Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session B22: Quantum Criticality and Novel Phases in felectron SystemsInvited

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Sponsoring Units: DCMP Chair: Joe Thompson, Los Alamos National Laboratory Room: New Orleans Theater A 
Monday, March 13, 2017 11:15AM  11:51AM 
B22.00001: Quasi1D heavy fermion magnet Yb$_2$Pt$_2$Pb in Magnetic Field Invited Speaker: William Gannon The Yb$^{3+}$ ions in Yb$_2$Pt$_2$Pb form large, seemingly classical Ising magnetic moments, with the large spinorbit coupling of the 4felectrons and the crystal electric field forming a $J=\pm 7/2$ Yb ground state doublet [1]. However, from this unlikely host, emerges a continuum of quantum excitations  spinons on one dimensional chains  in good agreement with the behavior expected for nearly isotropic, $S=\pm 1/2$, delectron magnetic moments [2]. These spinons, in a system with orbitally dominated magnetic constituents, are robust and at low temperatures exist up to 2.3 T, when all Yb magnetic moments become saturated. In magnetic fields larger than 0.5 T, the spinon gap is closed, modifying the quantum continuum through the formation of a fermi surface and spinon bound states between the Yb chains. The ground state doublet nature of the Yb ions ensures that at all fields, transverse excitations are virtually nonexistent, giving unprecedented access to only the longitudinal excitation channel without the presence of spin waves or other transverse damping mechanisms.\newline [1] M. S. Kim, \textit{et al.}, \textit{Phys. Rev. B.} \textbf{77}, 144425 (2008); K. Iwakawa \textit{et al.}, \textit{J. Phys. Soc. Jpn.} \textbf{81}, SB058 (2012);Y. Shimura \textit{et al.}, \textit{J. Phys. Soc. Jpn.} \textbf{81} 103601 (2012); M. S. Kim and M. C. Aronson, \textit{Phys. Rev. Lett} \textbf{110}, 017201 (2013); W. Miiller \textit{et al.}, \textit{Phys. Rev. B} \textbf{93}, 104419 (2016). [2] L. S. Wu \textit{et al.}, \textit{Science} \textbf{352}, 1206 (2016). [Preview Abstract] 
Monday, March 13, 2017 11:51AM  12:27PM 
B22.00002: Quantum criticality in geometrically frustrated heavyfermion systems Invited Speaker: Philipp Gegenwart Study of geometrically frustrated Kondo lattices has been motivated by the prediction of unconventional quantum criticality and metallic quantum spin liquid states. We focus on heavyfermion metals YbAgGe, CePdAl and CeRhSn. All of them crystallize in the hexagonal ZrNiAl structure with 4f moments forming a distorted kagom\'{e} network. Using magnetic field, chemical substitution as well as uniaxial pressure, various quantum critical points are investigated by millikelvin thermodynamic experiments. In YbAgGe quantumbicriticality is induced by magnetic field, leading drastic nonFermi liquid effects [1,2]. For CePd$_{\mathrm{1x}}$Ni$_{\mathrm{x}}$Al twodimensional (2D) AF quantum criticality arises at the suppression of 3D magnetic order and signatures of magnetic frustration remain even beyond the quantum critical point [3]. In CeRhSn evidence for quantum criticality induced by geometrical frustration has been found [4] and frustration is modified using uniaxial pressure. [1] J. Dong, Y. Tokiwa, S. L. Bud'ko, P. C. Canfield, P. Gegenwart, Phys. Rev. Lett. 110 (2013) 176402. [2] Y. Tokiwa, M. Garst, P. Gegenwart, S.L. Bud'ko, P.C. Canfield, Phys. Rev. Lett. 111 (2013) 116401. [3] A. Sakai, S. Lucas, P. Gegenwart, O. Stockert, H.v. L\"{o}hneysen, V. Fritsch, arXiv:1609.00816. [4] Y. Tokiwa, C. Stingl, M.S. Kim, T. Takabatake, P. Gegenwart, Sci. Adv. 1, e1500001 (2015). [Preview Abstract] 
Monday, March 13, 2017 12:27PM  1:03PM 
B22.00003: Global phase diagram and quantum criticality of the Isinganisotropic Kondo lattice Invited Speaker: Emilian Marius Nica Heavy fermion systems provide a prototype setting to study quantumphase transitions in stronglycorrelated systems. Experiments on many quantum critical heavyfermion metals have provided strong evidence for quantum criticality beyond the Landau framework, with magnetic order developing at a breakdown of the underlying Kondo effect and involving an abrupt collapse of the entire Fermi surface. To account for this local quantum criticality along with other possible types of quantum phase transitions, a global phase diagram has emerged [1] which, in addition to the competition between the Kondo effect and the tendency towards magnetism, also considers the effects of the quantum fluctuations of the local moments. Motivated by these developments, we investigated the effect of enhanced quantum fluctuations induced by a transverse magnetic field in an Isinganisotropic Kondo lattice model [2]. Solved within an extended dynamical mean field theory using the numerical renormalization group, our work represents one of the very first concrete theoretical studies on the interplay between the Doniach tuning of RKKY vs. Kondo interactions and the localmoment quantum fluctuations. We demonstrate that local quantum criticality survives along a line of critical points with unchanged critical exponents. In addition to elucidating the theory of the Global Phase Diagram, our results also motivate new experimental tests of this T$=$0 phase diagram. Work done in collaboration with Kevin Ingersent and Qimiao Si. [1] Q. Si, Physica B 378, 23 (2006); P. Coleman and A. Nevidomsky, J. Low. Temp. Phys. 161, 182 (2010). [2] E. M. Nica, K. Ingersent, and Q. Si, arXiv:1603.03829 (2016). [Preview Abstract] 
Monday, March 13, 2017 1:03PM  1:39PM 
B22.00004: Preserved Entropy, quantum criticality and fragile magnetism Invited Speaker: Paul Canfield A large swath of strongly correlated electron systems can be associated with the phenomenon of preserved entropy and fragile magnetism. In this talk I will present our thoughts and plans for the discovery and development of lanthanide and transition metal based, strongly correlated systems that are revealed by suppressed, fragile magnetism or grow out of preserved entropy. This talk is based on work published in Rep. Prog. Phys. 79 (2016) 084506 [Preview Abstract] 
Monday, March 13, 2017 1:39PM  2:15PM 
B22.00005: Emergent Phases in Heavy Fermions: a Magnetic Substitution Study Invited Speaker: Priscila Rosa Unconventional superconductivity frequently is found as an antiferromagnetic transition is tuned by chemical substitution or applied pressure toward a zerotemperature phase transition, a magnetic quantumcritical point. Different classes of unconventional superconductors (e.g. heavyfermions, cuprates, and Febased) display a collective magnetic excitation in their superconducting state, and a universal relationship exists between the energy of this spin resonance mode and the superconducting gap. In this talk, I will focus on the heavyfermion family of unconventional superconductors Ce$T$In$_{5}$ ($T =$ Co, Rh). I will show evidence for an emergent spindensity wave phase below the superconducting dome in pressurized CeRhIn$_{5}$ containing small amounts of magnetic substitution in the Ce site. This phase can be understood as the condensation of the spin resonance mode, providing a universal scenario for these materials. [Preview Abstract] 
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