Avoided Antiferromagnetic Order and Quantum Critical Point inCeCoIn5

Abstract

We measured specific heat and resistivity of heavy fermion CeCoIn5 between the superconducting critical field Hc2 = 5T and 9 T, with field in the [001] direction, and at temperatures down to 50mK. At 5T the data show Non Fermi Liquid behavior down to the lowest temperatures. At field above 8T the data exhibit crossover from the Fermi liquid to a Non Fermi Liquid behavior. We analyzed the scaling properties of the specific heat, and compared both resistivity and the specific heat with the predictions of a spin-fluctuation theory. Our analysis leads us to suggest that the NFL behavior is due to incipient antiferromagnetism (AF) in CeCoIn5 with the quantum critical point in the vicinity of the Hc2. Below Hc2 the AF phase which competes with the paramagnetic ground state is superseded by the superconducting transition.PACS numbers: 74.70. Tx, 71.27.+a, 74.25.Fy, 75.40.Cx When the symmetry of the ground state of a system changes as a function of an external or internal parameter, the system is said to undergo a quantum phase transition. If, in addition, this transition is second order, the system has a Quantum Critical Point (QCP) at the critical value of the parameter. The competition between the nearly degenerate ground states determines the behavior of the system over a range of temperatures and tuning parameter values in the vicinity of QCP. In this region of the phase diagram the properties of the system differ from those on either side of the transition, and often exhibit unusual dependence on the temperature and the tuning parameter. This has made quantum critical phenomena a subject of intense current interest.Study of quantum critical points in heavy fermion systems has been a focus of particular attention (for a recent review see Ref. 1). In these materials the competition typically takes place between a paramagnetic and a magnetically ordered ground states. The unconventional behavior near QCP is manifested in the deviation of the temperature dependence of measured properties from those of metals described by the Landau Fermi Liquid (FL) theory. In that theory the electronic specific heat is linear in temperature, C(T ) = γT , and the resistivity increases quadratically from a residual value, ρ = ρ 0 + AT 2 . In systems tuned to QCP the Sommerfeld coefficient, γ(T ) = C/T , commonly diverges as the temperature goes to zero, and has been variously argued to behave as either log T or T α , with α < 0. Resistivity with an exponent less than two is also ubiquitous in these compounds.Tuning the system through a QCP can be accomplished experimentally by varying sample's composition [2, 3], applying pressure [4], or applying magnetic field [5]. In non-stoichiometric compounds the Kondo disorder, where a range of Kondo temperatures T K appears due to different environments of the f-electron ions, is an important mechanism leading to a Non Fermi Liquid (NFL) behavior [6,7]. In these compounds it is not easy to separate this origin of NFL behavior from the consequences of the proximity to a QCP. Hence the stoichi...

Field-induced quantum critical route to a Fermi liquid in high-temperature superconductors

“…Notably, in CeCoIn 5 with quasi-twodimensional electronic structure, a quite similar field-induced QCP has been identified by the transport and specific heat measurements (27)(28)(29). In high magnetic fields, the resistivity recovers the AT 2 dependence at low temperatures in a similar manner near the upper critical field H c2 (0) (Ϸ5 T).…”

Superconductivity and Non-Fermi-Liquid Behavior in the Heavy-Fermion Compound CeCo1−xNixIn5

“…It is particularly remarkable that the T/B-scaling properties of the C p data related to the quantum critical fluctuation have been revealed in pure CeCoIn 5 . 19) Thus, the application of the similar analysis for the C p and M data obtained from the Ni-doped alloys may provide a clue for resolving the origin of the NFL behavior presently revealed.…”

“…42) 4.2 AFM quantum criticality in CeCo 1−x Ni x In 5 Here, we also discuss the nature of the NFL anomalies in CeCo 1−x Ni x In 5 . In pure CeCoIn 5 , the existence of the AFM-QCP at ∼ H c2 is inferred from the − ln T divergence in C p /T 19) and the weak T -linear increase in M/B with decreasing temperature. 10) On the other hand, our present investigation reveals that the − ln T divergence occurs in both C p /T and M/B at x = 0.25.…”

“…The NFL behaviors presently observed in C p /T and ρ at x = 0.25 are quite similar to those found at ∼ H c2 in CeCoIn 5 as well as at the critical Sn concentration in CeCo(In,Sn) 5 . 19,31,32) In Fig. 2(d), we summarize the x − T phase diagram at zero field for CeCo 1−x Ni x In 5 .…”

“…[13][14][15][16][17][18] Furthermore, the existence of the AFM-QCP at ∼ H c2 is strongly suggested from the observations of the NFL behavior in the paramagnetic phase above H c2 , including the − ln T divergence in specific heat divided by temperature, the T -linear dependence in magnetization, and electrical resistivity. 10,19,20) In fact, the long-range AFM orders are generated by substituting the ions for the elements in CeCoIn 5 , such as Nd for Ce, 21,22) Rh for Co, [23][24][25][26] and Cd, Hg, and Zn for In. [27][28][29][30] In contrast to the doping effect by those ions, the substitution of Sn for In simply suppresses the SC phase without generating the AFM order.…”