L. Benfatto

Phase Fluctuations in a Strongly Disordered s -Wave NbN Superconductor Close to the Metal-Insulator Transition

We explore the role of phase fluctuations in a three-dimensional s-wave superconductor, NbN, as we approach the critical disorder for destruction of the superconducting state. Close to critical disorder, we observe a finite gap in the electronic spectrum which persists at temperatures well above T(c). The superfluid density is strongly suppressed at low temperatures and evolves towards a linear-T variation at higher temperatures. These observations provide strong evidence that phase fluctuations play a central role in the formation of a pseudogap state in a disordered s-wave superconductor.

Measurement of magnetic penetration depth and superconducting energy gap in very thin epitaxial NbN films

We investigate evolution of the magnetic penetration depth and superconducting energy gap in epitaxial NbN films using a low frequency mutual inductance technique and tunneling spectroscopy using a low temperature scanning tunneling microscope (STM). The superconducting transition temperature (Tc) for films grown under optimal growth conditions decreases monotonically from 15.87K to 9.16K as the film thickness is decreased from 50nm to 3nm. With decrease in film thickness delta(0) monotonically decreases, whereas lambda(0) monotonically increases. We observe that Tc, lambda(o) and delta(0) are well described by Bardeen-Cooper-Schrieffer (BCS) theory in all films other than the two thinnest ones where we see evidence of the Kosterlitz-Thouless-Berezinski (KTB) transition close to Tc.

Orbital-dependent Fermi surface shrinking as a fingerprint of nematicity in FeSe

The large anisotropy in the electronic properties across a structural transition in several correlated systems has been identified as the key manifestation of electronic nematic order, breaking rotational symmetry. In this context, FeSe is attracting tremendous interest, since electronic nematicity develops over a wide range of temperatures, allowing accurate experimental investigation. Here we combine angle-resolved photoemission spectroscopy and theoretical calculations based on a realistic multi-orbital model to unveil the microscopic mechanism responsible for the evolution of the electronic structure of FeSe across the nematic transition. We show that the self-energy corrections due to the exchange of spin fluctuations between hole and electron pockets are responsible for an orbital-dependent shrinking of the Fermi Surface that affects mainly the

Broadening of the Berezinskii-Kosterlitz-Thouless superconducting transition by inhomogeneity and finite-size effects

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Kosterlitz-Thouless behavior in layered superconductors: the role of the vortex-core energy

parts of the Fermi surface. This result is consistent with our experimental observation of the Fermi Surface in the high-temperature tetragonal phase, that includes the

Enhanced Cooper pairing versus suppressed phase coherence shaping the superconducting dome in coupled aluminum nanograins

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Role of the vortex-core energy on the Berezinskii-Kosterlitz-Thouless transition in thin films of NbN.

electron sheet that was not clearly resolved before. In the low-temperature nematic phase, we experimentally confirm the appearance of a large (

Multiple gaps and superfluid density from interband pairing in a four-band model of the iron oxypnictides

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Enhancement of the finite-frequency superfluid response in the pseudogap regime of strongly disordered superconducting films.

50meV)

Phonon switching and combined Fano-Rice effect in optical spectra of bilayer graphene

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