Maitiro eMohr stripes uye flat belts musainzi yesainzi nequantum physics inonzi "Magic Angle" twisted bilayer graphene (TBLG) yakakwezva kufarira kukuru kubva kuvasayendisiti, kunyangwe zvinhu zvakawanda zvichitarisana nenharo huru. Muchidzidzo chitsva chakaburitswa mujenari reScience Progress, Emilio Colledo nevasayendisiti muDhipatimendi reFizikisi neZvinhu zveSainzi muUnited States neJapan vakaona superconductivity uye fananidzo mu twisted bilayer graphene. Mott insulator state ine twist angle yeinenge 0.93 degrees. Iyi angle idiki ne15% pane "magic angle" angle (1.1°) yakaverengerwa muchidzidzo chekare. Chidzidzo ichi chinoratidza kuti "magic angle" range ye twisted bilayer graphene yakakura kupfuura zvaitarisirwa kare.
Chidzidzo ichi chinopa ruzivo rutsva rwakakura rwekutsanangura zviitiko zvakasimba zve quantum mu twisted bilayer graphene yekushandiswa mu quantum physics. Nyanzvi dzefizikisi dzinotsanangura "Twistrons" se relative twist angle iri pakati pe advance van der Waals layers kugadzira moiré ne flat bands mu graphene. Pfungwa iyi yave nzira itsva uye yakasiyana yekuchinja zvakanyanya uye kugadzirisa hunhu hwechishandiso zvichibva pazvinhu zvine mativi maviri kuti zviwane current flow. Mhedzisiro inoshamisa ye "Twistrons" yakaratidzwa mubasa rekutanga revaongorori, zvichiratidza kuti kana single-layer graphene layers mbiri dzakaiswa pa "magic angle" twist angle ye θ=1.1±0.1°, bhendi rakatsetseka rinoonekwa.
Muchidzidzo ichi, mu twisted bilayer graphene (TBLG), chikamu chekudzikisa che microstrip yekutanga (chimiro chechimiro) che superlattice pa "magic angle" chaive chakazadzwa zvishoma. Chikwata chekutsvagisa chakaona kuti ichi Mott insulator (insulator ine superconducting properties) inoratidza superconductivity pamazinga edoping akakwira zvishoma uye akaderera. Dhayagiramu yechikamu inoratidza superconductor yekupisa kwepamusoro pakati pe superconducting transition temperature (Tc) neFermi temperature (Tf). Tsvagiridzo iyi yakakonzera kufarira kukuru uye gakava redzidziso pamusoro pechimiro che graphene band, topology uye mamwe masisitimu e "Magic Angle" semiconductor. Zvichienzaniswa nemushumo wekutanga wedzidziso, tsvakiridzo yekuedza haiwanzoitiki uye ichangotanga. Muchidzidzo ichi, timu yakaita zviyero zvekutumira pa "magic angle" twisted bilayer graphene ichiratidza mamiriro akakodzera ekudzivirira uye superconducting.
Kona yakakanganisika isingatarisirwi ye0.93 ± 0.01, iyo iri diki ne15% pane "Magic Angle" yakasimbiswa, ndiyowo diki yakashumwa kusvika pari zvino uye inoratidza hunhu hwe superconducting. Mhedzisiro iyi inoratidza kuti mamiriro matsva ekubatana anogona kuoneka mu "Magic Angle" twisted bilayer graphene, yakaderera pane "magic angle" yekutanga, kupfuura microstrip yekutanga yegraphene. Kuti vagadzire idzi "magic horn" twisted bilayer graphene devices, timu yakashandisa nzira ye "kubvarura nekuisa". Chimiro chiri pakati pehexagonal boron nitride (BN) layers chakavharirwa; chakagadzirwa kuita Hall rod geometry ine waya dzakawanda dzakabatana neCr/Au (chromium/gold) edge contacts. Chishandiso chose che "Magic Angle" twisted bilayer graphene chakagadzirwa pamusoro pegraphene layer yakashandiswa seback gate.
Masayendisiti anoshandisa nzira dzekuvhara dzakajairika (DC) uye alternating current (AC) kuyera michina iri mu HE4 ne HE3 cryostats dzakapombwa. Chikwata chakanyora hukama huripo pakati pe longitudinal resistance yemuchina (Rxx) uye extended gate voltage (VG) range uye vakaverenga magnetic field B patembiricha ye1.7K. Small electron-hole asymmetry yakaonekwa seyakavakirwa pa "Magic Angle" twisted bilayer graphene device. Sezvakaonekwa mumishumo yapfuura, chikwata chakanyora mhinduro idzi uye chakatsanangura mishumo yanga ichiita superconducting kusvika pari zvino. "Magic Angle" inoshandura minimum torsion angle ye bilayer graphene device. Nekunyatsoongorora Landau fan chart, vaongorori vakawana zvimwe zvinhu zvinozivikanwa.
Semuenzaniso, kukwirira kwehafu yekuzadza uye kuderera kwezvikamu zviviri zveLandau level zvinoenderana nemamiriro ekudzivirira akafanana neMoment akamboonekwa. Chikwata chakaratidza kuputsika mukuenzana kweapproximate spin valley SU(4) uye kuumbwa kwenzvimbo itsva yeFermi ine quasi-particle. Zvisinei, ruzivo rwacho runoda kuongororwa kwakanyatsojeka. Kuonekwa kwesuperconductivity kwakaonekwawo, izvo zvakawedzera Rxx (longitudinal resistance), zvakafanana nezvidzidzo zvekare. Chikwata chakazoongorora tembiricha yakakosha (Tc) yechikamu chesuperconducting. Sezvo pasina data rakawanikwa rekushandisa zvakanyanya masuperconductors mumuenzaniso uyu, masayendisiti akafungidzira tembiricha yakakosha inosvika 0.5K. Zvisinei, zvishandiso izvi zvinova zvisina basa kusvika zvakwanisa kuwana data rakajeka kubva kumamiriro esuperconducting. Kuti vaongorore zvakanyanya mamiriro esuperconducting, vaongorori vakayera hunhu hwemagetsi-magetsi mana (VI) emudziyo pahuwandu hwakasiyana hwevatakuri.
Kuramba kwakawanikwa kunoratidza kuti super current inoonekwa pamusoro pehuwandu hwakakura hwe density uye kunoratidza kudzvinyirirwa kwe super current kana simba remagineti rakafanana rikashandiswa. Kuti vawane kunzwisisa maitiro akaonekwa muchidzidzo ichi, vaongorori vakaverenga chimiro cheMoir band che "Magic Angle" twisted bilayer graphene device vachishandisa Bistritzer-MacDonald model uye ma parameter akavandudzwa. Zvichienzaniswa nekuverenga kwekare kwe "Magic Angle", Moire band ine simba shoma yakaverengerwa haina kuparadzaniswa ne high energy band. Kunyangwe twist angle yemuchina iri diki pane "magic angle" angle yakaverengerwa kune imwe nzvimbo, muchina uyu une chiitiko chakabatana zvakanyanya nezvidzidzo zvekare (Mort insulation and superconductivity), izvo nyanzvi dzefizikisi dzakaona kuti hazvitarisirwi uye zvinogoneka.
Mushure mekuongorora zvakanyanya maitiro pahuwandu hwakawanda (huwandu hwemamiriro aripo pane imwe neimwe simba), hunhu hwakaonekwa nevasayendisiti hunokonzerwa nemamiriro matsva ekudzivirira akabatana. Mune ramangwana, chidzidzo chakadzama chehuwandu hwemamiriro (DOS) chichaitwa kuti tinzwisise mamiriro asina kujairika ekudzivirira uye kuona kana anogona kuverengerwa sequantum spin liquids. Nenzira iyi, masayendisiti akaona superconductivity iri pedyo neMox-like insulating state mumudziyo we graphene wakamonyoroka usina girafu ine kona diki yekutenderera (0.93°). Chidzidzo ichi chinoratidza kuti kunyangwe pamakona madiki akadaro uye densities yakakwira, mhedzisiro ye electron correlation pahunhu hwe moiré yakafanana. Mune ramangwana, mipata ye spin yechikamu chekudzivirira ichadzidzwa, uye chikamu chitsva che superconducting chichadzidzwa patembiricha yakaderera. Tsvagiridzo yekuyedza ichabatanidzwa nekuedza kwedzidziso kuti tinzwisise kwakabva maitiro aya.
Nguva yekutumira: Gumiguru-08-2019