Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session H22: Heavy Fermions |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Eric Bauer, Los Alamos National Laboratory Room: D163 |
Tuesday, March 22, 2011 8:00AM - 8:12AM |
H22.00001: Field-induced Spin Fluctuations in Intermetallic Ce$X_{2}$Ge$_{2 }(X$= Cu, Ag, Au) Deepak Singh, A. Thamizhavel, Sung Chang, Jeffrey Lynn Intermetallic rare-earth compounds containing a lattice of 4 $f$ or 5 $f$- electrons are prototypical systems to study the magnetic quantum phase transition which mainly results from the fluctuation of the antiferromagnetic moment at T= 0 K. Therefore, understanding the mechanism behind spin fluctuations is important towards a meaningful universal formulation of the QPT phenomena. We have performed magnetic, thermodynamic and neutron scattering measurements on Ce$X_{2}$Ge2 (X = Cu, Ag, Au) compounds in single crystal form to further understand the mechanism behind spin fluctuations. Ce$X_{2}$Ge$_{2}$ crystallize in a ThCr$_{2}$Si$_{2}$-type tetragonal crystal structure and undergo antiferromagnetic transitions at T$_{N}$ = 4.2 K (Cu), 4.6 K (Ag) and 13.5 K (Au). Detail measurements of Q-vectors associated with the long-range order and the numerical modeling of the data revealed the propagation of amplitude modulated spin density wave in CeCu$_{2}$Ge$_{2}$ and CeAg$_{2}$Ge$_{2}$ with the propagation vectors of (0.29,0.29,0.52) and (0,0.705,0.11) respectively. Dynamic measurements of Ce$X_{2}$Ge$_{2}$ compounds in applied magnetic field, exhibiting the varying nature of spin fluctuations as $X$ changes, will be discussed and compared with other Ce-based intermetallic compounds. [Preview Abstract] |
Tuesday, March 22, 2011 8:12AM - 8:24AM |
H22.00002: Growth and properties of heavy fermion thin films and superlattices Yize Li, Mao Zheng, Brian Mulcahy, L.H. Greene, James N. Eckstein We have grown thin films of the heavy fermion phases CeCu$_{2} $Ge$_{2}$ (CCG) and CeFe$_{2}$Ge$_{2}$ (CFG) on MgO and DySrO3 substrates using molecular beam epitaxy. We find that the growth begins via island nucleation leading to a granular morphology, since there are two equivalent registrations of the film with the substrate. After nucleating, the grains grow flat with c-axis orientation. These single phase films show similar temperature(T) dependent transport behavior as seen in single crystals of the materials, including for CCG Kondo scattering and the emergence of coherent coupling of the heavy fermion transport channel at low T and for CFG a monotonic decrease in resistivity as the temperature is lowered. Superlattices combining CCG and CFG in different supercell architectures were also grown. In transport, they show a systematic evolution with composition between the distinct R(T) behavior of the two parent phases. A correlation between spectroscopic measurements and resistivity was found and details will be presented. [Preview Abstract] |
Tuesday, March 22, 2011 8:24AM - 8:36AM |
H22.00003: Neutron Scattering Study of the Field Induced Non-Fermi-Liquid Behavior in CeAuSb$_2$ Sung Chang, Deepak Singh, Arumugam Thamizhavel The modestly heavy Fermion compound CeAuSb$_2$ ($\gamma = 90
$~mJ/K$^2$~mol) was reported to exhibit highly anisotropic
magnetic properties with an antiferromagnetic transition
temperature $T_N \approx 5$~K~[1]. In addition, the
unconventional temperature dependence of the resistivity and
specific heat, observed when an external magnetic field
suppresses $T_N$ to 0~K, has lead to the identification of
CeAuSb$_2$ as a system showing possible magnetic field-induced
quantum critical behavior [2]. Here we report on neutron
scattering measurements of CeAuSb$_2$ in magnetic fields up to
9~T applied along the $\left |
Tuesday, March 22, 2011 8:36AM - 8:48AM |
H22.00004: Shubnikov-de Haas Effect measured on single crystals of CeOs$_4$Sb$_{12}$ and NdOs$_4$Sb$_{12}$ along the high symmetry directions P.-C. Ho, J. Singleton, M.B. Maple, D.B. Shrekenhamer, X. Lee, A. Thale, T. Yanagisawa The filled skutterudite compounds CeOs$_4$Sb$_{12}$, PrOs$_4$Sb$_{12}$, and NdOs$_4$Sb$_{12}$ are respectively a 1~K antiferromagnetic (AFM) Kondo insulator, a 1.85~K unconventional superconductor, and a 1~K mean-field type ferromagnet (FM), suggesting that superconductivity in PrOs$_4$Sb$_{12}$ may result from proximity to AFM and FM quantum-critical points. Fermi-surface measurements of NdOs$_4$Sb$_{12}$ and CeOs$_4$Sb$_{12}$ could therefore give insights into the pairing mechanism. We have used a MHz skin-depth technique to observe Shubnikov-de Haas oscillations (SdHos) in single crystals of these materials at fields of up to 60~T. In CeOs$_4$Sb$_{12}$ for {\bf H} // [001], a previously-unobserved semimetal-to-metal transition was detected at $\approx 25$~T; above this, a series of SdHos with a frequency of 1700~T and $ m_{\rm CR} \approx 3.6 m_{\rm e}$ emerge. For {\bf H} // [011] in NdOs$_4$Sb$_{12}$, a single series of SdHos, frequency $\approx 874$~T, was found. These may correspond to the $\beta$ band in PrOs$_4$Sb$_{12}$, but with a much smaller $m_{\rm CR} \approx 1.5 m_{\rm e}$. Research at CSU-Fresno is supported by RC CCSA $\#$7669 and the start-up fund; at NHMFL by DOE, NSF, and FL.; at UCSD by NSF$\#$0802478 and US DOE DE FG02-04ER46105; at Hokkaido U by MEXT, Japan. [Preview Abstract] |
Tuesday, March 22, 2011 8:48AM - 9:00AM |
H22.00005: The non-centrosymmetric heavy fermion ferromagnet Sm$_2$Fe$_{12}$P$_7$ Marc Janoschek, Ryan E. Baumbach, James J. Hamlin, Ivy K. Lum, M. Brian Maple The investigation of quantum critical points (QCPs) in heavy fermion compounds (HF) has proven to be a useful tool in gaining insight into strongly correlated electron physics. However, the body of work on HF systems mainly focuses on antiferromagnetic QCPs. We report measurements of the electrical resistivity, magnetization and specific heat on single crystals of the non- centrosymmetric compound Sm$_2$Fe$_{12}$P$_7$, that exhibits ferromagnetic (FM) order below T$_{M,1}$ = 6.3 K. The ratio of the effective magnetic moment in the paramagnetic state, to the saturation magnetic moment in the ordered state indicates that the ordered state is associated with itinerant electrons. An enhanced value for the coefficient of the electronic speci?c heat $\gamma$ $\sim$ 450 mJ mol$^{-1}$K$^{-1}$ is observed, that is accompanied by a large coefficient $A$ of the $T^2$ term in the electrical resistivity, suggesting a HF ground state. Three consecutive magnetic phase transitions, indicative of competing magnetic energy scales, and the observation of a metamagnetic transition additionally suggest proximity to a QCP. Thus, we propose that Sm$_2$Fe$_{12}$P$_7$ is a possible candidate to study a FM QCP in a HF compound. [Preview Abstract] |
Tuesday, March 22, 2011 9:00AM - 9:12AM |
H22.00006: Multiple regions of quantum criticality in YbAgGe G.M. Schmiedeshoff, S.L. Bud'ko, P.C. Canfield YbAgGe is a stoichiometric heavy fermion antiferromagnet that exhibits field-induced quantum criticality.~ We present and discuss thermal expansion and magnetostriction measurements that reveal a new field-induced state. On the low-field side of this state we find evidence for a first-order phase transition and suggest that YbAgGe may be close to a quantum critical end point at 4.5 T. On the high-field side we find evidence for a second-order phase transition suppressed to a quantum critical point near 7.2 T. We will discuss these results in light of global phase diagrams proposed for Kondo lattice systems. Work at Occidental College was supported by the National Science Foundation under DMR-1006118. Work at Ames Laboratory was supported by the Department of Energy, Basic Energy Sciences under Contract No. DE-AC02-07CH11358. [Preview Abstract] |
Tuesday, March 22, 2011 9:12AM - 9:24AM |
H22.00007: Quasiparticle duality in the Kondo-screened state of YbInCu4 Marco Guarise, Jason Hancock, John Sarrao, Thorsten Schmitt, Marco Grioni We present a study of the excitation spectra of YbInCu4. This system exhibits a first- order isoelectronic phase transition which separates regimes with very different $T/T_K$. Using infrared optics, we were first able to demonstrate the existence of a hybridization gap feature which is ubiquitous in heavy fermion systems. More recently, using the burgeoning technique of resonant inelastic X-ray scattering (RIXS) at the Yb M5 edge, we identify a feature at the same energy, strongly suggesting that components of this excitation have mixed itinerant and localized character. Prospects for the future studies using the RIXS technique in the context of heavy fermion materials will be discussed. [Preview Abstract] |
Tuesday, March 22, 2011 9:24AM - 9:36AM |
H22.00008: High-resolution angle-resolved photoemission studies of YbRh$_2$Si$_2$ using 7 eV laser S.-K. Mo, W.S. Lee, F. Schmitt, Y.L. Chen, D.H. Lu, C. Capan, D.J. Kim, Z. Fisk, C.-Q. Zhang, Z. Hussain, Z.-X. Shen We present angle-resolved photoemission spectra of prototypical heavy fermion compound YbRh$_2$Si$_2$ measured with 7 eV ultraviolet laser. Much improved energy and momentum resolutions enable us to resolve the sharp weakly dispersing peaks at the lowest energy of single-electron spectra. This coherent state grows in intensity and weight as temperature decreases below a characteristic temperature. The characteristic temperature is not only different from the single-ion Kondo temperature of YbRh$_2$Si$_2$ derived from thermodynamic measurements, it is of the same scale as the energy and the lifetime of the coherent state. [Preview Abstract] |
Tuesday, March 22, 2011 9:36AM - 9:48AM |
H22.00009: Zeeman-driven Lifshitz transition: A scenario for the Fermi-surface reconstruction in YbRh2Si2 Matthias Vojta, Andreas Hackl The heavy-fermion metal YbRh$_2$Si$_2$ displays a field-driven quantum phase transition where signatures of a Fermi-surface reconstruction have been identified, often interpreted as breakdown of the Kondo effect. We argue that instead many properties of the material can be consistently described assuming a Zeeman-driven Lifshitz transition of heavy-fermion bands. Using a suitable quasiparticle model, we find a smeared jump in the Hall constant and maxima in susceptibility and specific heat, very similar to experimental data. An intermediate non-Fermi liquid regime emerges due to the small effective Fermi energy near the transition. Further experiments to discriminate the different scenarios are proposed. [Preview Abstract] |
Tuesday, March 22, 2011 9:48AM - 10:00AM |
H22.00010: Neutron magnetic form factor in strongly correlated materials Maria Pezzoli, Kristjan Haule, Gabriel Kotliar We introduce a formalism to compute the neutron magnetic form factor F(q) within a first-principles Density Functional Theory (DFT) + Dynamical Mean Field Theory (DMFT). We use our method to compute the form factor of PuCoGa5. We find that the local physics of this material is described by a mixed valence mechanism of the type observed in elemental Plutonium. This picture explains nicely the experimental neutron form factor of PuCoGa5 and it is consistent with the photo-emission spectra shape and the value of the specific heat linear coefficient. [Preview Abstract] |
Tuesday, March 22, 2011 10:00AM - 10:12AM |
H22.00011: Formation of heavy electron bands by ordering in two-channel Kondo lattice Shintaro Hoshino, Junya Otsuki, Yoshio Kuramoto Itinerant and localized characters of electrons are one of the most fundamental problems in condensed matter physics. In typical Kondo lattice systems, the f electrons are localized in the high temperature region, and acquire the itinerancy by the interaction between f and conduction electrons with decreasing temperature. In the present work, however, we show that the localized character of f electrons changes into itinerant one at the transition point in two-channel Kondo lattice systems. We have analyzed the system using the dynamical mean-field theory combined with the continuous-time quantum Monte Carlo method. With one conduction electron per site, which corresponds to the quarter filling of each band, a channel order emerges in wide parameter region with metal-insulator transition. At the same time, the heavy electron bands are formed, which indicates the itinerant f-electron states. Since f electrons acquire the itinerancy only below the transition temperature, this behavior can be regarded as itinerant-localized transition of electronic states. We will discuss these behaviors through temperature dependence of the single-particle spectrum. [Preview Abstract] |
Tuesday, March 22, 2011 10:12AM - 10:24AM |
H22.00012: Hard X-Ray Photoelectron Spectroscopic Analysis of single crystal UPd$_{3}$, UGe$_{2}$, and USb$_{2}$ M. Beaux, T. Durakiewicz, J. Joyce, E. Bauer, L. Moreschini, F. Offi, M. Grioni, G. Monaco, G. Pannacione Hard X-ray Photoelectron Spectroscopy (HAXPES) with 7.6 keV photons has been performed on single crystals of UPd3, UGe2, and USb2 at the European Synchrotron Radiation Facility (ESRF). A potential correlation between the localization/itinerancy of the 5f electrons and the core levels of these materials is investigated. The greatly reduced surface sensitivity of HAXPES enabled observation of the bulk core levels in spite of some surface oxidation. An 800 meV splitting of the Sb 3d and 4d core levels was observed. The splitting of the Sb core levels is attributed to manifestations of two distinct binding modes within the USb2 single crystal as supported by consideration of interatomic distances and charge transfer calculations. [Preview Abstract] |
Tuesday, March 22, 2011 10:24AM - 10:36AM |
H22.00013: Small Angle Neutron Scattering and the Vortex Lattice of UPt$_3$ W.J. Gannon, W.P. Halperin, J.A. Sauls, J.P. Davis, K. Schlesinger, M.R. Eskildsen, J. Gavilano UPt$_3$ is among the most well studied of the unconventional superconductors. However, there are still many unanswered questions, two of which are: understanding chirality in the superconducting B-phase and understanding the nature of the B-C transition. Central to theories describing both of these areas are predictions for unusual vortex structures. Small angle neutron scattering (SANS) provides a unique way to explore the bulk vortex lattice (VL) and thus can be used to investigate the bulk superconducting state without electronic surface scattering which complicates results from other probes. Ongoing SANS experiments on high quality single crystals in a novel geometry seek to explore the the relationship between field history and the VL in UPt$_3$. Preliminary results show well defined diffraction patterns and narrow rocking curves at fields well into the C-phase and interesting behavior for a variety of field histories. These results will shed new light on chirality, the B-C transition, and VL (meta)stability. [Preview Abstract] |
Tuesday, March 22, 2011 10:36AM - 10:48AM |
H22.00014: Unconventional Anomalous Hall Effect in UCu$_{5}$ B.G. Ueland, C.F. Miclea, I. Martin, E.D. Bauer, R. Movshovich, F. Ronning, Z. Fisk, J.D. Thompson Field-dependent resistivity, magnetization, and specific heat measurements have been carried out on the heavy fermion compound UCu$_{5}$. We find an unconventional anomalous Hall resistance below the lower temperature magnetic transition at T$_{2} \quad \sim $ 1 K that is proportional to neither the magnetization nor the longitudinal resistivity. We discuss the origin of this resistance in terms of the itinerant carriers' interaction with the magnetically ordered U cations. Complementary measurements on Lu$_{1-x}$U$_{x}$Cu$_{5}$, x = 0 to 0.15 show how non-magnetic dilution affects the Hall resistance and magnetic phase diagram. Interestingly, light Lu substitution for U appears to stabilize the low temperature magnetic phase. [Preview Abstract] |
Tuesday, March 22, 2011 10:48AM - 11:00AM |
H22.00015: Temperature Dependent Hybridization Gaps Peter Riseborough A number of heavy-fermion/mixed-valent materials show hybridization gaps either at the Fermi-energy or close to the Fermi-energy. In the former case, a heavy-fermion semiconducting state ensues and in the later case, the system remains metallic at low temperatures. In either case, the electronic structure is extremely temperature-dependent. It has been observed that the gap closes and the heavy quasiparticle bands disappear at high temperatures. The magnitude of the gaps scale with effective quasiparticle masses. A phenomenological model is presented that exhibits a temperature-dependence which is consistent with the above behavior. The model is based on a periodic array of Anderson impurities in which the electron correlations are represented by the coupling to bosons with an Einstein spectra. The model can be solved via systematic approximation. The solution describes the temperature- dependence of coherent and incoherent structures in the electronic excitation spectra. The predicted hybridization gaps for the metallic case are compared with data from photoemission experiments on UPd$_2$Al$_3$. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700