In NQR study of superconducting CeCoIn5 under high pressure

Kohori, Yoh; Saito, Hayato; Kobayashi, Y.; Taira, H; Iwamoto, Yoshiki; Kohara, T.; Matsumoto, Takayoshi; Bauer, E. D.; Maple, M. B.; Sarrao, J. L.

doi:10.1016/j.jmmm.2003.11.196

Cited by 2 publications

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“…This is supported by measurements of resistivity in zero field, [9] specific heat, [13] and NQR [14] which appear to restore Fermi liquid behavior with increasing pressure in CeCoIn 5 . In addition, dHvA results at high fields show the effective mass of the 2-D cylindrical β sheet (which increases as H c2 is approached from above) decreases with increasing pressure.…”

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confidence: 58%

Pressure study of quantum criticality inCeCoIn5

et al. 2006

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We report resistivity measurements in the normal state of CeCoIn5 down to 40 mK and simultaneously in magnetic fields up to 9 T in the [001] crystallographic direction and under pressures up to 1.3 GPa. At ambient pressure the data are consistent with a field tuned quantum critical point coincident with the superconducting upper critical field Hc2, as observed previously. We find that with increasing pressure the quantum critical point moves inside the superconducting dome to lower fields. Thus, we can rule out that superconductivity is directly responsible for the non-Fermi liquid behavior in CeCoIn5. Instead, the data point toward an antiferromagnetic quantum critical point scenario. PACS numbers:A quantum critical point is simply the point at which a second order phase transition occurs at T = 0, where quantum fluctuations are present. Classical phase transitions are now well understood. While theoretically there is a natural extension to T = 0,[3, 4, 5] the experimental systems (and in particular heavy fermion systems) display serious discrepancies with these predictions. [6] As disorder may profoundly influence the behavior at a quantum critical point, there is a great benefit in examining quantum critical systems which are stoichiometric, and hence, relatively disorder free. CeCoIn 5 is one of a relatively small number of such systems.CeCoIn 5 is a heavy fermion superconductor with T c = 2.3 K.[7] The normal state possesses non-Fermi liquid properties in zero field (T linear resistivity, T ln(T ) specific heat, and modified Curie-Weiss χ, compared to the Fermi liquid expectations of T 2 resistivity, T linear specific heat, and constant χ) indicative of a nearby underlying quantum critical point. [8,9] By applying the magnetic field along the tetragonal c-axis a field-tuned quantum critical point (QCP) was identified at H QCP = 5 T. [1,2] The fact that the superconducting upper critical field H c2 is also at 5 T raises the question of whether superconducting fluctuations could be responsible for the field-tuned non-Fermi liquid behavior. However, this observation (that H c2 ≈ H QCP ) is likely to be an accidental coincidence for several reasons: i) it is not clear if a superconductor has sufficiently strong fluctuations to produce an extended critical regime, ii) the superconducting transition itself becomes first order below 0.7 K in CeCoIn 5 ,[10] which should cutoff any diverging fluctuations, and iii) similarities in the zero field pressure-temperature phase diagrams of CeRhIn 5 and CeCoIn 5 suggests that CeCoIn 5 at ambient pressure is in close proximity to an antiferromagnetic quantum critical point, as is observed in CeRhIn 5 .[9] However, two experiments designed to separate H QCP from H c2 , via magnetic field anisotropy [11] or Sn doping studies [12], failed to do so. Applying the magnetic field in the ab-plane increases H c2 to 12 T, while in Sn doping studies the c-axis H c2 was suppressed to as low as 2.75 T for CeCoIn 4.88 Sn 0.12 . Despite this variation in H c2 by more than a factor of 4, on...

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confidence: 58%

Pressure study of quantum criticality inCeCoIn5

et al. 2006

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“…The phase diagram of CeCoIn 5 turns out to be rather complex, raising the possibility of one or more quantum critical points. On the one hand, under pressure the ground state evolves into a conventional Fermi Liquid, and the effective mass decreases, as evidenced by resistivity [10], specific heat [11], de Haasvan Alphen [12] and 115 In NQR measurements [13]. Moreover, the similarity in the pressure dependence of T c in both CeCoIn 5 and the isostructural antiferromagnetic compound CeRhIn 5 points to the existence of a pressure-tuned antiferromagnetic quantum critical point close to ambient pressure in CeCoIn 5 [10].…”

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Field-tuned quantum critical point inCeCoIn5near the superconducting upper critical field

et al. 2005

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We report a systematic study of high magnetic field specific heat and resistivity in single crystals of CeCoIn5 for the field oriented in the basal plane (H ab) of this tetragonal heavy fermion superconductor. We observe a divergent electronic specific heat as well as an enhanced A coefficient of the T 2 law in resistivity at the lowest temperatures, as the field approaches the upper critical field of the superconducting transition. Together with the results for field along the tetragonal axis (H c), the emergent picture is that of a magnetic field tuned quantum critical point which exists in the vicinity of the superconducting H 0 c2 despite a variation of a factor of 2.4 in H 0 c2 for different field orientations. This suggests an underlying physical reason exists for the superconducting H 0 c2 to coincide with the quantum critical field. Moreover, we show that the recovery of a Fermi Liquid ground state with increasing magnetic field is more gradual, meaning that the fluctuations responsible for the observed quantum critical phenomena are more robust with respect to magnetic field, when the magnetic field is applied in-plane. Together with the close proximity of the quantum critical point and H 0 c2 in CeCoIn5 for both field orientation, the anisotropy in the recovery of the Fermi liquid state might constitute an important piece of information in identifying the nature of the fluctuations that become critical. PACS numbers:Quantum critical points mark the change in the ground state of a strongly correlated electron system, and the associated quantum fluctuations have tremendous consequences for the properties of the system at finite temperatures. Attention has focused on the heavy fermion superconductor CeCoIn 5 in the context of quantum criticality since its discovery [1]. Superconductivity in this material is not only unconventional (probably d-wave [2, 3]) and Pauli-limited (with the possible presence of a Fulde-Ferrell-Larkin-Ovchinnikov state at low temperatures) [4,5,6] but it is also built out of a normal state displaying Non Fermi Liquid behavior. Indeed, the normal state is characterized by a resistivity almost linear in temperature for a decade above T c in zero field [1], a specific heat coefficient diverging logarithmically over a large temperature range with a similar slope at zero and finite magnetic field [1,7], and a power law behavior in ac-susceptibility [1,7] and the nuclear spin-lattice relaxation rate [8]. All of this suggests the proximity to an antiferromagnetic instability. It is important to note that the specific heat is analogous to UBe 13 [9]. Since the entropy is conserved between the zero field superconducting state and the anomalous normal state at H 0 c2 , this implies that the mass enhancement leading to the heavy fermion ground state is interrupted by the formation of superconductivity and presumably the same spin fluctuations are responsible for both phenomena.The phase diagram of CeCoIn 5 turns out to be rather complex, raising the possibility of one or more quantum critical...

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In NQR study of superconducting CeCoIn5 under high pressure

Cited by 2 publications

References 3 publications

Pressure study of quantum criticality inCeCoIn5

Pressure study of quantum criticality inCeCoIn5

Field-tuned quantum critical point inCeCoIn5near the superconducting upper critical field

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