Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session F44: URu2Si2 and Related Actinides/Lanthanides |
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Sponsoring Units: DCMP Chair: John van Dyke, Iowa State U. Room: LACC 504 |
Tuesday, March 6, 2018 11:15AM - 11:27AM |
F44.00001: Topological Excitations of Hidden Order in URu2Si2 Under Extreme Electric Fields Laurel Winter, Arkady Shekhter, Brad Ramshaw, Neil Harrison, Eric Bauer, Philip Moll, Ross McDonald The macroscopic properties of quantum materials are heavily influenced by collective modes, however there are only a few examples where the coherence of the ground-state wavefunction directly contributes to the conductivity. Notable examples include the collective sliding of charge density waves when subjected to high electric fields and the macroscopic phase coherence that enables superconductors to carry dissipationless currents. In the long-studied heavy fermion URu2Si2 we observe such a connection between the quantum and macroscopic worlds in the low temperature hidden order state. Under large voltage bias non-linear contributions to the conductivity are observed that are directly analogous to the manifestation of phase slip centers in one-dimensional superconductors. LA-UR-17-30109 |
Tuesday, March 6, 2018 11:27AM - 11:39AM |
F44.00002: Structural studies of URu2Si2 near the hidden order transition using X-ray crystallography Xiaolan Sun, John Mydosh, M Brian Maple, Hsiang-Hsi Kung, Sangjun Lee, Gilberto De La Pena, Girsh Blumberg, Peter Abbamonte URu2Si2 is known for its hidden order transition at T=17.5K whose physical origin is still not agreed. We present an x-ray crystallographic study of the structure of URu2Si2 over the temperature range 23 K < T < 5.5 K. Using a large, image plate detector, we recorded 32 reflections and performed a full structure refinement at each temperature. We found that, as the temperature is lowered, the spacegroup of the crystal does not change, but the Si atoms translate along the b axis by 0.78Å (0.19 b) in response to the hidden order transition. Our study suggests that the order parameter associated with this transition is weakly coupled to a Si phonon of Eu symmetry. |
Tuesday, March 6, 2018 11:39AM - 11:51AM |
F44.00003: Rapid Suppression of the Energy Gap and the Possibility of a Gapless Hidden Order State in URu2-xRexSi2 Sheng Ran, George Schmiedeshoff, Naveen Pouse, Inho Jeon, Nicholas Butch, Ram Adhikari, Carmen Almasan, M Brian Maple We investigated the energy gap associated with the hidden order (HO) phase and the Gruneisen ratio in the URu2-xRexSi2system using a combination of thermal expansion coefficient and specific heat measurements. As the HO phase transition is suppressed to lower temperature, the ratio between the energy gap and the HO transition temperature decreases by three-fold. This rapid suppression of the energy gap potentially leads to a scenario of a "gapless" HO state, in which the energy gap of the HO phase vanishes before the HO transition temperature is suppressed to 0 K. We also investigated the Gruneisen ratio in the vicinity of the Re substituent composition where the HO is suppressed. The Gruneisen ratio shows divergent behavior at x = 0.12 and 0.15, providing evidence for the existence of a quantum critical point, which is consistent with our hypothesis of a "gapless" HO state. |
Tuesday, March 6, 2018 11:51AM - 12:03PM |
F44.00004: The effect of pressure and chemical substitution on the ordered phases in the URu2-xMxSi2 (M = Fe, Os) systems Christian Wolowiec, Sheng Ran, Inho Jeon, Naveen Pouse, Kevin Huang, Noravee Kanchanavatee, M Brian Maple We investigated the effect of applied pressure and chemical substitution on the hidden order (HO) and antiferromagnetic (AFM) phases in URu2Si2 and report electrical resistivity measurements of single crystals of URu2−xMxSi2 (M = Fe, Os) under pressure. A transition from the HO phase to the AFM phase in URu2Si2 occurs at a critical pressure of 1.5 GPa. The AFM phase is also induced upon substitution of Fe or Os ions for Ru at ambient pressure. We observed that as x is increased in URu2−xFexSi2, less external pressure is required to induce the AFM phase. This is explained by the reduction in unit cell volume owing to the substitution of smaller Fe ions for Ru, which may be interpreted as a chemical pressure. We also observed that as y is increased in URu2−yOsySi2, less external pressure is required to induce the AFM phase. This is contrary to the expectation that larger pressures would be required to induce the AFM phase in a system biased with a negative chemical pressure owing to the substitution of larger Os ions for Ru. This suggests that effects other than volume change may be responsible for the HO to AFM transition. |
Tuesday, March 6, 2018 12:03PM - 12:15PM |
F44.00005: Angular-dependent magnetoresistance measurements on single crystals of URu2-xFexSi2 in high magnetic fields Naveen Pouse, John Singleton, Fedor Balakirev, Ryan Baumbach, David Graf, You Lai, Kevin Huang, Sheng Ran, Christian Wolowiec, Inho Jeon, Noravee Kanchanavatee, M Brian Maple Magnetoresistance measurements with the current in the basal plane were performed on single crystals of URu2-xFexSi2 as a function of magnetic field H, angle θ of H with respect to the c-axis, and temperature T for several Fe concentrations x in the “hidden order” (HO) and large moment antiferromagnetic (LMAFM) regions of the T vs. x phase diagram. Measurements were made in DC fields of up to 33 T and pulsed fields of up to 65 T at the National High Magnetic Field Laboratories at Tallahassee and at Los Alamos, respectively. The Fourier components of the angular-dependence of the magnetoresistance for rotation about an axis through the basal plane were mapped out as a function of H, θ, T, and x through the HO and LMAFM phase transitions and the dependences of the HO and LMAFM transition temperatures on θ, H, and x were determined. |
Tuesday, March 6, 2018 12:15PM - 12:27PM |
F44.00006: Exploring Hidden Order through Co and Ir substitution in URu2Si2 Kalyan Sasmal, Trevor Keiber, Sheng Ran, Christian Wolowiec, Inho Jeon, Robert Robinson, Bob Wang, Noravee Kanchanavatee, M Brian Maple Hidden-order (HO) phase in heavy-fermion superconductor (SC) is an intriguing phenomena. Doping URu2Si2 at the Ru sites reveals how factors such as lattice constants, charge carriers, disorder and d- f- electron hybridization influence the HO phase and SC. The effects of M = Co, Ir substitution in URu2-xMxSi2 for low concentrations of x, are interpreted from x-ray diffraction, resistivity, DC magnetic susceptibility, and specific heat measurements. The features from physical property measurements which characterize the gapping of HO phase become vanishingly small with substitution, so that by x = 0.09 the HO phase is not discernible. For Co substitution, the HO and SC phase transition temperatures (THO and TSC) both decrease monotonically with concentration. With Ir, there is a much smaller suppression of TSC, and a non-monotonic evolution of THO with x. The results for M = Co, Ir indicative of a parasitic AFM phase, which has been shown to emerge in the HO region for Rh substitution are discussed. We compare THO, TSC, lattice constants and the magnitude of the HO feature of Co and Ir with reported M = Rh, P, Fe and Re. Our study offer a new insight into various intriguing ordered phases. |
Tuesday, March 6, 2018 12:27PM - 12:39PM |
F44.00007: Characterization of multiple phases in URu2-xMxSi2 for M = Co, Ir Trevor Keiber, Sheng Ran, Kalyan Sasmal, Christian Wolowiec, Inho Jeon, Noravee Kanchanavatee, Robert Robinson, Bob Wang, M Brian Maple The heavy-fermion compoundURu2Si2 was substituted with M = Co and Ir to form polycrystalline samples of the pseudo-ternary system URu2-xMxSi2. Phase diagrams are presented based on electrical resistivity, magnetization, specific heat, and x-ray diffraction measurements. Substitution with M = Co and Ir suppresses the hidden order features by x = 0.1, after which, no ordering is observed for 0.1 < x < 0.3. For M = Ir, an antiferromagnetic phase (AFM-1) gradually emerges with a Néel temperature (TN1) that increases from TN1 = 28 to 40 K over the region 0.3 < x < 0.5. At x = 0.5, the AFM-1 phase separates into three distinct peaks, each of which persists with little temperature change until x = 1.0. For higher x, there is again a region with no ordered phase, which persists until a structural phase transition occurs at x = 1.35. For M = Co, an AFM-2 phase emerges at x = 1.0 with TN2 = 80 (5) K; the phase boundary varies with x reaching a maximum of TN2 = 106 (5) K. The results of this study are compared with previous studies for M = Rh, Fe, Os, Re, and P in the context of electron doping, the chemical pressure, and structural disorder. |
Tuesday, March 6, 2018 12:39PM - 12:51PM |
F44.00008: Quantum oscillations and the collapse of hidden order in electron doped URu2Si2 Kevin Huang, Kuan-Wen Chen, Andrew Gallagher, You Lai, William Nelson, David Graf, Thomas Albrecht-Schmitt, Ryan Baumbach We have performed magneto-resistance measurements for single crystals of URu2Si2-xPx (x = 0, 0.006, 0.01, 0.02, and 0.102) in magnetic fields up to 45 T and down to 70 mK. Measurements were performed with the angle between the field and crystalline axes varied from θ = 0° - 120°, where θ = 0° for H // [100] and θ = 90° for H // [001]. Quantum oscillations are detected up to x = 0.02 and are most visible when H is nearly parallel to [100] owing to the large anisotropy of the field induced ordered phases. From this, we are able to describe the evolution of the Fermi surface topology with electron doping as hidden order collapses towards the paramagnetic state at low temperatures. At two angles, θ = 76° and 90°, temperature sweeps were performed up to ~700 mK. From Lifshiftz-Kosevich fits to the quantum oscillations amplitudes we find that the substitution dependent quasiparticle effective mass μeff displays a maximum at x = 0.01, consistent with earlier evidence from heat capacity measurements for an unexpected electronic instability in this x-range. |
Tuesday, March 6, 2018 12:51PM - 1:03PM |
F44.00009: Correlation between the hybridization process and emergent ground states in URu2Si2-xPx Shengzhi Zhang, Paul Tobash, Eric Bauer, Filip Ronning, Joe Thompson, Greta Chappell, Ryan Baumbach, Laura Greene, Wan Kyu Park The origin of the hidden order in URu2Si2 remains to be elucidated despite intensive investigations. Our previous study based on quasiparticle scattering spectroscopy (QPS) showed that a hybridization gap opens up well above the hidden order transition temperature, indicating that it is not responsible for the hidden order transition [1]. This is naturally understood by considering the hybridization process as a generic mechanism for emergent heavy fermi liquids in Kondo lattice systems. Then, how different is it in a system where a quantum critical parameter is tuned to result into different ground states? To address this question, we extend our QPS study into URu2Si2-xPx, which has recently been found to exhibit transitions into no-ordered and antiferromagnetic phases with increasing phosphorous content [2]. We will present conductance spectra obtained from this system spanning a wide phase space and discuss the implications of our results. [1] W. K. Park et al., Phys. Rev. Lett. 108, 246403 (2012); [2] A. Gallagher et al., Nature Commun. 7, 10712 (2016). |
Tuesday, March 6, 2018 1:03PM - 1:15PM |
F44.00010: Novel Canonical Heavy Fermion Compound Eteri Svanidze, Alfred Amon, Michael Nicklas, Andreas Leithe-Jasper, Yuri Grin The field of heavy fermion physics emerged nearly four decades ago and has since become one of the central research directions of condensed matter physics. While significant progress has been made in understanding heavy fermion behavior and accompanying phenomena, the global trends still remain unclear. One of the avenues in the search for heavy fermions has focused on compounds with high coordination, and, therefore, low concentration of uranium atoms. This approach has proven fruitful in the case of antiferromagnetic U2Zn17 and UCd11, as well as unconventional superconductor UBe13. The two former compounds are also the only two canonical heavy fermions. In this work, we present the discovery of the third canonical heavy fermion U11Hg45. This compound exhibits an antiferromagnetic transition at TN = 2 K, which can be suppressed by application of magnetic field. A high value of the Sommerfeld coefficient γ = 0.6 J/U mol K2 is likely related to the itineracy of the f-electrons, as evidenced by the high value of the Rhodes-Wohlfarth ratio along with the small entropy of the antiferromagnetic transition. |
Tuesday, March 6, 2018 1:15PM - 1:27PM |
F44.00011: Physical Properties of Topological PuB4 and PuB6 Compounds Eric Bauer, Adam Dioguardi, H. Yasuoka, Samantha Schrell, Laurel Winter, Hongchul Choi, W. Zhu, Paul Tobash, Ross McDonald, Stosh Kozimor, Jian-Xin Zhu, Thomas Albrecht-Schmitt, Joe Thompson, Filip Ronning The prediction and subsequent discovery of topological insulators with conducting surface states has attracted widespread attention [1,2]. While much of the research has focused on topological states without electronic correlations (e.g. Bi2Se3), the discovery of a conducting surface state in the Kondo insulator SmB6 has opened up the possibility of finding new examples of correlated topological insulators [3,4]. Actinide compounds, with their larger overlap of the f-electron orbitals with neighboring ligand orbitals, often have larger characteristic energy scales and provide fertile ground for searching for new and interesting topological materials. Indeed, Dynamical Mean Field Theory predicts that PuB6 should be a topological insulator with similar properties to those of SmB6 [5]. Here, we report the physical properties of PuB4 and PuB6 topological materials. |
Tuesday, March 6, 2018 1:27PM - 1:39PM |
F44.00012: Electronic Structure and Topological Classification of PuB4 Hongchul Choi, Wei Zhu, Samantha Schrell, Laurel Winter, Zhoushen Huang, Ross McDonald, Filip Ronning, Jian-Xin Zhu Topological insulators (TIs) have recently attracted intense theoretical and experimental interest for the existence of topologically-protected surface states in an otherwise insulating bulk. In the topological insulators, the spin-orbit coupling (SOC) plays an important role in locking the spin and momentum of electronic states. Since 5f-electrons maintain an intrinsically strong SOC, Kondo insulators will be an excellent candidate in the search of TIs. In this talk, we present our first-principles study of electronic structure and topological property of PuB4 in comparison with PuB6. We show how the SOC dramatically changes the band structure in these Pu compounds. The topological property is then analyzed by calculating the Z2 topological invariant in the Wilson loop method, and we show the surface electronic states from the calculations of the slab structure. The effects of electronic correlations are also discussed, and the results are compared against experiment. |
Tuesday, March 6, 2018 1:39PM - 1:51PM |
F44.00013: Orbital-dependent correlations in PuCoGa$_5$ Walber Hugo De Brito, Sangkook Choi, Gabriel Kotliar Among the group of Pu-based compounds, PuCoGa$_5$ has attracted major interest since its superconductivity develops at |
Tuesday, March 6, 2018 1:51PM - 2:03PM |
F44.00014: Staggered Hastatic order: the role of magnetic field and relevance to PrV2Al20 Guanghua Zhang, John Van Dyke, Rebecca Flint Materials with a non-Kramers doublet ground state exhibit valence fluctuations to an excited Kramers doublet, realizing the two channel Kondo effect and requiring that any heavy Fermi liquid breaks some symmetry. PrV2Al20, which has a cubic Γ3 4f2 non-Kramers doublet ground state and displays strong conduction and f electron coupling, serves as a promising candidate. However, its phase diagram in magnetic field is still a puzzle. Here, we explore the channel symmetry breaking heavy Fermi liquid, also known as hastatic order, within a simple two-channel Kondo-Heisenberg model. Particularly, we investigate the competition or cooperation among a uniform or staggered hastatic order and magnetism, and how that is affected by magnetic field. We show that, with reasonable parameters, one can roughly reproduce the PrV2Al20 in-field phase diagram. We find that as the magnetic field increases, the system undergoes a first order transition from staggered into uniform hastatic order, which then is also suppressed by higher field. We also discuss possible experimental measurements are to test these results. |
Tuesday, March 6, 2018 2:03PM - 2:15PM |
F44.00015: Comparing hastatic and quadrupolar order in cubic Pr-1-2-20 systems John Van Dyke, Guanghua Zhang, Rebecca Flint Non-Kramers doublet materials can host a variety of interesting phases including quadrupolar order, superconductivity, and hastatic order. The latter state is a symmetry-breaking heavy Fermi liquid or Kondo insulator arising from valence fluctuations of the non-Kramers level to an excited Kramers doublet. We use a slave boson mean-field analysis of a simple yet realistic two-channel Anderson lattice model to contrast the experimental signatures of the spatially uniform hastatic state with those of ferroquadrupolar order, noting the challenges in distinguishing the two states experimentally. In particular, measurements of time-reversal symmetry breaking are found to be essential. These issues are exemplified by the PrT2Al20 (T=Ti, V) materials. In PrTi2Al20, ferroquadrupolar ordering was observed without evidence of hastatic order. The situation is more complicated for PrV2Al20, where a suspected antiferroquadrupolar phase undergoes a first order transition in magnetic field below 2 T. We discuss the possibility that this feature represents the development of the hastatic ordered state, and how this scenario may be experimentally tested. |
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