Topological superconductivity in magnetic adatom lattices

Joel Röntynen

Topological superconductivity in magnetic adatom lattices

Julkaisun otsikon käännös: Topologinen suprajohtavuus magneettisissa atomihiloissa

Joel Röntynen

Teknillisen fysiikan laitos

Tutkimustuotos: Doctoral Thesis › Collection of Articles

Abstrakti

Topologiset materiaalit ovat viimeisten kolmen vuosikymmenen aikana nousseet yhdeksi aktiivisimmista tutkimuskentistä kondensoituneen aineen fysiikassa. Topologian rooli näiden materiaalien ominaisuuksien määräytymisessä on perustavanlaatuisesti muuttanut ymmärrystämme siitä, miten materian perusosaset järjestyvät tuottaessaan eri aineen olomuotoja. Topologisissa materiaaleissa topologia ilmenee reunatiloina ja eksoottisina kvasihiukkasina, joiden erityislaatuisien ominaisuuksien ennustetaan tuottavan monenlaisia teknologisia sovelluksia. Tässä väitöskirjassa olen tutkinut topologista suprajohtavuutta, missä ennustetaan esiintyvän lokalisoituneita Majorana-eksitaatioita. Nämä Majorana-kvasihiukkaset rikkovat tavanomaisen jaottelun bosoneihin ja fermioneihin, sillä ne noudattavat niin kutsuttua epäabelista kvanttistatistiikkaa. Täten Majorana-hiukkaset edustavat perustavanlaatuisella tavalla aivan uudenlaista fysiikkaa. Lisäksi Majorana-hiukkasia visioidaan käytettävän topologisesti suojatussa kvanttilaskennassa, millä on toteutuessaan kauaskantoisia vaikutuksia tietojenkäsittelylle. Näistä syistä Majorana-tilojen kokeellinen havaitseminen on eräs ajankohtaisimmista tavoitteista kondensoituneen aineen fysiikassa tällä hetkellä. Tässä väitöskirjassa tutkitut systeemit koostuvat magneettisista atomirakenteista suprajohteen päällä. Julkaisut I ja II käsittelevät lokalisoituneita Majorana-tiloja atomiketjuissa. Julkaisussa I osoitimme muun muassa, että toisiinsa kytkeytyneissä ketjuissa Majorana-tiloja löytyy laajemmalta parametrialueelta kuin erillisissä ketjuissa. Julkaisussa II osoitettiin, että supravirran avulla on mahdollista kontrolloida siirtymää topologisen ja triviaalin faasin välillä. Julkaisusuissa III ja IV osoitimme, että kaksiulotteiset atomihilat toteuttavat px+ipy-suprajohtavuuden yleistyksen ja siten nämä systeemit ovat mielenkiintoinen lisä epätavanomaisten suprajohteiden listaan. Systeemin mosaiikkimainen faasidiagrammi on seurausta pitkän kantaman elektronihyppäyksestä. Kahdessa ulottuvuudessa Majorana-tilat kulkevat pitkin hilan reunoja ja niiden lukumäärän määrää topologinen invariantti nimeltä Chernin luku. Ennustimme että tyypillisissä materiaaleissa Chernin luku voi olla hyvin suuri. Suurilla Chernin luvuilla varustettujen topologisten faasien runsas määrä asettaa tutkitun systeemin yhdeksi monipuolisimmista tähän mennessä löydetyistä topologisista materiaaleista. Koska kaksiulotteisten atomihilarakenteiden kokeellinen tutkimus on jo suunnitteilla, tutkittu systeemi on lupaava alusta topologisten faasien tutkimukselle.

Julkaisun otsikon käännös	Topologinen suprajohtavuus magneettisissa atomihiloissa
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Valvoja/neuvonantaja	Hakonen, Pertti, Vastuuprofessori Ojanen, Teemu, Ohjaaja
Kustantaja	Aalto University
Painoksen ISBN	978-952-60-6851-0
Sähköinen ISBN	978-952-60-6852-7
Tila	Julkaistu - 2016
OKM-julkaisutyyppi	G5 Tohtorinväitöskirja (artikkeli)

Tutkimusalat

topologiset materiaalit
topologinen suprajohtavuus
Majorana-tilat

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http://urn.fi/URN:ISBN:978-952-60-6852-7Lisenssi: Määrittelemätön

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title = "Topological superconductivity in magnetic adatom lattices",

abstract = "Topological matter has emerged as one of the most prominent research fronts in condensed matter physics over the past three decades. The discovery of the role of topology in materials has shaped our fundamental understanding of how the constituents of matter organize themselves to produce various phases. Topology in these systems manifests as boundary states and exotic quasiparticles, whose intriguing properties are anticipated to facilitate various technological applications. In this thesis I have contributed to the search for topological superconductivity, which is expected to support localized, particle-like excitations called Majorana bound states. Majorana bound states break the dichotomy of bosons and fermions by obeying non-Abelian exchange statistics. Hence a Majorana bound state would be a manifestation of a fundamentally new type of physics. Furthermore, Majorana braiding is envisioned to be utilized in topologically protected quantum computing, which could revolutionize the future of computing. The experimental discovery of Majorana bound states is an outstanding goal in condensed matter physics at the moment. The systems investigated in this thesis consists of magnetic adsorbed atoms (adatoms) deposited on top of a conventional superconductor. In publications I and II we investigated the appearance of Majorana bound states in adatom chains. The main result in publication I is that coupled chains are more likely to exhibit Majorana bound states than uncoupled chains. In publication II we showed that a supercurrent can be used to control the topological phase, which could be helpful for the manipulation of Majorana bound states. In publications III and IV we showed that two-dimensional adatom structures support a generalization of px+ipy superconductivity, making it an interesting addition to the list of materials with unconventional superconductivity. The complex, mosaic-like structure of the topological phase diagram is remarkably rich due to long-range electron hopping. The number of propagating Majorana modes at the boundary is given by a topological invariant called a Chern number. We predicted that for typical experimentally available materials this number can be much larger than unity. The abundance of various topological phases with a large number of protected edge states makes the studied system potentially one of the richest topological materials discovered so far. Since two-dimensional structures in such systems are next in line to be studied experimentally, magnetic adatom structures provide a promising platform for realizing exotic phases of matter of fundamental interest.",

keywords = "topological matter, topological superconductivity, Majorana modes, topologiset materiaalit, topologinen suprajohtavuus, Majorana-tilat, topological matter, topological superconductivity, Majorana modes",

author = "Joel R{\"o}ntynen",

year = "2016",

language = "English",

isbn = "978-952-60-6851-0",

series = "Aalto University publication series DOCTORAL DISSERTATIONS",

publisher = "Aalto University",

number = "111",

address = "Finland",

school = "Aalto University",

}

TY - THES

T1 - Topological superconductivity in magnetic adatom lattices

AU - Röntynen, Joel

PY - 2016

Y1 - 2016

N2 - Topological matter has emerged as one of the most prominent research fronts in condensed matter physics over the past three decades. The discovery of the role of topology in materials has shaped our fundamental understanding of how the constituents of matter organize themselves to produce various phases. Topology in these systems manifests as boundary states and exotic quasiparticles, whose intriguing properties are anticipated to facilitate various technological applications. In this thesis I have contributed to the search for topological superconductivity, which is expected to support localized, particle-like excitations called Majorana bound states. Majorana bound states break the dichotomy of bosons and fermions by obeying non-Abelian exchange statistics. Hence a Majorana bound state would be a manifestation of a fundamentally new type of physics. Furthermore, Majorana braiding is envisioned to be utilized in topologically protected quantum computing, which could revolutionize the future of computing. The experimental discovery of Majorana bound states is an outstanding goal in condensed matter physics at the moment. The systems investigated in this thesis consists of magnetic adsorbed atoms (adatoms) deposited on top of a conventional superconductor. In publications I and II we investigated the appearance of Majorana bound states in adatom chains. The main result in publication I is that coupled chains are more likely to exhibit Majorana bound states than uncoupled chains. In publication II we showed that a supercurrent can be used to control the topological phase, which could be helpful for the manipulation of Majorana bound states. In publications III and IV we showed that two-dimensional adatom structures support a generalization of px+ipy superconductivity, making it an interesting addition to the list of materials with unconventional superconductivity. The complex, mosaic-like structure of the topological phase diagram is remarkably rich due to long-range electron hopping. The number of propagating Majorana modes at the boundary is given by a topological invariant called a Chern number. We predicted that for typical experimentally available materials this number can be much larger than unity. The abundance of various topological phases with a large number of protected edge states makes the studied system potentially one of the richest topological materials discovered so far. Since two-dimensional structures in such systems are next in line to be studied experimentally, magnetic adatom structures provide a promising platform for realizing exotic phases of matter of fundamental interest.

AB - Topological matter has emerged as one of the most prominent research fronts in condensed matter physics over the past three decades. The discovery of the role of topology in materials has shaped our fundamental understanding of how the constituents of matter organize themselves to produce various phases. Topology in these systems manifests as boundary states and exotic quasiparticles, whose intriguing properties are anticipated to facilitate various technological applications. In this thesis I have contributed to the search for topological superconductivity, which is expected to support localized, particle-like excitations called Majorana bound states. Majorana bound states break the dichotomy of bosons and fermions by obeying non-Abelian exchange statistics. Hence a Majorana bound state would be a manifestation of a fundamentally new type of physics. Furthermore, Majorana braiding is envisioned to be utilized in topologically protected quantum computing, which could revolutionize the future of computing. The experimental discovery of Majorana bound states is an outstanding goal in condensed matter physics at the moment. The systems investigated in this thesis consists of magnetic adsorbed atoms (adatoms) deposited on top of a conventional superconductor. In publications I and II we investigated the appearance of Majorana bound states in adatom chains. The main result in publication I is that coupled chains are more likely to exhibit Majorana bound states than uncoupled chains. In publication II we showed that a supercurrent can be used to control the topological phase, which could be helpful for the manipulation of Majorana bound states. In publications III and IV we showed that two-dimensional adatom structures support a generalization of px+ipy superconductivity, making it an interesting addition to the list of materials with unconventional superconductivity. The complex, mosaic-like structure of the topological phase diagram is remarkably rich due to long-range electron hopping. The number of propagating Majorana modes at the boundary is given by a topological invariant called a Chern number. We predicted that for typical experimentally available materials this number can be much larger than unity. The abundance of various topological phases with a large number of protected edge states makes the studied system potentially one of the richest topological materials discovered so far. Since two-dimensional structures in such systems are next in line to be studied experimentally, magnetic adatom structures provide a promising platform for realizing exotic phases of matter of fundamental interest.

KW - topological matter

KW - topological superconductivity

KW - Majorana modes

KW - topologiset materiaalit

KW - topologinen suprajohtavuus

KW - Majorana-tilat

KW - topological matter

KW - topological superconductivity

KW - Majorana modes

M3 - Doctoral Thesis

SN - 978-952-60-6851-0

T3 - Aalto University publication series DOCTORAL DISSERTATIONS

PB - Aalto University

ER -

Topological superconductivity in magnetic adatom lattices

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