J. L. Sarrao

Publications (367)645.11 Total impact

• Source

  Available from: Dennis Nordlund

  Article: Multiconfigurational nature of 5f orbitals in uranium and plutonium intermetallics

  C.H. Booth, Yu Jiang, D.L. Wang, J.N. Mitchell, P.H. Tobash, E.D. Bauer, M.A. Wall, P.G. Allen, D. Sokaras, D. Nordlund, T.-C. Weng, M.A. Torrez, J.L. Sarrao
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  ABSTRACT: Uranium and plutonium’s 5f electrons are tenuously poised between strongly bonding with ligand spd-states and residing close to the nucleus. The unusual properties of these elements and their compounds (e.g., the six different allotropes of elemental plutonium) are widely believed to depend on the related attributes of f-orbital occupancy and delocalization for which a quantitative measure is lacking. By employing resonant X-ray emission spectroscopy (RXES) and X-ray absorption near-edge structure (XANES) spectroscopy and making comparisons to specific heat measurements, we demonstrate the presence of multiconfigurational f-orbital states in the actinide elements U and Pu and in a wide range of uranium and plutonium intermetallic compounds. These results provide a robust experimental basis for a new framework toward understanding the strongly-correlated behavior of actinide materials.
  Proceedings of the National Academy of Sciences 06/2012; 109(26):10205-10209. · 9.68 Impact Factor
• Article: Multiconfigurational nature of 5f orbitals in uranium and plutonium intermetallics.

  C H Booth, Yu Jiang, D L Wang, J N Mitchell, P H Tobash, E D Bauer, M A Wall, P G Allen, D Sokaras, D Nordlund, T-C Weng, M A Torrez, J L Sarrao
  [show abstract] [hide abstract]
  ABSTRACT: Uranium and plutonium's 5f electrons are tenuously poised between strongly bonding with ligand spd-states and residing close to the nucleus. The unusual properties of these elements and their compounds (e.g., the six different allotropes of elemental plutonium) are widely believed to depend on the related attributes of f-orbital occupancy and delocalization for which a quantitative measure is lacking. By employing resonant X-ray emission spectroscopy (RXES) and X-ray absorption near-edge structure (XANES) spectroscopy and making comparisons to specific heat measurements, we demonstrate the presence of multiconfigurational f-orbital states in the actinide elements U and Pu and in a wide range of uranium and plutonium intermetallic compounds. These results provide a robust experimental basis for a new framework toward understanding the strongly-correlated behavior of actinide materials.
  Proceedings of the National Academy of Sciences 06/2012; 109(26):10205-9. · 9.68 Impact Factor
• Article: Coherent energy scale revealed by ultrafast dynamics of UX$_{3}$ (X=Al, Sn, Ga) single crystals

  Saritha K. Nair, J. -X. Zhu, J. L. Sarrao, A. J. Taylor, Elbert E. M. Chia
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  ABSTRACT: Temperature dependence of relaxation dynamics of UX$_{3}$ (X = Al, Ga, Sn) compounds is studied using time resolved pump-probe technique in the reflectance geometry. UGa$_{3}$ is an itinerant antiferromagnet, while UAl$_{3}$ and USn$_{3}$ are spin fluctuation systems. For UGa$_{3}$, our data are consistent with the formation of a spin density wave SDW gap as evidenced from the quasidivergence of the relaxation time $\tau$ near the N\'{e}el temperature $T_{N}$. For UAl$_{3}$ and USn$_{3}$, the relaxation dynamics shows a change from single exponential to two exponential behavior below a particular temperature, suggestive of coherence formation of the 5\textit{f} electrons with the conduction band electrons. This particular temperature can be attributed to the spin fluctuation temperature $T_{sf}$, a measure of the strength of Kondo coherence. Our $T_{sf}$ is consistent with other data such as resistivity and susceptibility measurements. The temperature dependence of the relaxation amplitude and time of UAl$_{3}$ and USn$_{3}$ were also fitted by the Rothwarf-Taylor model. Our results show ultrafast optical spectroscopy is sensitive to c-\textit{f} Kondo hybridization in the \textit{f}-electron systems.
  06/2012;
• Article: Divergence of the Grüneisen Parameter and Magnetocaloric Effect at Heavy Fermion Quantum Critical Points

  P. Gegenwart, Y. Tokiwa, J. G. Donath, R. Küchler, C. Bergmann, H. S. Jeevan, E. D. Bauer, J. L. Sarrao, C. Geibel, F. Steglich
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  ABSTRACT: At any pressure sensitive quantum critical point (QCP) the thermal expansion is more singular than the specific heat leading to a divergence of the Grüneisen parameter. For a magnetic field sensitive QCP, the complementary property is the magnetic Grüneisen ratio which equals the magnetocaloric effect. Here we use both properties to investigate magnetic QCPs in different heavy fermion (HF) metals starting from CeNi2Ge2. The influence of dimensionality on quantum criticality is addressed by the comparison of cubic CeIn3−x Sn x with layered CeMIn5−x Sn x (M=Co, Rh) systems, in which Sn doping both acts as tuning parameter and introduces slight disorder. Near the field-tuned QCP in undoped CeCoIn5 a crossover scale T ⋆ is discovered which separates 2D (at T>T ⋆) from 3D (at T<T ⋆) quantum criticality. Disorder, introduced by Sn-doping, is found to increase T ⋆, stabilizing 3D behavior. We also compare the magnetic Grüneisen ratio in the approach of the field-tuned QCP in YbRh2Si2 with zero-field Grüneisen parameter data on YbRh2(Si1−x Ge x )2 (x=0, x=0.05). Both properties indicate quantum criticality incompatible with the predictions of the itinerant theory. KeywordsQuantum critical point-Heavy fermion systems
  Journal of Low Temperature Physics 04/2012; 161(1):117-133. · 1.19 Impact Factor
• Source

  Available from: ias.ac.in

  Article: Possible Fulde-Ferrell-Larkin-Ovchinnikov inhomogeneous superconducting state in CeCoIn5

  R. Movshovich, A. Bianchi, C. Capan, P. G. Pagliuso, J. L. Sarrao
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  ABSTRACT: We present specific heat and thermal conductivity of the heavy fermion superconductor CeCoIn5 in the vicinity of the superconducting critical fieldH c2, measured with magnetic field in the plane of this quasi-2D compound and at temperatures down to 50 mK. The superconducting phase diagram and the first order nature of the superconducting phase transition at high fields close to a critical fieldH c2 indicate the importance of the Pauli limiting effect in CeCoIn5. In the same range of magnetic field we observe a second specific heat anomaly within the superconducting state, and interpret it as a signature of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) inhomogeneous superconducting state. In addition, the thermal conductivity data as a function of field display a kink at a fieldH k below the superconducting critical field, which closely coincides with the low temperature anomaly in specific heat tentatively identified with the appearance of the FFLO superconducting state. The enhancement of thermal conductivity within the FFLO state calls for further theoretical investigations of the real space structure of the order parameter (and in particular, the structure of vortices) and of the thermal transport within the inhomogeneous FFLO state.
  Pramana 04/2012; 66(1):227-237. · 0.57 Impact Factor
• Source

  Available from: Simon Gerber

  Article: Vortex lattice studies in CeCoIn5 with H is orthogonal to c.

  P Das, J S White, A T Holmes, S Gerber, E M Forgan, A D Bianchi, M Kenzelmann, M Zolliker, J L Gavilano, E D Bauer, J L Sarrao, C Petrovic, M R Eskildsen
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  ABSTRACT: We present small angle neutron scattering studies of the vortex lattice (VL) in CeCoIn5 with magnetic fields applied parallel (H) to the antinodal [100] and nodal [110] directions. For H is parallel to [100], a single VL orientation is observed, while a 90° reorientation transition is found for H is parallel to [110]. For both field orientations and VL configurations we find a distorted hexagonal VL with an anisotropy, Γ=2.0±0.05. The VL form factor shows strong Pauli paramagnetic effects similar to what have previously been reported for H is parallel to [001]. At high fields, above which the upper critical field (H(c2)) becomes a first-order transition, an increased disordering of the VL is observed.
  Physical Review Letters 02/2012; 108(8):087002. · 7.37 Impact Factor
• Article: Complex mixed state of the Pauli-limited superconductor CeCoIn_ {5}

  X. Gratens, L. Mendonça-Ferreira, Y. Kopelevich, Jr. N. F. Oliveira, R. R. Urbano, R. A. Ribeiro, R. Movshovich, J. L. Sarrao, J. D. Thompson, Z. Fisk, P. G. Pagliuso
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  ABSTRACT: Magnetization measurements were performed on CeCoIn5 at temperatures down to 20 mK and magnetic fields up to 17 T applied along different crystallographic orientations. For field configurations nearly parallel to the ab plane (θ≲40∘ and T≤50 mK), we have found an intriguing vortex dynamics regime revealed by a hysteretic and metastable anomalous peak effect (APE), which gives evidence of surface barrier effects enhanced by antiferromagnetic fluctuations in the mixed state of CeCoIn5. Furthermore, we have observed crossover features in the torque and magnetization traces at fields below Hc2, which are consistent with vortices lattice phase transitions and with the anomalies speculated to be the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) superconducting state in CeCoIn5. All of the above features were found to be dramatically perturbed in Ce0.98Gd0.02CoIn5.
  Phys. Rev. B. 02/2012; 85(5).
• Source

  Available from: C. Petrovic

  Article: Vortex lattice studies in CeCoIn5 with H perpendicular to c

  P. Das, J. S. White, A. T. Holmes, S. Gerber, E. M. Forgan, A. D. Bianchi, M. Kenzelmann, M. Zolliker, J. L. Gavilano, E. D. Bauer, J. L. Sarrao, C. Petrovic, M. R. Eskildsen
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  ABSTRACT: We present small angle neutron scattering studies of the vortex lattice (VL) in CeCoIn5 with magnetic fields applied parallel (H) to the antinodal [100] and nodal [110] directions. For H || [100], a single VL orientation is observed, while a 90 degree reorientation transition is found for H || [110]. For both field orientations and VL configurations we find a distorted hexagonal VL with an anisotropy, Gamma = 2.0 +/- 0.05. The VL form factor shows strong Pauli paramagnetic effects similar to what have previously been reported for H || [001]. At high fields, above which the upper critical field (Hc2) becomes a first-order transition, an increased disordering of the VL is observed.
  01/2012;
• Article: Observation of the hybridization gap and Fano resonance in the Kondo lattice URu2Si2

  W. K. Park, P. H. Tobash, F. Ronning, E. D. Bauer, J. L. Sarrao, J. D. Thompson, L. H. Greene
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  ABSTRACT: The nature of the second order phase transition that occurs in URu2Si2 at 17.5 K remains puzzling despite intensive research over the past two and half decades. A key question emerging in the field is whether a hybridization gap between the renormalized bands can be identified as the long-sought 'hidden' order parameter. We report on the measurement of a hybridization gap in URu2Si2 employing a spectroscopic technique based on quasiparticle scattering across a ballistic metallic junction. The differential conductance exhibits an asymmetric double-peak structure, a clear signature for a Fano resonance in a Kondo lattice. The extracted hybridization gap opens well above the transition temperature, indicating that it is not the hidden order parameter. Our results put stringent constraints on the origin of the hidden order transition in URu2Si2 and demonstrate that quasiparticle scattering spectroscopy can probe the band renormalizations in a Kondo lattice via detection of a novel type of Fano resonance.
  10/2011;
• Chapter: From CeIn3 to PuCoGa5: Trends in Heavy Fermion Superconductivity

  J. L. Sarrao, J. D. Thompson
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  ABSTRACT: We review the serendipitous discovery of superconductivity in PuCoGa5 and its relationship to CeMIn5 (M=Co, Ir, Rh). Outstanding issues in our understanding of the phase diagrams of CeMIn5 are also discussed. Finally, we speculate about the relationship between pressure-induced superconductivity in CeIn3 at 200 mK and ambient-pressure superconductivity in PuCoGa5 at 18.5 K and the prospects for other high-temperature unconventional superconductors. Key wordsPuCoGa5 –CeCoIn5 –CeIn3 –Plutonium–Heavy Fermion Superconductivity
  06/2011: pages 345-351;
• Source

  Available from: skku.ac.kr

  Article: Unconventional quantum criticality in the pressure-induced heavy-fermion superconductor CeRhIn(5).

  Tuson Park, V A Sidorov, H Lee, F Ronning, E D Bauer, J L Sarrao, J D Thompson
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  ABSTRACT: The lack of superconductivity in several candidate materials that exhibit a non-spin density wave quantum critical point has raised the question of whether the associated spectra of quantum fluctuations are beneficial to forming superconducting electron pairs. Here we discuss the possibility that the prototypical heavy-fermion antiferromagnet CeRhIn(5) may be the first example of unconventional superconductors where superconductivity arises from Kondo-breakdown quantum criticality.
  Journal of Physics Condensed Matter 02/2011; 23(9):094218. · 2.55 Impact Factor
• Source

  Available from: Peter M. Oppeneer

  Article: Anomalous femtosecond quasiparticle dynamics of hidden order state in URu2Si2

  G. L. Dakovski, Y. W. Li, S. M. Gilbertson, G. Rodriguez, A. V. Balatsky, J. X. Zhu, K. Gofryk, E. D. Bauer, P. H. Tobash, A. Taylor, J. L. Sarrao, P. M. Oppeneer, P. S. Riseborough, J. A. Mydosh, T. Durakiewicz
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  ABSTRACT: At T-0 = 17.5 K an exotic phase emerges from a heavy fermion state in URu2Si2. The nature of this hidden order (HO) phase has so far evaded explanation. Formation of an unknown quasiparticle (QP) structure is believed to be responsible for the massive removal of entropy at the HO transition, however, experiments and ab initio calculations have been unable to reveal the essential character of the QP. Here we use femtosecond pump-probe time-and angle-resolved photoemission spectroscopy (tr-ARPES) to elucidate the ultrafast dynamics of the QP. We show how the Fermi surface is renormalized by shifting states away from the Fermi level at specific locations, characterized by vector q(< 110 >) = 0.56 +/- 0.08 angstrom(-1). Measurements of the temperature-time response reveal that, upon entering the HO, the QP lifetime in those locations increases from 42 fs to few hundred fs. The formation of the long-lived QPs is identified here as a principal actor of the HO.
  Physical Review B. 01/2011; 84(16).
• Article: Electronic structure of single crystal UPd3, UGe2, and USb2 from hard X-ray and angle-resolved photoelectron spectroscopy

  M. F. Beaux, T. Durakiewicz, L. Moreschini, M. Grioni, F. Offi, G. Monaco, G. Panaccione, J. J. Joyce, E. D. Bauer, J. L. Sarrao, M. T. Butterfield, E. Guziewicz
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  ABSTRACT: Electronic structure of single crystal UPd3, UGe2, and USb2 has been measured from hard X-ray photoelectron spectroscopy (HAXPES) with 7.6 keV photons at the European Synchrotron Radiation Facility (ESRF). Lower photon energy angle-resolved photoelectron spectroscopy (ARPES) was also performed at the Synchrotron Radiation Center (SRC). Herein the following results are presented: (1) ARPES results demonstrate hybridization between the U 5f and Pd 4d electrons within UPd3. (ii) The greatly reduced surface sensitivity of HAXPES enabled observation of the bulk core levels in spite of surface oxidation. Photoelectron mean-free-path versus oxide layer thickness considerations were used to model the effectiveness of HAXPES for probing bulk features of in-air cleaved samples. (iii) Two distinct features separated by 800 meV were observed for the Sd 3d core level. These two features are attributed to manifestations of two distinct Sb sites within the USb2 single crystal as supported by consideration of interatomic distances and enthalpy-of-formation. (iv) Doniach-Sunjic line shape analysis of core level spectral features revealed correlations between asymmetry coefficients and 5f localization. (C) 2011 Elsevier B.V. All rights reserved.
  Journal of Electron Spectroscopy and Related Phenomena 01/2011; 184(8-10):517-524. · 1.96 Impact Factor
• Article: Superconducting quantum critical point in CeCoIn(5-x)Sn(x).

  S M Ramos, M B Fontes, E N Hering, M A Continentino, E Baggio-Saitovich, F Dinóla Neto, E M Bittar, P G Pagliuso, E D Bauer, J L Sarrao, J D Thompson
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  ABSTRACT: We report a combined pressure-doping study in the nearly two-dimensional heavy fermion superconductor CeCoIn5 as its superconducting phase is driven to the normal state by Sn doping and/or applied pressure. Temperature-pressure-dependent electrical resistivity measurements were performed at the vicinity of a superconducting quantum critical point where Tc→0. A universal plot of the concentration- and pressure-dependent phase diagram suggests that for the concentrations studied a single mechanism is responsible for reducing Tc and bringing the system to the superconducting quantum critical point. A two-band model with hybridization controlled by pressure and doping provides a consistent description of the phase diagram and the suppression of the d-wave superconductivity in this material.
  Physical Review Letters 09/2010; 105(12):126401. · 7.37 Impact Factor
• Source

  Available from: Kenneth S. Burch

  Article: Hybridization and superconducting gaps in the heavy-fermion superconductor PuCoGa5 probed via the dynamics of photoinduced quasiparticles.

  D Talbayev, K S Burch, Elbert E M Chia, S A Trugman, J-X Zhu, E D Bauer, J A Kennison, J N Mitchell, J D Thompson, J L Sarrao, A J Taylor
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  ABSTRACT: We have examined the relaxation of photoinduced quasiparticles in the heavy-fermion superconductor PuCoGa5. The deduced electron-phonon coupling constant is incompatible with the measured superconducting transition temperature Tc=18.5  K, which speaks against phonon-mediated superconductivity. Upon lowering the temperature, we observe an order-of-magnitude increase of the quasiparticle relaxation time in agreement with the phonon bottleneck scenario--evidence for a hybridization gap in the electronic density of states. The modification of photoinduced reflectance in the superconducting state is consistent with the heavy character of the quasiparticles that participate in Cooper pairing.
  Physical Review Letters 06/2010; 104(22):227002. · 7.37 Impact Factor
• Article: Evidence for a magnetically driven superconducting Q phase of CeCoIn5.

  M Kenzelmann, S Gerber, N Egetenmeyer, J L Gavilano, Th Strässle, A D Bianchi, E Ressouche, R Movshovich, E D Bauer, J L Sarrao, J D Thompson
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  ABSTRACT: We have studied the magnetic order inside the superconducting phase of CeCoIn5 for fields along the [1 0 0] crystallographic direction using neutron diffraction. We find a spin-density wave order with an incommensurate modulation Q=(q,q,1/2) and q=0.45(1), which within our experimental uncertainty is indistinguishable from the spin-density wave found for fields applied along [1 -1 0]. The magnetic order is thus modulated along the lines of nodes of the d{x{2}-y{2}} superconducting order parameter, suggesting that it is driven by the electron nesting along the superconducting line nodes. We postulate that the onset of magnetic order leads to reconstruction of the superconducting gap function and a magnetically induced pair density wave.
  Physical Review Letters 03/2010; 104(12):127001. · 7.37 Impact Factor
• Source

  Available from: J. L. Gavilano

  Article: Observations of Pauli paramagnetic effects on the flux line lattice in CeCoIn5

  J S White, P Das, M R Eskildsen, L DeBeer-Schmitt, E M Forgan, A D Bianchi, M Kenzelmann, M Zolliker, S Gerber, J L Gavilano, J Mesot, R Movshovich, E D Bauer, J L Sarrao, C Petrovic
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  ABSTRACT: From small-angle neutron scattering studies of the flux line lattice (FLL) in CeCoIn5, with magnetic field applied parallel to the crystal c-axis, we obtain the field- and temperature-dependence of the FLL form factor, which is a measure of the spatial variation of the field in the mixed state. We extend our earlier work [A.D. Bianchi et al. 2008 Science 319, 177] to temperatures up to 1250 mK. Over the entire temperature range, paramagnetism in the flux line cores results in an increase of the form factor with field. Near H_c2 the form factor decreases again, and our results indicate that this fall-off extends outside the proposed FFLO region. Instead, we attribute the decrease to a paramagnetic suppression of Cooper pairing. At higher temperatures, a gradual crossover towards more conventional mixed state behavior is observed. Comment: Submitted to New Journal of Physics, 13 pages, 4 figures
  New Journal of Physics 02/2010; 10:023026. · 4.18 Impact Factor
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  Available from: ArXiv

  Article: Scanning Tunneling Microscopy studies on CeCoIn$_5$ and CeIrIn$_5$

  S Ernst, S. Wirth, F. Steglich, Z. Fisk, J. L. Sarrao, J D Thompson
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  ABSTRACT: High--quality single crystals of the heavy fermion superconductors CeCoIn$_5$ and CeIrIn$_5$ have been studied by means of low--temperature Scanning Tunneling Microscopy. Methods were established to facilitate \textit{in-situ} sample cleaving. Spectroscopy in CeCoIn$_5$ reveals a gap which persists to above $T_c$, possibly evidencing a precursor state to SC. Atomically resolved topographs show a rearrangement of the atoms at the crystal surface. This modification at the surface might influence the surface properties as detected by tunneling spectroscopy.
  02/2010;
• Source

  Available from: arxiv.org

  Article: Field-induced coupled superconductivity and spin density wave order in the heavy fermion compound CeCoIn5.

  J Spehling, R H Heffner, J E Sonier, N Curro, C H Wang, B Hitti, G Morris, E D Bauer, J L Sarrao, F J Litterst, H-H Klauss
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  ABSTRACT: The high-field superconducting state in CeCoIn(5) has been studied by transverse field muon spin rotation measurements with an applied field parallel to the crystallographic c axis close to the upper critical field mu(0)H(c2) = 4.97 T. At magnetic fields mu(0)H > or = 4.8 T the muon Knight shift is enhanced and the superconducting transition changes from second order towards first order as predicted for Pauli-limited superconductors. The field and temperature dependence of the transverse muon spin relaxation rate sigma reveal paramagnetic spin fluctuations in the field regime from 2 T < or = mu(0)H < 4.8 T. In the normal state close to H(c2) correlated spin fluctuations as described by the self-consistent renormalization theory are observed. The results support the formation of a mode-coupled superconducting and antiferromagnetically ordered phase in CeCoIn(5) for H directed parallel to the c axis.
  Physical Review Letters 12/2009; 103(23):237003. · 7.37 Impact Factor
• Article: Quantum criticality in layered compared with cubic

  J. G. Donath, F. Steglich, E. D. Bauer, F. Ronning, J. L. Sarrao, P. Gegenwart
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  ABSTRACT: We report low-temperature thermal-expansion measurements on single crystals of the layered heavy fermion system CeRhIn5−xSnx (0.3≤x≤0.6) and compare it with a previous study on the related cubic system CeIn3−xSnx (Küchler R. et al., Phys. Rev. Lett., 96 (2006) 256403). Both systems display a quantum critical point as proven by a divergent Grüneisen ratio. Most remarkably, the three-dimensional itinerant model explains quantum criticality in both systems, suggesting that the crystalline anisotropy in CeRhIn5−xSnx is unimportant. This is ascribed to the effect of weak disorder in these doped systems.
  EPL (Europhysics Letters) 09/2009; 87(5):57011. · 2.17 Impact Factor