Ukuziphatha kwemigca ye-Mohr kunye neebhanti ezisicaba kwisayensi yesayensi kunye ne-quantum physics ebizwa ngokuba yi-"Magic Angle" i-twisted bilayer graphene (TBLG) itsale umdla omkhulu kwizazinzulu, nangona iipropati ezininzi zijongene neengxoxo ezishushu. Kuphononongo olutsha olupapashwe kwijenali yeNkcubeko yeSayensi, u-Emilio Colledo kunye noosonzululwazi kwiSebe leFiziksi kunye neSayensi yeMpahla e-United States naseJapan baqwalasele i-superconductivity kunye nesifaniso kwi-twisted bilayer graphene. Imott insulator karhulumente ineengile twist malunga 0.93 degrees. Le engile incinane nge-15% kuneengile “yomlingo” (1.1°) ebalwa kuphononongo lwangaphambili. Olu phononongo lubonisa ukuba "i-angle yomlingo" uluhlu lwe-bilayer ejijekileyo yegraphene inkulu kunokuba bekulindelwe ngaphambili.
Olu phononongo lubonelela ngobutyebi bolwazi olutsha lokucazulula into eyomeleleyo ye-quantum kwi-bilayer graphene ejijekileyo yokusetyenziswa kwifiziksi ye-quantum. Iingcali zefiziksi zichaza "i-Twistronics" njenge-engile yokujija phakathi kwe-van der Waals emeleneyo ukuvelisa i-moiré kunye neebhanti ezisicaba kwigraphene. Le ngcamango iye yaba yindlela entsha kunye neyodwa yokutshintsha ngokuphawulekayo kunye nokwenza ngokwezifiso iipropati zesixhobo ezisekelwe kwizinto ezi-dimensional-dimensional ukufezekisa ukuhamba kwangoku. Isiphumo esimangalisayo se-"Twistronics" sibonakaliswe kumsebenzi wobuvulindlela wabaphandi, ebonisa ukuba xa iileya ezimbini zegraphene ze-single-layer zifakwe kwi-"angle yomlingo" ye-twist angle ye-θ=1.1±0.1 °, ibhendi ecaba kakhulu ibonakala. .
Kolu phononongo, kwi-twisted bilayer graphene (TBLG), isigaba se-insulating se-microstrip yokuqala (i-structural feature) ye-superlattice kwi-"angle yomlingo" yayizaliswe isiqingatha. Iqela lophando lafumanisa ukuba le yi-insulator ye-Mott (i-insulator eneempawu ze-superconducting) ebonisa i-superconductivity kumanqanaba aphezulu kunye naphantsi kwe-doping. Umzobo wesigaba ubonisa i-superconductor ephezulu yokushisa phakathi kweqondo lokushisa lokutshintsha kwe-superconducting (Tc) kunye nobushushu beFermi (Tf). Olu phando lwakhokelela kumdla omkhulu kunye neengxoxo zethiyori malunga nesakhiwo sebhendi yegraphene, i-topology kunye neenkqubo ezongezelelweyo ze "Magic Angle" zemiconductor. Xa kuthelekiswa nengxelo yethiyori yokuqala, uphando lovavanyo lunqabile kwaye sele luqalile. Kolu phononongo, iqela lenze imilinganiselo yothumelo kwi "magic angle" twisted bilayer graphene ebonisa i-insulating efanelekileyo kunye ne-superconducting states.
I-angle egqwethekileyo ngokungalindelekanga ye-0.93 ± 0.01, eyi-15% encinci kune-"Magic Angle" esekiweyo, ikwayeyona incinci ekuxelwe kuyo ukuza kuthi ga ngoku kwaye ibonisa iipropati ze-superconducting. Ezi ziphumo zibonisa ukuba imeko entsha yolungelelwaniso inokuvela kwi-"Magic Angle" ejijekileyo ye-bilayer graphene, esezantsi kune-primary "magic angle", ngaphaya kwe-microstrip yokuqala yegraphene. Ukwakha ezi “zimpondo zomlingo” ezijijekileyo ze-bilayer graphene zixhobo, iqela lisebenzise indlela “yokukrazula nokupakisha”. Ulwakhiwo phakathi kwe-hexagonal boron nitride (BN) layers ifakwe; ifaniswe kwijiyometri yentonga yeHolo eneengcingo ezininzi ezidityaniswe kwi-Cr/Au (ichromium/igolide) zomda wonxibelelwano. Isixhobo sonke se-"Magic Angle" esijijekileyo se-bilayer segraphene senziwe ngaphezulu komgangatho wegraphene osetyenziswa njengesango elingasemva.
Iingcali zenzululwazi zisebenzisa i-standard standard current (DC) kunye neendlela zokutshixa zangoku (AC) ukulinganisa izixhobo kwi-HE4 kunye ne-HE3 cryostats empompelweyo. Iqela lirekhode ubudlelwane phakathi kokumelana ne-longitudinal yesixhobo (Rxx) kunye ne-voltage eyandisiweyo yesango (VG) kunye noluhlu lwe-magnetic field B kwiqondo lokushisa le-1.7K. I-asymmetry encinci ye-electron-hole yabonwa njengepropati yendalo ye "Magic Angle" isixhobo esijijekileyo se-bilayer graphene. Njengoko kuphawulwe kwiingxelo zangaphambili, iqela lirekhode ezi ziphumo kwaye lichaza ngokweenkcukacha iingxelo eziye zaqhuba kakuhle ukuza kuthi ga ngoku. Uphawu "I-Angle yomlingo" ijija ubuncinci be-engile ye-torsion yesixhobo se-bilayer segraphene. Ngokuphononongwa ngokusondeleyo kwetshathi ye-Landau fan, abaphandi bafumana iimpawu eziphawulekayo.
Umzekelo, incopho yokuzaliswa kwesiqingatha kunye nokuwohloka okuphindwe kabini kwinqanaba le-Landau zihambelana neendawo eziqatshelweyo ze-Moment-like insulation states. Iqela libonise ikhefu kwi-symmetry ye-spin valley eqikelelweyo ye-SU (4) kunye nokwakhiwa kwendawo entsha ye-quasi-particle Fermi. Nangona kunjalo, iinkcukacha zifuna uhlolo oluneenkcukacha ngakumbi. Ukubonakala kwe-superconductivity kwabonwa kwakhona, eyandisa i-Rxx (i-longitudinal resistance), efana nezifundo zangaphambili. Emva koko iqela lihlolisise ubushushu obubalulekileyo (Tc) besigaba se-superconducting. Ekubeni akukho datha ifunyenweyo ye-doping efanelekileyo yee-superconductors kule sampuli, izazinzulu zicinga ukushisa okubalulekileyo ukuya kuthi ga kwi-0.5K. Nangona kunjalo, ezi zixhobo zingasebenzi de zikwazi ukufumana idatha ecacileyo kwi-superconducting state. Ukuphanda ngakumbi ngemeko ye-superconducting, abaphandi balinganise iimpawu ze-four-terminal voltage-current (VI) zesixhobo kuxinaniso olwahlukileyo lomthwali.
Uxhathiso olufunyenweyo lubonisa ukuba i-super current ijongwa phezu koluhlu olukhulu loxinaniso kwaye ibonisa ukucinezelwa kwe-super current xa kusenziwa i-parallel magnetic field. Ukufumana ingqiqo ngokuziphatha okubonwe kwisifundo, abaphandi babala i-Moir band structure ye "Magic Angle" ephothiweyo isixhobo se-graphene ye-bilayer usebenzisa imodeli ye-Bistritzer-MacDonald kunye neeparitha eziphuculweyo. Xa kuthelekiswa nokubala kwangaphambili kwe-angle "Magic Angle", i-Moire yamandla ephantsi ebalwayo ayihlukanga kwi-band yamandla aphezulu. Nangona i-engile yokujija yesixhobo incinci kune-engile “yomlingo” ebalwa kwenye indawo, isixhobo sinesenzeko esiyelelene ngamandla kwizifundo zangaphambili (i-Mort insulation kunye ne-superconductivity), iingcali zefiziksi zafumanisa ukuba ibingalindelekanga kwaye inokwenzeka.
Emva kokuvavanya ngakumbi indlela yokuziphatha kuxinaniso olukhulu (inani lamazwe akhoyo kumandla ngamnye), iimpawu eziqatshelwe zizazinzulu zibalelwa kwizizwe ezisanda kuvela ezinxulumene nokugqunyelelwa. Kwixesha elizayo, uphononongo oluneenkcukacha ezithe kratya malunga noxinaniso lwamazwe (DOS) luya kuqhutywa ukuze kuqondwe imeko engaqhelekanga yokugquma kunye nokufumanisa ukuba zinokuhlelwa njengolwelo lwe-quantum spin. Ngale ndlela, izazinzulu ziye zabona i-superconductivity kufuphi nemo yokugquma i-Mox kwisixhobo esijijekileyo se-bilayer segraphene esine-engile encinci yokujija (0.93°). Olu pho nonongo lubonisa ukuba nakwii-angles ezincinci kunye nokuxinana okuphezulu, umphumo wokulungelelaniswa kwe-electron kwiipropati ze-moiré ziyafana. Kwixesha elizayo, iintlambo ze-spin zesigaba se-insulating ziya kufundwa, kwaye isigaba esitsha se-superconducting siya kufundwa kwiqondo lokushisa eliphantsi. Uphando lovavanyo luya kudibaniswa kunye neenzame zethiyori ukuqonda imvelaphi yale ndlela yokuziphatha.
Ixesha lokuposa: Oct-08-2019