Quantum anomalous Hall nyhuv

Quantum anomalous Hall nyhuv
Cov nyhuv QAH yog ib qho quantum mechanical phenomenon characterized by the quantization of the Hall resistance in the absent of external magnetic field. Qhov quantization no tshwm sim los ntawm cov khoom topological ntawm cov qauv hluav taws xob hauv hluav taws xob, tshwj xeeb tshaj yog thaum tus lej Chern tsis yog -zero. Nyob rau hauv ib txwm quantum Hall systems, ib tug muaj zog magnetic teb yog siv los cuam tshuam lub sij hawm -reversal symmetry, uas ua rau cov tsim ntawm Landau theem thiab tom qab quantization ntawm Hall kuj. Nyob rau hauv sib piv, cov nyhuv QAH tshwm sim nyob rau hauv lub systems nrog ib tug tawg intrinsic lub sij hawm -reversal symmetry, xws li cov uas muaj zog spin- orbit coupling thiab ferromagnetic kev txiav txim.
Rhombic graphene Moiré qauv
Graphene yog ib txheej uas tsim los ntawm carbon atoms teem nyob rau hauv ib tug honeycomb lattice, muaj extraordinary hluav taws xob khoom, nrog rau massless Dirac fermions. Thaum ntau txheej txheej ntawm graphene yog stacked nrog ib tug me me twist lub kaum sab xis, ib tug Moiré qauv tshwm sim, tsim ib tug txheej ntawm tshiab hluav taws xob bands, nrog lub band dav ho txo. Qhov tshwm sim Moiré superlattice ua raws li cov khoom siv siv lead ua lattice, tso cai rau kev hloov kho ntawm cov khoom siv hluav taws xob los ntawm lub kaum sab xis thiab lwm yam tsis zoo (xws li hluav taws xob teb thiab hom).
Tsib - txheej rhombic graphene (PRG) yog ib qho tshwj xeeb multilayer graphene system uas tau nyiam cov xim zoo nkauj vim nws lub zog tshwj xeeb band qauv thiab lub peev xwm los tuav cov kab txawv quantum theem. Thaum PRG ua ke nrog hexagonal boron nitride (hBN) substrate, Moiré superlattice yog tsim, uas ntxiv hloov cov qauv hluav taws xob. Cov kev tshawb fawb tsis ntev los no tau nthuav tawm qhov tshwm sim ntawm fractional quantum anomalous Hall (FQAH) hauv cov kab ke no, qhia tias muaj kev cuam tshuam ntawm cov hluav taws xob muaj zog.
Kev nkag siab theoretical ntawm QAH Effect hauv PRG Moiré Structures
Txhawm rau nkag siab lub hauv paus chiv keeb ntawm QAH cov nyhuv hauv PRG moiré cov qauv, nws yog ib qho tsim nyog yuav tsum tau kawm txog cov qauv hluav taws xob hauv hluav taws xob thiab lub luag haujlwm ntawm electron-electron kev sib cuam tshuam. Tsis yog-kev sib cuam tshuam cov qauv kev suav ua ke qhia txog qhov muaj ze li ntawm cov bands tiaj tus nrog tsis yog- tsis tseem ceeb topology, tus cwj pwm los ntawm tsis yog - pes tsawg Chern. Txawm li cas los xij, cov qhab no tsis txaus los txhawb nws tus kheej los saib xyuas QAH cov nyhuv.
Electron-electron kev sib cuam tshuam ua lub luag haujlwm tseem ceeb hauv kev ruaj khov QAH theem. Lub Coulomb repulsion ntawm electrons tuaj yeem ua rau muaj kev sib raug zoo hauv hluav taws xob, xws li Wigner crystals thiab fractional quantum Hall states. Nyob rau hauv rooj plaub ntawm tus qauv PRG Moiré, kev sib cuam tshuam tuaj yeem ua kom lub ntsej muag sib txuas ntxiv thiab cais lawv, txhim kho lawv txoj kev ruaj ntseg thiab ua kom yooj yim rau kev soj ntsuam ntawm QAH cov nyhuv.
Microscopic theoretical suav muab cov kev pom zoo rau cov txheej txheem ntawm QAH cov nyhuv hauv PRG MoS2 cov qauv. Cov kev suav no qhia tau hais tias electron- kev sib cuam tshuam hauv hluav taws xob tuaj yeem ua rau muaj qhov sib txawv ntawm qhov sib txawv, ua rau muaj qhov tshwm sim ntawm lub zog hluav taws xob nrog valley polarization naj npawb 1. Cov qhab no yog qhov chaw zoo heev thiab muaj zog rau kev cuam tshuam, ua rau nws yog qhov kev xaiv zoo tshaj plaws rau kev ua cov nyhuv QAH.
Cov lus qhia yav tom ntej thiab muaj peev xwm siv tau
Kev tshawb pom ntawm QAH cov nyhuv hauv PRG Moiré qauv tau qhib txoj hauv kev zoo siab rau kev tshawb fawb yav tom ntej. Cov kev tshawb fawb ntxiv thiab kev sim yuav tsum tau tshawb nrhiav cov theem kev nplua nuj ntawm cov kab ke no, suav nrog kev muaj peev xwm ntawm lwm yam kab txawv quantum theem (xws li topological insulators thiab superconductors). Tsis tas li ntawd, kev nkag siab txog lub luag haujlwm ntawm kev tsis sib haum xeeb thiab lwm yam kev cuam tshuam sab nraud ntawm QAH cov txiaj ntsig yog qhov tseem ceeb rau kev siv tswv yim.
Cov nyhuv quantum anomalous Hall muaj peev xwm los hloov kho thaj chaw ntawm cov khoom siv hluav taws xob, ua rau kev tsim cov khoom siv qis - zog, siab - ceev thiab cov cuab yeej ua haujlwm tau zoo. Piv txwv li, quantum anomalous Hall cov cuab yeej siv tau los tsim quantum Hall ntug xeev nrog xoom dissipation, yog li ua kom muaj txiaj ntsig zoo thiab muaj zog hluav taws xob. Ntxiv mus, los ntawm kev tswj cov khoom siv hluav taws xob ntawm Moiré cov ntaub ntawv, nws muab lub platform cog lus rau kev tshawb nrhiav quantum cov ntaub ntawv ua thiab quantum xam.