Abstract
Abstract
YRh4B4, which exhibits high-
T
c
superconductivity in the RRh4B4 system, has two types of crystal structures, CeCo4B4 type (pt-type) and LuRu4B4 type (bct-type). Both types of structure have similar
T
c
(pt-type;
T
c
= 10.6 K, bct-type;
T
c
= 9.8 K), but the
μ
0
H
c
2
of both compounds is very different, pt-type;
μ
0
H
c
2
= 2.50 T and bct-type;
μ
0
H
c
2
= 9.85 T. From our results, one can see that the difference in
T
c
between pt-YRh4B4 and bct-YRh4B4 is mainly caused from the difference of the density of state at Fermi energy. The high-
T
c
in pt-YRh4B4 is derived from the high Debye temperature caused by vibrations of boron. In contrast, in bct-YRh4B4 it is caused by a stronger electron–phonon coupling than in pt-YRh4B4. Regarding the symmetry of superconductivity, it is suggested that pt-YRh4B4 is a clean limit superconductor and has basically a fully gapped superconducting gap, but is slightly anisotropic from the results of
C
el
∝
exp
(
−
Δ
/
k
B
T
) below
T
c
and
Δ
γ
(
H
)
∝
H
0.65
. However, bct-YRh4B4 is a dirty limit superconductor and has an anisotropic superconducting gap from the results of
C
el
∝
T
3
below
T
c
and
Δ
γ
(
H
)
∝
H
.
Subject
Materials Chemistry,Electrical and Electronic Engineering,Metals and Alloys,Condensed Matter Physics,Ceramics and Composites