Tus cwj pwm ntawm Mohr kab txaij thiab cov hlua khi hauv kev tshawb fawb ntawm kev tshawb fawb thiab quantum physics hu ua "Magic Angle" twisted bilayer graphene (TBLG) tau nyiam cov kws tshawb fawb, txawm tias muaj ntau lub zog ntsib kev sib cav sib ceg. Nyob rau hauv ib txoj kev tshawb fawb tshiab luam tawm nyob rau hauv phau ntawv Journal Science Progress, Emilio Colledo thiab cov kws tshawb fawb hauv Department of Physics thiab Materials Science hauv Tebchaws Meskas thiab Nyij Pooj tau soj ntsuam cov khoom siv hluav taws xob thiab kev sib piv hauv kev sib tw bilayer graphene. Lub xeev Mott insulator muaj lub kaum sab xis ntawm 0.93 degrees. Lub kaum sab xis no yog 15% me dua lub kaum sab xis "magic" (1.1 °) xam hauv kev tshawb fawb dhau los. Txoj kev tshawb no qhia tau hais tias qhov "magic angle" ntau yam ntawm twisted bilayer graphene yog loj dua li yav tas los xav.
Txoj kev tshawb no muab ntau cov ntaub ntawv tshiab rau kev txiav txim siab qhov muaj zog quantum phenomena hauv twisted bilayer graphene rau kev siv hauv quantum physics. Physicists txhais "Twistronics" raws li tus txheeb ze twist lub kaum sab xis ntawm cov nyob ib sab van der Waals txheej los tsim moiré thiab ca bands nyob rau 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 cuab yeej cuab tam raws li cov khoom siv ob sab kom ua tiav cov dej ntws tam sim no. Cov txiaj ntsig zoo kawg nkaus ntawm "Twistronics" tau ua piv txwv hauv kev ua haujlwm ntawm cov neeg tshawb nrhiav, ua kom pom tias thaum ob txheej txheej graphene ib leeg tau muab tso rau ntawm "magic angle" twist lub kaum sab xis ntawm θ = 1.1 ± 0.1 °, ib lub tiaj tiaj zoo nkauj heev. .
Nyob rau hauv txoj kev tshawb no, nyob rau hauv lub twisted bilayer graphene (TBLG), lub insulating theem ntawm thawj microstrip (cov yam ntxwv feature) ntawm lub superlattice ntawm lub "magic lub kaum sab xis" yog semi-filled. Pab neeg tshawb fawb tau txiav txim siab tias qhov no yog Mott insulator (ib qho insulator nrog superconducting zog) uas nthuav tawm superconductivity ntawm me ntsis siab dua thiab qis dua doping. Daim duab theem qhia tau hais tias qhov kub siab superconductor nruab nrab ntawm superconducting hloov kub (Tc) thiab Fermi kub (Tf). Qhov kev tshawb fawb no ua rau muaj kev txaus siab thiab kev sib cav tswv yim ntawm graphene band qauv, topology thiab ntxiv "Magic Angle" semiconductor systems. Piv nrog rau daim ntawv tshaj tawm theoretical qub, kev tshawb nrhiav kev sim tsis tshua muaj thiab nyuam qhuav pib. Nyob rau hauv txoj kev tshawb no, pab neeg no tau ua kev ntsuas kev sib kis ntawm "magic angle" twisted bilayer graphene uas qhia txog cov insulating thiab superconducting xeev.
Lub kaum sab xis distorted ntawm 0.93 ± 0.01, uas yog 15% me dua qhov tsim "Magic Angle", kuj yog qhov tsawg tshaj plaws tshaj tawm rau hnub tim thiab nthuav tawm cov khoom siv superconducting. Cov txiaj ntsig no qhia tau tias qhov kev sib raug zoo tshiab tuaj yeem tshwm sim hauv "Magic Angle" twisted bilayer graphene, qis dua thawj "magic angle", dhau ntawm thawj microstrip ntawm graphene. Txhawm rau tsim cov "magic horn" twisted bilayer graphene cov cuab yeej, pab pawg siv "kua kua muag thiab pawg" mus kom ze. Cov qauv ntawm hexagonal boron nitride (BN) txheej yog encapsulated; patterned rau hauv Hall rod geometry nrog ntau cov xov hlau txuas rau Cr/Au (chromium/gold) ntug hu. Tag nrho "Magic Angle" twisted bilayer graphene ntaus ntawv tau tsim nyob rau sab saum toj ntawm graphene txheej siv los ua lub rooj vag rov qab.
Cov kws tshawb fawb siv cov txheej txheem ncaj qha tam sim no (DC) thiab alternating tam sim no (AC) ntsuas ntsuas cov cuab yeej hauv cov twj tso kua mis HE4 thiab HE3 cryostats. Pab neeg no tau sau cov kev sib raug zoo ntawm cov cuab yeej longitudinal resistance (Rxx) thiab qhov txuas txuas ntawm qhov hluav taws xob (VG) ntau yam thiab suav cov magnetic teb B ntawm qhov kub ntawm 1.7K. Me me electron-qhov asymmetry tau pom tias yog ib qho cuab yeej ntawm "Magic Angle" twisted bilayer graphene ntaus ntawv. Raws li tau pom nyob rau hauv cov ntawv tshaj tawm dhau los, pab pawg tau sau cov txiaj ntsig no thiab piav qhia cov lus ceeb toom uas tau ua dhau los txog tam sim no. Tus yam ntxwv "Magic Angle" twists qhov tsawg kawg nkaus torsion lub kaum sab xis ntawm lub bilayer graphene ntaus ntawv. Nrog rau kev soj ntsuam ze dua ntawm Landau kiv cua daim ntawv qhia, cov kws tshawb fawb tau txais qee qhov tseem ceeb.
Piv txwv li, lub ncov ntawm ib nrab sau thiab ob-fold degeneracy ntawm Landau theem yog raws li yav tas los soj ntsuam Moment-zoo li rwb thaiv tsev xeev. Pab neeg no tau pom qhov tawg ntawm qhov sib npaug ntawm qhov sib npaug ntawm lub hav SU(4) thiab tsim cov quasi-particle Fermi tshiab. Txawm li cas los xij, cov ntsiab lus xav tau kev soj ntsuam kom ntxaws ntxiv. Cov tsos ntawm superconductivity kuj tau pom, uas nce Rxx (longitudinal resistance), zoo ib yam li cov kev tshawb fawb yav dhau los. Pab neeg no tau tshuaj xyuas qhov ntsuas kub tseem ceeb (Tc) ntawm theem superconducting. Txij li thaum tsis muaj cov ntaub ntawv tau txais kev pom zoo doping ntawm superconductors hauv cov qauv no, cov kws tshawb fawb tau xav tias qhov ntsuas kub tseem ceeb txog li 0.5K. Txawm li cas los xij, cov khoom siv no ua tsis tau zoo txog thaum lawv muaj peev xwm tau txais cov ntaub ntawv meej los ntawm lub xeev superconducting. Txhawm rau tshawb xyuas lub xeev superconducting, cov kws tshawb fawb tau ntsuas plaub qhov hluav taws xob tam sim no (VI) cov yam ntxwv ntawm cov khoom siv sib txawv.
Cov kev tawm tsam tau pom tias super tam sim no tau pom ntau tshaj qhov chaw qis dua thiab qhia txog kev nce qib ntawm super tam sim no thaum lub parallel sib nqus. Txhawm rau kom nkag siab txog tus cwj pwm tau pom hauv txoj kev tshawb fawb, cov kws tshawb fawb tau suav cov qauv Moir band ntawm "Magic Angle" twisted bilayer graphene cov cuab yeej siv Bistritzer-MacDonald qauv thiab txhim kho qhov tsis zoo. Piv nrog rau kev suav yav dhau los ntawm "Magic Angle" lub kaum ntse ntse, suav nrog lub zog qis Moire band tsis raug cais tawm ntawm lub zog siab. Txawm hais tias lub kaum sab xis ntawm lub cuab yeej yog me dua lub kaum sab xis "magic angle" xam nyob rau lwm qhov, cov cuab yeej muaj qhov tshwm sim uas muaj feem xyuam nrog cov kev tshawb fawb yav dhau los (Mort rwb thaiv tsev thiab superconductivity), uas cov kws tshawb fawb pom tias tsis xav txog thiab ua tau.
Tom qab txuas ntxiv ntsuas tus cwj pwm loj (tus naj npawb ntawm cov xeev muaj nyob rau ntawm txhua lub zog), cov yam ntxwv tau pom tias cov kws tshawb fawb pom tau tias muaj cov koom haum uas tshiab tshiab. Nyob rau hauv lub neej yav tom ntej, kev tshawb fawb ntxaws ntxiv ntawm qhov ntom ntom ntawm cov xeev (DOS) yuav raug ua kom nkag siab txog lub xeev khib nyiab thiab txiav txim siab seb lawv puas tuaj yeem faib ua quantum spin kua. Nyob rau hauv txoj kev no, cov kws tshawb fawb pom superconductivity nyob ze ntawm Mox zoo li insulating lub xeev nyob rau hauv ib tug twisted bilayer graphene ntaus ntawv nrog ib tug me me twist kaum (0.93 °). Txoj kev tshawb no qhia tau hais tias txawm nyob rau ntawm cov ces kaum me me thiab siab ceev, cov nyhuv ntawm electron correlation ntawm cov khoom ntawm moiré yog tib yam. Nyob rau hauv lub neej yav tom ntej, lub spin valleys ntawm lub insulating theem yuav kawm, thiab ib tug tshiab superconducting theem yuav tau kawm nyob rau hauv ib tug qis kub. Kev sim kev tshawb fawb yuav ua ke nrog kev siv theoretical kom nkag siab txog keeb kwm ntawm tus cwj pwm no.
Post lub sij hawm: Oct-08-2019