Paglione Research Group
for Nanophysics and Advanced Materials
Department of Physics
University of Maryland
Searching the Smithsonian Minerals Collection
As part of a large search for new superconductors funded by the AFOSR MURI program, the team of Rick Greene, Johnpierre Paglione and Ichiro Takeuchi and collaborators at Iowa State University and Lawrence Livermore National Laboratory are screening natural mineral samples from the Department of Mineral Sciences at the Smithsonian Institution’s National Museum of Natural History. Read more in a News article entitled "Minerals and meteorites: Searching for new superconductors" published in Physics Today.
Associate Member Appointment to CIFAR
Principal investigator Johnpierre Paglione has been appointed as an Associate member of the Quantum Materials Program of the Canadian Institute for Advanced Research (CIFAR), a private, non-profit institute of advanced study with nearly 400 researchers in 16 countries participating in long-term, multidisciplinary, global research networks. The Quantum Materials program is a global research effort which includes twenty-five non-Canadian researchers based in countries other than Canada, including France, Germany, Switzerland, the United Kingdom, China, Japan and the United States. See announcement here.
75th Birthday Workshop on Superconductivity
Thanks to everyone for participating in the workshop dedicated to the career of Professor Richard L. Greene on the occasion of his 75th birthday. The event was a great success, bringing together many of the world's experts on superconductivity research and providing many excellent talks and discussion on the latest developments in both low- and high-temperature superconductivity, which has been a focus of Professor Greene's long and distinguished career. See some videos and other information here.
Hints of High-Tc Mechanism in Iron-Based Superconductor
In a large collaboration involving UMD, NIST, McMaster University and the University of Cambridge, we report a study of the intrinsic separation of antiferromagnetism and high-Tc superconducting phases in the La-doping series, Ca1−xLaxFe2As2. By fine-tuning samples with a range of La concentrations through the AFM-SC critical point with applied pressure, we use both quasi-hydrostatic as well as hydrostatic pressure experiments to show clear evidence of an onset of the superconducting phase upon continuous pressure tuning beyond the magnetic ordered phase. We conclude that the superconductivity observed in rare earth-doped CaFe2As2 is
intrinsic to the material and does not arise due to an impurity phase, yielding a resultant phase diagram strikingly
similar to that of the highest-Tc "1111" oxypnictide superconductors.
Pressure-Induced Superconductivity in a Topological Insulator
Recently, superconductivity has been found in materials with topologically nontrivial band structures, such as in CuxBi2Se3 and YPtBi, providing not only intrinsic systems with which to study the interplay between superconductivity and TI states, but also the potential to realize a new class of odd-parity, unconventional superconductivity. In this study, we investigate the ground state of Bi2Se3 at ultra-high pressures by using a designer diamond anvil cell capable of measuring both longitudinal and transverse resistivities up to 50 GPa. We observe a superconducting phase that achieves a maximum transition temperature of 7 K that remains anomalously constant up to the highest pressures achieved in this study. Together with an upper critical field that surpasses both orbital and Pauli limits, this is indicative of an unconventional superconducting state in pure Bi2Se3. This work is published in Physical Review Letters (August 2013).
Probing Hybridization and Topological Surface States in a Model Kondo Insulator
In a Kondo lattice, it is expected that the inter-ion correlations together with the Kondo screening effect lead to the ‘freeze’ of the electrons in the material. However, clear evidence for the evolution of the electronic structure in the absence of complications from other mechanisms has not been achieved. On the other hand, it has been demonstrated that the strong interactions between electrons and local spins could lead to surface electrons whose spin and momentum are interlocked with each other so that they are energetically unfavorable to be back scattered without a spin flip. Such a protected surface state has been recently predicted to coexist with the Kondo screening effect in some insulating materials, leading to a distinct category of matters, i.e. topological Kondo insulator. In this work, we investigate the quasiparticle tunneling spectroscopy of SmB6 and report the first evidence for the development of the Kondo screening in the material, and find evidence that supports the predictions of nontrivial topology in Kondo systems.
Universal Pair-breaking effect revealed in iron-based superconductors
Headed by graduate student Kevin Kirshenbaum, this study aimed to elucidate the reason why iron-based superconductors respond relatively weakly to "dirt", or impurities in their structure, maintaining very high superconducting transition temperatures. Measurements of the transport scattering rate demonstrated the existence of a universal pair-breaking relation for a wide range of optimally transition-metal-doped iron-based superconductors with the ThCr2Si2 crystal structure, suggesting a common scattering mechanism and pairing potential across the entire series. The rate of suppression of the superconducting transition temperature Tc and the contrast between the optimum clean-limit value of 26 K and the higher Tc values achieved in non-transition-metal substitution series provides important constraints on the pairing symmetry and mechanism in the intermetallic iron-based superconductors.
This work was published as a Rapid Communication in Phys. Rev. B - Read more here. (October 2012)