Tus cwj pwm ntawm Mohr kab txaij thiab cov siv tiaj tiaj hauv kev tshawb fawb txog kev tshawb fawb thiab quantum physics hu ua "Magic Angle" twisted bilayer graphene (TBLG) tau nyiam cov kws tshawb fawb heev, txawm hais tias ntau yam khoom ntsib kev sib cav sib ceg kub. Hauv kev tshawb fawb tshiab luam tawm hauv phau ntawv xov xwm Science Progress, Emilio Colledo thiab cov kws tshawb fawb hauv Department of Physics thiab Materials Science hauv Tebchaws Meskas thiab Nyiv Pooj tau pom superconductivity thiab kev sib piv hauv twisted bilayer graphene. Lub xeev Mott insulator muaj lub kaum sab xis ntawm kwv yees li 0.93 degrees. Lub kaum sab xis no yog 15% me dua li lub kaum sab xis "magic angle" (1.1 °) xam hauv kev tshawb fawb yav dhau los. Kev tshawb fawb no qhia tau hais tias qhov ntau ntawm "magic angle" ntawm twisted bilayer graphene loj dua li qhov xav tau yav dhau los.
Txoj kev tshawb fawb no muab ntau cov ntaub ntawv tshiab rau kev txhais cov xwm txheej quantum muaj zog hauv twisted bilayer graphene rau kev siv hauv quantum physics. Cov kws tshawb fawb txhais "Twistronics" ua lub kaum sab xis sib piv ntawm cov khaubncaws sab nraud povtseg van der Waals uas nyob ib sab los tsim cov moiré thiab cov kab tiaj tiaj hauv graphene. Lub tswv yim no tau dhau los ua ib txoj hauv kev tshiab thiab tshwj xeeb rau kev hloov pauv thiab kho cov khoom siv raws li cov ntaub ntawv ob-seem kom ua tiav cov dej ntws tam sim no. Qhov cuam tshuam zoo kawg nkaus ntawm "Twistronics" tau ua piv txwv hauv kev ua haujlwm thawj zaug ntawm cov kws tshawb fawb, qhia tias thaum ob txheej graphene ib txheej raug teeb tsa ntawm "lub kaum sab xis khawv koob" lub kaum sab xis ntawm θ = 1.1 ± 0.1 °, ib txoj kab tiaj tiaj heev tshwm sim.
Hauv kev tshawb fawb no, hauv cov graphene twisted bilayer (TBLG), theem insulating ntawm thawj microstrip (cov yam ntxwv ntawm cov qauv) ntawm superlattice ntawm "magic angle" yog semi-filled. Pab pawg tshawb fawb tau txiav txim siab tias qhov no yog Mott insulator (ib qho insulator nrog cov khoom superconducting) uas qhia txog superconductivity ntawm qib siab dua thiab qis dua me ntsis doping. Daim duab theem qhia txog qhov kub siab superconductor ntawm qhov kub hloov pauv superconducting (Tc) thiab qhov kub Fermi (Tf). Kev tshawb fawb no ua rau muaj kev txaus siab thiab kev sib cav txog kev xav txog graphene band qauv, topology thiab ntxiv "Magic Angle" semiconductor systems. Piv nrog rau daim ntawv qhia theoretical thawj, kev tshawb fawb sim tsis tshua muaj thiab nyuam qhuav pib. Hauv kev tshawb fawb no, pab pawg neeg tau ua qhov kev ntsuas kis ntawm "magic angle" twisted bilayer graphene qhia txog cov xwm txheej insulating thiab superconducting.
Lub kaum sab xis uas tsis tau xav txog ntawm 0.93 ± 0.01, uas yog 15% me dua li "Magic Angle", kuj yog qhov me tshaj plaws uas tau tshaj tawm txog niaj hnub no thiab qhia txog cov khoom superconducting. Cov txiaj ntsig no qhia tau tias lub xeev sib raug zoo tshiab tuaj yeem tshwm sim hauv "Magic Angle" twisted bilayer graphene, qis dua li thawj "magic angle", dhau ntawm thawj microstrip ntawm graphene. Txhawm rau tsim cov "magic horn" twisted bilayer graphene devices, pab pawg neeg tau siv txoj hauv kev "rhuav thiab sib sau ua ke". Cov qauv ntawm cov khaubncaws sab nraud povtseg hexagonal boron nitride (BN) yog encapsulated; patterned rau hauv Hall rod geometry nrog ntau lub xov hlau txuas nrog Cr / Au (chromium / kub) ntug kev sib cuag. Tag nrho "Magic Angle" twisted bilayer graphene device tau tsim rau saum cov txheej graphene siv ua lub rooj vag tom qab.
Cov kws tshawb fawb siv cov txheej txheem xauv hluav taws xob ncaj qha (DC) thiab hloov pauv hluav taws xob (AC) los ntsuas cov khoom siv hauv cov twj tso kua mis HE4 thiab HE3 cryostats. Pab neeg tau sau tseg kev sib raug zoo ntawm lub cuab yeej lub zog tiv thaiv ntev (Rxx) thiab qhov hluav taws xob ntawm lub rooj vag ntev (VG) thiab xam lub zog sib nqus B ntawm qhov kub ntawm 1.7K. Qhov tsis sib xws me me ntawm lub qhov hluav taws xob tau pom tias yog ib qho khoom muaj nqis ntawm "Magic Angle" twisted bilayer graphene device. Raws li tau pom hauv cov ntawv ceeb toom dhau los, pab neeg tau sau tseg cov txiaj ntsig no thiab piav qhia txog cov ntawv ceeb toom uas tau ua superconducting txog tam sim no. Tus yam ntxwv "Magic Angle" twistes lub kaum sab xis tsawg kawg nkaus ntawm lub cuab yeej bilayer graphene. Nrog kev tshuaj xyuas ze dua ntawm Landau kiv cua daim ntawv qhia, cov kws tshawb fawb tau txais qee yam ntxwv tseem ceeb.
Piv txwv li, qhov siab tshaj plaws ntawm ib nrab sau thiab qhov ob npaug degeneracy ntawm Landau theem yog sib xws nrog cov xwm txheej rwb thaiv tsev zoo li Moment uas tau pom ua ntej. Pab neeg tau qhia txog kev tawg hauv qhov sib npaug ntawm qhov kwv yees spin valley SU (4) thiab kev tsim ntawm qhov chaw quasi-particle Fermi tshiab. Txawm li cas los xij, cov ntsiab lus xav tau kev tshuaj xyuas kom ntxaws ntxiv. Qhov tshwm sim ntawm superconductivity kuj tau pom, uas ua rau Rxx (longitudinal resistance), zoo ib yam li cov kev tshawb fawb yav dhau los. Pab neeg tom qab ntawd tau tshuaj xyuas qhov kub tseem ceeb (Tc) ntawm theem superconducting. Vim tias tsis muaj cov ntaub ntawv tau txais rau kev doping zoo tshaj plaws ntawm cov superconductors hauv cov qauv no, cov kws tshawb fawb xav tias qhov kub tseem ceeb txog li 0.5K. Txawm li cas los xij, cov khoom siv no ua tsis zoo kom txog thaum lawv tuaj yeem tau txais cov ntaub ntawv meej los ntawm lub xeev superconducting. Txhawm rau tshawb nrhiav ntxiv txog lub xeev superconducting, cov kws tshawb fawb tau ntsuas plaub-terminal voltage-current (VI) yam ntxwv ntawm lub cuab yeej ntawm ntau qhov sib txawv ntawm cov neeg nqa khoom.
Qhov kev tiv thaiv tau txais qhia tau hais tias super current raug pom hla qhov ntau ntawm qhov ceev thiab qhia txog kev txo qis ntawm super current thaum siv lub zog sib nqus sib luag. Txhawm rau kom nkag siab txog tus cwj pwm pom hauv kev tshawb fawb, cov kws tshawb fawb tau xam cov qauv Moir band ntawm "Magic Angle" twisted bilayer graphene device siv Bistritzer-MacDonald tus qauv thiab cov kev ntsuas zoo dua. Piv rau qhov kev xam yav dhau los ntawm "Magic Angle" lub kaum sab xis, qhov kev xam qis zog Moire band tsis raug cais tawm ntawm qhov siab zog band. Txawm hais tias lub cuab yeej lub kaum sab xis twist me dua li lub kaum sab xis "magic angle" uas tau xam rau lwm qhov, lub cuab yeej muaj qhov tshwm sim uas muaj feem cuam tshuam nrog kev tshawb fawb yav dhau los (Mort insulation thiab superconductivity), uas cov kws kho mob pom tias tsis tau xav txog thiab ua tau.
Tom qab soj ntsuam ntxiv txog tus cwj pwm ntawm qhov ceev loj (tus naj npawb ntawm cov xeev muaj nyob rau txhua lub zog), cov yam ntxwv uas cov kws tshawb fawb pom tau yog vim cov xeev rwb thaiv tsev tshiab. Yav tom ntej, yuav muaj kev tshawb fawb ntxiv txog qhov ceev ntawm cov xeev (DOS) kom nkag siab txog qhov xwm txheej txawv ntawm rwb thaiv tsev thiab txiav txim siab seb lawv puas tuaj yeem raug cais ua cov kua quantum spin. Ua li no, cov kws tshawb fawb tau pom superconductivity ze ntawm Mox-zoo li insulating lub xeev hauv lub twisted bilayer graphene device nrog lub kaum sab xis me me (0.93 °). Txoj kev tshawb fawb no qhia tau tias txawm tias ntawm cov ces kaum me me thiab qhov ceev siab, qhov cuam tshuam ntawm electron correlation rau cov khoom ntawm moiré yog tib yam. Yav tom ntej, cov kwj deg spin ntawm theem rwb thaiv tsev yuav raug kawm, thiab theem superconducting tshiab yuav raug kawm ntawm qhov kub qis dua. Kev tshawb fawb sim yuav raug ua ke nrog kev siv zog theoretical kom nkag siab txog keeb kwm ntawm tus cwj pwm no.
Lub sijhawm tshaj tawm: Lub Kaum Hli-08-2019