arXiv subjects

A. Dirnaichner

Publications and source records attributed to A. Dirnaichner.

6 recordsLinked to original sources

arXiv2020

From Transparent Conduction to Coulomb Blockade at Fixed Hole Number

We present a complex set of transport spectroscopy data on a clean single-wall carbon nanotube device in high magnetic fields. At zero axial field, the device displays in hole conduction with increasingly negative gate voltage a fast transition towards high contact transparency and eventually Fabry-Perot interference of conductance. When increasing the axial field component up to B=17T, the contact transparency and the overall conductance are reduced all the way to Coulomb blockade, clearly displaying the subsequent charging with the first 10 holes. The continuous transition between the transport regimes is dominated by a rich spectrum of Kondo-like resonances, with distinct features in the stability diagrams.

cond-mat.mes-hall↗

arXiv2020

Magnetic field control of the Franck-Condon coupling of few-electron quantum states

Suspended carbon nanotubes display at cryogenic temperatures a distinct interaction between the quantized longitudinal vibration of the macromolecule and its embedded quantum dot, visible via Franck-Condon conductance side bands in transport spectroscopy. We present data on such side bands at known absolute number N=1 and N=2 of conduction band electrons and consequently well-defined electronic ground and excited states in a clean nanotube device. The interaction evolves only at a finite axial magnetic field and displays a distinct magnetic field dependence of the Franck-Condon coupling, different for different electronic base states and indicating a valley-dependent electron-vibron coupling. A tentative cause of these effects, reshaping of the electronic wavefunction by the magnetic field, is discussed and demonstrated in a model.

cond-mat.mes-hall↗

arXiv2019

Shaping electron wave functions in a carbon nanotube with a parallel magnetic field

A magnetic field, through its vector potential, usually causes measurable changes in the electron wave function only in the direction transverse to the field. Here we demonstrate experimentally and theoretically that in carbon nanotube quantum dots, combining cylindrical topology and bipartite hexagonal lattice, a magnetic field along the nanotube axis impacts also the longitudinal profile of the electronic states. With the high (up to 17T) magnetic fields in our experiment the wave functions can be tuned all the way from "half-wave resonator" shape, with nodes at both ends, to "quarter-wave resonator" shape, with an antinode at one end. This in turn causes a distinct dependence of the conductance on the magnetic field. Our results demonstrate a new strategy for the control of wave functions using magnetic fields in quantum systems with nontrivial lattice and topology.

cond-mat.mes-hall↗

arXiv2018

Lab::Measurement - A portable and extensible framework for controlling lab equipment and conducting measurements

Lab::Measurement is a framework for test and measurement automatization using Perl 5. While primarily developed with applications in mesoscopic physics in mind, it is widely adaptable. Internally, a layer model is implemented. Communication protocols such as IEEE 488, USB Test & Measurement, or, e.g., VXI-11 are addressed by the connection layer. The wide range of supported connection backends enables unique cross-platform portability. At the instrument layer, objects correspond to equipment connected to the measurement PC (e.g., voltage sources, magnet power supplies, multimeters, etc.). The high-level sweep layer automates the creation of measurement loops, with simultaneous plotting and data logging. An extensive unit testing framework is used to verify functionality even without connected equipment. Lab::Measurement is distributed as free and open source software.

physics.ins-det↗

arXiv2016

Secondary electron interference from trigonal warping in clean carbon nanotubes

We investigate Fabry-Perot interference in an ultraclean carbon nanotube resonator. The conductance shows a clear superstructure superimposed onto conventional Fabry-Perot oscillations. A sliding average over the fast oscillations reveals a characteristic slow modulation of the conductance as a function of the gate voltage. We identify the origin of this secondary interference in intervalley and intravalley backscattering processes which involve wave vectors of different magnitude, reflecting the trigonal warping of the Dirac cones. As a consequence, the analysis of the secondary interference pattern allows us to estimate the chiral angle of the carbon nanotube.

cond-mat.mes-hall↗

arXiv2015

Broken SU(4) symmetry in a Kondo-correlated carbon nanotube

Understanding the interplay between many-body phenomena and non-equilibrium in systems with entangled spin and orbital degrees of freedom is a central objective in nano-electronics. We demonstrate that the combination of Coulomb interaction, spin-orbit coupling and valley mixing results in a particular selection of the inelastic virtual processes contributing to the Kondo resonance in carbon nanotubes at low temperatures. This effect is dictated by conjugation properties of the underlying carbon nanotube spectrum at zero and finite magnetic field. Our measurements on a clean carbon nanotube are complemented by calculations based on a new approach to the non-equilibrium Kondo problem which well reproduces the rich experimental observations in Kondo transport.

cond-mat.mes-hall↗