Abstract
Specific heat C( T) and upper critical field H c2( T) measurements have been performed on two single crystal specimens (denoted A and B) of the antiferromagnetic heavy-electron superconductor URu 2Si 2. Specific heat measurements on both single crystals reveal two distinct jumps, indicative of two superconducting phases. This is reminiscent of the antiferromagnetic heavy-electron compound UPt 3 in which multiple superconducting transitions have been observed and attributed to coupled antiferromagnetic and multicomponent superconducting order parameters, although two superconducting phases associated with two different states of the crystal cannot be ruled out. The relative magnitudes of the two specific heat jumps observed in crystal B suggest that the two superconducting phases occupy nearly equal volume fractions of the crystal. At temperatures below the lower jump, the specific heat of both crystals can be described by C 3( T) = γ s (0) T+ AT 3 with γ 3(0) ≈ 0.5 γ n (0), where γ n(0) is the value of the normal-state electronic specific heat coefficient γ n( T), extrapolated to T = 0. The two critical temperatures inferred from the specific heat jumps in crystal B, measured in magnetic fields H between 0 and 15kOe applied parallel to the c-axis, have a similar dependence on H. Resistive measurements of H c2( T) on specimens from crystal A between 0 and 60 kOe reveal a kink near 2 kOe for H⌈ c and strong positive curvature in H c2( T) below ∼3 kOe for H⌈ a.
Highlights
The heavy-electron superconductors CeCu,Si, 111U, Be, PI, UPt, [31a,nd URu,Si, [4-61 have attracted considerable attention because of the possibility that they exhibit an unconventional type of superconductivity involving novel types of pairing and/or pairing mechanisms [7]
We report specific heat and upper critical field measurements on single crystal specimens of the antiferromagnetic heavy-electron superconductor
Back-scattered Laue X-ray diffraction, electron microprobe analysis, and scanning electron microscopy SEM were performed on crystal B in order to establish that it is a single crystal of uniform composition
Summary
The heavy-electron superconductors CeCu,Si, 111U, Be,, PI, UPt, [31a,nd URu,Si, [4-61 have attracted considerable attention because of the possibility that they exhibit an unconventional type of superconductivity involving novel types of pairing and/or pairing mechanisms [7]. UBe,, , UPt,, and URu,Si, have different crystal structures (cubic, hexagonal, and tetragonal, respectively) and electron effective masses m* (-300m, [8], -2OOm, [9], and -25m, [5],respectively), common physical characteristics appear to be emerging which illustrate the intimate relationship between superconductivity and magnetism and may provide a basis for developing a fundamental understanding of superconductivity in these remarkable materials These characteristics include the occurrence of antiferromagnetic ordering with a small magnetic moment p of a few hundredths of a Bohr magneton below a NCel temperature TN = lOT,i where T, is the superconducting critical temperature, and the destruction of superconductivity accompanied by the appearance of magnetic order with a much larger magnetic moment of several tenths of a Bohr magneton upon substituting another element. C(T, H) and upper critical field H,,(T) curves which are indicative of unconventional superconductivity
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