The author at the University of California
La Jolla, in 1966
Some decades later
Jerome has graduated at the University Paris-Sorbonnes in 1961. He
has obtained a PhD in Physics at CEN-Saclay in 1965 under the
supervision of Professor A. Abragam, then moved to the University of
California for a post doctoral visit under Professor W. Kohn. He
began his research activity at the University of Paris-Sud, Orsay in
1967 in the Solid State Physics Laboratory of Profs R. Castaing, A.
Guinier and J. Friedel where he has developed high pressure
measurements for the study of metals and alloys at low temperature.
is Emeritus Director of Research at CNRS and became a
corresponding member of the French Academy of Sciences in 1990 and
full member in 2005.
major contribution of Denis Jerome to the advancement of
physics is the discovery of Organic Superconductivity in the One
Dimensional Organic Bechgaard salt (TMTSF2PF6) in 1979 at the
University of Paris-Sud, Orsay.
has also contributed to the study of the physical properties of a
vast number of one
dimensional and two dimensional organic conductors and established a
generic phase diagram for these families.
has been active in the experimental investigation of the
metal-insulator Mott transition (doped silicon, transition metal
oxides and 2D organic conductors).
and book chapters on organic condcuctors and organic
can be found a large collection of review articles and book
chapters on the field of organic one dimensional conductors and
transition in impurity doped silicon, Si-P
Metal-Insulator transition occurring in pure silicon as doping is
increased is a Mott transition in a disordered electronic system.
This phenomenon has been studied in phosporous doped silicon using double resonance ENDOR techniques leading to :
the insulating side, N<3x1018 cm-3, the
nuclear relaxation is due to the modulation of the dipolar electron
nucleus interaction through the hopping of carriers between
electron wave function does reveal sharp peaks around impurity sites
even in the metallic state.see
excitonic transition is expected to take place in semi-metals when
conditions for perfect nesting of electron and hole pockets are
Response functions have been determined and possible materials such as Bismuth or divalent metals like Strontium or Ytterbium have been considered for the experimental observation of this new phase. see papers
Helium gas high pressure
and hydrostatic pressure up to 35 kbar
of some of the high pressure set up developed at Orsay using
gas pressure media enabling hydrostatic pressure down to low
temperatures, teflon cells techniques with either a capillary
tubing and a low temperature intensifier or clamp cells using
berylium –copper and nickel-chromium- aluminum alloys.see
compounds, transition metal dichalcogenides
metal dichalcogenides such as TX2 compound where T=V,
Nb,Ta, Tl,etc,.. and X= S, Se, etc,..are two dimensional
conductors also known as layered compounds.
often undergo a lattice distortion at low temperature leading to a
structure which is incommensurate
with the original lattice.
distorted phases have been studied via transport and NMR
investigations under pressure. These studies have clearly
established a relation existing between the onset of a periodic
distortion at To and the onset of superconductivity at a lower
temperature Tc .
on 2H-NbSe2, 4Hb-TaS2, 2H-NbS2, 2H-TaS2 have shown that the drop
of the density of states at Fermi level occuring below To becoming
suppressed under pressure is responsible in turn for the increase
of Tc under pressure.
has been the first single crystal where NMR experiments have shown
the incommensurate nature of the periodic distortion.see papers
Organic superconductivity in quasi-one
dimensional organic salts, Bechgaard and Fabre salts, TM2X
Superconductivity of organic matter has been
discovered in December 1979 at Orsay by D. Jerome, A. Mazaud, M.
Ribault and K. Bechgaard and published in 1980.
The first organic material revealing the essential
features for superconductivity, (zero resistance state and
Meissner expulsion of the magnetic flux) is the organic salt
(TMTSF)2PF6 namely (tetramethyl tetra
selenafulvalene)2 hexafluorophosphate under an hydrostatic
pressure of 9 kbar at Tc=1K.
The peculiarity of this salt stems from the design of these materials made of flat, conjugated fulvalene electron donating molecules, packed in columns along the a-axis. This direction has a high, metallic conductivity due to the intrachain overlap of pi-molecular orbitals ; the transverse directions have much weaker intermolecular couplings and thus much lower conductivity. It is the reason why they are often called quasi one dimensional conductors (and superconductors).
Following the inital discovery of superconductivity
in (TMTSF)2PF6 intense
experimental activity in physics and chemistry has shown that the
PF6 compound is only a member of a much broader family
of compounds, TM2X, where the mono anion X can also be ClO4,
NO3, AsF6, etc,..and the cation molecule is
either the 4-selenium or the 4-sulfur atom molecule TMTTF.
TM2X compounds belong to the same isostructural
family (Bechgaard-Fabre family) all (but NO3)
undergoing a superconducting instability at low temperature under
pressure with the exception of ClO4 which becomes superconducting
at ambient pressure with Tc=1.2K.
The generic phase diagram that was gradually built
over the years around these materials stands out as a model of
unity for experimental and theoretical physics of low dimensional
correlated systems and chemistry.
Main features of the TM2X generic diagram are Mott
localization at high temperature and charge ordering, spin-Peierls
, spin density wave phases and superconductivity at low
temperature. In addition, they have revealed a new effect of the
magnetic field whenever a metallic phase is stable at low
temperature namely, the stabilization of field induced spin
density wave phases (FISDW) in which the Hall effect is quantized.
Recent transport, NMR and thermodynamic
investigations under oriented magnetic field support the existence
of d-wave coupling for the superconducting pairing mechanism with
line nodes on the Fermi surface. This unconventional
superconductivity is likely due to the interchain exchange of
antiferromagnetic fluctuations following the suggestion of Caron
and Bourbonnais in 1986.see papers
Two dimensional Organic Superconductors
The BEDT-TTF (ET) donor molecule is the main for
several series of organic salts in which a strong interchain
coupling along a transverse axis give rise to a large conductivity
along both a and b axis. Very much like TM2X compounds, the
ET2X two dimensional compounds form isotructural families
where the Mott insulating state shares a common border with
superconductivity. The superconducting Tc’s of these materials can
be raised up to 13K in the ET kappa-phases. Furthermore,
kappa-phase compounds have provided evidences for d-wave
superconductivity according to NMR Knight shift and relaxation
work on charge transfer organic conductors started in October 1973
shortly after the announcement by the Philadelphia group of a huge
conductivity peak around 59K in
tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ). The use of
high pressure was justified by a work of M. Weger and co-workers
suggesting the possibility for superconductivity in this charge
transfer compound once the Peierls Metal-insulator transition at
56K is suppressed under a high enough pressure.
High pressure studies have led to several important results:
in the two leg spin ladders Sr2Ca12Cu24O41
(the so-called telephone number compound) under
a pressure of 31 kbar, studied
by transport and 63Cu NMR. (Sr/Ca)14Cu24041
spin ladders have also been studied by 63Cu
and 17O NMR under pressure. Hole redistribution and
spin excitations in Sr14-x CaxCu24O41(x=0, 12) spin ladder
compounds are derived.see
Solid electrolytes, beta-alumina see papers
Platino-cyanate (KCP) 1D conductors and
inorganic superconducing polymer SNx see papers
Mott transition in V2O3 see papers
High Tc cuprates see papers
Miscellanous see papers