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Martin Leijnse

Position:    Associate Professor (Docent, Lektor)

E-mail:    martin.leijnse@ftf.lth.se
Phone:   
Cell phone:   
Room:   
Address:    Box 118
221 00 Lund
      Sweden

University:    Lund University
Division:    Solid State Physics
Research Area(s):    Quantum Physics
Nanoelectronics- & photonics
Interests:    Mesoscopic physics. Majorana fermions, quantum computation, quantum transport, thermoelectrics

 
martin.leijnse

Coordinator of Education within NanoLund

Commissions of trust

Research

I am a theoretical condensed matter physicist primarily interested in nanoscale systems. On such small length scales, the physics is drastically different from what we know in our all-day life and is dominated by the laws of quantum mechanics. I investigate different ways of taking advantage of quantum mechanics to design for example electronic components with desirable properties. Specific research topics include: 
 
Superconducting proximity effect and Majorana fermions. When a superconductor is tunnel coupled to for example a semiconductor, tunneling of Cooper pairs leads to proximity-induced superconductivity in the semiconductor. I am interested in how this can be used to engineer superconductors with new exciting properties, such as topological superconductors hosting so-called Majorana fermion excitations. I am also studying how Majoranas can best be used for quantum information processing. In addition, I investigate how superconductors can be used to mediate a long-distance coupling between other quantum systems, for example spin qubits defined in nanowires. 
 
Quantum transport in nanostructures. Using primarily quantum master equation approaches, I study nonequilibrium transport in strongly interacting nanostructures, such as quantum dots, nanowires, and single-molecule devices. One goal is to understand how quantum transport can be used to extract spectroscopic information about a nanoscale system. Another goal is to propose devices where a combination of interaction and quantum mechanical effects give rise to some desired functionality, such as spin-polarized currents, negative differential resistance, or rectification.
 
Heat transport and thermoelectric devices. The thermoelectric effect allows direct conversion of a heat gradient into an electric current or voltage. I investigate the prospect of using the unique electronic properties of nanoscale devices to make highly efficient thermoelectric energy converters. Thermoelectic efficiency is reduced by losses from heat currents carried by phonons. Therefore, I investigate also phonon transport in nanosctructures, with the goal of designing devices where phonon transport is blocked without destroying the electronic transport properties. 

Research group

  • Michael Hell (Postdoc, joint position with Copenhagen University): Superconductor-semiconductor hybrid structures and Majorana bound states.
  • Florinda Viñas (PhD student): Theoretical studies of the electronic and quantum transport properties of core-shell nanowires and of quantum dots in such wires.
  • Martin Josefsson (PhD student): Theory of thermoelectrics in nanoscale systems.
Co-supervisor for PhD students:
  • Chunlin Yu (main supervisor Hongqi Xu): Experimental studies of Majorana fermions and hybrid quantum devices with semiconductor nanowires coupled to superconductors.
  • Bekmurat Dalelkham (main supervisor Hongqi Xu): Experimental studies of Majorana fermions and hybrid quantum devices with semiconductor nanowires coupled to superconductors.
  • Malin Nilsson (main supervisor Claes Thelander): Experimental studies of low-dimensional transport physics in semiconductor core-shell nanowires.
Alumni
  • Johan Ekström (MSc student): Majorana bound states in spatially inhomogeneous nanowires.
  • Georg Wolgast (MSc student): Simulations of qubits based on Majorana bound states.
  • John Lovén (MSc student): Theory of nanowire superlattices for thermoelectric energy conversion.
  • Hossein Karbaschi (visiting PhD student for 6 months): theory of thermoelectrics in nanowires.
  • Elsa de Geer (BSc student): Diffusive thermoelectric transport in nanowires.

Teaching

I currently teach the courses Elektroniska material (Electronic materials), The physics of low-dimensional structures (together with Mats-Erik Pistol) and a PhD level course on Theory of superconductivity

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