1,129 research outputs found
NMR study of the Superconducting gap variation near the Mott transition in CsC
Former extensive studies of superconductivity in the \textit{A}C
compounds, where \textit{A} is an alkali, have led to consider that Bardeen
Cooper Schrieffer (BCS) electron-phonon pairing prevails in those compounds,
though the incidence of electronic Coulomb repulsion has been highly debated.
The discovery of two isomeric fulleride compounds CsC which
exhibit a transition with pressure from a Mott insulator (MI) to a
superconducting (SC) state clearly re-opens that question. Using pressure ()
as a single control parameter of the C balls lattice spacing, one can
now study the progressive evolution of the SC properties when the electronic
correlations are increased towards the critical pressure of the Mott
transition. We have used C and Cs NMR measurements on the cubic
phase A15-CsC just above kbar, where the SC
transition temperature displays a dome shape with decreasing cell
volume. From the dependence below of the nuclear spin lattice
relaxation rate we determine the electronic excitations in the
SC state, that is , the SC gap value. We find that
increases with decreasing towards , where decreases on the
SC dome, so that increases regularly upon approaching the
Mott transition. These results bring clear evidence that the increasing
correlations near the Mott transition are not significantly detrimental to SC.
They rather suggest that repulsive electron interactions might even reinforce
elecron-phonon SC, being then partly responsible for the large values,
as proposed by theoretical models taking the electronic correlations as a key
ingredient.Comment: 5 pages, 4 figures, Supplemental Materia
Numerical modeling for the evaluation of grout penetration in fractured rock masses
Grouting aims to reduce the permeability of rock mass below the required value and has been widely used in rock engineering field for a long time
Specific Heat Study of an S=1/2 Alternating Heisenberg Chain System F_5PNN Under Magnetic Field
We have measured the specific heat of an S=1/2 antiferromagnetic alternating
Heisenberg chain pentafulorophenyl nitronyl nitroxide under magnetic fields up
to H>H_C2. This compound has the field-induced magnetic ordered (FIMO) phase
between H_C1 and H_C2. Characteristic behaviors are observed depending on the
magnetic field up to above H_C2 outside of the H-T boundary for the FIMO.
Temperature and field dependence of the specific heat are qualitatively in good
agreement with the theoretical calculation on an S=1/2 two-leg ladder. [Wang et
al. Phys. Rev. Lett 84 5399 (2000)] This agreement suggests that the observed
behaviors are related with the low-energy excitation in the Tomonaga-Luttinger
liquid.Comment: 4pages, 4figures, replaced with revised version accepted to Physical
Review Letter
- …