Evolution of hyperfine parameters across a quantum critical point inCeRhIn5

Abstract

We report Nuclear Magnetic Resonance (NMR) data for both the In(1) and In(2) sites in the heavy fermion material CeRhIn5 under hydrostatic pressure. The Knight shift data reveal a suppression of the hyperfine coupling to the In(1) site as a function of pressure, and the electric field gradient, ναα, at the In(2) site exhibits a change of slope, dναα/dP , at Pc1 = 1.75 GPa. These changes to these coupling constants reflect alterations to the electronic structure at the quantum critical point. PACS numbers: 75.30.Mb, 76.60.Cq, 74.62.Fj, 74.70.Tx Heavy fermion metals often exhibit strong electronelectron interactions that can be tuned across a quantum phase transition between localized f-electron magnetism and itinerant heavy-mass Fermi liquid behavior.1-3 Between these two extremes, fluctuations associated with an antiferromagnetic quantum critical point (QCP) can give rise to non-Fermi liquid behavior and unconventional superconductivity.4-7 CeRhIn 5 is a prototypical heavy fermion compound that is antiferromagnetic below T N = 3.8 K at ambient pressure, and superconducting below a maximum T c = 2.3 K for hydrostatic pressures above P c1 = 1.75 GPa.8 Several measurements have uncovered changes in the basic properties of this material as pressure is tuned across this QCP. de-Haas van Alphen (dHvA) studies revealed a discontinuous change in the Fermi surface and divergence of the effective mass across P c1 , consistent with the local 4f Ce moments becoming itinerant above this pressure.9 Transport measurements in the paramagnetic normal phase have uncovered evidence for local quantum critical fluctuations in the vicinity of this QCP giving rise to non-Fermi liquid behavior.10-12 Recent neutron scattering experiments indicate an incommensurate spin spiral structure in the ordered phase that persists up to P c1 driven by frustrated magnetic exchange interactions. 13-17Nuclear magnetic resonance (NMR) has played a central role in the study of CeRhIn 5 and other heavy fermion materials.19,20 The hyperfine interaction in these materials enable the nuclei to passively probe the static and dynamic properties of the electronic spins, and NMR is readily adapted for extreme environments such as high pressure and ultralow temperatures. As a result, this technique is ideal for probing the microscopic response of materials across both conventional and quantum phase transitions. Strong electron-electron interactions modify the scattering between quasiparticles near a QCP, and theoretical models can be compared with experimental measurements of NMR quantities such as the Knight shift, K, and the spin-lattice relaxation rate, T −1 1 . 5,21-23These studies, however, are predicated on the assumption that the hyperfine couplings do not change throughout the phase diagram. In CeRhIn 5 , this assumption has led to some contradictory results. For example, nuclear quadrupolar resonance (NQR) measurements of T vealed a decrease in the spin fluctuations near the QCP, in contrast to transport measurements that indicate enhanced spin fluc...

Localized-to-itinerant transition preceding antiferromagnetic quantum critical point and gapless superconductivity in CeRh0.5Ir0.5In5

“…Figure 2b shows the frequency-swept 115 In-nuclear magnetic resonance (NMR) spectra at a constant field. The spectrum is consistent with previously reported spectra of CeRhIn 5 34 . From these data, we establish the temperature dependence of the 115 In(1)-NMR center line plotted in Fig.…”

“…To probe the character of f electrons as a function of pressure, we use the In(1) 115 In-NQR frequency ν Q . In general, ν Q is determined by the surrounding lattice and on-site electrons with the latter being dominant in strongly correlated electron systems 38 ; in the current case the latter reflects f-c hybridization that generates an electric field gradient (EFG) at the In(1)-site, as was found in previous 115 In-NQR and NMR studies on CeIn 3 39 and CeRhIn 5 34 under pressure. Figure 4a-c shows the pressure dependence of the In(1) NQR spectrum and ν Q (see Supplementary Note 2 and Supplementary Fig.…”

“…2a) of CeRh 0.5 Ir 0.5 In 5 to be smaller than that of the host material CeR-hIn 5 because 115 A(1) = 25 kOe μ À1 B in CeRhIn 5 decreases with increasing pressure but becomes constant at 115 A(1)~7 kOe μ À1 B above P = 1 GPa. Such a pressure-dependent 115 A(1) will affect the information inferred from 1/T 1 34 and, therefore, it is important to determine 115 A(1) for CeRh 0.5 Ir 0.5 In 5 before proceeding to details of its T 1 results under pressure. Figure 2b shows the frequency-swept 115 In-nuclear magnetic resonance (NMR) spectra at a constant field.…”

29Si nuclear magnetic resonance study of URu2Si2 under pressure

“…Pressure increases the overlap between the U f orbitals and the conduction electrons, leading to an enhanced Kondo scale. A similar increase was recently observed in NMR experiments in CeRhIn 5 under pressure [32]. Furthermore, T HO also increases with pressure, so the onset temperature for fluctuations would naturally increase.…”

Optically detected magnetic resonance of nitrogen vacancies in a diamond anvil cell using designer diamond anvils

“…1-3 Magnetic resonance is an important tool that can be realized under pressure and can provide important microscopic information about the electronic degrees of freedom. 4,5 Although bulk measurements have been realized at pressures up to 500 GPa, 3 magnetic resonance has been limited to pressures below 20 GPa. 6,7 Pressures greater than 4 GPa can usually only be achieved by anvil cells, which present significant technical challenges because not only is the sample space limited (typically on the order of 10-100 nL), but an inductive coil must also surround the sample in order to excite and detect the resonance.…”