Dr. Andrew K. Mitchell

Transcription

1 Dr. Andrew K. Mitchell Contact Information Research Interests Institut für Theoretische Physik Nationality: British Universität zu Köln DOB: 16/11/1982 Zülpicher Str. 77 Tel: (+49) Köln Germany Web: mitchell The central theoretical theme of my current research in theoretical physics is the study of condensed matter systems with strong electron correlations. Analytic work is complemented by numerical calculations to investigate a wide range of many-body phenomena, where the underlying behaviour can be understood in terms of effective quantum impurity problems: Coupled quantum dot nanodevices, nanotubes and other mesoscopic systems: interplay of electron correlations, spin, orbital and molecular effects [1 11]. Molecular electronics: exact analytic or numerical calculation of conductance lineshapes in nanodevices [1,3,5,7 10]. Phase transitions and finite-temperature signatures of criticality [3,5 10]. Real-space correlations: screening cloud detection and STM measurements [1,2,6]. Nanotube quantum dots and 1d systems [1,6]. Two-channel Kondo systems and non-fermi liquid behaviour [3,5 9]. Emergent symmetries and particles: Majorana fermions in correlated systems [3,5,7 9]. Development and extensions of Dynamical Mean Field Theory (DMFT). DMFT for molecular electronics: modelling many-body behaviour of complex molecules coupled to metallic leads. Disordered systems: effect of correlations on localization. Real-space entanglement of spins in a dissipative environment; frustration of decoherence. Two-impurity devices exhibiting quantum criticality [1,3,5,8]. Connections and exact relations between critical points of different models [4,5,7]. Exact conformal field theory results for Green functions and conductance [3,8]. Novel quantum phase transitions arising from frustration [9,10]. Impurities in graphene and STM for topological insulators: role of chemical potential. Career History Postdoctoral Researcher : February 2010 present Institute of Theoretical Physics, University of Cologne, Germany Principal Investigator: Priv.-Doz. Dr. Ralf Bulla Education D.Phil, Theoretical Chemistry : Balliol College, University of Oxford, UK Thesis title: Two-channel Kondo phases in coupled quantum dots. Project supervisor: Professor David E. Logan. Examined December 2009 by Dr Alex Hewson (Imperial College, London) and Dr William Barford (Balliol College, Oxford University). Project summary: Theoretical study of coupled quantum dots connected to two metallic leads. A rich range of many-body behaviour was uncovered, ranging from the classic Kondo effect, to quantum critical non-fermi liquid behaviour associated with the twochannel and two-impurity Kondo models, and frustration-induced phase transitions. Coulson Prize, Royal Society of Chemistry (2008) - awarded for the best presentation at the annual chemistry graduate student meeting. Jowett Senior Exhibition - Balliol College, Oxford (2007).

2 M.Chem, Chemistry (First Class Honours): Keble College, University of Oxford, UK Thesis title: Theoretical studies of a double quantum dot. Thesis Prize - Awarded for the best thesis in the year (out of 170 people) (2005). Rowe Prize - Awarded for outstanding performance in Finals (2004). Distinction - Quantum mechanics supplementary subject (2003). Scholarship - Keble College ( ). Distinction - Physical Sciences Preliminary examinations (2002). Previous Education Nottingham High School, Nottingham, UK ( ) A-Levels : Physics (A), Mathematics (A), Further Mathematics (A), Chemistry (A), General Studies (A) UK maths, physics and chemistry Olympiads: Gold certificates. Arden Comprehensive School, Birmingham, UK ( ) GCSEs : 9 at grade A*, 1 at grade A Maths Challenge: Gold certificate Publications [1] Screening cloud detection in nanotube double quantum dots, A. K. Mitchell, and R. Bulla, in preparation [2] Real-space correlations in Kondo systems, A. K. Mitchell, M. Becker, and R. Bulla, in preparation [3] Universal low-temperature crossover in two-channel Kondo models, A. K. Mitchell, and E. Sela, Under review: Phys. Rev. B (2012) see also preprint, available at arxiv: [4] Local Magnetization in the Boundary Ising Chain at Finite Temperature, E. Sela, and A. K. Mitchell, J. Phys. Stat. Mech. P04006 (2012) [5] Two-channel Kondo physics in two-impurity Kondo models, A. K. Mitchell, E. Sela, and D. E. Logan, Phys. Rev. Lett. 108, (2012) [6] Real-space renormalization group flow in quantum impurity systems: local moment formation and the Kondo screening cloud, A. K. Mitchell, M. Becker, and R. Bulla, Phys. Rev. B 84, (2011). Editor s Suggestion [7] Two-channel Kondo physics in odd impurity chains, A. K. Mitchell, D. E. Logan and H. R. Krishnamurthy, Phys. Rev. B 84, (2011) [8] Exact crossover Green function in the two-channel and two-impurity Kondo models, E. Sela, A. K. Mitchell, and L. Fritz, Phys. Rev. Lett. 106, (2011) [9] Two-channel Kondo phases and frustration-induced transitions in triple quantum dots, A. K. Mitchell and D. E. Logan, Phys. Rev. B 81, (2010) [10] Quantum phase transition in quantum dot trimers, A. K. Mitchell, T. F. Jarrold and D. E. Logan, Phys. Rev. B 79, (2009) [11] Gate voltage effects in capacitively coupled quantum dots, A. K. Mitchell, M. R. Galpin and D. E. Logan, Europhys. Lett. 76, 95 (2006)

3 Teaching and Pastoral Numerical methods for many-particle systems : March 2012 Graduate course for the Bonn-Cologne Graduate School, comprising ten 90-minute lectures in quantum many-body theory for the solid state. I prepared and delivered lectures on a variety of topics such as exact diagonalization, Monte Carlo, density matrix renormalization group (DMRG) and numerical renormalization group (NRG). I also devised the associated computer practicals and problem classes. Classical Theoretical Physics : SS 2010 and SS 2011 Class tutor for the department of physics at the University of Cologne. Topics include: Newtonian mechanics, conservation laws, Kepler problem and three-body problems, harmonic oscillators, electrostatics, microscopic and macroscopic electrodynamics, relativistic invariance, Lagrangian mechanics. Mathematics for the Physical Sciences : Class tutor for the department of chemistry at the University of Oxford. Two weekly groups of ten first-year undergraduates. Topics include: basic algebra and trigonometry, differentiation and integration, calculus of multiple variables, differential equations, and matrices. I have taught extensively for: Pembroke College ( ) Jesus College ( ) Wadham College ( ) Physics for the Physical Sciences : Class tutor for the department of chemistry at the University of Oxford. Weekly classes for undergraduates at Wadham College. Introductory physics course, from classical to quantum mechanics. Topics include: classical and wave mechanics, kinetic theory, electrostatics, magnetism, optics, and foundations of quantum mechanics. Physical Chemistry : 2007 Tutor for final-year undergraduates from Keble College at the University of Oxford. Advanced topics in physical chemistry include: thermodynamics, quantum mechanics, spectroscopy, kinetics, molecular interactions, electronic structure, and statistical mechanics. Balliol College Warden : As Warden of the graduate complex at Balliol College, I was responsible for the welfare of 70 graduate students. The role also entailed administrative, decanal and health and safety duties. As a College Officer, I also sat on the MCR and various College committees. Balliol College MCR Committee : Elected onto the general committee of the Middle Common Room at Balliol College. During this time, I was responsible for a redevelopment project within the graduate complex.

4 Computational Skills Expert in Fortran 90, Mathematica, L A TEX, REVTeX, MS Word, Powerpoint, xhtml. Experience with C, C++, Python, Java and Maple. Development and extension of my own numerical renormalization group (NRG) programs, to solve numerically a wide range of correlated many-electron problems involving coupled impurities/quantum dots with one and two metallic leads or conduction channels. Thermodynamic and dynamical quantities are calculated using the complete Fock space full density matrix approach. Conductance lineshapes calculated from finite-temperature single-particle Green functions obtained by NRG. In some cases, we have also derived exact analytic expressions for the low-energy conductance using the techniques of conformal field theory although Kondo scales and operator coefficients are inherently undetermined and must still be calculated numerically by NRG. Development of my own dynamical mean field theory (DMFT) programs for periodic/lattice systems and layered heterostructures, employing a parallelized NRG code to solve effective impurity models, and exploiting multi-precision algorithms to determine the effective medium self-consistently. Experience with ALPS open-source program libraries for quantum Monte Carlo (QMC) and density matrix renormalization group (DMRG). Conferences, Seminars and Posters Royal Society of Chemistry graduate student meeting University of Manchester, UK (April 16th 2008) Seminar title: Frustration-induced transitions in triple quantum dots (the talk was judged by an independent panel and awarded the Coulson prize) Theoretical Chemistry Group student seminar series Oxford University, UK (March 11th 2009) Seminar title: Two-channel Kondo behaviour in quantum dot chains Institute of Theoretical Physics, University of Cologne, Germany (January 6th 2010) Seminar title: Two-channel and two-impurity Kondo physics in quantum dot chains and rings Complex Transition Metal Compounds and Disorder: Internal Review Karlsruhe Institute of Technology, Germany (April 2010) Poster title: Dynamical Mean Field Theory for the Periodic Anderson Model: Exhaustion SFB 608 Workshop: Strongly correlated transition metal compounds Bergisch Gladbach, Germany (September 8 10th 2010) Poster title: Real-space correlations in Kondo systems University of Cologne, Germany (February 3rd 2011) Seminar title: Quantum impurity problems in real-space: signatures of RG flow Spring Meeting of the DPG Dresden, Germany (March 13 18th 2011) Poster title: Criticality in coupled quantum dots Theory Colloquium Department of Physics, University of Cologne, Germany (May 6th 2011) Seminar title: Real-Space Renormalization Group Flow in Kondo Systems Developments and Prospects in Quantum Impurity Physics Max Planck Institute for the Physics of Complex Systems, Dresden (June 6 10th 2011) Poster title: Real-space behaviour of the two-channel Kondo model and systems with disorder

5 DFG 960 Internal Meeting: quantum phase transitions University of Cologne, Germany (June 17th 2011) Poster title: Crossover from periodic to dilute impurity limit: emergence of coherence Tokyo-Cologne Workshop on Strongly Correlated Transition-Metal Compounds University of Cologne, Germany (September 7 10th 2011) Poster title: Universal conductance signatures in the two-impurity Kondo model University of Cologne, Germany (October 26th 2011) Seminar title: Nanotube double quantum dots and the Kondo screening cloud Spring Meeting of the DPG Berlin, Germany (March 26 30th 2012) Seminar title: Non-Fermi liquid physics in two-channel Kondo models University of Cologne, Germany (April 11th 2012) Seminar title: Quantum impurity problems with two conduction channels Professional Activities Ad-hoc reviewer for Physical Review B and Physica B. Organization of graduate workshop for the Bonn-Cologne Graduate School (March 2012). References Available on request.