Simultaneous resistivity onset and first-order vortex-lattice phase transition in Bi
2
Sr
2
CaCu
2
O
8
D. T. Fuchs, E. Zeldov, and D. Majer
Department of Condensed Matter Physics, The Weizmann Institute of Science, Rehovot 76100, Israel
R. A. Doyle
Department of Condensed Matter Physics, The Weizmann Institute of Science, Rehovot 76100, Israel
and Interdisciplinary Research Center in Superconductivity, University of Cambridge, Cambridge CB3 OHE, England
T. Tamegai and S. Ooi
Department of Applied Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113, Japan
M. Konczykowski
Laboratoire des Solides Irradie ´s, CNRS URA-1380, E
´
cole Polyte ´chnique, 91128 Palaiseau, France
Received 13 February 1996; revised manuscript received 8 April 1996
Simultaneous measurements of resistivity and local magnetization using microscopic Hall sensors were
carried out on Bi
2
Sr
2
CaCu
2
O
8
crystals as a function of applied field and temperature. The resistivity onset is
found to occur concurrently with the first-order vortex-lattice phase transition, determined by the equilibrium
magnetization step. This behavior strongly suggests that the vortex lattice melts at the phase transition. The
apparently reversible magnetization below the transition is ascribed to substantial flux creep.
S0163-18299650826-X
Recent theoretical predictions of a possible first-order
vortex-lattice phase transition in type-II superconductors in
the presence of thermal fluctuations,
1–3
as opposed to tradi-
tional second-order mean-field expectations, have stimulated
a broad experimental effort in search of this fundamental
phase transition. A wide range of experimental techniques
has been exploited in this pursuit in high-T
c
superconductors,
4–21
as well as in low-T
c
materials.
22,23
The
first significant experimental evidence that this new type of
transition may exist was the observation of a sharp resistive
transition in clean YBa
2
Cu
3
O
7
YBCO crystals.
5–8
In spite
of extensive experimental efforts,
4
this resistive transition
has so far only been observed in YBCO crystals even though
a similar transition is anticipated to occur in all high-T
c
su-
perconductors. In this paper we show that a clear resistive
transition exists in Bi
2
Sr
2
CaCu
2
O
8
BSCCO crystals as
well. This behavior is strongly indicative of a first-order
vortex-lattice melting transition. Resistivity however is not a
thermodynamic property and a true first-order phase transi-
tion should also have clear thermodynamic fingerprints. Re-
cently, a first-order-phase transition in BSCCO crystals was
thermodynamically established by equilibrium magnetization
measurements.
14–17
In order to unambiguously link the two
phenomena we have, in addition, carried out simultaneous
measurements of magnetization and resistivity. Our central
result is that the thermodynamic magnetization step and the
resistive onset occur concurrently at the first-order vortex-
lattice phase transition in BSCCO.
The BSCCO crystals studied in this work were prepared
by the traveling solvent floating zone technique
24
in two dif-
ferent laboratories. Crystal A ( T
c
=83.5 K was cut to di-
mensions of 230040050 m
3
, crystal B ( T
c
=86 K to
68017515 m
3
, and crystal C ( T
c
=90 K to 2000
45025 m
3
. Four electrical contacts for transport mea-
surements were attached to the top surface of crystals A and
B using Ag epoxy annealed at 550 °C. The bottom ab crys-
talline surface was placed in direct contact with an array of
nine two-dimensional-electron-gas GaAs/AlGaAs Hall sen-
sors each of area 1010 m
2
.
14,25
The experimental setup
see inset of Fig. 1 allowed simultaneous measurement of
the local magnetic field B in the central region of the crystal
and the four-probe resistance R . The magnetic field H
a
was
applied parallel to the c axis of the crystal, and the measure-
ments were carried out as a function of temperature and ap-
plied field. The resulting data for crystal B are very similar to
the data for crystal A described further below.
In order to exclude possible artefactal effects associated
with the nonuniform current distribution in this geometry,
and the resulting mixture of
ab
and
c
resistivities
26,27
mea-
sured by the planar contacts on crystals A and B, we also
prepared a purely in-plane configuration on crystal C. In ad-
dition to the four contacts on the top surface two contacts
were made to the edges of the sample in order to ensure a
uniform current distribution. The two central top contacts
were used as voltage contacts whereas the transport current
was injected either through the contacts on the top or the
edges. The behavior at the resistive onset, which is described
in detail below, was not significantly affected by the differ-
ent current distributions in the two configurations. However,
the finite thickness of the epoxy contacts at the edge of the
crystal C prevented the simultaneous use of Hall sensors for
local magnetization measurements of this crystal. Since the
resistive data for all three crystals show the same basic fea-
tures, we concentrate in what follows on the simultaneous
measurements of both resistivity and magnetization in crystal
A.
Figure 1 shows the result of simultaneous measurement of
the resistance and the local magnetization B -B
out
as a func-
PHYSICAL REVIEW B 1 JULY 1996-II VOLUME 54, NUMBER 2
54 0163-1829/96/542/7964/$10.00 R796 © 1996 The American Physical Society