Quantum dynamics of spin active and d-wave Josephson junctions
Doktorsavhandling, 2010

Conventional tunnel Josephson junctions form the basic building blocks of superconducting electronics. Their operation is based on comparatively simple dynamics where the superconducting phases across the junctions is the only dynamical degree of freedom. The goal of the project on which this thesis is based, is to understand the physics and develop a consistent theoretical description of the quantum dynamics of unconventional Josephson structures: spin active junctions, junctions containing low energy quasiparticles, and junctions composed of $d$-wave superconductors. Spin active Josephson junctions involve the additional degree of freedom of quasiparticle spin. Here we theoretically investigate the spin-structure of the current carrying interface bound states - Andreev Bound States (ABS), and induced ground state spin polarization of a short (shorter than the superconducting coherence length) nanowire junction containing a localized magnetic moment. We show that temporal variation of the superconducting phase difference and magnetic moment induce rotations in spin polarized and unpolarized subspaces respectively, which is manifested by temporal oscillation of the Josephson current. The interlevel transitions obey a selection rule that forbids manipulations in a certain region of external parameters and results from specific properties of Andreev bound states in magnetic contacts where, in a certain regime of phase bias and strength of magnetic scatterer, ABS belong to different eigenstates of the combined charge and parity inversion symmetry operator. A general framework is developed to include low energy quasiparticle states into the dynamics of Josephson junctions. Such states exist in e.g. constriction type junctions with high transparency channels or resonant states, as well as in junctions of unconventional superconductors. The existence of such states prevent the separation of energy scales which in conventional tunnel junctions freezes out the quasiparticle degrees of freedom. We show that the resonant interaction with such low energy states rather than the Josephson potential defines the nonlinear Josephson dynamics at small amplitudes. The framework is applied to high temperature Josephson junctions, whose unconventional order parameter admits ABS with energies in the middle of the superconducting gap - Mid Gap States (MGS). In addition to the non-linear dynamics induced by the MGS, we identify a reentrance effect in the transition between thermal activation and macroscopic quantum tunneling associated with the MGS, and connect this phenomenon to experimental observations.

Josephson effect

macroscopic quantum tunneling

high-temperature superconducvity

superconducting junctions

spin-active junctions

nonequilibrium superconductivity

Andreev bound states

Kollektorn
Opponent: Yuli Nazarov

Författare

Jens Harro Michelsen

Chalmers, Mikroteknologi och nanovetenskap (MC2), Tillämpad kvantfysik

Reentrance of macroscopic quantum tunneling in cuprate superconductors

Advances in Science and Technology,; Vol. 75(2010)p. 155-

Paper i proceeding

Quantum phase dynamics of high-Tc Josephson junctions

Journal of Physics: Conference Series,; Vol. 150(2009)p. 052159-

Paper i proceeding

Nonadiabatic Josephson dynamics in junctions with in-gap quasiparticles

Low Temperature Physics,; Vol. 36(2010)p. 925-932 [1154-1162]-

Artikel i vetenskaplig tidskrift

Manipulation with Andreev states in spin active mesoscopic Josephson junctions

Physical Review B - Condensed Matter and Materials Physics,; Vol. 77(2008)

Artikel i vetenskaplig tidskrift

Reentrance Effect in Macroscopic Quantum Tunneling and Nonadiabatic Josephson Dynamics in d-Wave Junctions

Physical Review Letters,; Vol. 105(2010)p. 127001-

Artikel i vetenskaplig tidskrift

I den här avhandlingen undersöker jag kvant-dynamiska effekter i övergångar som är känsliga för de tunnlande partiklarnas spin, och övergångar mellan så kallade d-vågs supraledare där ordningsparametern i supraledarna har en ovanlig symmetri.

In this thesis we investigate the quantum dynamical effects in junctions that are sensitive to the spin of the tunneling particles, as well as junctions between so called d-wave superconductors where the order parameter of the superconductors has an unusual symmetry compared to the conventional superconductors.

Ämneskategorier

Den kondenserade materiens fysik

ISBN

978-91-7385-431-3

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 3112

Kollektorn

Opponent: Yuli Nazarov