Electron pairing in the vast majority of superconductors follows the Bardeen-Cooper-Schrieffer theory of superconductivity, which describes the condensation of electrons into pairs with antiparallel ...spins in a singlet state with an s-wave symmetry. Unconventional superconductivity was predicted in single-layer graphene (SLG), with the electrons pairing with a p-wave or chiral d-wave symmetry, depending on the position of the Fermi energy with respect to the Dirac point. By placing SLG on an electron-doped (non-chiral) d-wave superconductor and performing local scanning tunnelling microscopy and spectroscopy, here we show evidence for a p-wave triggered superconducting density of states in SLG. The realization of unconventional superconductivity in SLG offers an exciting new route for the development of p-wave superconductivity using two-dimensional materials with transition temperatures above 4.2 K.
Considerable evidence for proximity-induced triplet superconductivity on the ferromagnetic side of a superconductor-ferromagnet (S-F) interface now exists; however, the corresponding effect on the ...superconductor side has hardly been addressed. We have performed scanning tunneling spectroscopy measurements on NbN superconducting thin films proximity coupled to the half-metallic ferromagnet La sub(2/3)Ca sub(1/3) Mn O sub(3) (LCMO) as a function of magnetic field. We have found that at zero and low applied magnetic fields the tunneling spectra on NbN typically show an anomalous gap structure with suppressed coherence peaks and, in some cases, a zero-bias conductance peak. As the field increases to the magnetic saturation of LCMO where the magnetization is homogeneous, the spectra become more BCS-like and the critical temperature of the NbN increases, implying a reduced proximity effect. Our results therefore suggest that triplet-pairing correlations are also induced in the S side of an S-F bilayer.
The properties of oxides are critically controlled by the oxygen stoichiometry. Minimal variations in oxygen content can lead to vast changes in their properties. The addition of oxygen during ...synthesis may not be a precise enough knob for tuning the oxygen stoichiometry when the material has several stable and close oxidation states. We use sputtered V
2
O
3
films as an example to show that rapid transfer of the sample away from the heating element after growth causes a temperature decrease (quenching) quick enough to freeze the correct oxygen stoichiometry in the sample. This procedure has allowed us to improve dramatically the V
2
O
3
electronic properties without any adverse measurable effects on the structural properties. In this fashion, the metal–insulator transition resistance change was increased by two orders of magnitude, while the transition width was decreased by 20 K.
Despite decades of efforts, the origin of metal-insulator transitions (MITs) in strongly correlated materials remains one of the main long-standing problems in condensed-matter physics. An archetypal ...example is V2O3, which undergoes simultaneous electronic, structural, and magnetic phase transitions. This remarkable feature highlights the many degrees of freedom at play in this material. In this work, acting solely on the magnetic degree of freedom, we reveal an anomalous feature in the electronic transport of V2O3: On cooling, the magnetoresistance changes from positive to negative values well above the MIT temperature, and shows divergent behavior at the transition. The effects are attributed to the magnetic field quenching antiferromagnetic fluctuations above the Néel temperature TN, and preventing long-range antiferromagnetic ordering below TN. In both cases, suppressing the antiferromagnetic ordering prevents the opening of the incipient electronic gap. This interpretation is supported by Hubbard model calculations which fully reproduce the experimental behavior. Our study sheds light on this classic problem providing a clear and physical interpretation of the nature of the metal-insulator transition.
Nature Communications 8: Article number: 14024 (2017); Published: 19 January 2017; Updated: 1 March 2017 The present address for U. Sassi is incorrect in this Article. This author does not have a ...present address. The correct full affiliation details for this author are given below: Cambridge Graphene Centre, University of Cambridge, Cambridge CB3 0FA, UK.
The properties of oxides are critically controlled by the oxygen stoichiometry. Minimal variations in oxygen content can lead to vast changes in their properties. The addition of oxygen during ...synthesis may not be a precise enough knob for tuning the oxygen stoichiometry when the material has several stable and close oxidation states. We use sputtered V.sub.2O.sub.3 films as an example to show that rapid transfer of the sample away from the heating element after growth causes a temperature decrease (quenching) quick enough to freeze the correct oxygen stoichiometry in the sample. This procedure has allowed us to improve dramatically the V.sub.2O.sub.3 electronic properties without any adverse measurable effects on the structural properties. In this fashion, the metal-insulator transition resistance change was increased by two orders of magnitude, while the transition width was decreased by 20 K.
Scanning tunneling spectroscopy measurements performed on La sub(0.7)Ca sub(0.3)Mn sub(3)O (LCMO) films epitaxially grown on Pr sub(1.85) Ce sub(0.15) CuO sub(4) (PCCO) reveal localized penetration ...of superconductivity into the LCMO up to distances much larger than is possible for Cooper pairs in a singlet spin state to exist. This long-range proximity effect is manifested in the tunneling spectra as gaps and, less abundantly, as zero-bias conductance peaks (ZBCPs). Since ZBCPs were not found on the bare PCCO films, their appearance is attributed to an anisotropic (p wave or d wave) triplet-pairing superconductor order parameter induced in the LCMO.
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