Université de Fribourg

Unveiling the complete dispersion of the giant Rashba split surface states of ferroelectric α−GeTe(111) by alkali doping

Kremer, Geoffroy ; Jaouen, Thomas ; Salzmann, Björn ; Nicolaï, L. ; Rumo, Maxime ; Nicholson, Christopher W. ; Hildebrand, Baptiste ; Dil, J. Hugo ; Springholz, G. ; Krempasky, Juraj ; Monney, Claude

In: Physical Review Research, 2020, vol. 2, no. 3, p. 033115

α−GeTe(111) is a noncentrosymmetric ferroelectric material for which a strong spin- orbit interaction gives rise to giant Rashba split states in the bulk and at the surface. The detailed dispersions of the surface states inside the bulk band gap remains an open question because they are located in the unoccupied part of the electronic structure, making them inaccessible to static...

Université de Fribourg

Ultrafast dynamics of the surface photovoltage in potassium-doped black phosphorus

Kremer, Geoffroy ; Rumo, Maxime ; Yue, Changming ; Pulkkinen, Aki ; Nicholson, Christopher W. ; Jaouen, Thomas ; Von Rohr, Fabian ; Werner, Philipp ; Monney, Claude

In: Physical Review B, 2021, vol. 104, no. 3, p. 035125

Black phosphorus is a quasi-two-dimensional layered semiconductor with a narrow direct band gap of 0.3 eV. A giant surface Stark effect can be produced by the potassium doping of black phosphorus, leading to a semiconductor to semimetal phase transition originating from the creation of a strong surface dipole and associated band bending. By using time- and angle-resolved photoemission ...

Université de Fribourg

Light-induced evaporative cooling of holes in the Hubbard model

Werner, Philipp ; Eckstein, Martin ; Müller, Markus ; Refael, Gil

In: Nature Communications, 2019, vol. 10, no. 1, p. 5556

An elusive goal in the field of driven quantum matter is the induction of long-range order. Here, we propose a mechanism based on light-induced evaporative cooling of holes in a correlated fermionic system. Since the entropy of a filled narrow band grows rapidly with hole doping, the isentropic transfer of holes from a doped Mott insulator to such a band results in a drop of temperature....

Université de Fribourg

Polydopamine nanoparticle doped nanofluid for solar thermal energy collector efficiency increase

Hauser, Daniel ; Steinmetz, Lukas ; Balog, Sandor ; Taladriz‐Blanco, Patricia ; Septiadi, Dedy ; Wilts, Bodo D. ; Petri‐Fink, Alke ; Rothen‐Rutishauser, Barbara

In: Advanced Sustainable Systems, 2020, vol. 4, no. 1, p. 1900101

Polydopamine can form black nanoparticles and has recently been gaining attention due to its extraordinary heating properties upon excitation with light. Herein, polydopamine hybrid nanoparticles are synthesized in different sizes and subsequently added to a solar fluid to analyze heating ability. The solar fluids with the differently sized hybrid polydopamine particles are compared to a...