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Kromer, F.; Helfrich, R.; Lang, Michael; Steglich, F.; Langhammer, Christoph; Bach, Annika; Michels, T.; Kim, J. S.; Stewart, G. R.

doi:10.1103/physrevlett.81.4476

Cited by 68 publications

(85 citation statements)

References 20 publications

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“…14 At nearly the same field ∼ 4 T, the specific heat and thermal expansion measurements 9,10 have suggested that there is an anomaly at B * below B c2 , as mentioned in Introduction. Ac-susceptibility also shows an anomaly at ∼ 4 T for T ∼ 0.25 K. 15 All works may suggest the same anomaly because these anomalies have been observed in nealy same field range: B ≤ 4.5 T in the superconducting phase diagram.…”

Section: J P H Y S S O C J P N D O W N L O a D E D F R O M J mentioning

confidence: 99%

“…It has been proposed that this anomaly is a precursor of another phase transition observed in the U 1−x Th x Be 13 system at T c2 , 8 because it seems that T L (x) smoothly merges into * E-mail address: yusei@phys.sci.hokudai.ac.jp T c2 (x) on a T -x phase diagram. 9,10 In order to obtain further information about this unusual superconductivity of UBe 13 , we have performed lowtemperature specific heat and static dc magnetization measurements for the superconducting state of UBe 13 using a high-quality single crystal. In the present paper, we report the superconducting phase diagram along [110] axis by our specific heat and dc magnetization measurements.…”

Section: Introductionmentioning

confidence: 99%

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Specific Heat and Magnetization Studies of the Superconducting Mixed State of UBe₁₃

et al. 2011

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Low-temperature specific heat and static dc magnetizetion measurements have been performed for the superconducting state of the heavy-fermion compound UBe 13 . The superconducting phase diagram B c2 -T (B || [110]) has been obtained by our specific heat and magnetization measurements. From the slope of the upper critical field and specific heat jumps at superconducting transition temperatures in magnetic fields, we have also obtained a temperature dependence of Ginzburg-Landau parameter κ 2 along [110]. It has been revealed that κ 2 decreases with decreasing temperature down to 0.5 K, which indicates that a paramagnetic effect may be present at least down to 0.5 K for [110].

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Section: J P H Y S S O C J P N D O W N L O a D E D F R O M J mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Specific Heat and Magnetization Studies of the Superconducting Mixed State of UBe₁₃

et al. 2011

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“…This anomaly cannot be seen in the temperature dependence of the specific heat at zero field, but in field, the isothermal specific heat curves C(B) show a broad anomaly at a corresponding field called B * (T L ). 17) On the other hand, an L-type UBe 13 has a lower T c of ∼ 0.75 K, and it exhibits an obvious anomaly named T A below T c in the temperature dependence of the zero-field specific heat. It has been found that T A corresponds to the thermal-expansion anomaly T L .…”

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Maki Parameter and Upper Critical Field of the Heavy-Fermion Superconductor UBe₁₃

et al. 2011

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We have performed low-temperature specific-heat measurements in magnetic fields for a single crystal UBe 13 . It has been observed that our sample exhibits a superconducting transition at an intermediate temperature (T c ∼ 0.81 K) between previously reported values for two variant samples called H type and L type. The specific heat C(T ) of our sample shows a T 3 behavior below ∼ 0.7 T c , which is similar to the behavior of the H-type sample, suggesting the existence of point nodes in the superconducting gap function. We have obtained the upper-critical-field curves H c2 for the [001], [110], and [111] crystal axes, which show no anisotropy at least down to the lowest measured temperature of 0.5 K. We have also derived the Maki parameter κ 2 , and it has been revealed that the κ 2 steeply decreases isotropically upon cooling just below T c . Paramagnetic effects and the symmetry of Cooper pairing of UBe 13 are discussed. KEYWORDS: Unconventional Superconductor, Heavy Fermion, Paramagnetic EffectThe heavy-fermion compound UBe 13 has attracted much attention since the discovery of unconventional superconductivity 27 years ago. 1) UBe 13 has a cubic structure with the space group O h 6 (Fm−3c), and exhibits a superconducting (SC) transition at around 0.85 K with a large specific-heat jump ∆C. Despite prolonged scientific efforts to unravel the superconductivity of this material, many open questions remain, in particular concerning the symmetry of Cooper pairing and the unusual SC phase diagram. 2, 3)As for the SC gap structure, which is related to the parity of Cooper pairing, the temperature dependence of low-T specific heat C(T ) 4) and magnetic field penetration depth λ(T ) 5) suggest the presence of point nodes, whereas nuclear magnetic resonance (NMR) spin-relaxation rate 1/T 1 6) and ultrasonic attenuation α(T ) 7) suggest a line node. A p-wave AndersonBrinkman-Morel (ABM) state, which is identified as the A phase in superfluid 3 He,8) has been proposed for the SC of UBe 13 from the T 3 -like behavior observed in the low-T specific heat.4) An early NMR study also suggests the occurrence of the ABM state, because the Knight shift does not decrease below T c . 9) However, recent muon spin-rotation (µSR) measurements performed in field, H || [001], have revealed that the muon Knight shift shows a clear decrease below T c . 10)Furthermore, a recent NMR study by Tou et al. has suggested that the Knight shift decreases below T * ( ∼ 0.7 K < T c ) for [001], whereas increases below T * for [111]. 11) Therefore, no consensus has been achieved regarding the behavior of Knight shift below T c as well as the SC-gap structure. Namely, it is still debated whether the Cooper-pairing state of UBe 13 is triplet or singlet.In order to obtain further information about the parity of Cooper pairing, it is important to investigate the presence (or absence) of paramagnetic effects. The value of H c2 estimated experimentally by extrapolation to T = 0 for UBe 13 is about 80-130 kOe, which is much larger than the Pauli limit * E-mai...

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“…The common feature of the parent compounds [8,9,10,11,12,13,14] is a distinct, moderately high temperature (above ∼ 100 K), coupled, structural/antiferromagnetic phase transition that generally is argued to be of the first order. Thermal expansion is often claimed to be uniquely sensitive to just such magnetic, structural and superconducting transitions [15]. For example, in Co-doped BaFe 2 As 2 , anisotropic thermal expansion measurements [16,17,18] have been instrumental in inferring unusually large, anisotropic, uniaxial pressure derivatives of superconducting transition temperature.…”

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Anisotropic thermal expansion ofAEFe₂As₂(AE= Ba, Sr, Ca) single crystals

Bud’ko

Canfield

2010

Philosophical Magazine

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We report anisotropic thermal expansion of the parent, AEFe 2 As 2 (AE = Ba, Sr, and Ca), compounds. Above the structural/antiferromagnetic phase transition anisotropy of the thermal expansion coefficients is observed, with the coefficient along the a-axis being significantly smaller than the coefficient for the c-axis. The high temperature (200 K ≤ T ≤ 300 K) coefficients themselves have similar values for the compounds studied. The sharp anomalies associated with the structural/antiferromagnetic phase transitions are clearly seen in the thermal expansion measurements. For all three pure compounds the "average" a-value increases and the c-lattice parameter decreases on warming through the transition with the smallest change in the lattice parameters observed for SrFe 2 As 2 . The data are in general agreement with the literature data from X-ray and neutron diffraction experiments.Keywords: iron-arsenides; thermal expansion; anisotropy; structural phase transition;For over a year many experimental and theoretical aspects of physics of ternary AETM 2 As 2 (AE = Ba, Sr, and Ca; TM = transition metal) compounds were studied in great detail. One of the motivations for such studies was a desire to shed some light on what are the salient parameters that govern doping-or pressureinduced superconductivity [1,2,3,4,5,6,7] in these materials. The common feature of the parent compounds [8,9,10,11,12,13,14] is a distinct, moderately high temperature (above ∼ 100 K), coupled, structural/antiferromagnetic phase transition that generally is argued to be of the first order. Thermal expansion is often claimed to be uniquely sensitive to just such magnetic, structural and superconducting transitions [15]. For example, in Co-doped BaFe 2 As 2 , anisotropic thermal expansion measurements [16,17,18] have been instrumental in inferring unusually large, anisotropic, uniaxial pressure derivatives of superconducting transition temperature. For the parent AETM 2 As 2 materials though, we are aware only of data from pure BeFe 2 As 2 [16]. In this work we present and compare anisotropic thermal expansion measurements for three parent compounds, AEFe 2 As 2 (AE = Ba, Sr, and Ca). (Data for BaFe 2 As 2 are taken from [16].) For completeness, data on Sn -grown BeFe 2 As 2 [19] are included as well.Single crystals of AEFe 2 As 2 (AE = Ba, Sr, and Ca) were grown using conventional high temperature solution growth technique [20]. Details of growth conditions and physical properties of these samples are outlined in [10,13,19,21]. It should be noted, though, that BaFe 2 As 2 samples grown out of FeAs as well as Sn have been examined. The SrFe 2 As 2 and CaFe 2 As 2 samples were both grown out of Sn. The BaFe 2 As 2 /FeAs, SrFe 2 As 2 /Sn and CaFe 2 As 2 /Sn samples are considered to be pure and well ordered whereas BaFe 2 As 2 /Sn is known to

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Revision of the Phase Diagram of SuperconductingU1−xThx

Cited by 68 publications

References 20 publications

Specific Heat and Magnetization Studies of the Superconducting Mixed State of UBe₁₃

Specific Heat and Magnetization Studies of the Superconducting Mixed State of UBe₁₃

Maki Parameter and Upper Critical Field of the Heavy-Fermion Superconductor UBe₁₃

Anisotropic thermal expansion ofAEFe₂As₂(AE= Ba, Sr, Ca) single crystals

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Revision of the Phase Diagram of SuperconductingU1−xThx

Cited by 68 publications

References 20 publications

Specific Heat and Magnetization Studies of the Superconducting Mixed State of UBe13

Specific Heat and Magnetization Studies of the Superconducting Mixed State of UBe13

Maki Parameter and Upper Critical Field of the Heavy-Fermion Superconductor UBe13

Anisotropic thermal expansion ofAEFe2As2(AE= Ba, Sr, Ca) single crystals

Contact Info

Product

Resources

About

Specific Heat and Magnetization Studies of the Superconducting Mixed State of UBe₁₃

Specific Heat and Magnetization Studies of the Superconducting Mixed State of UBe₁₃

Maki Parameter and Upper Critical Field of the Heavy-Fermion Superconductor UBe₁₃

Anisotropic thermal expansion ofAEFe₂As₂(AE= Ba, Sr, Ca) single crystals