Selected Publications

- Andreev Reflection in Superfluid He-3: A Probe for Quantum Turbulence

Bradley et al., Annual Review of Condensed Matter Physics Vol. 8: 407-430 (2017) - Operating Nanobeams in a Quantum Fluid

Bradley et al., Nature Scientific Reports**7**, 4876 (2017) - Single Quantum Level Electron Turnstile

D.M.T. Van Zanten et al., Phys. Rev. Lett.**116**166801 (2016) - Topological Superconductivity and High Chern Numbers in 2D Ferromagnetic Shiba Lattices

J. RĂ¶ntynen, T. Ojanen, Phys. Rev. Lett.**114**236803, (2015) - Squeezing of Quantum Noise of Motion in a Micromechanical Resonator

J.-M. Pirkkalainen et al., Phys. Rev. Lett**115**, 24 (2015) - Direct-current superconducting quantum interference devices for the readout of metallic magnetic calorimeters

S. Kempf, A. Ferring, A. Fleischmann, C. Enss, Supercond. Sci. Technol.**28**, 045008 (2015)

## Collective amplitude mode fluctuations in a flat band superconductor formed at a semimetal surface

*V.J. Kauppila, T. Hyart, T.T. Heikkila*

We study the fluctuations of the amplitude (i.e., the Higgs-Anderson) mode in a superconducting system of coupled Dirac particles proposed as a model for possible surface or interface superconductivity in rhombohedral graphite. This system also serves as a generic model of a topological semimetal with an interaction-driven transition on its surface. We show that the absence of Fermi energy and vanishing of the excitation gap of the collective amplitude mode in the model leads to a large fluctuation contribution to thermodynamic quantities, such as the heat capacity. As a consequence, the mean-field theory becomes inaccurate, indicating that the interactions lead to a strongly correlated state. We also present a microscopic derivation of the Ginzburg-Landau theory corresponding to this model.

*physical review b 93 2*

doi:

*10.1103/PhysRevB.93.024505*