Superconductor CeRhIn5 Research Articles

Coincidence of magnetic and valence quantum critical points in CeRhIn5 under pressure

We present accurate electrical resistivity measurements along the two principle crystallographic axes of the pressure-induced heavy-fermion superconductor CeRhIn5 up to 5.63 GPa. For both directions, a valence crossover line is identified in the p-T plane and the extrapolation of this line to zero temperature coincides with the collapse of the magnetic ordering temperature. Furthermore, it is found that the p-T phase diagram of CeRhIn5 in the valence crossover region is very similar to that of CeCu2Si2. These results point to the essential role of Ce-4f electron delocalization in both destroying magnetic order and realizing superconductivity in CeRhIn5 under pressure.

Electronic in-plane symmetry breaking at field-tuned quantum criticality in CeRhIn5.

Electronic nematic materials are characterized by a lowered symmetry of the electronic system compared to the underlying lattice, in analogy to the directional alignment without translational order in nematic liquid crystals. Such nematic phases appear in the copper- and iron-based high-temperature superconductors, and their role in establishing superconductivity remains an open question. Nematicity may take an active part, cooperating or competing with superconductivity, or may appear accidentally in such systems. Here we present experimental evidence for a phase of fluctuating nematic character in a heavy-fermion superconductor, CeRhIn5 (ref. 5). We observe a magnetic-field-induced state in the vicinity of a field-tuned antiferromagnetic quantum critical point at Hc ≈ 50 tesla. This phase appears above an out-of-plane critical field H* ≈ 28 tesla and is characterized by a substantial in-plane resistivity anisotropy in the presence of a small in-plane field component. The in-plane symmetry breaking has little apparent connection to the underlying lattice, as evidenced by the small magnitude of the magnetostriction anomaly at H*. Furthermore, no anomalies appear in the magnetic torque, suggesting the absence of metamagnetism in this field range. The appearance of nematic behaviour in a prototypical heavy-fermion superconductor highlights the interrelation of nematicity and unconventional superconductivity, suggesting nematicity to be common among correlated materials.

Controlling superconductivity by tunable quantum critical points.

The heavy fermion compound CeRhIn5 is a rare example where a quantum critical point, hidden by a dome of superconductivity, has been explicitly revealed and found to have a local nature. The lack of additional examples of local types of quantum critical points associated with superconductivity, however, has made it difficult to unravel the role of quantum fluctuations in forming Cooper pairs. Here, we show the precise control of superconductivity by tunable quantum critical points in CeRhIn5. Slight tin-substitution for indium in CeRhIn5 shifts its antiferromagnetic quantum critical point from 2.3 GPa to 1.3 GPa and induces a residual impurity scattering 300 times larger than that of pure CeRhIn5, which should be sufficient to preclude superconductivity. Nevertheless, superconductivity occurs at the quantum critical point of the tin-doped metal. These results underline that fluctuations from the antiferromagnetic quantum criticality promote unconventional superconductivity in CeRhIn5.

Heavy fermions: superconductivity and its relationship to quantum criticality

Anti-ferromagnetic (AF) heavy-fermion (HF) metals frequently exhibit a quantum critical point (QCP), i.e. a continuous disappearance of AF order at zero temperature as a function of a non-thermal control parameter, like pressure. Commonly, unconventional (d-wave) superconductivity (SC) is observed in the vicinity of such a QCP. In this article, the interplay between quantum criticality and SC in HF metals is discussed. The latter can be well described in the framework of the Kondo lattice (KL) model. After introducing HFs and giving an overview on HF superconductivity, the characteristic energy scales in KL systems are addressed. Subsequently, we concentrate on the isostructural compounds CeCu2Si2 and YbRh2Si2. CeCu2Si2 is a prototypical HF superconductor which shows a QCP of itinerant, i.e. three-dimensional (3D) spin-density-wave (SDW) type. Overdamped, nearly quantum-critical SDW fluctuations are concluded from inelastic-neutron-scattering results to be the driving force for SC (Tc ≈ 0.6 K) in this compound. While the QCP in several other Ce-based HF superconductors is presumably of the SDW variety too, it is likely to be of the local, i.e. Kondo destroying type in the pressure-induced superconductor CeRhIn5. YbRh2Si2 has been identified as a prototype HF metal exhibiting such a Kondo breakdown QCP, often named a (T = 0) 4f-orbital selective Mott transition. This compound is not a superconductor at T ˃ 10 mK. Systematically searching for and studying SC near Kondo destroying QCPs may offer a link to unconventional SC in other families of correlated materials, such as the doped Mott insulators in the high-Tc cuprates and some of the organic charge-transfer salts.

Field‐induced quantum critical point in the pressure‐induced superconductor CeRhIn5

AbstractWhen subjected to pressure, the prototypical heavy‐fermion antiferromagnet CeRhIn5 becomes superconducting, forming a broad dome of superconductivity (SC) centred around 2.35 GPa (=P2) with maximal Tc of 2.3 K. Above the superconducting dome, the normal state shows strange metallic behaviours, including a divergence in the specific heat and a sub‐T‐linear electrical resistivity. The discovery of a field‐induced magnetic phase that coexists with SC for a range of pressures P ≤ P2 has been interpreted as evidence for a quantum phase transition, which could explain the non‐Fermi‐liquid behaviour observed in the normal state. Here we report electrical resistivity measurements of CeRhIn5 under magnetic field at P2, where the resistivity is sub‐T‐linear for temperatures above Tc (or TFL) and a T2‐coefficient A found below TFL diverges as Hc2 is approached. These results are similar to the field‐induced quantum critical compound CeCoIn5 and confirm the presence of a quantum critical point in the pressure‐induced superconductor CeRhIn5. Temperature‐field phase diagram of CeRhIn5 at 2.35 GPa.magnified image

Coexistence of antiferromagnetism and superconductivity in CePt2ln7

The physical properties of CePt2ln7 are presented at pressures up to 3.12 GPa. Antiferromagnetic order occurs at TN = 5.5 K at ambient pressure and first increases with pressure up to P ~ 1.5 GPa, then decreases with further applied pressure up to 3.12 GPa. Another feature, attributed to superconductivity, is observed at 1 K at 1 GPa in the specific heat that grows in magnitude and increases to 2.1 K when the magnetism is weak at 3.12 GPa. Therefore, CePt2ln7 displays an evolution with pressure and a coexistence of magnetism and superconductivity that is remarkably similar to that of the heavy fermion superconductor CeRhIn5.

Tuning the Pressure-Induced Superconducting Phase in DopedCeRhIn5

Pressure- and temperature-dependent heat capacity and electrical resistivity experiments on Sn- and La-doped CeRhIn5 are reported for two samples with specific concentrations, Ce(0.90)La(0.10)RhIn5 and CeRhIn(4.84)Sn(0.16), which present the same TN=2.8 K. The obtained P-T phase diagrams for doped CeRhIn5 compared to that for the pure compound show that Sn doping shifts the diagram to lower pressures while La doping does exactly the opposite, indicating that the important energy scale to define the pressure range for superconductivity in CeRhIn5 is the strength of the on-site Kondo coupling.

Novel superconductivity at the magnetic critical point in heavy-fermion systems: asystematic study of NQR under pressure

We report on the discovery of exotic superconductivity (SC) and novel magnetism in heavy-fermion (HF)compounds, CeCu2Si2, CeRhIn5 andCeIn3, on the vergeof antiferromagnetism (AFM) through nuclear-quadrupole-resonance (NQR) measurements under pressure(P). The exotic SCin a homogeneous CeCu2Si2 (Tc = 0.7 K) revealed antiferromagnetic critical fluctuations at the border to AFM or amarginal AFM. Remarkably, it has been found that the application of magnetic fieldinduces a spin-density-wave (SDW) transition by suppressing the SC near theupper critical field. Furthermore, the uniform mixed phase of SC and AFM inCeCu2(Si1−xGex)2 emerges on a microscopic level, once a tiny amount of 1% Ge(x = 0.01) is substituted for Si to expand its lattice. The application of minute pressure(P∼0.19 GPa) suppresses the sudden emergence of the AFM caused by doping Ge. Thepersistence of the low-lying magnetic excitations at temperatures lower thanTc and TN is ascribed to the uniform mixed phase of SC and AFM.Likewise, the P-inducedHF superconductor CeRhIn5 coexists with AFM on a microscopic level inP = 1.5–1.9 GPa. It is demonstrated that SC does not yield any trace of gap opening in low-lyingexcitations below the onset temperature, presumably associated with an amplitudefluctuation of superconducting order parameter. The unconventional gapless nature of SCin the low-lying excitation spectrum emerges due to the uniform mixed phase of AFM andSC.By contrast, in CeIn3, the P-induced phase separation of AFM and paramagnetism (PM) takes place withoutany trace for a quantum phase transition. The outstanding finding is thatSC sets in at both the phases magnetically separated into AFM and PM inP = 2.28–2.5 GPa. A new type of SC forms the uniform mixed phase with AFM and the HF SCoccurs in PM. We propose that the magnetic excitations such as spin-densityfluctuations induced by the first-order phase transition from AFM to PM mightmediate attractive interaction to form the Cooper pairs in the novel phase of AFM.

Hidden magnetism and quantum criticality in the heavy fermion superconductor CeRhIn5

With only a few exceptions that are well understood, conventional superconductivity does not coexist with long-range magnetic order (for example, ref. 1). Unconventional superconductivity, on the other hand, develops near a phase boundary separating magnetically ordered and magnetically disordered phases. A maximum in the superconducting transition temperature T(c) develops where this boundary extrapolates to zero Kelvin, suggesting that fluctuations associated with this magnetic quantum-critical point are essential for unconventional superconductivity. Invariably, though, unconventional superconductivity masks the magnetic phase boundary when T < T(c), preventing proof of a magnetic quantum-critical point. Here we report specific-heat measurements of the pressure-tuned unconventional superconductor CeRhIn5 in which we find a line of quantum-phase transitions induced inside the superconducting state by an applied magnetic field. This quantum-critical line separates a phase of coexisting antiferromagnetism and superconductivity from a purely unconventional superconducting phase, and terminates at a quantum tetracritical point where the magnetic field completely suppresses superconductivity. The T --> 0 K magnetic field-pressure phase diagram of CeRhIn5 is well described with a theoretical model developed to explain field-induced magnetism in the high-T(c) copper oxides, but in which a clear delineation of quantum-phase boundaries has not been possible. These experiments establish a common relationship among hidden magnetism, quantum criticality and unconventional superconductivity in copper oxides and heavy-electron systems such as CeRhIn5.

115In-NQR study of antiferromagnetism and superconductivity in CeRhIn5 and CeIn3 under pressure

We report the novel phase diagram of superconductivity (SC) and antiferromagnetism (AFM) in heavy-fermion (HF) pressure( P )-induced superconductors CeRhIn 5 and CeIn 5 through nuclear-quadrupole-resonance (NQR) measurements under P . The P -induced superconductivity in CeRhIn 5 coexists with AFM on a microscopic level in P =1.5–1.9 GPa. By contrast, in CeIn 3 , the P -induced phase separation of AFM and paramagnetism (PM) takes place without any trace of a quantum phase transition. The outstanding finding is that SC sets in at both the phases magnetically separated into AFM and PM in P =2.28–2.5 GPa.

The phase diagram of antiferromagnetism and superconductivity inCeRhIn5: astudy of 115In NQR under pressure

We report on the pressure (P) versus temperature (T) phase diagram of the P-induced heavy fermion (HF) superconductorCeRhIn5 via nuclear quadrupole resonance (NQR) measurements underP. AtP = 2.1 GPa,the T dependence of the nuclear spin–lattice relaxation rate1/T1 revealed antiferromagnetic critical fluctuations due to the closeness of antiferromagnetism. AsP decreases slightly down to 1.9 GPa, a pseudogap emerges above K, suggesting the appearance of superconducting fluctuations associated with a strongcoupling effect among quasiparticles.

Gapless magnetic and quasiparticle excitations due to the coexistence of antiferromagnetism and superconductivity in CeRhIn5: a study of 115In NQR under pressure.

We report systematic measurements of ac susceptibility, nuclear-quadrupole-resonance spectrum, and nuclear-spin-lattice-relaxation time (T1) on the pressure (P)-induced heavy-fermion superconductor CeRhIn5. The temperature (T) dependence of 1/T(1) at P=1.6 GPa has revealed that antiferromagnetism (AFM) and superconductivity (SC) coexist microscopically, exhibiting the respective transition at T(N)=2.8 K and T(MF)(c)=0.9 K. It is demonstrated that SC does not yield any trace of gap opening in low-lying excitations below T(onset)(c)=2 K, but T(MF)(c)=0.9 K, followed by a T(1)T=const law. These results point to the unconventional characteristics of SC coexisting with AFM. We highlight that both of the results deserve theoretical work on the gapless nature in the low-lying excitation spectrum due to the coexistence of AFM and SC and the lack of the mean-field regime below T(onset)(c)=2 K.

Magnetism and superconductivity in CeRhIn5 under chemical and hydrostatic pressures

Abstract Nuclear quadrupolar resonance measurements find that, under hydrostatic or chemical pressure, the heavy fermion antiferromagnet CeRhIn5 becomes more itinerant and the Neel temperature TN increases slightly at low pressures but decreases at large pressures. In CeRh0.5Ir0.5In5, unconventional superconductivity sets in well below TN, with enhanced T c ≈1 K .

Anisotropic three-dimensional magnetic fluctuations in heavy fermionCeRhIn5

CeRhIn5 is a heavy fermion antiferromagnet that orders at 3.8 K. The observation of pressure-induced superconductivity in CeRhIn5 at a very high Tc of 2.1 K for heavy fermion materials has led to speculations regarding to its magnetic fluctuation spectrum. Using magnetic neutron scattering, we report anisotropic three-dimensional antiferromagnetic fluctuations with an energy scale of less than 1.7 meV for temperatures as high as 3Tc. In addition, the effect of the magnetic fluctuations on electrical resistivity is well described by the Born approximation.

Transport properties of CeRhIn5 under high pressures up to 8.5 GPa

Transport properties of a pressure-induced superconductor CeRhIn5 were investigated under high pressures up to 8.5GPa by using a diamond-anvil cell. Superconductivity was observed in a wide pressure range from 1.5 to 7.6GPa.We also investigated the transport properties in the external magnetic field in order to study a characteristic temperature dependence of the resistivity in the normal state.

Systematic NQR study of the pressure-induced transition from antiferromagnetic to superconducting state in CeRhIn5

We report 115In nuclear-quadrupole-resonance (NQR) measurements of the pressure(P)-induced superconductor CeRhIn5 in the antiferromagnetic (AF) and superconducting (SC) states. In the AF region, the internal field at the In site is substantially reduced from 1.75kOe at P=0 to 0.39kOe at P=1.23GPa, while TN slightly changes with increasing P. This suggests that either the size or the direction of the ordered moment changes as P increases. In the SC state at P=2.1GPa, the nuclear spin-lattice relaxation rate has revealed a T3 dependence without the coherence peak just below Tc, giving evidence for the unconventional superconductivity.