Spin and Charge Ordering in the Quantum Hall Regime PDF
Preview Spin and Charge Ordering in the Quantum Hall Regime
Springer Theses Recognizing Outstanding Ph.D. Research Benedikt Frieß Spin and Charge Ordering in the Quantum Hall Regime Springer Theses Recognizing Outstanding Ph.D. Research Aims and Scope The series “Springer Theses” brings together a selection of the very best Ph.D. theses from around the world and across the physical sciences. Nominated and endorsed by two recognized specialists, each published volume has been selected foritsscientificexcellenceandthehighimpactofitscontentsforthepertinentfield of research. For greater accessibility to non-specialists, the published versions includeanextendedintroduction,aswellasaforewordbythestudent’ssupervisor explainingthespecialrelevanceoftheworkforthefield.Asawhole,theserieswill provide a valuable resource both for newcomers to the research fields described, and for other scientists seeking detailed background information on special questions. Finally, it provides an accredited documentation of the valuable contributions made by today’s younger generation of scientists. Theses are accepted into the series by invited nomination only and must fulfill all of the following criteria (cid:129) They must be written in good English. (cid:129) ThetopicshouldfallwithintheconfinesofChemistry,Physics,EarthSciences, Engineeringandrelatedinterdisciplinary fields such asMaterials,Nanoscience, Chemical Engineering, Complex Systems and Biophysics. (cid:129) The work reported in the thesis must represent a significant scientific advance. (cid:129) Ifthethesisincludespreviouslypublishedmaterial,permissiontoreproducethis must be gained from the respective copyright holder. (cid:129) They must have been examined and passed during the 12 months prior to nomination. (cid:129) Each thesis should include a foreword by the supervisor outlining the signifi- cance of its content. (cid:129) The theses should have a clearly defined structure including an introduction accessible to scientists not expert in that particular field. More information about this series at http://www.springer.com/series/8790 ß Benedikt Frie Spin and Charge Ordering in the Quantum Hall Regime Doctoral Thesis accepted by the Technical University of Munich, Germany 123 Author Supervisor Dr. BenediktFrieß Prof. KlausvonKlitzing MaxPlanckInstitute for SolidState MaxPlanckInstitute for SolidState Research Research Stuttgart Stuttgart Germany Germany ISSN 2190-5053 ISSN 2190-5061 (electronic) SpringerTheses ISBN978-3-319-33535-3 ISBN978-3-319-33536-0 (eBook) DOI 10.1007/978-3-319-33536-0 LibraryofCongressControlNumber:2016937505 ©SpringerInternationalPublishingSwitzerland2016 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpart of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission orinformationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar methodologynowknownorhereafterdeveloped. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publicationdoesnotimply,evenintheabsenceofaspecificstatement,thatsuchnamesareexemptfrom therelevantprotectivelawsandregulationsandthereforefreeforgeneraluse. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authorsortheeditorsgiveawarranty,expressorimplied,withrespecttothematerialcontainedhereinor foranyerrorsoromissionsthatmayhavebeenmade. Printedonacid-freepaper ThisSpringerimprintispublishedbySpringerNature TheregisteredcompanyisSpringerInternationalPublishingAGSwitzerland Artisticrenderingofthespinandcharge orderinginasemiconductorheterostructure ’ Supervisor s Foreword QuantumHallphysicsstartedmorethan35yearsagoandisstillanexpandingfield, thanks to new high-quality materials such as graphene and zinc oxide, new theo- retical concepts including topological insulators and topological quantum compu- tation, and last but not least, due to important applications in metrology that will lead to a new international system of units based on constants of nature. Themostimportantingredientinthisresearchfieldismerelyatwo-dimensional electronsystem(2DES)inastrongperpendicularmagneticfieldleading(inanideal system) to a discrete energy spectrum. The 2DES is not a mathematical simplifi- cation of a three-dimensional system; it truly opens a new dimension in science, especially if magnetic flux quanta are added. New quasiparticles called composite bosons, composite fermions, or anions are realized with new electronic properties. Insomecases,quasiparticleswithnon-abelianstatisticsareexpectedthatmaywell revolutionize quantum information technology. The host material in this research fieldofbasic scienceplays asecondary role andthe influenceof thecrystal onthe 2DESisnormallyincludedinparameterssuchastheeffectivemassandtheg-factor of the electrons. Unfortunately, even high-quality crystals are never perfect, and their residual defects and impurities very often mask the intrinsic properties of the electronic system. A two-dimensional electron layer on the clean surface of liquid helium is very nearly an ideal system for basic science in the two-dimensional world,buttheelectronconcentrationsintheseexperimentsarelimitedtoverysmall values so that the diversity of quantum Hall physics cannot be exploited in these systems. Atpresent,thebest-controlled2DESforbasicresearchisrealizedattheinterface betweenGaAsandAlGaAs,andeverytimethequalityofthissystem(characterized by the mobility of electrons) has been increased, new phenomena were observed. The integer quantum Hall effect can be discussed within a simple independent-electron picture, where the discrete energy levels for electrons in a strong magnetic field (Landau levels) are fully occupied and an incompressible electronsystemisformed.Disorderdoesnotdestroythiseffect.Quitethecontrary, it stabilizes this quantum phenomenon. However, many other fascinating electron vii viii Supervisor’sForeword phases based on electron–electron interactions such as the fractional quantum Hall effect,Wignercrystals,orexcitoncondensationbecomevisibleonlyifthedisorder isnegligiblysmall.Twootherprominentphenomenabasedoncorrelatedelectrons, namelytheformationofbubblesandstripes,arethefocusoftheresearchperformed by Benedikt Frieß as described in this thesis. ContrarytotheintuitivepictureofelectronsinaplanewithCoulombrepulsion, the expected homogeneous electron concentration can be drastically changed by redistributing the electrons if, for example, the increase in Coulomb energy is overcompensated by the gain in exchange energy. The electrons in a half-filled Landau level may redistribute in stripes representing a mixture of fully occupied Landau levels with alternating numbers of completely filled energy levels. The resulting electronic anisotropy can clearly be seen in angular-dependent resistivity measurements, but another technique used by Benedikt Frieß, the analysis of the velocity change of surface acoustic waves due to the screening properties of the electron system, yields unexpectedly new information about the compressibility of the spatially varying electron system. Such density-modulated phases are of generalinterestbecausetheyexistinnatureinmanycases,includingsomehigh-T C superconductors. Contrary to other systems, the control of the electron concentra- tion in GaAs/AlGaAs heterostructures offers a unique opportunity to study these phases in detail. Very sensitive probes are available for characterizing the density-modulated phases because the charge-modulated system is generally con- nected to a spin-density modulation, which can be detected sensitively by local probes via the Knight shift. Thisthesisprovidesnotonlyacomprehensiveintroductiontomodernaspectsof quantum Hall physics but also an impressive overview of experimental details and techniques for characterizing quantum Hall systems with a focus on new methods based on electron–nuclear spin interactions. Stuttgart Prof. Dr. Dr. h.c. mult. January 2016 Klaus von Klitzing Acknowledgments Thepresentthesiswouldhavelackedmuchofitsprofundityifitweren’tforthegreat supportIhavereceivedfrommanypeople.Inparticular,Iamhighlyindebtedto… (cid:129) Professor Klaus von Klitzing for giving me the privilege to become one of his students and for providing exceptional support in many regards. I highly value the many insightful discussions and constructive suggestions. His enthusiasm and supportive mind has been greatly inspiring to me. (cid:129) Dr. habil. Jurgen Smet for guiding me through all the ups and downs of the recent years. His extensive support combined with all necessary liberties pro- videdbestpossibleresearchconditionsandpushedmetoexcel.Icouldnothave wished for a better environment. (cid:129) my external supervisor Prof. Bernd Rosenow (Universität Leipzig) for the numerous helpful discussions. The present work strongly benefited from his wealth of experience and profound knowledge. (cid:129) Professor Rudolf Gross (TU München), who kindly agreed to become the second referee of my doctoral exam. (cid:129) Dr. Vladimir Umansky (Weizmann Institute of Science) for providing some of the world’s best 2DES. (cid:129) thecleanroomteamforbringingthe2DESintoshape.Mostofall,Iwouldlike to thank Marion Hagel for her persistent help in sample processing. (cid:129) our skillful technicians, Steffen Wahl, Gunther Euchner, Steffen Pischke, Ingo Hagel and Manfred Schmid, for their invaluablehelpwhen it comes tocooling the samples to ultra-low temperatures. (cid:129) Dr.JohannesNüblerforintroducingmetothebroadsweepoflow-temperature physics.Ilearnedalot from him,from theintricacies oflabworktothedetails of quantum Hall physics. (cid:129) allmyfriendsandcolleaguesintheSmetgroup.Thejoyyoubroughtmeinthe past years beggars description. I highly appreciate the many scientific, philo- sophical and mundane discussions. Most prominently I would like to mention Matthias Kühne, Ding Zhang, Federico Paolucci, Daniel Kärcher, Thomas Weitz, Youngwook Kim, Johannes Geurs and Patrick Herlinger. ix xx AAcckknnoowwlleeddggmmeennttss (cid:129) Joseph Falson (University ofToyko, now at MPI) for bringingthe rich physics of ZnO/MgZnO heterostructures and himself to Stuttgart. (cid:129) Professor Daniel Loss (Universität Basel) for inviting me to Basel and sharing his knowledge about nuclear magnetic ordering. (cid:129) ProfessorYongqingLi(ChineseAcademyofSciences)forfruitfulcollaboration on thefield oftopological insulatorsand quantumHall spin physics. Iam truly grateful for the invitation to Beijing. (cid:129) Dr. Yang Peng and Prof. Felix von Oppen (both FU Berlin) for helping us to develop a theoretical understanding of the surface acoustic wave experiments (cid:129) Christian Reichl and Prof. Werner Wegscheider (ETH Zürich) for providing additional high-quality samples. (cid:129) Ruth Jenz for keeping the bureaucracy at bay and for her friendly nature. (cid:129) the financial and non-material support by the Studienstiftung des deutschen Volkes during my undergraduate studies. (cid:129) my friends and family for their invaluable support throughout my life. Most of all, I feel deeply obliged to my parents. They sparked in me the excitement for nature and technology early on and taught me to think critically. (cid:129) Julia for enriching my daily life. Thank you for being so patient and under- standingthroughthickandthinandforcheeringmeupwhenthingswentwrong in the lab.
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