Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session G46: Ce- and Pu-Based 115 Materials and Related Systems |
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Sponsoring Units: DCMP Chair: Johnpierre Paglione, University of Mayland Room: Mile High Ballroom 4E |
Tuesday, March 4, 2014 11:15AM - 11:27AM |
G46.00001: Phase-Sensitive Bogoliubov Quasi-Particle Interference Spectroscopy in CeCoIn$_5$ John Van Dyke, Freek Massee, Milan Allan, J.C. Davis, Cedomir Petrovic, Dirk Morr Recent scanning tunneling spectroscopy experiments [1] have provided unprecedented insight into the momentum structure of the superconducting gap in CeCoIn$_5$ using quasi-particle interference (QPI) spectroscopy. In this talk, we demonstrate that the symmetry of the superconducting gap in CeCoIn$_5$ can be determined via phase-sensitive quasi-particle interference (PQPI) spectroscopy. This method is based on the insight that the intensity of the QPI spectrum is different for potential and magnetic defects. Using this idea, we present a theory for phase-sensitive QPI spectroscopy in heavy fermion materials. We demonstrate that a variation in the phase of the superconducting gap along the Fermi surface can be identified by comparing QPI spectra in zero and finite magnetic fields. Analysing recent experimental QPI results on CeCoIn$_5$ in $H=0$ and 3 Tesla magnetic fields, we show that the resulting PQPI spectrum provides strong evidence for a $d_{x^2-y^2}$ symmetry of the superconducting gap [2]. [1] M.P. Allan et al., Nature Physics 9, 468-473 (2013) [2] J. Van Dyke, F. Massee, M.P. Allan, J.C. Davis, C. Petrovic, D.K. Morr, submitted. [Preview Abstract] |
Tuesday, March 4, 2014 11:27AM - 11:39AM |
G46.00002: High Pressure NMR study of Knight Shift Anomaly on the heavy electron material CeRhIn5 Ching Lin, Nicholas Curro, Kent Shirer, John Crocker, Adam Dioguardi, Abigail Shockley, Matthew Lawson We have measured the Nuclear Magnetic Resonance Knight Shift in the heavy f-electron material CeRhIn5 in order to investigate the coherence temperature T$^{\mathrm{\ast }}$ as a function of pressure up to 2GPa. We find that the Knight Shift of both In(1) and In(2) sites changes significantly with pressure. Our results are consistent with the phase diagram proposed by Yang and Pines. [Preview Abstract] |
Tuesday, March 4, 2014 11:39AM - 11:51AM |
G46.00003: Evolution of the Hyperfine Couplings with Pressure in CeRhIn$_5$ Nicholas Curro, Ching Lin, Kent Shirer, John Crocker, Adam Dioguardi, Abigail Shockley, Matthew Lawson Measurements of the Knight shift in CeRhIn$_5$ under pressure reveal several changes to the hyperfine coupling constants at both the In(1) and In(2) sites. We discuss these changes, both to the on-site contact term as well as the transferred term to the local moments. Our data suggest that the changes we observe reflect changes in the hybridization of the Ce 4f moments as the system is tuned from an antiferromagnetic ground state to superconducting. [Preview Abstract] |
Tuesday, March 4, 2014 11:51AM - 12:03PM |
G46.00004: Fermi surface collapse, gap, coherence: an ARPES study of the hybridization in Ce$_2$RhIn$_8$ Fanny Rodolakis, Cris Adriano, Francisco Restrepo, Priscila F.S. Rosa, Pascoal Pagliuso, Juan Carlos Campuzano The crossover of localized magnetic moments at high temperatures into itinerant states of heavy mass at low temperatures in some metals containing \emph{f} electrons, first addressed by Kondo, is a fundamental problem in condensed matter physics involving a temperature dependent hybridization between \emph{f} levels and conduction electrons (\emph{ce}). Here we present an extensive angular resolved photoemission spectroscopy study performed in Ce$_2$RhIn$_8$\ as a function of temperature. Our experiments reveal the presence of three energy scales, differing by an order of magnitude from each other: first at room temperature, where the \emph{f} levels are localized, we observe a small Fermi surface (FS), which undergoes dramatic topological changes toward a large FS near the minimum in the resistivity around 200K; the opening of a spectral gap below 30K without a change in topology of the Fermi surface; and finally, below 5K, composite quasiparticles form, as the resistivity suddenly decreases. The expectation that hybridization, spectral gap, and \emph{f} electron coherence go hand in hand should be expanded to include the possibility of separate energy scales for each of these phenomena. [Preview Abstract] |
Tuesday, March 4, 2014 12:03PM - 12:15PM |
G46.00005: CePt$_{2}$In$_{7}$: Shubnikov-de Haas measurements on micro-structured samples under high pressures J. Kanter, P. Moll, S. Friedemann, P. Alireza, M. Sutherland, S. Goh, F. Ronning, E.D. Bauer, B. Batlogg CePt$_{2}$In$_{7}$ belongs to the Ce$_{m}$M$_{n}$In$_{3m+2n}$ heavy fermion family, but compared to the Ce$M$In$_{5}$ members of this group, exhibits a more two dimensional electronic structure. At zero pressure the ground state is antiferromagnetically ordered. Under pressure the antiferromagnetic order is suppressed and a superconducting phase is induced, with a maximum T$_{c}$ above a quantum critical point around 31 kbar. To investigate the changes in the Fermi Surface and effective electron masses around the quantum critical point, Shubnikov-de Haas measurements were conducted under high pressures in an anvil cell. The samples were micro-structured and contacted using a Focused Ion Beam (FIB). The Focused Ion Beam enables sample contacting and structuring down to a sub-micrometer scale, making the measurement of several samples with complex shapes and multiple contacts on a single anvil feasible. [Preview Abstract] |
Tuesday, March 4, 2014 12:15PM - 12:27PM |
G46.00006: Doping study of the heavy fermion superconductor CePt$_{2}$In$_{7}$ Nirmal Ghimire, Filip Ronning, J. Thompson, Eric Bauer The CeMIn$_{5}$ (M$=$Co, Rh, Ir) materials are prototypical heavy fermion superconductors close to antiferromagnetism, making them ideal candidates to investigate the interplay of unconventional superconductivity and magnetism and to explore quantum criticality. CeRhIn$_{5}$ displays all of the signatures of a material close to an antiferromagnetic quantum critical point (QCP): 1) the antiferromagnetism at T$_{N} =$ 3.8 K is suppressed under applied pressure at Pc$=$2.5 GPa, 2) non-Fermi liquid behavior in the electrical resistivity and specific heat is observed near Pc, and 3) a dome of unconventional superconductivity appears with Tc max$=$2.6 K. To investigate the nature of the quantum criticality in the Ce$_{m}$M$_{n}$In$_{3m+2n}$ family, we focus attention on the newest member, CePt$_{2}$In$_{7}$, with m$=$1 and n$=$2, where m and n are CeIn$_{3}$ and MIn$_{2}$ layers. Similar to its cousin CeRhIn$_{5}$ (m$=$1, n$=$1), it shows a dome of superconductivity and signatures of quantum criticality under pressure in the vicinity of where the Neel temperature is suppressed at Pc$=$3 GPa. As an alternative to the application of pressure to access the QCP, we present the magnetic, thermal and transport properties of doped CePt$_{2}$In$_{7}$. [Preview Abstract] |
Tuesday, March 4, 2014 12:27PM - 12:39PM |
G46.00007: Dispersion of Spin Resonance mode in Yb Doped CeCoIn5 Yu Song, Mengshu Liu, Benjamin White, Brian Maple, Pengcheng Dai It is commonly believed superconductivity in CeCoIn5 has a d wave symmetry, given such symmetry the spin exciton interpretation of the spin resonance which has been widely applied to many systems where such a mode is observed, predicts a downward dispersion of the resonance mode (PRL 101, 187001 (2008)). Here we discuss our neutron scattering results on Yb doped CeCoIn5, our results can clearly differentiate whether the resonance mode is indeed a spin exciton or if it's a magnon-like exciton as argued in another work (PRL 101, 087001 (2008)). [Preview Abstract] |
Tuesday, March 4, 2014 12:39PM - 12:51PM |
G46.00008: Theory of Composite Paring in Yb doped CeCoIn$_5$ Onur Erten, Piers Coleman Recent experiments on the $R$ ($R$= La, Yb) doped CeCoIn$_5$ have yielded fascinating results. La, which acts as an inert cation kills superconductivity rapidly[1], whereas superconductivity is much more robust in the case of Yb doping[2]. Experiments also show that unlike La, Yb is in a mixed valent state for all concentrations of doping. Motivated with these experiments, we investigate the effects of doping and disorder on composite paring by diluting two channel Kondo lattice model. This talk will discuss the doping dependence of the coherence temperature and $T_c$ and various possibilities for the discrepancies between thin films and bulk samples. [1] S. Nakatsuji {\it et al.} Phys. Rev. Lett. {\bf 89}, 106402 (2002) [2] L. Shu {\it et al.} Phys. Rev. Lett {\bf 106}, 156403 (2011) [Preview Abstract] |
Tuesday, March 4, 2014 12:51PM - 1:03PM |
G46.00009: Low Temperature Magnetometry Measurements of the Heavy Fermion Superconductor Nd1$-x$Ce$x$CoIn5 with x $=$ 0.98, 0.95, and 0.90 Kevin Storr, Kenneth Purcell, Torrance Rasco, Sarah Schwartz, Cedomir Petrovic The Nd$_{\mathrm{1-x}}$Ce$_{x}$CoIn$_{5}$ alloys evolve from local moment magnetism $x=$0 to heavy fermion superconductivity $x=$1, as the Nd substitution alters the level of 4f-conduction electron coupling. Superconductivity has been shown to exist in Nd concentrations between x $=$ 0 and x $=$ 0.22. We report the temperature and angular dependence of the critical field of the superconducting state of the x $=$ 0.98, 0.95, and 0.90 doping levels at temperatures ranging from 20 -- 500 mK, investigating the evolution of the phase diagram for different concentrations of Nd at these previously unexplored low temperatures. No evidence of a low temperature mixed superconducting and magnetic mixed state was observed such that as that seen in CeCoIn5. The suppression of the critical field is more dramatic than the application of pressure and was observed to be rather anisotropic in line with the higher temperature measurements. [Preview Abstract] |
Tuesday, March 4, 2014 1:03PM - 1:15PM |
G46.00010: Incommensurate Magnetic Order in Ce(1-x)Yb(x)RhIn(5) Steven Disseler, S. Jang, B.D. White, Yang Zhao, Jeff Lynn, M.B. Maple We present a detailed study of a series of Yb-doped CeRhIn5 single crystals through measurements of the bulk magnetic properties and elastic neutron scattering. We find that all samples up to x $=$ 0.8 undergo a magnetic ordering transition below 4 K, despite observations that the Yb-valence rapidly decreases toward a non-magnetic state at high concentrations. Furthermore, we find that this magnetically ordered state is described by an incommensurate structure similar to the parent compound, and with a propagation wave vector that is weakly dependent on concentration. The authors acknowledge funding source US DOE DE-FG02-04-ER46105. [Preview Abstract] |
Tuesday, March 4, 2014 1:15PM - 1:27PM |
G46.00011: Controllable Rashba spin-orbit interaction in artificially engineered superlattices CeCoIn$_{5}$/YbCoIn$_{5}$ Masaaki Shimozawa, Swee Goh, Ryota Endo, Ryo Kobayashi, Tatsuya Watashige, Yuta Mizukami, Hiroaki Ikeda, Hiroaki Shishido, Youichi Yanase, Takahito Terashima, Takasada Shibauchi, Yuji Matsuda Recently the inversion symmetry breaking (ISB) together with strong spin-orbit interaction is suggested to affect the electron pairing in superconductivity, leading to various physical phenomena. However, it is hard to tune the degree of ISB in bulk crystals because the degree is determined by the crystal structure itself. Here, by using the molecular beam epitaxy technology, we fabricate artificial heavy fermion superlattices with the alternating layers of heavy fermion CeCoIn$_{5}$ and nonmagnetic metal YbCoIn$_{5}$ with atomic scale thicknesses. We demonstrate that the Rashba spin-orbit interaction arising from ISB is largely tunable by introduction of the thickness modulation in YbCoIn$_{5}$ block-layers, which leads to profound changes in the nature of the superconductivity. [Preview Abstract] |
Tuesday, March 4, 2014 1:27PM - 1:39PM |
G46.00012: Many-body coherence in $f$-electron Ce$_{\mathrm{1-x}}$Yb$_{\mathrm{x}}$CoIn$_{5}$ alloys Y.P. Singh, D.J. Haney, X.Y. Huang, M. Dzero, I. Lum, B.D. White, M.B. Maple, C.C. Almasan We investigated experimentally the onset of the many-body coherence in the $f$-orbital single crystalline alloys Ce$_{\mathrm{1-x}}$Yb$_{\mathrm{x}}$CoIn$_{5}$ (0.00 $\le $ x $\le $ 0.775). Specifically, we performed thermodynamic and magneto-transport measurements to study the evolution of the many-body electronic state as the Kondo lattice of Ce moments is transformed into an array of Ce impurities. Our analysis of the residual resistivity data unveils the presence of correlations between Yb ions for x \textgreater 0.50. For concentrations around 50{\%} of Yb we observe the smooth crossover from the predominantly localized moment regime to the predominantly itinerant regime. Indeed, our analysis of specific heat data reveals that for 0.65 $\le $ x $\le $ 0.775, Yb $f$-electrons strongly interact with the conduction electrons while the Ce moments remain completely decoupled. The sub-linear temperature dependence of resistivity across the whole range of Yb concentrations suggests the presence of a nontrivial scattering mechanism for the conduction electrons. [Preview Abstract] |
Tuesday, March 4, 2014 1:39PM - 1:51PM |
G46.00013: NQR Study of the Heavy-Fermion Pu-115 Superconductors G. Koutroulakis, H. Yasuoka, P.H. Tobash, J.N. Mitchell, E.D. Bauer, J.D. Thompson We present $^{115}$In nuclear quadrupolar resonance (NQR) measurements on the heavy-fermion superconductors Pu$M$In$_5$ ($M$=Co, Rh; $T_c$=2.5K, 1.6K, respectively), in the temperature range \mbox{$0.29{\rm K}\leq T\leq 100{\rm K}$}. From the identified spectral lines, we deduce the quadrupolar parameters for the two inequivalent In sites, which are found to be qualitatively similar to those for other Ce- and Pu-115s. The quadrupolar frequency $\nu_Q$ varies with temperature in the normal state as per the empirical formula for conventional metals. As superconductivity develops, however, $\nu_Q$ exhibits a sharp, albeit small shift, which is a key prediction of the theory of composite superconducting (SC) pairing [1]. The temperature variation of the nuclear spin-lattice relaxation rate $T_1^{-1}$ delineates distinctive regimes of dynamic behavior. An excess of strong in-plane antiferromagnetic spin fluctuations is observed in the vicinity of $T_c$, which are believed to be playing a central role in the formation of the SC condensate. Analysis of the $T_1^{-1}$ data in the SC state suggests that these compounds are strong-coupling $d$-wave superconductors. [1]R. Flint, A. H. Nevidomskyy, and P. Coleman, Phys. Rev. B {\bf 84}, 064514 (2011). [Preview Abstract] |
Tuesday, March 4, 2014 1:51PM - 2:03PM |
G46.00014: Probing the Nature of Superconductivity in the Heavy Fermion PuMGa$_{5}$ and PuMIn$_{5}$ (M$=$Co, Rh) Compounds Eric Bauer, Paul Tobash, Jeremy Mitchell, Joe Thompson The discovery of superconductivity in PuCoGa$_{5}$ with a T$_{\mathrm{c}} =$ 18.5 K has generated renewed interest in Pu-based compounds. PuCoGa$_{5}$, and its superconducting cousin PuRhGa$_{5}$ (T$_{\mathrm{c}} =$ 8.7 K), have the same crystal structure as the tetragonal CeMIn$_{5}$ (T$=$Co, Rh, Ir) heavy fermion superconductors, suggesting that the structure plays a key role in generating superconductivity in these materials. While a variety of measurements have firmly established that the CeTIn$_{5}$ compounds are unconventional $d$-wave superconductors, most probably mediated by antiferromagnetic spin fluctuations, it is less clear what drives the high transition temperature in PuCoGa$_{5}$, which is an order of magnitude larger than all other know Ce- or U-based heavy fermion superconductors. The physical properties of two new members of this ``115'' family of superconductors, PuRhIn$_{5}$ and PuCoIn$_{5}$, indicate that they reside close to an antiferromagnetic quantum critical point, while the smaller effective masses and much smaller unit cell volumes of PuCoGa$_{5}$ and PuRhGa$_{5}$ suggest that they may be near a T$=$0 valence instability or that the Pu 5f electrons couple to conduction electrons in multiple channels to form ``composite'' superconducting pairs. The nature of superconductivity in these four Pu115 materials will be discussed. [Preview Abstract] |
Tuesday, March 4, 2014 2:03PM - 2:15PM |
G46.00015: Possibility of nodal $s^\pm$ pairing symmetry in plutonium-based 115 superconductors Matthias J. Graf, Tanmoy Das, Jian-Xin Zhu We performed RPA calculations to investigate the role of spin-fluctuations in the superconducting state of Pu-115 compounds. First-principles electronic structure calculations were used as input, combined with the spin-fluctuation exchange approximation, to compute within the RPA method the nesting conditions on the Fermi surface. Of special interest for superconductivity are hot spots caused by nesting near the wave vectors ($\pi,\pi,q_z$) connecting the four Fermi surfaces. Surprisingly, in this multiband material the normal-state instability toward superconductivity is dominated by a nodal gap with $s^\pm$ symmetry over a more typical $d_{x^2-y^2}$-wave gap. We will discuss the possibility of magnetic resonances in the superconducting state and how to differentiate between these closely competing pairing symmetries in inelastic neutron scattering and point-contact spectroscopy. [Preview Abstract] |
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