Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session R05: Advances in Heavy Fermion PhysicsInvited
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Sponsoring Units: DCMP DMP Chair: Priscila Rosa, Los Alamos National Laboratory Room: LACC 152 |
Thursday, March 8, 2018 8:00AM - 8:36AM |
R05.00001: The resistive transition to superconductivity in YbRh2Si2. Invited Speaker: John Saunders We report electrical transport measurements on the putative heavy fermion superconductor YbRh2Si2 [1]. Measurements of the Nyquist noise were made on a high quality single crystal sample, over the temperature range 1K to 0.6 mK. On cooling below 12 mK, there is a clear transition from normal metal into a state in which the resistance decreases with decreasing temperature, initially approximately linearly, towards zero. We propose this to be a superconducting state, with phase fluctuations. The transition to a zero-resistance phase-coherent superconducting state is identified at 3.6 mK. The Nyquist noise was then studied in magnetic fields up to 9 mT, applied in plane, perpendicular to the c-axis. The zero resistance state was observed to be quenched above approximately 6 mT. At 9 mT we observe “re-entrance” of the normal state resistance at the lowest temperature. In the light of this critical field behavior, we discuss the nature of the superconductivity in the system, and the interplay with both electronic and nuclear magnetism. This work opens the prospect of tuning the magnetism by choice of Yb isotope in enriched samples, and studies at ultralow temperatures of electric transport at the field-tuned quantum critical point. |
Thursday, March 8, 2018 8:36AM - 9:12AM |
R05.00002: Electronic in-plane symmetry breaking at field-tuned quantum criticality in CeRhIn5 Invited Speaker: Philip Moll At the heart of the heavy-fermion problem is the interaction between f-electrons and the itinerant electronic system. Their character may be best described in localized or itinerant pictures, depending on the Kondo- and RKKY-interactions. CeRhIn5 falls in the localized category, and antiferromagnetism appears at TN~3.8K. Applying pressure increases the hybridization, and thus magnetism is suppressed in favor of superconductivity. Magnetic fields are another important parameter tuning the 4f-waveform, and recently a peculiar transition at H*~28T into a new phase emerging in vicinity of field-tuned AFM quantum critical point at Hc~50T has been reported. We present new experimental evidence for a nematic character of this high-field phase. Electronic nematics 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 phases appear in the copper- and iron-based high-temperature superconductors, and their role in establishing superconductivity remains an open question. In the nematic phase of CeRhIn5, a large in-plane resistivity anisotropy appears in the presence of a small in-plane field component. The anisotropy has little apparent connection to the lattice, rendering it a candidate for XY-nematicity. No anomalies are observed in the magnetic torque, suggesting the absence of metamagnetism. The appearance of nematic behavior in a prototypical heavy fermion superconductor highlights the interrelation of nematicity and unconventional superconductivity, suggesting nematicity to be common among correlated materials. |
Thursday, March 8, 2018 9:12AM - 9:48AM |
R05.00003: Superconductivity and anomalous connection between antiferromagnetic and superconducting phases in pressurized CeRhGe3 and related non-centrosymmetric compounds Invited Speaker: Liling Sun I will report the discovery of superconductivity in pressurized CeRhGe3, until now the only remaining non-superconducting member of the isostructural family of non-centrosymmetric heavy-fermion compounds CeTX3 (T = Co, Rh, Ir and X = Si, Ge). Superconductivity appears in CeRhGe3 at a pressure of 19.6 GPa and the transition temperature Tc reaches a maximum value of 1.3 K at 21.5 GPa. This finding provides an opportunity to establish systematic correlations between superconductivity and materials properties within this family. Though ambient-pressure unit-cell volumes and critical pressures for superconductivity vary substantially across the series, all family members reach a maximum Tcmax at a common (±1.7%) critical cell volume Vcrit, and Tcmax at Vcrit increases with increasing spin-orbit coupling strength of the d-electrons. These correlations show that substantial Kondo hybridization/coupling and spin-orbit coupling favor superconductivity in this family, the latter reflecting the role of broken centro-symmetry. Further, anomalous connection between antiferromagnetic and superconducting phases found in pressurized CeRhGe3 will also be presented. |
Thursday, March 8, 2018 9:48AM - 10:24AM |
R05.00004: Coherent Band Excitations in CePd3 Invited Speaker: Raymond Osborn A crossover from coherent quasiparticle bands at low temperature to incoherent electronic fluctuations at high temperature is a hallmark of strongly correlated electron systems, ranging from heavy fermions to high temperature superconductors. Realistic calculations that combine Density Functional Theory with Dynamical Mean Field Theory (DFT+DMFT) in order to incorporate both local correlations and itinerant bands predict a gradual loss of quasiparticle spectral weight at the Fermi energy with increasing temperature, but comparisons with spectroscopic data have been limited. For example, in cerium compounds, many of the relevant electronic states are unoccupied and therefore inaccessible to ARPES measurements. However, recent instrumental advances at spallation neutron sources allow inelastic neutron scattering (INS) to be used as an alternative probe of quasiparticle coherence. The dynamic magnetic susceptibility, Im χ(Q,ω), is proportional to the joint electronic density-of-states, amplified by particle-hole interactions. I will present the results of a comparison of four-dimensional INS data, measured over a large (Q,ω)-volume on a single crystal of CePd3, with DFT+DMFT calculations.1 The formation of coherent f-electron bands at low temperature produces modulations of intensity throughout the Brillouin zone, which are suppressed with increasing temperature. The agreement between experiment and theory on an absolute scale shows that we have a robust first-principles understanding of the temperature dependence of f-electron coherence. |
Thursday, March 8, 2018 10:24AM - 11:00AM |
R05.00005: DFT+DMFT study of the dynamic magnetic susceptibility in heavy fermion materials Invited Speaker: Hyowon Park Understanding the nature of strong correlation physics in heavy fermion materials is challenging due to both localized and itinerant behaviors of f-electrons in these materials. Density functional theory plus dynamical mean field theory (DFT+DMFT) is a successful ab initio method for describing this dual nature of electrons in strongly correlated materials. However, calculations of the dynamical magnetic susceptibility over the whole Brillouin zone have proved challenging because of the need to incorporate both the self-energy of the renormalized quasiparticles and two-particle vertex corrections. I will review recent calculations using DFT+DMFT in both d-electron systems with collective spin excitations, such as the iron pnictides, and f-electron systems, such as CePd3, that have successfully captured both the Q-dependence and the energy scale of the neutron scattering arising due to the particle-hole excitation of strongly renormalized bands as a function of temperature. |
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