Publications

We report conductance and thermopower measurements of metallic atomic-size contacts, namely gold and platinum, using a scanning tunneling microscope (STM) at room temperature. We find that few-atom gold contacts have an average negative thermopower, whereas platinum contacts present a positive thermopower, showing that for both metals, the sign of the thermopower in the nanoscale differs from that of bulk wires.

We also find that the magnitude of the thermopower exhibits minima at the maxima of…

We investigate the multiphoton photoluminescence characteristics of gold nanoantennas fabricated from single crystals and polycrystalline films. By exciting these nanostructures with ultrashort pulses tunable in the near-infrared range, we observe distinct features in the broadband photoluminescence spectrum. By comparing antennas of different crystallinity and shape, we demonstrate that the nanoscopic geometry of plasmonic devices determines the shape of the emission spectra. Our findings rule…

The valley degree of freedom in the electronic band structure of silicon, graphene, and other materials is often considered to be an obstacle for quantum computing (QC) based on electron spins in quantum dots. Here we show that control over the valley state opens new possibilities for quantum information processing. Combining qubits encoded in the singlet-triplet subspace of spin and valley states allows for universal QC using a universal two-qubit gate directly provided by the exchange…

Role of entropy in domain wall motion in thermal gradients

Thermally driven domain wall (DW) motion caused solely by magnonic spin currents was forecast theoretically and has been measured recently in a magnetic insulator using magneto-optical Kerr effect microscopy. We present an analytical calculation of the DW velocity as well as the Walker breakdown within the framework of the Landau Lifshitz Bloch equation of motion
The temperature gradient leads to a torque term acting on the…

We study the nonequilibrium steady state of a mechanical resonator in the quantum regime realized by a suspended carbon nanotube quantum dot in contact with two ferromagnets. Because of the spin-orbit interaction and/or an external magnetic field gradient, the spin on the dot couples directly to the flexural eigenmodes.

Accordingly, the nanomechanical motion induces inelastic spin flips of the tunneling electrons. A spin-polarized current at finite bias voltage causes either heating or active…

Femtosecond laser pulses have been used to excite coherent optical phonons in single crystalline Bi₂Te₃. Oscillations from low and high frequency phonons of two A_1g and one E_g symmetry modes are observed. In order to clarify the process of coherent phonon generation, the time domain measurements were complemented by spontaneous Raman scattering. The comparison of frequency and time domain results reveals the discrepancies between the time and frequency domain measurements among which the most…

We demonstrate sub-cycle manipulation of mid-infrared optical waveforms in the time domain. This goal is accomplished via efficient reflection at a semiconductor surface induced by femtosecond interband excitation.

The ultrafast response of this process allows slicing of high-field multi-terahertz transients down to the single optical cycle. Ultrabroadband and phase-stable transients with peak amplitudes beyond 10 MV cm⁻¹ are obtained, paving the way for efficient coherent control of…

The response to strain in covalently bound single layers has a large impact on the growth and properties. We investigate the quasi-two-dimensional hexagonal boron nitride on Rh(111), which is interesting due to its high intrinsic corrugation.

We use combined atomic force and scanning tunneling microscopy to measure the response of this monolayer to probing forces. Three-dimensional force maps and the atomic resolution of the layer enable us to determine lateral and vertical stiffness of this…

CdSe/polyfluorene hybrid particles are directly obtained by high temperature synthesis of CdSe nanocrystals in the presence of amine or phosphonic acid functionalized polyfluorenes. Analytical ultracentrifugation studies of these hybrid particles give a rare quantitative insight into the binding of the polyfluorene ligands to the nanocrystal. Efficient energy transfer from polyfluorene to the nanocrystal is revealed by single particle photoluminescence studies.

T. de Roo, J. Haase, J. Keller,…