Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session H20: Cerium 115 Compounds |
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Sponsoring Units: DCMP GMAG Chair: Nicholas Butch, NIST Room: 280 |
Tuesday, March 14, 2017 2:30PM - 2:42PM |
H20.00001: Anisotropic transport and metamagnetism in microstructured CeRhIn$_5$ Kent R. Shirer, Kimberly A. Modic, Fedor F. Balakirev, Ross D. McDonald, Brad J. Ramshaw, Eric D. Bauer, Filip Ronning, Philip J.W. Moll We present magnetoresistance data on high quality, focused ion beam (FIB)-fabricated microstructures of CeRhIn$_5$, a strongly correlated metal which is antiferromagnetic (AFM) below $T_N \sim 3.8$K due to the local 4f-moments of the cerium. Under applied pressure, the AFM gives way to an unconventional superconducting state in zero magnetic field. Additionally, the AFM, which exhibits a transverse spiral structure, undergoes a metamagnetic transition at $H_c \sim 2$T for magnetic fields applied perpendicular to the c-axis of the crystal. To effectively probe anisotropic properties of the electronic structure, we microstructure samples with extremely well-defined geometries. Microstructures of CeRhIn$_5$ prepared using FIB-techniques demonstrate quantum oscillations, large residual resistivity ratios, and good quantitative agreement with bulk data. We discuss how the AFM transition removes spin scattering anisotropically, and we show a- and c-direction resistivity measurements near the metamagnetic transition as well as its angular dependence. [Preview Abstract] |
Tuesday, March 14, 2017 2:42PM - 2:54PM |
H20.00002: Magnetic frustration in a prototypical strongly correlated electron system David Fobes, S.-Z. Lin, F. Ronning, E.D. Bauer, J.D. Thompson, M. Janoschek, N.J. Ghimire, C.D. Batista, G. Ehlers, V. Hutanu, L. Harriger, R. Bewley Near-degenerate ground states are a common theme in quantum materials, e.g. near a quantum critical point (QCP) emergent phases such as superconductivity (SC) typically compete with other ordered phases. Alternatively, frustrated magnetic interactions may result in degenerate magnetic configurations. In the heavy fermion material CeRhIn$_5$, in which SC emerges near a QCP, we additionally observe frustrated magnetic interactions. Utilizing the Axial Next-Nearest-Neighbor Ising (ANNNI) model, where uniaxial magnetic anisotropy can be induced via the application of magnetic fields, we have quantitatively reproduced the experimental temperature vs. magnetic field phase diagram and spin wave exception spectra. To reproduce this phase diagram we obtained the field-dependent exchange integrals and anisotropy-induced spin wave gaps via neutron spectroscopy and the ordered magnetic moment via hot-neutron-optimized neutron diffraction. An essential consequence of the ANNNI model are nearly-degenerate magnetic microphases near the magnetic ordering temperature, which we confirm via high-resolution neutron diffraction. These results suggest that a complete model of quantum criticality should include magnetic frustration. [Preview Abstract] |
Tuesday, March 14, 2017 2:54PM - 3:06PM |
H20.00003: Pressure dependence of Ce valence in CeRhIn$_{5}$ Zachary Brubaker, Paul Chow, Yuming Xiao, Rena Zieve, Jason Jeffries Though many theoretical descriptions have been put forth, the mechanism facilitating superconductivity in heavy-fermion materials remains a topic of discussion. Magnetic fluctuations are often thought to mediate superconductivity in Ce-based superconductors, but this scenario fails to adequately describe superconductivity far from magnetic order. The critical valence fluctuation (CVF) scenario has been proposed to explain some superconducting domes, including those far from magnetic order, commonly found in the Ce-122 and Ce-115 families. Because the CVF scenario relies on valence fluctuations mediating superconductivity, there should exist a sharp valence crossover near the critical pressure of the material studied. We have studied the Ce valence in CeRhIn$_{5}$ under pressure using x-ray absorption spectroscopy in partial fluorescent yield mode at 300 K. We find a constant Ce valence of 3.0 up to a pressure of 5.5 GPa, far above the predicted valence crossover at P$_{c}=$2.35 GPa. [Preview Abstract] |
Tuesday, March 14, 2017 3:06PM - 3:18PM |
H20.00004: Quantum criticality in CeRh$_{\mathrm{0.58}}$Ir$_{\mathrm{0.42}}$In$_{\mathrm{5}}$: Kondo-breakdown and spin-density critical points Yongkang Luo, Xin Lu, A. P. Dioguardi, P. F. S. Rosa, E. D. Bauer, Qimiao Si, J. D. Thompson An appropriate description of the state of matter that appears as a second order quantum phase transition, \textit{viz}. quantum-critical point (QCP), poses fundamental and still not fully answered questions for both conventional and unconventional QCPs. Experiments are needed both to test their basic conclusions and to guide their further refinement. Here, charge and entropy transport properties of the heavy-fermion compound CeRh$_{\mathrm{0.58}}$Ir$_{\mathrm{0.42}}$In$_{\mathrm{5}}$ measured as a function of pressure, reveal two qualitatively different QCPs in a single material driven by only a non-symmetry-breaking tuning parameter. A discontinuous jump in thermopower signals an unconventional QCP at $p_{c}_{\mathrm{1}}$ accompanied with an abrupt Fermi-surface reconstruction that is followed by a conventional spin-density-wave critical point at $p_{c}_{\mathrm{2}}$ across which the Fermi surface evolves smoothly. Such a sequence of critical points is anticipated by theoretical predictions for a “global” phase diagram of heavy-fermion materials. References: [1] Y. Luo \textit{et al.}, arXiv: 1606.07848 (2016). [Preview Abstract] |
Tuesday, March 14, 2017 3:18PM - 3:30PM |
H20.00005: Maximizing superconducting coupling strength in heavy-fermion hybrid superlattices of CeCoIn$_5$/CeRhIn$_5$ Masahiro Naritsuka, Tomohiro Ishii, Souhei Miyake, Yuichi Kasahara, Takahito Terashima, Yuji Matsuda, Yoshifumi Tokiwa, Masaaki Shimozawa, Takasada Shibauchi, P. F. S. Rosa, Yongkang Luo, Filip Ronning, Joe D. Thompson Interplay between superconductivity and magnetism continues to provide central topics in condensed matter physics. Among others, Ce{\it T}In$_5$ ({\it T} = Co, Rh) compounds offer one of the suitable platforms for the study of this important issue. An intriguing issue concerns coexistence of superconductivity and antiferromagnetism which could be realized at an artificial interface of different materials, but it is not clear how the two different states are affected each other at the interface. Here, by molecular beam epitaxy, we fabricate hybrid superlattices consisting of alternating layers of superconducting CeCoIn$_5$ and antiferromagnetic CeRhIn$_5$. In the hybrid superlattices, we found the presence of both superconducting and antiferromagnetic phases. At ambient pressure, the superconductivity is strongly Pauli limited. On the other hand, with approaching to the quantum critical point of CeRhIn$_5$ layers under applied pressure, the superconductivity is no longer Pauli limited. These results provide the evidence of maximizing superconducting coupling strength in a superlattice structure built of superconducting layer and quantum critical layer. [Preview Abstract] |
Tuesday, March 14, 2017 3:30PM - 3:42PM |
H20.00006: A comparative study of CeCoIn5 and CeIrIn5 using DFT+DMFT Changming Yue, Yilin Wang, Xi Dai We present a comparative study of low temperature properties in heavy fermion materials CeCoIn5 and CeIrIn5 by means of the combination of density function theory and single-site dynamical mean-field theory. An efficient continuous-time quantum Monte-Carlo impurity solver in which charge fluctuations of $f^{n}\rightarrow f^{n\pm1}$ are treated as virtual processes without applying explicit Schrieffer-Wolff transformation is adopted in the simulation. The detailed evolutions of quasi-particle weight, Ce-$4f$ density of states, momentum-resolved spectral functions and specific heat etc., are calculated in a temperature range $T\in[10,100]$K. Upon decreasing temperature, both materials emerge heavily renormalized quasi-particle bands which are consistent with the ARPES experiments. Furthermore, we find that CeIrIn5, with a higher density states and a wider dispersion near Fermi level, is more itinerant than CeCoIn5. [Preview Abstract] |
Tuesday, March 14, 2017 3:42PM - 3:54PM |
H20.00007: 3D Fermi Surface of CeCoIn$_5$ from ARPES and DMFT J.D. Denlinger, Sooyoung Jang, J.W. Allen, V.S. Zapf, M.B. Maple, Jae Nyeong Kim, Bo-Gyu Jang, Ji Hoon Shim The three-dimensional Fermi surface (FS) of the Kondo lattice system CeCoIn$_5$ is determined using angle-resolved photoemission (ARPES) with comparison to first principles dynamical mean field theory (DMFT) calculations. Photon-, angle- and polarization-dependent ARPES mapping of the electronic structure from two orthogonal (001) and (100) cleaved surfaces reveals the deficiencies of both $f$-$itinerant$ and $f$-$localized$ density functional theory (DFT) calculations. While the well-known quasi-2D $\alpha$ sheet and the 3D $\beta$ sheet FS topologies are well described by $itinerant$ DFT, a complex $\gamma$ hole-like FS topology centered on $Z$ is newly revealed which exists only in the $localized$ DFT, and yet it hosts strong $f$ spectral weight as highlighted by Ce 4$d$-4$f$ resonant ARPES. DMFT is shown to capture the low energy scale participation of $f$ electrons in the $localized$-$like$ FS topology in agreement with ARPES, as well as reveal insights into the origins of differing effective masses of FS sheets from the complex hybridization interaction with the ground-state and first-excited CEF $f$-levels. [Preview Abstract] |
Tuesday, March 14, 2017 3:54PM - 4:06PM |
H20.00008: Atomic-scale spatial modulation of zero-bias conductance in CeCoIn$_{5}$ Yasuo Yoshida, Howon Kim, Yasuhiro Tada, Yukio Hasegawa, Michi-to Suzuki, Yoshinori Haga, Naoyuki Tateiwa, Zachary Fisk Understanding the pairing mechanism of unconventional superconductivity has been a long-standing problem in condensed matter physics. Scanning tunneling microscopy (STM) has been utilized to pursue the pairing mechanism especially on high-$T_{C}$ cuprates and recently on the heavy fermion superconductor CeCoIn$_{5}$. However, the observed superconducting gap spectrum on CeCoIn$_{5}$ contains unexpectedly large zero-bias conductance (ZBC) even well below the critical temperature. By performing precise low-temperature STM measurements, we found that the amount of ZBC is larger on In sites and smaller on Ce sites in CeIn planes. We interpret this atomic-scale modulation as a consequence of different hybridization strengths of Ce 5$d$ and In 4$p$ bands with Ce 4$f$ band, indicating that both the unexpected ZBC and the spatial modulation are attributed to the fact that Ce 4$f$ electrons indeed play a main role for the superconductivity. [Preview Abstract] |
Tuesday, March 14, 2017 4:06PM - 4:18PM |
H20.00009: Enhanced Thermal Transport along the Nodal Direction of d-wave Superconductor CeCoIn$_5$ Roman Movshovich, Duk Y. Kim, Shi-Zeng Lin, Franziska Weickert, Eric D. Bauer, Filip Ronning, J. D. Thompson Four-fold oscillation in thermal conductivity with respect to the direction of the magnetic field is a strong evidence of a $d$-wave superconductivity. Previously, a smooth oscillation was found when the thermal conductivity of unconventional superconductor CeCoIn$_5$ was measured along [100], the anti-nodal direction for its $d_{x^2-y^2}$-wave order parameter, with magnetic field rotating in the $ab$-plane. We present measurements of the thermal conductivity in CeCoIn$_5$ with the heat current along the [110], nodal, direction. A sharp resonance-like peak in thermal conductivity was observed when the magnetic field is also in the [110] direction, parallel to the heat current. We can qualitatively understand this zero-angle resonance within the present theory for the heat transport in $d$-wave superconductors. The theory, however, fails to quantitatively reproduce the details of the field-evolution of the data. The contribution of the vortex core states and Pauli limiting effect should be considered to develop a realistic theory for the thermal transport in unconventional superconductors. [Preview Abstract] |
Tuesday, March 14, 2017 4:18PM - 4:30PM |
H20.00010: Thermal Transport in Nd-doped CeCoIn$_5$ Duk Y. Kim, Shi-Zeng Lin, Franziska Weickert, P. F. S. Rosa, Eric D. Bauer, Filip Ronning, J. D. Thompson, Roman Movshovich Heavy-fermion superconductor CeCoIn$_5$ shows spin-density-wave (SDW) magnetic order in its superconducting state when a high magnetic field is applied. In this $Q$-phase, the antiferromagnetic order has a single ordering wave vector, and switches its orientation very sharply as magnetic field is rotated within the $ab$-plane around the [100] (anti-nodal) direction. This hypersensitivity induces a sharp jump of the thermal conductivity. Recently, the SDW with the same ordering wave vector was observed in Nd-doped CeCoIn$_5$ in zero magnetic field. We have measured the thermal conductivity of 5\% Nd-doped CeCoIn$_5$ in the magnetic field rotating within the $ab$-plane. The anisotropy is significantly smaller in the doped material, and the switching transition is much broader. The superconducting transition near $H_{c2}$ is first order, as for the pure CeCoIn$_5$, which indicates the Pauli limited superconductivity. [Preview Abstract] |
Tuesday, March 14, 2017 4:30PM - 4:42PM |
H20.00011: Real space visualization of Kondo holes in Zn-doped CeCoIn$_{\mathrm{5}}$ thin films studied by STM. Masahiro Haze, Yohei Torii, Yosuke Hanaoka, Shigeru Kasahara, Yuichi Kasahara, Takahito Terashima, Tetsuo Hanaguri, Yuji Matsuda The effects of magnetic impurities in a metal, i.e. “Kondo impurities”, have been well established and extensively studied experimentally and theoretically. At low temperatures, magnetic moments of the impurities are screened by conduction electrons through the Kondo effect. On the other hand, the roles of nonmagnetic impurities in a periodic lattice consisted of $f$-electron atoms, i.e. “Kondo holes”, have been unclear, because of the lack of local measurements. However, the Kondo holes have significant attentions due to the complex many-body effects by the Coulomb interaction. Here, in order to investigate the Kondo holes, we performed measurements of scanning tunneling microscopy (STM), which can reveal the electronic structure with high energy and spatial resolution. Although it is difficult to obtain atomically flat surfaces in bulk crystals, we have successfully prepared atomically flat thin films of Zn-doped CeCoIn$_{\mathrm{5\thinspace }}$by molecular beam epitaxy (MBE) and performed\textit{ in situ} STM measurements. We clearly resolved the spatial modulation of local density of states around the Kondo holes caused by the suppression of the hybridization. We also discuss quasi-particle interference patterns in Zn-doped CeCoIn$_{\mathrm{5}}$. [Preview Abstract] |
Tuesday, March 14, 2017 4:42PM - 4:54PM |
H20.00012: High temperature heaviness in CeCoIn$_5$ Sooyoung Jang, J.D. Denlinger, J.W. Allen, V. S. Zapf, M.B. Maple, Jae Nyeong Kim, Bo-Gyu Jang, Ji Hoon Shim The temperature-dependent evolution of the Kondo lattice is a long-standing topic of theoretical and experimental investigation and yet it lacks a truly microscopic description of the relation of the basic $f-d$ hybridization processes to the fundamental $T$ scales of Kondo screening and Fermi-liquid lattice coherence. The $T$-dependence of $f-d$ hybridization dispersions and $f$ spectral weight in the Kondo lattice system CeCoIn$_5$ is investigated using $f$-resonant angle-resolved photoemission (ARPES) with comparison to first principles dynamical mean field theory (DMFT) calculations. Three different $f-d$ hybridization scenarios at different $k$-locations of the Fermi surface(FS) are measured from two orthogonal (001) and (100) cleaved surfaces. In contrast to a commonly accepted belief that $f-d$ hybridization occurs only below the lattice coherence temperature of $T^*$ $\sim$ 45 K, ARPES, in agreement with DMFT, reveals $f$ participation in the FS at temperatures much higher than $T^*$, well into the incoherent partial-screening regime of logarithmic Kondo-coupling spin-flip scattering. [Preview Abstract] |
Tuesday, March 14, 2017 4:54PM - 5:06PM |
H20.00013: Cd-doped CeCoIn5 NMR Data Under Pressure Blaine Bush, Lawrence Simon, AJ LaPanta, Nicholas Curro We present nuclear magnetic resonance (NMR) data on the heavy fermion compound Cd-doped CeCoIn$_5$, in particular CeCo(In$_{1-x}$Cd$_x$)$_5$, $x=0.075$. NMR spectra for the $^{115}$In and $^{59}$Co nuclei were collected, both under pressure and at ambient pressure. The Cd doping introduces impurities which increase antiferromagnetic order and suppress superconductivity. The onset of antiferromagnetism can be seen in splitting of $^{115}$In peaks as islands of magnetic order nucleate around Cd sites. [Preview Abstract] |
Tuesday, March 14, 2017 5:06PM - 5:18PM |
H20.00014: Impurities near an Antiferromagnetic-Singlet Quantum Critical Point Tiago Mendes Santos, Natanael Costa, Thereza Paiva, Raimundo dos Santos, George Batrouni, Nicholas Curro, Richard Scalettar Heavy fermion systems, and other strongly correlated electron materials, often exhibit a competition between antiferromagnetic (AF) and singlet ground states. Using exact Quantum Monte Carlo (QMC) simulations, we examine the effect of impurities in the vicinity of such AF-singlet quantum critical points, through an appropriately defined ``impurity susceptibility," $\chi_{\rm imp}$. Our key finding is a connection, within a single calculational framework, between AF domains induced on the singlet side of the transition, and the behavior of the nuclear magnetic resonance (NMR) relaxation rate $1/T_1$. We show that local NMR measurements provide a diagnostic for the location of the QCP which agrees remarkably well with the vanishing of the AF order parameter and large values of $\chi_{\rm imp}$. We will also discuss the temperature dependence of the linewidth of the NMR spectrum. We connect our results with experiments on Cd-doped CeCoIn$_5$. [Preview Abstract] |
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