Phase diagram ofUPt3from ultrasonic velocity measurements

Abstract

We present measurements of longitudinal ultrasonic velocity on single crystals of the heavy-fermion superconductor UPt3. The measurements show clear signatures of second-order phase transitions in the superconducting state, with the velocity anomalies well accounted for by Ginzburg-Landau theory. From these signatures we construct a phase diagram for UPt 3 that reveals all the boundary lines that have been identified as possible phase transitions. We are able to track the phase transition lines to a tetracritical point, located on the upper-critical-field curve, to within the width of the normalsuperconducting transition.PACS numbers: 74.30. Gn, 62.80.+f, 74.70.Tx This Letter presents the first complete phase diagram in the field-temperature plane for the heavy-fermion superconductor UPt3 derived from a single measurement technique. UPt3 has shown a variety of interesting properties in the superconducting state which strongly suggest unconventional superconductivity with a multicomponent order parameter. Power-law temperature dependences of ultrasonic attenuation 1 " 3 and heat capacity 4 have been interpreted in terms of a gap with line or point nodes on the Fermi surface. More convincingly, a series of experiments have revealed the presence of more than one superconducting phase: Initially, ultrasonic-attenuation measurements showed the presence of two superconducting phases depending on the magnetic field; 5 " 7 subsequently, heat-capacity measurements demonstrated the presence of multiple superconducting phases even in zero field. 8,9 A composite phase diagram assembled from different measurements (ultrasonic-attenuation, 5 heat-capacity, 9 and torsional-oscillator data 10 ) on different samples indicates that UPt3 has at least two and possibly three superconducting phases. However, this interpretation relies on data from a variety of measurement techniques on samples with transition temperatures ranging from 420 to 540 mK.Here we present measurements of ultrasonic velocity on two samples of UPt3. Our velocity measurements yield a more complete phase diagram for superconducting UPt3 than has previously been available. Earlier attenuation measurements on one of the samples 7 (sample No. 1) revealed a peak in the attenuation (the 7/FL peak) in field sweeps at constant temperature, as well as a peak (the X peak) in temperature sweeps in low field. From these attenuation studies it was not possible to follow Hf^(T) very close to the upper-critical-field line HdiT).Thus, it was not possible to answer with confidence the basic question of how many phases there are in UPt3. Theoretical proposals for the phase diagram of UPt 3 have been published by several authors. 11 ' 13 Our results bear directly on these theories:The phase diagrams obtained by a single measuring technique on both of the samples studied give strong support for a tetracritical point intersecting the uppercritical-field line, for fields both parallel and perpendicular to the c axis. In addition, the velocity anomalies at both zero-field transitio...

Quasiclassical determination of the in-plane magnetic field phase diagram of superconductingSr2RuO4

“…It is possible that experiments have not seen the predicted specific heat jumps due to the broadening associated with fluctuations in the vortex phase, or due to sample inhomogeneities. In the case of UPt 3 , for which multiple phase transitions in the vortex phase have been observed, the entire phase diagram was found through ultrasound measurements 41 . Specific heat measurements mapped out some portions of the phase diagram 42 but they did not show clear anomalies throughout the entire phase diagram 43 .…”

E1gmodel of superconductingUPt3Park1, Joynt2 1996Phys. Rev. B232330View full textAdd to dashboardCite

“…6.1, 6.2, 6.3. Differentiation leads to two linear equations for M and η = ηx 5) which give the behavior of the order parameters below T c1 . Above T c1 we have simply…”

“…Much of this discussion has centered on the unusual nature of the superconducting state. Experiments to map out the phase diagram of UPt 3 in the field-temperature (H − T ) plane using both specific heat [1,2] and longitudinal sound absorption [3,4] and velocity [5,6] have revealed multiple superconducting phases. In particular these measurements show that two superconducting phases exist even at zero field, as was predicted [7] by an analysis of the free energy for a two-component order parameter in the presence of antiferromagnetism.…”

“…The phase diagram we obtain from our calculations is shown along with the ultrasonic velocity data from Ref. [5] in Fig. 4 along with the values of the parameters used to obtain it.…”

AC susceptibility and anisotropic flux pinning in uncoventional superconductor UPt3

“…Superconductivity of UPt 3 is interesting, in particular due to its complex H-T diagram, as observed by ultrasound attenuation, specific heat [1], and dilatometry studies [2]. The conclusions about the presence of internal phase transition lines follow from the observation of different anomalies in the properties studied as a function of temperature or magnetic field.…”