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

Abstract

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...

Quantum Critical Quasiparticle Scattering within the Superconducting State ofCeCoIn5

“…Lowtemperature transport [9,32] and specific heat [10] studies have revealed a magnetic field-tuned QCP, with a critical field H that anomalously coincides with H c2 , the upper critical field for superconductivity. The pinning of H to H c2 was subsequently shown to hold regardless of field orientation [11] or suppression of the superconducting state by impurities [12], suggesting a novel form of quantum criticality closely linked with the superconducting state. Recent work has revealed other examples of systems that appear to have a field-tuned QCP pinned to H c2 , including cuprates [13,14] and iron pnictides [15].…”

Behavior of the Quantum Critical Point and the Fermi-Liquid Domain in the Heavy Fermion Superconductor CeCoIn5 Studied by Resistivity

“…16) It has been stressed 17) that because the superconducting transition is first order, a QCP right at H c2 (0) could not originate from the superconducting transition, but explaining the coincidence of a magnetic QCP with H c2 (0) is by no way simple (see for example the discussion in ref. 18). …”

Antiferromagnetic Order and π-Triplet Pairing in the Fulde–Ferrell–Larkin–Ovchinnikov State

“…[25][26][27] It is expected that this AFM order will be closely related to the AFM quantum critical point observed in CeCoIn 5 . 28,29) Therefore, the nuclear magnetic resonance (NMR) 25,27) and neutron scattering 26) measurements may have uncovered a novel superconducting state in this strongly correlated electron system. In particular, the neutron scattering measurement has explored the properties of the AFM order and found that the wave vector of the AFM order is incommensurate q IC ¼ Q þ IC with IC along the ½1; À1; 0 direction for magnetic fields in the ab-plane of the tetragonal lattice.…”