Ana Maldonado

Dirac surface states and nature of superconductivity in Noncentrosymmetric BiPd

In non-magnetic bulk materials, inversion symmetry protects the spin degeneracy. If the bulk crystal structure lacks a centre of inversion, however, spin–orbit interactions lift the spin degeneracy, leading to a Rashba metal whose Fermi surfaces exhibit an intricate spin texture. In superconducting Rashba metals a pairing wavefunction constructed from these complex spin structures will generally contain both singlet and triplet character. Here we examine the possible triplet components of the order parameter in noncentrosymmetric BiPd, combining for the first time in a noncentrosymmetric superconductor macroscopic characterization, atomic-scale ultra-low-temperature scanning tunnelling spectroscopy, and relativistic first-principles calculations. While the superconducting state of BiPd appears topologically trivial, consistent with Bardeen–Cooper–Schrieffer theory with an order parameter governed by a single isotropic s-wave gap, we show that the material exhibits Dirac-cone surface states with a helical spin polarization.

Superconducting gap and vortex lattice of the heavy-fermion compound CeCu2Si2

We gratefully acknowledge K. Machida and Y. Fasano for stimulating discussions. Z.S. acknowledges support from Netherlands Organisation for Scientific Research (NWO) (Grant No. 680.50.1119). A.M. and P.W. acknowledge support from the Engineering and Physical Sciences Research Council (EPSRC, EP/I031014/1)

Scanning tunneling spectroscopy under large current flow through the sample

We describe a method to make scanning tunneling microscopy/spectroscopy imaging at very low temperatures while driving a constant electric current up to some tens of mA through the sample. It gives a new local probe, which we term current driven scanning tunneling microscopy/spectroscopy. We show spectroscopic and topographic measurements under the application of a current in superconducting Al and NbSe(2) at 100 mK. Perspective of applications of this local imaging method includes local vortex motion experiments, and Doppler shift local density of states studies.

Supercurrent on a vortex core in 2H-NbSe2: Current-driven scanning tunneling spectroscopy measurements

P. Rodiere provided us with the 2H-NbSe2 sample.We acknowledge support from MINECO and MEC of Spain (the Consolider Ingenio Molecular Nanoscience CSD2007-00010 program, FIS2011-23488, ACI-2009-0905, and an FPU grant), of COST MP1201, and of the Comunidad de Madrid through the Nanobiomagnet program

Tunneling spectroscopy of the superconducting state of URu2Si2

This work was supported by the Spanish MICINN and MEC (Consolider Ingenio Molecular Nanoscience CSD2007-00010 program, FIS2011-23488, ACI-2009-0905, and FPU grant), by the Comunidad de Madrid through program Nanobiomagnet, and by ERC (NewHeavyFermion) and French ANR projects (CORMAT, SINUS, DELICE)

Scanning microscopies of superconductors at very low temperatures

Abstract We discuss basics of Scanning Tunneling Microscopy and Spectroscopy (STM/S) of the superconducting state with normal and superconducting tips. We present a new method to measure the local variations in the Andreev reflection amplitude between a superconducting tip and the sample. This method is termed Scanning Andreev Reflection Spectroscopy (SAS). We also briefly discuss vortex imaging with STM/S under an applied current through the sample, and show the vortex lattice as a function of the angle between the magnetic field and sample’s surface.

Temperature dependent tunneling spectroscopy in the heavy fermion CeRu2Si2 and in the antiferromagnet CeRh2Si2

CeRu(2)Si(2) and CeRh(2)Si(2) are two similar heavy fermion stoichiometric compounds located on the two sides of a magnetic quantum critical phase transition. CeRh(2)Si(2) is an antiferromagnet below T(N) = 36 K with moderate electronic masses whereas CeRu(2)Si(2) is a paramagnetic metal with particularly heavy electrons. Here we present tunneling spectroscopy measurements as a function of temperature (from 0.15 to 45 K). The tunneling conductance at 0.15 K reveals V-shaped dips around the Fermi level in both compounds, which disappear in CeRu(2)Si(2) above the coherence temperature, and in CeRh(2)Si(2) above the Néel temperature. In the latter case, two different kinds of V-shaped tunneling conductance dips are found.