Csaba G Péterfalvi | University of Konstanz, Germany (original) (raw)

articles by Csaba G Péterfalvi

physica status solidi (b), 2010

We theoretically study the scattering of a plane wave of a ballistic electron on a circular n-p j... more We theoretically study the scattering of a plane wave of a ballistic electron on a circular n-p junction in single and bilayer graphene. We compare the exact wave function inside the junction to that obtained from a semiclassical formula developed in catastrophe optics. In the semiclassical picture short-wavelength electrons are treated as rays of particles that can get reflected and refracted at the n-p junction according to Snell's law with negative refraction index.

The Journal of Chemical Physics, 2014

Using a first principles approach to electron transport, we calculate the electrical and thermoel... more Using a first principles approach to electron transport, we calculate the electrical and thermoelectrical transport properties of a series of molecular wires containing benzo-difuran subunits. We demonstrate that the side groups introduce Fano resonances, the energy of which is changing with the electronegativity of selected atoms in it. We also study the relative effect of single, double or triple bonds along the molecular backbone and find that single bonds yield the highest thermopower, approximately 22µV/K at room temperature, which is comparable with the highest measured values for single-molecule thermopower reported to date.

New Journal of Physics, 2012

We propose an implementation of a valley selective electronic Veselago lens in bilayer graphene. ... more We propose an implementation of a valley selective electronic Veselago lens in bilayer graphene. We demonstrate that in the presence of an appropriately oriented potential step, low-energy electrons radiating from a point source can be re-focused coherently within the same band. The phenomenon is due to the trigonal warping of the band structure that leads to a negative refraction index. We show that the interference pattern can be controlled by an external mechanical strain.

Physical Review B, 2009

We present a theoretical study of electron wave functions in ballistic circular n-p junctions of ... more We present a theoretical study of electron wave functions in ballistic circular n-p junctions of bilayer graphene. Similarly to the case of a circular n-p junction of monolayer graphene, we find that (i) the wave functions form caustics inside the circular region, and (ii) the shape of these caustics are well described by a geometrical optics model using the concept of a negative refractive index. In contrast to the monolayer case, we show that the strong focusing effect is absent in the bilayer. We explain these findings in terms of the angular dependence of Klein tunneling at a planar n-p junction.

We show that the wavefunctions form caustics in circular graphene p-n junctions which in the fram... more We show that the wavefunctions form caustics in circular graphene p-n junctions which in the framework of geometrical optics can be interpreted with negative refractive index.

We present a theoretical study of elastic spin-dependent electron scattering caused by a nonunifo... more We present a theoretical study of elastic spin-dependent electron scattering caused by a nonuniform Rashba spin-orbit coupling strength. Using the spin-generalized method of partial waves the scattering amplitude is exactly derived for the case of a circular shape of scattering region. We found that the polarization of the scattered waves are strongly anisotropic functions of the scattering angle. This feature can be utilized to design a good all-electric spin-polarizer. General properties of the scattering process are also investigated in the high and low energy limits.

Physical Review B, 2012

Devices formed from single molecules attached to noble-metal electrodes exhibit large conductance... more Devices formed from single molecules attached to noble-metal electrodes exhibit large conductance fluctuations, which inhibit their development as reproducible functional units. We demonstrate that single molecules with planar anchor groups attached carbon-based electrodes are more resilient to atomic-scale variation in the contacts and exhibit significantly-lower conductance fluctuations. We examine the conductance of a 2,6-dibenzylamino core-substituted naphthalenediimide (NDI) chromophore attached to carbon electrodes by either phenanthrene anchors or by more extended anchor groups, which include OPE spacers. We demonstrate for the more spatially-extended anchor groups, conductance fluctuations are significantly reduced. The current-voltage characteristic arising from long-range tunnelling, is found to be strongly non-linear with pronounced conductance suppression below a threshold voltage of approximately 2.5 volts.

We theoretically study a silicon triple quantum dot (TQD) system coupled to a superconducting mic... more We theoretically study a silicon triple quantum dot (TQD) system coupled to a superconducting microwave resonator. The response signal of an injected probe signal can be used to extract information about the level structure by measuring the transmission and phase shift of the output field. This information can further be used to gain knowledge about the valley splittings and valley phases in the individual dots. Since relevant valley states are typically split by several , a finite temperature or an applied external bias voltage is required to populate energetically excited states. The theoretical methods in this paper include a capacitor model to fit experimental charging energies, an extended Hubbard model to describe the tunneling dynamics, a rate equation model to find the occupation probabilities, and an input–output model to determine the response signal of the resonator.

We study an accumulation mode Si/SiGe double quantum dot (DQD) containing a single electron that ... more We study an accumulation mode Si/SiGe double quantum dot (DQD) containing a single electron that is dipole coupled to microwave photons in a superconducting cavity. Measurements of the cavity transmission reveal dispersive features due to the DQD valley states in Si. The occupation of the valley states can be increased by raising the temperature or applying a finite source-drain bias across the DQD, resulting in an increased signal. Using the cavity input-output theory and a four-level model of the DQD, it is possible to efficiently extract valley splittings and the inter- and intravalley tunnel couplings.

We calculate the pure dephasing time of three-electron exchange-only qubits due to interaction wi... more We calculate the pure dephasing time of three-electron exchange-only qubits due to interaction with the nuclear hyperfine field. Within the S=Sz=1/2 spin subspace, we derive formulas for the dephasing time as a function of the position within the stability diagram consisting of the (1,1,1) charge region and the neighboring charge sectors coupled by tunneling. The nuclear field and the tunneling are taken into account in a second order approximation. The analytical solutions accurately reproduce the numerical evaluation of the full problem, and in comparison with existing experimental data, we find that the dephasing times are longer but on the same time scale as for single spins.

We derive the boundary conditions for and similar transition-metal dichalcogenide honeycomb (2H p... more We derive the boundary conditions for and similar transition-metal dichalcogenide honeycomb (2H polytype) monolayers with the same type of Hamiltonian within the continuum model around the K points. In an effective two-band description, the electron-hole symmetry breaking quadratic terms are also taken into account. We model the effect of the edges with a linear edge constraint method that has been applied previously to graphene. Focusing mainly on zigzag edges, we find that different reconstruction geometries with different edge atoms can generally be described with one scalar parameter varying between 0 and . We analyze the edge states and their dispersion relation in in particular, and we find good agreement with the results of previous density functional theory calculations for various edge types.

physica status solidi (b), 2010

We theoretically study the scattering of a plane wave of a ballistic electron on a circular n-p j... more We theoretically study the scattering of a plane wave of a ballistic electron on a circular n-p junction in single and bilayer graphene. We compare the exact wave function inside the junction to that obtained from a semiclassical formula developed in catastrophe optics. In the semiclassical picture short-wavelength electrons are treated as rays of particles that can get reflected and refracted at the n-p junction according to Snell's law with negative refraction index.

The Journal of Chemical Physics, 2014

Using a first principles approach to electron transport, we calculate the electrical and thermoel... more Using a first principles approach to electron transport, we calculate the electrical and thermoelectrical transport properties of a series of molecular wires containing benzo-difuran subunits. We demonstrate that the side groups introduce Fano resonances, the energy of which is changing with the electronegativity of selected atoms in it. We also study the relative effect of single, double or triple bonds along the molecular backbone and find that single bonds yield the highest thermopower, approximately 22µV/K at room temperature, which is comparable with the highest measured values for single-molecule thermopower reported to date.

New Journal of Physics, 2012

We propose an implementation of a valley selective electronic Veselago lens in bilayer graphene. ... more We propose an implementation of a valley selective electronic Veselago lens in bilayer graphene. We demonstrate that in the presence of an appropriately oriented potential step, low-energy electrons radiating from a point source can be re-focused coherently within the same band. The phenomenon is due to the trigonal warping of the band structure that leads to a negative refraction index. We show that the interference pattern can be controlled by an external mechanical strain.

Physical Review B, 2009

We present a theoretical study of electron wave functions in ballistic circular n-p junctions of ... more We present a theoretical study of electron wave functions in ballistic circular n-p junctions of bilayer graphene. Similarly to the case of a circular n-p junction of monolayer graphene, we find that (i) the wave functions form caustics inside the circular region, and (ii) the shape of these caustics are well described by a geometrical optics model using the concept of a negative refractive index. In contrast to the monolayer case, we show that the strong focusing effect is absent in the bilayer. We explain these findings in terms of the angular dependence of Klein tunneling at a planar n-p junction.

We show that the wavefunctions form caustics in circular graphene p-n junctions which in the fram... more We show that the wavefunctions form caustics in circular graphene p-n junctions which in the framework of geometrical optics can be interpreted with negative refractive index.

We present a theoretical study of elastic spin-dependent electron scattering caused by a nonunifo... more We present a theoretical study of elastic spin-dependent electron scattering caused by a nonuniform Rashba spin-orbit coupling strength. Using the spin-generalized method of partial waves the scattering amplitude is exactly derived for the case of a circular shape of scattering region. We found that the polarization of the scattered waves are strongly anisotropic functions of the scattering angle. This feature can be utilized to design a good all-electric spin-polarizer. General properties of the scattering process are also investigated in the high and low energy limits.

Physical Review B, 2012

Devices formed from single molecules attached to noble-metal electrodes exhibit large conductance... more Devices formed from single molecules attached to noble-metal electrodes exhibit large conductance fluctuations, which inhibit their development as reproducible functional units. We demonstrate that single molecules with planar anchor groups attached carbon-based electrodes are more resilient to atomic-scale variation in the contacts and exhibit significantly-lower conductance fluctuations. We examine the conductance of a 2,6-dibenzylamino core-substituted naphthalenediimide (NDI) chromophore attached to carbon electrodes by either phenanthrene anchors or by more extended anchor groups, which include OPE spacers. We demonstrate for the more spatially-extended anchor groups, conductance fluctuations are significantly reduced. The current-voltage characteristic arising from long-range tunnelling, is found to be strongly non-linear with pronounced conductance suppression below a threshold voltage of approximately 2.5 volts.

We theoretically study a silicon triple quantum dot (TQD) system coupled to a superconducting mic... more We theoretically study a silicon triple quantum dot (TQD) system coupled to a superconducting microwave resonator. The response signal of an injected probe signal can be used to extract information about the level structure by measuring the transmission and phase shift of the output field. This information can further be used to gain knowledge about the valley splittings and valley phases in the individual dots. Since relevant valley states are typically split by several , a finite temperature or an applied external bias voltage is required to populate energetically excited states. The theoretical methods in this paper include a capacitor model to fit experimental charging energies, an extended Hubbard model to describe the tunneling dynamics, a rate equation model to find the occupation probabilities, and an input–output model to determine the response signal of the resonator.

We study an accumulation mode Si/SiGe double quantum dot (DQD) containing a single electron that ... more We study an accumulation mode Si/SiGe double quantum dot (DQD) containing a single electron that is dipole coupled to microwave photons in a superconducting cavity. Measurements of the cavity transmission reveal dispersive features due to the DQD valley states in Si. The occupation of the valley states can be increased by raising the temperature or applying a finite source-drain bias across the DQD, resulting in an increased signal. Using the cavity input-output theory and a four-level model of the DQD, it is possible to efficiently extract valley splittings and the inter- and intravalley tunnel couplings.

We calculate the pure dephasing time of three-electron exchange-only qubits due to interaction wi... more We calculate the pure dephasing time of three-electron exchange-only qubits due to interaction with the nuclear hyperfine field. Within the S=Sz=1/2 spin subspace, we derive formulas for the dephasing time as a function of the position within the stability diagram consisting of the (1,1,1) charge region and the neighboring charge sectors coupled by tunneling. The nuclear field and the tunneling are taken into account in a second order approximation. The analytical solutions accurately reproduce the numerical evaluation of the full problem, and in comparison with existing experimental data, we find that the dephasing times are longer but on the same time scale as for single spins.

We derive the boundary conditions for and similar transition-metal dichalcogenide honeycomb (2H p... more We derive the boundary conditions for and similar transition-metal dichalcogenide honeycomb (2H polytype) monolayers with the same type of Hamiltonian within the continuum model around the K points. In an effective two-band description, the electron-hole symmetry breaking quadratic terms are also taken into account. We model the effect of the edges with a linear edge constraint method that has been applied previously to graphene. Focusing mainly on zigzag edges, we find that different reconstruction geometries with different edge atoms can generally be described with one scalar parameter varying between 0 and . We analyze the edge states and their dispersion relation in in particular, and we find good agreement with the results of previous density functional theory calculations for various edge types.