu, gululi linalemba zotsatira izi ndikufotokozera malipoti omwe akhala akuchita superconducting mpaka pano. "Magic Angle" yodziwika bwino imapotoza ngodya yocheperako ya chipangizo cha bilayer graphene. Poyang'anitsitsa tchati cha fan cha Landau, ofufuza adapeza zinthu zina zodziwika bwino.
Mwachitsanzo, nsonga ya theka la kudzazidwa ndi kufooka kwa kawiri kwa mulingo wa Landau zikugwirizana ndi momwe zinthu zinalili kale. Gululi linawonetsa kusweka kwa kusinthasintha kwa chigwa cha SU(4) chozungulira komanso kupangika kwa malo atsopano a Fermi. Komabe, tsatanetsataneyo amafunikira kuwunika kwatsatanetsatane. Kuwonekera kwa superconductivity kunawonedwanso, komwe kunawonjezera Rxx (kukana kwa nthawi yayitali), mofanana ndi maphunziro am'mbuyomu. Gululo kenako linayang'ana kutentha kofunikira (Tc) kwa gawo la superconducting. Popeza palibe deta yomwe idapezeka yokhudza doping yabwino ya ma superconductors mu chitsanzochi, asayansi adaganiza kuti kutentha kofunikira mpaka 0.5K. Komabe, zida izi zimakhala zosagwira ntchito mpaka zitatha kupeza deta yomveka bwino kuchokera ku superconducting state. Kuti apitirize kufufuza momwe superconducting state ilili, ofufuzawo anayeza makhalidwe a voltage-current (VI) ya chipangizocho pamitundu yosiyanasiyana ya carrier.
Kukana komwe kwapezeka kukuwonetsa kuti mphamvu yamagetsi ya supercurrent imawonedwa pamlingo waukulu wa density ndipo kumawonetsa kuletsa kwa mphamvu yamagetsi ya supercurrent pamene mphamvu yamagetsi yofanana ikugwiritsidwa ntchito. Kuti amvetsetse momwe zinthu zilili mu kafukufukuyu, ofufuzawo adawerengera kapangidwe ka gulu la Moir la chipangizo cha graphene chopotoka cha "Magic Angle" pogwiritsa ntchito chitsanzo cha Bistritzer-MacDonald ndi magawo okonzedwa bwino. Poyerekeza ndi kuwerengera kwakale kwa ngodya ya "Magic Angle", gulu la Moire lomwe lili ndi mphamvu zochepa silimasiyana ndi gulu lamphamvu kwambiri. Ngakhale ngodya yopotoka ya chipangizocho ndi yaying'ono kuposa ngodya ya "magic angle" yomwe idawerengedwa kwina, chipangizocho chili ndi chinthu chomwe chikugwirizana kwambiri ndi maphunziro am'mbuyomu (Mort insulation ndi superconductivity), zomwe akatswiri a sayansi ya zakuthambo adapeza kuti sizosayembekezereka komanso zotheka.
Pambuyo pofufuza mozama za khalidweli pa kuchuluka kwakukulu (chiwerengero cha momwe zinthu zilili pa mphamvu iliyonse), makhalidwe omwe asayansiwa akuwona akugwirizanitsidwa ndi momwe zinthu zatsopano zotetezera zimakhalira. M'tsogolomu, kafukufuku wowonjezereka wa kuchuluka kwa zinthu (DOS) adzachitika kuti amvetsetse momwe zinthu zilili komanso kuti adziwe ngati zingathe kugawidwa ngati madzi a quantum spin. Mwanjira imeneyi, asayansi adawona kuti mphamvu yoyendetsa magetsi ili pafupi ndi mphamvu yoteteza magetsi ya Mox mu chipangizo cha graphene chopindika chokhala ndi ngodya yaying'ono yopotoka (0.93°). Kafukufukuyu akuwonetsa kuti ngakhale pa ngodya zazing'ono komanso kuchuluka kwakukulu, zotsatira za kulumikizana kwa ma electron pa katundu wa moiré ndi zomwezo. M'tsogolomu, zigwa za spin za gawo lotetezera magetsi zidzaphunziridwa, ndipo gawo latsopano loyendetsa magetsi lidzaphunziridwa pa kutentha kochepa. Kafukufuku woyesera adzaphatikizidwa ndi zoyesayesa za chiphunzitso kuti amvetse chiyambi cha khalidweli.
Nthawi yotumizira: Okutobala-08-2019