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Author:Suoranta, Lauri
Title:Velocity renormalization in graphene
Nopeuden renormalisaatio grafeenissa
Publication type:Master's thesis
Publication year:2010
Pages:[8] + 49      Language:   eng
Department/School:Informaatio- ja luonnontieteiden tiedekunta
Main subject:Fysiikka (laskennallinen fysiikka)   (Tfy-105)
Supervisor:Nieminen, Risto
Instructor:Lähde, Timo
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark Aalto  114   | Archive
Keywords:graphene
many-body interaction
low-dimensional system
effective field theory
lattice field theory
Hybrid Monte Carlo
tadpole improvement
Mott insulator
velocity renormalization
quantum phase transition
grafeeni
monihiukkasvuorovaikutus
mataladimensioinen systeemi
efektiivinen kenttäteoria
hilakenttäteoria
hybridi- Monte Carlo
silmukkakorjaus
Mottin eriste
nopeuden renormalisaatio
kvanttifaasitransitio
Abstract (eng): Graphene has been subject to intense theoretical and experimental research since its discovery in 2005.
The lowered dimensionality of graphene leads to strong many-body interactions.
This casts doubt on applicability of traditional models in solid state physics.
In this work we describe the low-energy excitations of graphene in terms interacting fermionic quasiparticles.

We present results from Monte Carlo simulations of this effective field theory, using the tadpole improvement method to eliminate discretization artefacts present in previous simulations.
The simulations demonstrate that graphene undergoes a quantum phase transition from its observed semimetallic phase to a Mott insulating phase.
The critical coupling under which the transition takes place depends on the fermion velocity.
We compute the excitation spectrum, from which we extract renormalized value of the fermion velocity.
Our results indicate that the renormalization has a significant effect on the critical coupling.
Abstract (fin): Grafeeni on ollut intensiivisen teoreettisen ja kokeellisen tutkimuksen kohde eristämisestään 2005 lähtien.
Grafeenin madaltanut dimensionaalisuus johtaa voimakkaisiin usean kappaleen vuorovaikutuksiin.
Tämä asettaa kyseenalaiseksi perinteisten kiinteän olonmuodon fysiikan mallien sovellettavuuden.

Tässä työssä kuvaamme grafeenin matalaenergiset viritystilat vuorovaikuttavina fermionisina kvasihiukkasina.
Esitämme tulokset efektiivisen kenttäteorian Monte Carlo -simulaatioista, joista on eliminoitu aiemmissa simulaatioissa esiintyneitä diskretoinnin jäänteitä käyttäen silmukkakorjausta.

Simulaatiot osoittavat grafeenin muuttuvan kvanttifaasitransitiossa tavanomaisesta semimetallisesta faasista Mottin eristeeksi.
Kriittinen kytkentävakio, jolla transitio havaitaan, riippuu fermionien nopeudesta.
Työssä määritetään viritystilojen spektri ja renormalisoitu fermionien nopeus.
Tulokset merkitsevät renormalisaatiolla olevan huomattava vaikutus kriittiseen kytkentävakioon.
ED:2010-11-19
INSSI record number: 41340
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