Indlela yokuziphatha kwemigca kaMohr kunye neebhanti ezithe tyaba kwisayensi yesayensi kunye nefiziksi ye-quantum ebizwa ngokuba yi-"Magic Angle" twisted bilayer graphene (TBLG) itsale umdla omkhulu koososayensi, nangona iipropati ezininzi zijongene nengxoxo eshushu. Kwisifundo esitsha esipapashwe kwijenali iScience Progress, u-Emilio Colledo kunye noososayensi kwiSebe leFiziksi kunye neSayensi yezinto eMelika naseJapan baqaphele i-superconductivity kunye ne-analogy kwi-twisted bilayer graphene. Imeko ye-Mott insulator ine-twist angle emalunga ne-0.93 degrees. Le angle incinci nge-15% kune-"magic angle" angle (1.1°) ebalwe kwisifundo sangaphambili. Olu phononongo lubonisa ukuba uluhlu "lwe-magic angle" lwe-twisted bilayer graphene lukhulu kunokuba bekulindelwe ngaphambili.
Olu phononongo lubonelela ngolwazi olutsha oluninzi lokufumanisa izinto ezinamandla ze-quantum kwi-twisted bilayer graphene kwizicelo kwi-quantum physics. Iingcali zefiziksi zichaza "i-Twistronics" njenge-relative twist angle phakathi kwe-van der Waals layers ezikufutshane ukuvelisa i-moiré kunye ne-flat bands kwi-graphene. Le ngcamango ibe yindlela entsha neyodwa yokutshintsha kakhulu nokwenza ngokwezifiso iipropati zesixhobo ngokusekelwe kwizixhobo ezinemilinganiselo emibini ukufezekisa ukuhamba kwangoku. Isiphumo esimangalisayo se-"Twistronics" siboniswe kumsebenzi wokuqala wabaphandi, obonisa ukuba xa iileya ezimbini ze-graphene ezineleya enye zibekwe kwi-"magic angle" twist angle ye-θ=1.1±0.1°, kuvela ibhendi ethe tyaba kakhulu.
Kolu phononongo, kwi-twisted bilayer graphene (TBLG), isigaba sokukhusela se-microstrip yokuqala (uphawu lwesakhiwo) se-superlattice kwi-"magic angle" yayizaliswe kancinci. Iqela lophando lifumanise ukuba le yi-Mott insulator (isivikelo esineempawu ze-superconducting) esibonisa i-superconductivity kumanqanaba aphezulu kancinci naphantsi e-doping. Umzobo wesigaba ubonisa i-superconductor yobushushu obuphezulu phakathi kobushushu botshintsho lwe-superconducting (Tc) kunye nobushushu be-Fermi (Tf). Olu phando lukhokelele kumdla omkhulu kunye nengxoxo yethiyori malunga nesakhiwo sebhendi ye-graphene, i-topology kunye neenkqubo ezongezelelweyo ze-semiconductor ze-"Magic Angle". Xa kuthelekiswa nengxelo yokuqala yethiyori, uphando lovavanyo aluqhelekanga kwaye lusandula ukuqala. Kolu phononongo, iqela lenze imilinganiselo yokudlulisela kwi-"magic angle" twisted bilayer graphene ebonisa iimeko ezifanelekileyo zokukhusela kunye ne-superconducting.
I-engile egqwethekileyo engalindelekanga ye-0.93 ± 0.01, encinci nge-15% kune-"Magic Angle" esekwe, nayo yeyona incinci exeliweyo ukuza kuthi ga ngoku kwaye ibonisa iimpawu ze-superconducting. Ezi ziphumo zibonisa ukuba imeko entsha yokuhambelana inokuvela kwi-"Magic Angle" twisted bilayer graphene, engaphantsi kune-"magic angle" yokuqala, ngaphaya kwe-microstrip yokuqala ye-graphene. Ukwakha ezi zixhobo ze-"magic horn" twisted bilayer graphene, iqela lisebenzise indlela "yokukrazula nokubeka". Ulwakhiwo phakathi kwe-hexagonal boron nitride (BN) layers lufakwe ngaphakathi; lubekwe kwi-Hall rod geometry eneengcingo ezininzi ezidityaniswe kwii-contacts ze-Cr/Au (chromium/gold). Isixhobo se-graphene se-"Magic Angle" twisted bilayer senziwe phezu kwe-graphene layer esetyenziswa njengesango elingasemva.
Izazinzulu zisebenzisa iindlela zokutshixa ezisemgangathweni (DC) kunye neendlela zokutshixa ezitshintshanayo (AC) ukulinganisa izixhobo kwi-HE4 kunye ne-HE3 cryostats ezipompiweyo. Iqela lirekhode ubudlelwane phakathi kokumelana kwexesha elide (Rxx) kwesixhobo kunye nobubanzi be-voltage yesango elandisiweyo (VG) kwaye labala i-magnetic field B kubushushu be-1.7K. I-asymmetry encinci ye-electron-hole ibonwe njengepropathi yendalo yesixhobo se-graphene esijijekileyo se-"Magic Angle". Njengoko kubonwe kwiingxelo zangaphambili, iqela lirekhode ezi ziphumo kwaye lichaze iingxelo ebeziqhuba kakuhle ukuza kuthi ga ngoku. I-"Magic Angle" ephawulekayo ijika i-angle encinci ye-torsion yesixhobo se-graphene se-bilayer. Ngokuphonononga ngokusondeleyo itshathi yefeni yeLandau, abaphandi bafumene iimpawu ezithile eziphawulekayo.
Umzekelo, incochoyi ekuzaliseni isiqingatha kunye nokuwohloka okuphindwe kabini kwenqanaba leLandau kuhambelana neemeko zokufakelwa ezifana neMoment ezibonwe ngaphambili. Iqela libonise ukuphuka kulungelelwaniso lwe-approximate spin valley SU(4) kunye nokwakheka komphezulu omtsha we-quasi-particle Fermi. Nangona kunjalo, iinkcukacha zifuna uhlolo oluneenkcukacha ngakumbi. Ukubonakala kwe-superconductivity nako kwabonwa, okwanyusa i-Rxx (ukumelana kwexesha elide), okufana nezifundo zangaphambili. Iqela emva koko lahlola ubushushu obubalulekileyo (Tc) besigaba se-superconducting. Ekubeni kungekho datha ifunyenweyo yokusetyenziswa kwe-doping efanelekileyo kwe-superconductors kule sampuli, izazinzulu zicinge ukuba ubushushu obubalulekileyo bufikelela kwi-0.5K. Nangona kunjalo, ezi zixhobo azisebenzi de zikwazi ukufumana idatha ecacileyo evela kwimeko ye-superconducting. Ukuze baphande ngakumbi imeko ye-superconducting, abaphandi balinganise iimpawu ze-voltage-current (VI) ezine-terminal yesixhobo kwiindidi ezahlukeneyo zokuthwala.
Ukumelana okufunyenweyo kubonisa ukuba i-super current ibonwa kuluhlu olukhulu loxinano kwaye ibonisa ukucinezelwa kwe-super current xa kusetyenziswa i-magnetic field efanayo. Ukuze bafumane ukuqonda ngokuziphatha okubonwe kolu phononongo, abaphandi babale ulwakhiwo lwe-Moir band yesixhobo se-graphene esijijekileyo se-"Magic Angle" besebenzisa imodeli yeBistritzer-MacDonald kunye neeparameter eziphuculweyo. Xa kuthelekiswa nokubalwa kwangaphambili kwe-angle ye-"Magic Angle", i-Moire band enee-low energy ebaliweyo ayihlukaniswanga kwi-high energy band. Nangona i-angle ye-twist yesixhobo incinci kune-angle ye-"magic angle" ebalwe kwenye indawo, esi sixhobo sinento enxulumene kakhulu nezifundo zangaphambili (i-Mort insulation kunye ne-superconductivity), ezifunyenwe zizazinzulu ukuba azilindelwanga kwaye zinokwenzeka.
Emva kokuvavanya ngakumbi indlela yokuziphatha kwi-large densities (inani le-states ezikhoyo kwi-energy nganye), iimpawu ezibonwe zizazinzulu zibangelwa yi-insulation states ezisandula kuvela. Kwixesha elizayo, kuza kwenziwa uphando oluneenkcukacha ngakumbi lwe-density of states (DOS) ukuze kuqondwe imeko engaqhelekanga ye-insulation kunye nokufumanisa ukuba zingahlulwa njenge-quantum spin liquids. Ngale ndlela, izazinzulu zibone i-superconductivity kufutshane ne-Mox-like insulation state kwisixhobo se-graphene esijijekileyo esine-twist small twist angle (0.93°). Olu phononongo lubonisa ukuba nakwii-engile ezincinci kunye ne-high densities, isiphumo se-electron correlation kwi-properties ze-moiré siyafana. Kwixesha elizayo, ii-spin valleys ze-insulation phase ziya kufundwa, kwaye i-superconducting phase entsha iya kufundwa kubushushu obuphantsi. Uphando lovavanyo luya kudityaniswa nemizamo yethiyori yokuqonda imvelaphi yale ndlela yokuziphatha.
Ixesha lokuthumela: Okthobha-08-2019