2005 APS March Meeting
Monday–Friday, March 21–25, 2005;
Los Angeles, CA
Session X2: Fulde-Ferrell-Larkin-Ovchinnikov Superconductivity in Heavy Fermion Compounds
8:00 AM–11:00 AM,
Friday, March 25, 2005
LACC
Room: 151
Sponsoring
Unit:
DCMP
Chair: Stanley Tozer, NHMFL
Abstract ID: BAPS.2005.MAR.X2.5
Abstract: X2.00005 : Texture in the superconducting order parameter of CeCoIn$_5$; FFLO state as evidenced by ultrasound and NMR
10:24 AM–11:00 AM
Preview Abstract
Abstract
Author:
Yuji Matsuda
(Department of Physics, Kyoto university)
A myriad of fascinating properties have been proposed for unconventional
superconductors in the presence of a strong magnetic field. Among the possible
exotic superconducting (SC) phases, a spatially nonuniform SC state originating
from the paramagnetism of conduction electrons has become a subject of particular
interest after the pioneering work by Fulde and Ferrel and Larkin and Ovchinnikov
(FFLO) in the mid-1960's. We present here ultrasound and NMR studies of the
quasi-2D heavy-fermion superconductor CeCoIn$_5$ with extremely large Pauli
paramagnetic susceptibility, which is believed to host a FFLO state.
Ultrasound velocity measurements reveal an unusual structural transformation of
the flux line lattice (FLL) in the vicinity of the upper critical field and with a magnetic
field applied parallel to the $ab$ plane. The transition field coincides with that at
which heat capacity measurements reveal a second order phase transition. The
lowering of the sound velocity at the transition is consistent with the collapse of the
FLL tilt modulus and a crossover to quasi two-dimensional FLL pinning.
In the vicinity of the upper critical field , the $^{115}$In NMR spectrum also
exhibits a dramatic change below $T^*(H)$ which well coincides with the position of
reported anomalies in specific heat and ultrasound velocity. Below $T^*(H)$ a new
resonance line appears at higher frequency, which can be attributed to the normal
quasiparticle sheets formed in the SC regime. The NMR spectrum also indicate
that the vortex core structure of CeCoIn$_5$ appears to be markedly different from
that of ordinary superconductors.
On the basis of these results, we were able to establish a clear evidence of the
spatially inhomogeneous SC state at high field and low temperatures, precisely as
expected in a FFLO state.
In collaboration with T.Watanabe, Y.Kasahara, K.Izawa (Univ. of Tokyo), C.J. van der
Beek(Ecole Polytechnique),K.Kakuyanagi, K.Kumagai (Hokkaido Univ.), M.Nohara,
T.Hanaguri, H.Takagi,(Univ. of Tokyo) H.Shishido, R.Settai, and Y.Onuki(Osaka Univ.)
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2005.MAR.X2.5