Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session R06: Quantum Phase Transitions and Critical Points |
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Sponsoring Units: DCMP Chair: Raquel Ribeiro, Universidade Federal do ABC Room: BCEC 109A |
Thursday, March 7, 2019 8:00AM - 8:12AM |
R06.00001: Anomalous critical exponents in itinerant ferromagnets Ni_{1-x}Rh_{x} (x = 0.3 - 0.375) close to a quantum phase transition Chien-Lung Huang, Bianca Spiess, Sebastian Kuntz, Kai Grube, Alannah Hallas, Kyle Bayliff, Tiglet Besara, Theo Siegrist, Yipeng Cai, James Beare, Graeme Luke, Emilia Morosan We studied the critical behavior of itinerant ferromagnets Ni_{1-x}Rh_{x} with x = 0.3 - 0.375 based on the Arrott-Noakes scaling analysis. The ferromagnetic ordering temperature is continuously suppressed to zero at a critical concentration x_{c} ~ 0.375. For x = 0.3, mean-field like exponents β ~ 0.5,γ ~ 1.5, and δ ~ 3 are observed. With increasing x, critical exponents vary smoothly and reach at β ~ 0.6,γ ~ 0.7, and δ ~ 2.3 for x = 0.37. The evolution of exponents with x and the exponent values close to x_{c} cannot be described by any known universality class for classical models. The possible explanation for the trend of exponents is that, close to x_{c}, strong quantum fluctuations enhance the role of disorder and drive the system to a new strong-coupling regime. |
Thursday, March 7, 2019 8:12AM - 8:24AM |
R06.00002: Search for a magnetic quantum critical point in LuFe_{2}Ge_{2} substitution series Raquel Ribeiro, Sergey Budko, Paul Canfield As part of an extensive study of the RFe_{2}Ge_{2} series [1] a SDW-like transition was discovered in LuFe_{2}Ge_{2} near 9 K. Given that LuFe_{2}Ge_{2} has the same structure as the AFe_{2}As_{2} (A =Alkali and Alkali-Earth) Fe-based superconductors, the possibility of LuFe_{2}Ge_{2} manifesting fragile magentism [2], and even exotic, emergent states that could be revealed as T-SDW is suppressed toward zero, was enticing. To address this, a study of Y, Sc, Co and Ru substitutions into LuFe_{2}Ge_{2} was made [3]. Although phase diagrams constructed down to 2-3 K failed to reveal emergent effects [3], in this talk we will present magnetization and specific heat data down to 400 mK and 100 mK respectively. Updated phase diagrams will be presented and discussed. |
Thursday, March 7, 2019 8:24AM - 8:36AM |
R06.00003: Hall Coefficient of Pure Chromium at Finite Temperatures and High Pressures Stephen Armstrong, Yishu Wang, Daniel Silevitch, Yejun Feng, Thomas F Rosenbaum Elemental chromium is a spin density wave antiferromagnet which may be tuned through a second order quantum phase transition by the application of pressure or by chemical doping with e.g. vanadium. For both routes, the Hall coefficient has proven to be a powerful probe of the quantum critical region. In the low temperature limit, the Hall coefficient varies rapidly through the transition due to Fermi surface reconstruction. However, critical scaling of the Hall coefficient differs between pressure and doping driven transitions, establishing disorder as a relevant parameter in defining the universality class of a quantum phase transition. For doped chromium, the measured finite temperature behavior of the Hall coefficient cannot be described by band theory, and instead has been interpreted as evidence of a pseudogap phase. Here, we examine the pressure-driven Hall coefficient in pure chromium at finite temperature in search of signatures of a pseudogap phase in the absence of disorder. |
Thursday, March 7, 2019 8:36AM - 8:48AM |
R06.00004: Ferromagnetic quantum phase transition in compressed CePd_{2}P_{2} Timothy A Elmslie, Derrick VanGennep, You Lai, David E Graf, Ryan Baumbach, James J. Hamlin The correlated electron material CePd_{2}P_{2} crystallizes in the ThCr_{2}Si_{2} structure and orders ferromagnetically at 28 K. Recently, Y. Lai et al. [1] found evidence for a ferromagnetic quantum critical point induced by chemical compression via substitution of Ni for Pd. In this present work, we examine the T-H-p phase diagram of single crystalline CePd_{2}P_{2} to 25 GPa using a combination of resistivity, magnetic susceptibility, and x-ray diffraction measurements. We find that the ferromagnetism is destroyed near 20 GPa. These results are compared to similar experiments on the ferromagnets CeTiGe_{3} [2] and LaCrGe_{3} [3]. |
Thursday, March 7, 2019 8:48AM - 9:00AM |
R06.00005: Observation of Griffiths phase at an anti-ferromagnetic quantum critical point in Ce(Cu_{1−x}Co_{x})_{2}Ge_{2} Rajesh Tripathi, Debarchan Das, Christoph Geibel, Sudesh Kumar Dhar, Zakir Hossain A comprehensive study has been carried out on polycrystalline samples of Ce(Cu_{1}_{-}_{x}Co_{x})_{2}Ge_{2 }by means of electrical resistivity, magnetic susceptibility, specific heat and thermo electric power measurements. The long-range antiferromagnetic order, at T_{N} = 4.1 K in CeCu_{2}Ge_{2}, is suppressed by non-iso-electronic cobalt (Co) doping at a critical value of the concentration x_{c} = 0.6, accompanied by non-Fermi-liquid behavior. A power-law dependence of heat capacity and susceptibility i.e. C(T )/T and χ(T ) ∝ T ^{-}^{1+λ} down to 0.4 K are observed around x_{c} = 0.6 which is compatible with the quantum Griffiths phase scenario and attributed to an antiferromagnetic quantum critical point. Our results on Ce(Cu_{1-}_{x}Co_{x})_{2}Ge_{2 }manifest a complex magnetic phase diagram, where we have observed a continuous decrease of T_{N} with large negative slope down to T_{N} = 0.83 K at x = 0.1, and then a comparatively small negative slope takes over. We conclude that the rapid decrease of T_{N} upon Co-doping is mainly due to carrier concentration change and associated change of T_{K} and T_{RKKY} . We have not seen any superconducting phase in the quantum critical regime down to 0.4 K |
Thursday, March 7, 2019 9:00AM - 9:12AM |
R06.00006: Pressure-induced quantum critical behavior and magnetic order in YbNi_{3}Ga_{9} with a chiral crystal structure: AC-calorimetric measurements up to 12 GPa Kazunori Umeo, Takumi Otaki, Yudai Arai, Shigeo Ohara, Toshiro Takabatake YbNi_{3}X_{9} (X=Al, Ga) crystallize in the trigonal ErNi_{3}Al_{9}-type structure with a chiral space group R32. YbNi_{3}Al_{9} undergoes a magnetic transition at T_{M}=3.4 K. By substituting Cu for Ni, a chiral soliton lattice (CSL) is realized under magnetic fields B⊥c. While YbNi_{3}Ga_{9} resides in an intermediate-valence regime under ambient pressure, application of pressure P is expected to drive this compound into a magnetic ordered state. Indeed, a magnetic order above P_{c}=9 GPa was inferred from the electrical resistivity and AC magnetic susceptibility measurements. |
Thursday, March 7, 2019 9:12AM - 9:24AM |
R06.00007: Tuning a quantum phase boundary with microwaves Matthew Libersky, Thomas F Rosenbaum, Daniel Silevitch The ferromagnet LiHoF_{4} is a realization of the dipole-coupled transverse field Ising model with a Curie temperature of 1.53 K and a transverse-field-driven quantum phase transition (QPT) at 5 T. The strong hyperfine coupling of the Ho^{3+} ion leads to an effective spin rescaling to I+J below 400 mK, increasing the transverse field required to drive the QPT. This spin rescaling can be suppressed by exciting the nuclear moments into their highest spin states using a strong RF field in the microwave band as a pump. We employ a high-Q loop-gap resonator tuned to approximately 3 GHz to drive the nuclear spins and simultaneously perform dc magnetometry to probe the bulk magnetization. We tune the location of the phase transition as a function of microwave power, and explore the further possibility of studying quantum quench dynamics in a system with a thermodynamic number of spins. |
Thursday, March 7, 2019 9:24AM - 9:36AM |
R06.00008: Electrical transport near an Ising nematic quantum critical point Xiaoyu Wang, Erez Berg Electrical transport properties near an Ising-nematic quantum critical point are of both theoretical and experimental interest. The difficulty of the problem is in part due to the fact that the electronic scattering mediated by critical fluctuations are momentum-conserving, and that one needs to incoporate additional current relaxation mechanisms into the low-energy theory. In this talk, we discuss two mechanisms relevant in such systems, namely Umklapp scattering and compensated metal. We present a memory matrix calculation of the DC resistivity, which treats the quasiparticle density at each patch on the Fermi surface as a slow variable. We work in the temperature regime where electrons are coherent but the fluctuations are Landau-damped. We show that in the case of Umklapp scattering, resistivity shows a smooth crossover from T^{2 }at low temperatures to sublinear at high temperatures. For a compensated metal where current and momentum are orthogonal, resistivity shows a surprising T-linear behavior. Connections to recent numerical simulations and experiments will be discussed. |
Thursday, March 7, 2019 9:36AM - 9:48AM |
R06.00009: Phonon Quantum Phase Transition Ricardo Pablo Pedro, Nina Andrejevic, Yoichiro Tsurimaki, Zhiwei Ding, Te-Huan Lu, Gerald D Mahan, Shengxi Huang, Mingda Li The emergence of novel quantum phenomena is often shown in materials close to a zero temperature phase transition. Much of the effort to study these new effects, like Kondo entanglement and its breakdown in heavy-fermion metals, has been focused mainly in fermionic systems. Here, we demonstrate that a phonon (bosonic) system can exhibit a quantum phase transition with dislocations. The quantum critical point (QCP) reached by the phonons arises at a second-order transition between two-ground states corresponding to a conventional phonon state (symmetric phase) and a dynamically-induced dipole field (symmetry-broken phase), at zero temperature. The distinct ground states arise from a competition between the phonon-dislocation anharmonic interaction and the topological nature of the dislocation. Furthermore, through renormalization group analysis, this phonon system provides a very different type of quantum critically which can be used to tailor phonon transport at the single-mode level [arXiv:1809.06495]. |
Thursday, March 7, 2019 9:48AM - 10:00AM |
R06.00010: Quantum Critical Polar Metals Pavel Volkov, Piers Coleman, Premala Chandra Recent studies show that ferroelectric materials can be tuned to quantum criticality. Doping these systems gives rise to quantum critical polar metals, where structural phase transitions formally replace ferroelectric ones. This raises the following key questions: how does the presence of itinerant carriers alter the nature of the transition and what is the interaction between the electrons in this novel quantum critical fluid? Motivated by these considerations, we develop an analytic model for a Fermi sea of conduction electrons coupled to a critical ferroelectric mode, where screening is taken into account. Using diagrammatic methods we consider the suppression of the transition in the system with increasing doping, and develop a description of the dielectric properties of the quantum critical polar metal. Experimental implications for doped strontium titanate and similar systems are discussed. |
Thursday, March 7, 2019 10:00AM - 10:12AM |
R06.00011: Lattice effects on the transport properties of a quasi-two-dimensional metal near a nematic quantum critical point Vanuildo De Carvalho, Rafael M Fernandes Electronic nematic order is often accompanied by a lattice distortion. The presence of elastic degrees of freedom is known not only to enhance the transition temperature, but, most importantly, to promote long-range interactions that strongly affect the character of the classical and quantum nematic transitions. In this talk, we investigate the impact of the lattice degrees of freedom on the transport properties near a metallic nematic quantum critical point in quasi-two-dimensional systems. We solve numerically the semi-classical Boltzmann equation by considering impurity scattering as the only source for momentum relaxation. The usual non-Fermi liquid power-law for the resistivity, ρ(T)∝T^{4/3}, is replaced at very low temperatures by the standard T^{2} behavior. For intermediate temperatures, we obtain an effective temperature-dependent exponent α in ρ(T)∝T^{α}. We discuss the relevance of our results to recent experiments in S-doped FeSe, which displays a putative nematic quantum critical point. |
Thursday, March 7, 2019 10:12AM - 10:24AM |
R06.00012: Dynamic multiferroicity of a ferroelectric quantum critical point Kirsty Dunnett, Jian-Xin Zhu, Nicola Spaldin, Vladimir Juricic, Alexander Balatsky Dynamical multiferroicity, where fluctuations of electric dipoles lead to magnetisation, is an example of where two coexisting orders are impossible to disentangle [1]. We calculate the magnetic susceptibility near the ferroelectric quantum critical point (FE QCP) and find a region with enhanced magnetic signatures that appears near the FE QCP, and is controlled by the tuning parameter of the ferroelectric phase. We thus suggest that any ferroelectric quantum critical point may be an inherent multiferroic quantum critical point. The effect is small but observable, and we suggest the quantum paraelectric strontium titanate as a candidate material where the magnitude of the induced magnetic moments can be ~5 x 10^{7} µ_{B} per unit cell |
Thursday, March 7, 2019 10:24AM - 10:36AM |
R06.00013: Quantum Criticality and the Non-linear I-V Curve of Two-channel Kondo-Luttinger System Chao-Yun Lin, Yung-Yeh Chang, Colin Rylands, Natan Andrei, Chung-Hou Chung We theoretically study the quantum phase transition and non-linear I-V curve of a Kondo impurity in a Luttinger liquid wire. With decreasing Luttinger parameter K (or increasing electron interactions), it has been known since 1990s that the system undergoes a quantum phase transition from 1-channel (1CK) to 2-channel Kondo (2CK) ground states at K=1/2. However, the quantum critical properties near this transition is not known to date due to the lack of controlled theoretical tools to examine the physics near the strong coupling 2CK fixed point. Via bosonization-refermionization approach, we map the system near 1CK-2CK quantum critical point (QCP) and near the Toulouse limit onto an effective fermionic model in weak coupling regime subject to a bosoinc bath. The 1CK-2CK QCP is identified via renormalization group technique. The analytical form of the non-linear differential conductance and various critical exponents near this novel QCP are obtained. Our results are relevant for the recent experiment in a dissipative quantum dot via a double-barrier potential. |
Thursday, March 7, 2019 10:36AM - 10:48AM |
R06.00014: Unconventional superconductivity driven by Kondo-destruction quantum criticality Ang Cai, Jed Pixley, Kevin Ingersent, Qimiao Si How quantum criticality affects superconductivity is a central issue in strongly correlated systems. Particularly pressing is for the beyond-Landau type quantum criticality, such as appearing in heavy fermion systems in the form of Kondo destruction [1]. This is exemplified by the heavy fermion superconductor CeRhIn_{5}, which has an antiferromagnetic quantum critical point (QCP) accompanied by a sharp Fermi surface reconstruction, and in which d-wave superconductivity develops with a high T_{c} [2]. Here we address the pairing instabilities near a Kondo destruction QCP by studying the Anderson lattice model using the Cluster Extended-DMFT approach [3]. For extreme Ising anisotropic case, the paring susceptibility is significantly enhanced near the QCP. Whereas for SU(2) symmetric case, we find superconducting order around the QCP [4]; T_{c }is comparably high as compared with the observation in CeRhIn_{5 }under optimal pressure. In both cases, we find the paring tendency to be stronger for the Kondo destruction type QCP than for the spin density wave type. |
Thursday, March 7, 2019 10:48AM - 11:00AM |
R06.00015: Kondo destruction in multipolar order: Implications for heavy-fermion quantum criticality Hsin-Hua Lai, Emilian Nica, Wenjun Hu, Shoushu Gong, Silke Paschen, Qimiao Si Motivated by the quantum-critical heavy-fermion systems [1,2] exhibiting multipolar orders, we theoretically study an effective field theory of a Kondo lattice model involving both spin and quadrupole degrees of freedom. The field theory contains a quantum non-linear sigma model of the antiferroquadrupolar (AFQ) phase in spin-1 systems, with Kondo couplings to conduction electrons. In the absence of the Kondo coupling, we demonstrate the stability of the AFQ phase using density matrix renormalization group analysis in the underlying spin model. We proceed to analyze the effect of the Kondo couplings, using a mixed fermion-boson renormalization group procedure [3]. We show that the Kondo couplings are exactly marginal, which implies a Kondo destruction in the multipolar phase. Our results provide theoretical basis for the recently advanced notion of sequential Kondo-destruction [1]. Implications of our results for the global phase diagram of the heavy fermion systems are discussed. [1] V. Martelli et al., arXiv:1709.09376. [2] J. Custers et al, Nat. Mater. 11, 189 (2012). [3] S. J. Yamamoto and Q. Si, Phys. Rev. B 81, 205106 (2010). |
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