Ukuziphatha kwe-Mohr stripes kanye namabhande ayisicaba kwisayensi yesayensi kanye ne-quantum physics okubizwa ngokuthi i-“Magic Angle” twisted bilayer graphene (TBLG) kudonsele isithakazelo esikhulu kososayensi, yize izakhiwo eziningi zibhekene nempikiswano eshisayo. Esifundweni esisha esanyatheliswa kuyi-Science Progress, u-Emilio Colledo kanye nososayensi eMnyangweni Wefiziksi Nesayensi Yezinto Ezisetshenziswayo e-United States naseJapan babone i-superconductivity kanye nokufana kwi-twisted bilayer graphene. Isimo se-Mott insulator sine-twist angle engaba ngu-0.93 degrees. Le angle incane ngo-15% kune-“magic angle” angle (1.1°) ebalwe esifundweni esedlule. Lolu cwaningo lubonisa ukuthi ububanzi “be-magic angle” be-twisted bilayer graphene bukhulu kunalokho obekulindelwe ngaphambilini.
Lolu cwaningo luhlinzeka ngolwazi olusha oluningi lokuthola izenzakalo ze-quantum ezinamandla ku-graphene ye-bilayer egobile ukuze kusetshenziswe ku-physics ye-quantum. Izazi ze-physics zichaza i-“Twistronics” njenge-angle egobile ehlobene phakathi kwezingqimba ze-van der Waals eziseduze ukuze kukhiqizwe ama-moiré nama-flat band ku-graphene. Lo mqondo usuyindlela entsha neyingqayizivele yokushintsha kakhulu nokwenza ngezifiso izakhiwo zedivayisi ngokusekelwe ezintweni ezinezinhlangothi ezimbili ukuze kufezwe ukugeleza kwamanje. Umphumela omangalisayo we-“Twistronics” wabonakaliswa emsebenzini wokuphayona wabacwaningi, okubonisa ukuthi lapho izingqimba ezimbili ze-graphene ezinezingqimba eyodwa zibekwe e-angle egobile “ye-magic angle” engu-θ=1.1±0.1°, kuvela ibhendi egobile kakhulu.
Kulesi sifundo, ku-twisted bilayer graphene (TBLG), isigaba sokufaka ugesi se-microstrip yokuqala (isici sesakhiwo) se-superlattice "engela yomlingo" sasigcwele kancane. Ithimba locwaningo lithole ukuthi lesi yi-Mott insulator (isivikelo esinezakhiwo ze-superconducting) esibonisa i-superconductivity emazingeni aphezulu kancane naphansi e-doping. Umdwebo wesigaba ukhombisa i-superconductor yokushisa okuphezulu phakathi kokushisa kokuguquguquka kwe-superconducting (Tc) kanye nokushisa kwe-Fermi (Tf). Lolu cwaningo luholele ekuthakaseleni okukhulu kanye nempikiswano yethiyori ngesakhiwo sebhendi ye-graphene, i-topology kanye nezinhlelo ezengeziwe ze-semiconductor ze-"Magic Angle". Uma kuqhathaniswa nombiko wokuqala wethiyori, ucwaningo lokuhlola aluvamile futhi lusanda kuqala. Kulesi sifundo, ithimba lenze izilinganiso zokudlulisela ku-"magic angle" twisted bilayer graphene ekhombisa izimo ezifanele zokufaka ugesi kanye ne-superconducting.
I-engeli ephambukile ngokungalindelekile engu-0.93 ± 0.01, encane ngo-15% kune-"Magic Angle" esungulwe, nayo incane kakhulu ebikiwe kuze kube manje futhi ibonisa izakhiwo ze-superconducting. Le miphumela ikhombisa ukuthi isimo esisha sokuhlobana singavela ku-"Magic Angle" twisted bilayer graphene, ephansi kune-"magic angle" eyinhloko, ngale kwe-microstrip yokuqala ye-graphene. Ukuze bakhe lawa madivayisi e-"magic horn" twisted bilayer graphene, ithimba lisebenzise indlela "yokuklebhula nokufaka". Isakhiwo esiphakathi kwezingqimba ze-hexagonal boron nitride (BN) sihlanganiswe; sihlelwe ngendlela ye-Hall rod geometry enezintambo eziningi ezixhunywe kuma-contact edge edge e-Cr/Au (chromium/gold). Lonke idivayisi ye-"Magic Angle" twisted bilayer graphene yenziwe phezu kwengqimba ye-graphene esetshenziswa njengesango langemuva.
Ososayensi basebenzisa amasu okukhiya ajwayelekile aqondile (DC) kanye namanje ashintshanayo (AC) ukukala amadivayisi kuma-cryostat e-HE4 kanye ne-HE3 adonswe nge-pump. Ithimba liqophe ubudlelwano phakathi kokumelana kwe-longitudinal (Rxx) yedivayisi kanye nobubanzi be-voltage yesango elandisiwe (VG) futhi labala insimu yamagnetic B ekushiseni okungu-1.7K. I-asymmetry encane ye-electron-hole yabonwa njengempahla engokwemvelo yedivayisi ye-graphene ejijekile ye-"Magic Angle". Njengoba kubonwe emibikweni yangaphambilini, ithimba liqophe le miphumela futhi lachaza imibiko ebilokhu iqhuba kahle kuze kube manje. I-"Magic Angle" ephawulekayo ijika i-angle encane ye-torsion yedivayisi ye-graphene ye-bilayer. Ngokuhlolisisa ishadi labalandeli be-Landau, abacwaningi bathole izici ezithile eziphawulekayo.
Isibonelo, ukuphakama kokugcwalisa okuyingxenye kanye nokuwohloka okuphindwe kabili kwezinga le-Landau kuhambisana nezimo zokushisa ezifana ne-Moment ezibonwe ngaphambilini. Ithimba libonise ikhefu ekulinganisweni kwe-approximate spin valley SU(4) kanye nokwakheka kobuso obusha be-quasi-particle Fermi. Kodwa-ke, imininingwane idinga ukuhlolwa okuningiliziwe. Ukubonakala kwe-superconductivity nakho kwabonwa, okwakhulisa i-Rxx (ukumelana kwe-longitudinal), okufana nezifundo zangaphambilini. Ithimba labe selihlola izinga lokushisa elibucayi (Tc) lesigaba se-superconducting. Njengoba kungekho datha etholakele yokufakwa kahle kwe-superconductors kulesi sampula, ososayensi bacabange ukuthi izinga lokushisa elibucayi lifinyelela ku-0.5K. Kodwa-ke, lawa madivayisi aba angasebenzi kuze kube yilapho ekwazi ukuthola idatha ecacile evela esimweni se-superconducting. Ukuze baqhubeke nokuphenya ngesimo se-superconducting, abacwaningi balinganise izici ze-voltage-current (VI) zedivayisi ngobuningi obuhlukene benkampani.
Ukumelana okutholiwe kukhombisa ukuthi i-super current ibonwa ngaphezu kobubanzi obukhulu bokuxinana futhi kukhombisa ukucindezelwa kwe-super current lapho kusetshenziswa insimu yamagnetic efanayo. Ukuze bathole ukuqonda ngokuziphatha okubonwe ocwaningweni, abacwaningi babale isakhiwo se-Moir band sedivayisi ye-graphene ejijekile ye-"Magic Angle" besebenzisa imodeli ye-Bistritzer-MacDonald kanye namapharamitha athuthukisiwe. Uma kuqhathaniswa nokubalwa kwangaphambilini kwe-angle ye-"Magic Angle", i-Moire band yamandla aphansi ebaliwe ayihlukanisiwe ne-high energy band. Nakuba i-angle ye-twist yedivayisi incane kune-angle ye-"magic angle" ebaliwe kwenye indawo, idivayisi inesimo esihlobene kakhulu nezifundo zangaphambilini (i-Mort insulation kanye ne-superconductivity), ososayensi be-physics abathole ukuthi ayilindelekile futhi ingenzeka.
Ngemva kokuhlola kabanzi ukuziphatha ngobuningi obukhulu (inani lezimo ezitholakalayo kumandla ngamunye), izici ezibonwe ososayensi zihlotshaniswa nezimo zokufakelwa ezisanda kuvela. Esikhathini esizayo, kuzokwenziwa ucwaningo oluningiliziwe lwe-density of states (DOS) ukuze kuqondwe isimo esingavamile sokufakelwa nokuthola ukuthi zingahlukaniswa yini njenge-quantum spin liquids. Ngale ndlela, ososayensi babone i-superconductivity eduze nesimo sokufakelwa esifana ne-Mox kudivayisi ye-graphene ejijekile ene-twist angle encane (0.93°). Lolu cwaningo lubonisa ukuthi ngisho nakuma-engeli amancane kangaka kanye nobuningi obuphezulu, umphumela wokuhlangana kwama-electron ezimpahleni ze-moiré uyafana. Esikhathini esizayo, kuzofundwa izigodi ze-spin zesigaba sokufakelwa, futhi kuzofundwa isigaba esisha sokufakelwa amandla ngokushisa okuphansi. Ucwaningo lokuhlola luzohlanganiswa nemizamo yethiyori yokuqonda umsuka walokhu kuziphatha.
Isikhathi sokuthunyelwe: Okthoba-08-2019