Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session B52: Invited Session: Emergent Quantum Phases and Their Transitions in Correlated Electron Systems |
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Sponsoring Units: DCMP Chair: Qimiao Si, Rice University Room: Grand Ballroom C2 |
Monday, March 2, 2015 11:15AM - 11:51AM |
B52.00001: Yb$_{2}$Pt$_{2}$Pb: Emergent Criticality on the Frustrated Shastry-Sutherland Lattice Invited Speaker: Meigan Aronson Metallic Yb$_{2}$Pt$_{2}$Pb forms in the U$_{2}$Pt$_{2}$Sn structure, with layers of Yb ions forming the orthogonal dimers of the Shastry-Sutherland lattice (SSL). The Yb$^{3+}$ moments are strongly Ising-like, with an energetically isolated doublet ground state. Fits to the temperature dependent susceptibility confirm that dimerization occurs, and that the B$=$0 energy separation of the singlet ground state and the triplet excited state $\Delta $ $\sim$ 4-5 K. Yb$_{2}$Pt$_{2}$Pb orders antiferromagnetically at 2.06 K, with a striped modulation of the dimer moments in the SSL planes with two wave vectors q$_{AF}=$(0.2,$\pm$ 0.2,0) rlu. The Yb moments are oriented perpendicular to the (1,$\pm$ 1,0) dimer bond directions, and the dimers form the rungs of two orthogonal spin ladders along the c-axis. A nondispersing and inelastic excitation with energy $\sim$ 0.4 meV is found for wave vectors in the SSL plane, in good agreement with the singlet-triplet gap $\Delta $ inferred from susceptibility measurements. The dispersion of the excitations along (00l) closely resembles that of a spinon continuum, such as those found in spin chain compounds, with an effective c-axis exchange of $\sim$ 0.12 meV. Yb$_{2}$Pt$_{2}$Pb is a unique system, where strong quantum fluctuations related to the spin-ladder or SSL characters of this compound may lead to unusual correlations in this excellent metallic host. [Preview Abstract] |
Monday, March 2, 2015 11:51AM - 12:27PM |
B52.00002: Magnetic Frustration in the Shastry-Sutherland Kondo lattice and the Global Phase Diagram of Heavy Fermion Metals Invited Speaker: Jedediah Pixley Over the past decade there has been significant theoretical and experimental progress in our understanding of antiferromagnetic quantum critical heavy fermion metals [1]. Recent years have seen a surge of studies on heavy fermion compounds with local moments that reside on geometrically frustrated lattices, which may host entirely new types of quantum critical points [2]. With a particular emphasis on Yb$_{2}$Pt$_{2}$Pb [3] and related 221 systems [4,5], we consider the Shastry-Sutherland Kondo lattice [6]. We determine the zero temperature phase diagram as a function of magnetic frustration and Kondo coupling. We study the transition between the valence bond solid phase of the Shastry-Sutherland lattice and a heavy fermi liquid, and find a phase diagram remarkably similar to the theoretically proposed global phase diagram of heavy fermion metals. We discuss the implications of our results for other geometrically frustrated heavy fermion metals. \\[4pt] [1] Q. Si, J. H. Pixley, et al, J. Phys. Soc. Jpn. \textbf{83} 061005 (2014).\\[0pt] [2] Q. Si and F. Steglich, Science \textbf{329}, 1161 (2010).\\[0pt] [3] M. S. Kim and M. C. Aronson, Phys. Rev. Lett. \textbf{110}, 017201 (2013).\\[0pt] [4] J. G. Sereni et al, Phys. Rev. B81, 184429 (2010)\\[0pt] [5] T. Muramatsu et al, Phys. Rev. B83, 180404(R) (2011).\\[0pt] [6] J. H. Pixley, R. Yu and Q. Si, Phys. Rev. Lett. \textbf{113}, 176402 (2014). [Preview Abstract] |
Monday, March 2, 2015 12:27PM - 1:03PM |
B52.00003: Fragile antiferromagnetism in the heavy-fermion compound YbBiPt Invited Speaker: Alan I. Goldman The discovery of YbBiPt [1] generated strong interest due to its extraordinary Sommerfield coefficient ($\gamma \approx $ 8 J/mol-K$^{2})$ and the fact that all of its relevant energy scales including the Kondo temperature, Weiss temperature, crystal field splitting, and a proposed antiferromagnetic (AFM) ordering below $T_{\textrm{N}} =$ 0.4 K are small and comparable, suggesting a complex interplay of competing interactions at low temperature. Much of the recent attention on YbBiPt has focused on the possibility of a magnetic-field-tuned AFM quantum critical point occurring at a low critical magnetic field of $\mu_{0}H_{\textrm{c}}$ = 0.4 T [2]. Although thermodynamic and transport measurements in ambient fields suggested that YbBiPt manifests AFM order below $T_{\textrm{N}}$, scattering measurements over the past 22 years failed to identify magnetic ordering in powder or single-crystal samples. In this talk, I will present recent elastic and inelastic neutron scattering experiments on single crystals of YbBiPt that demonstrated clear scattering signatures of unusual AFM order at low temperature [3]. The ambient field elastic scattering consists of two components: a narrower component that appears below $T_{\textrm{N}} \approx $ 0.4 K, which can be identified with features observed in the bulk transport measurements; and a broad scattering component that persists up to $T^{\ast} \approx $ 0.7 K corresponding to AFM correlations extending over $\approx $ 20 {\AA}.\\[4pt] [1] P. C. Canfield \textit{et al}., J. Appl. Phys. \textbf{70}, 5800 (1991); Z. Fisk \textit{et al}., Phys. Rev. Lett. \textbf{67}, 3310 (1991).\\[0pt] [2] E. D. Mun \textit{et al}., Phys. Rev. B \textbf{87}, 075120 (2013).\\[0pt] [3] B. G. Ueland\textit{ et al}., Phys. Rev. B \textbf{89}, 180403(R) (2014). [Preview Abstract] |
Monday, March 2, 2015 1:03PM - 1:39PM |
B52.00004: Strange metal without magnetic instability in $\beta-$YbAlB$_4$ Invited Speaker: Satoru Nakatsuji Many prototypical quantum critical materials found within the class of $4f$ heavy fermion compounds are known to have an almost integral valence and appear at the border of magnetism. An exception to this rule was recently discovered in $\beta-$YbAlB$_4$, which exhibits quantum criticality despite strong mixed valency.\footnote{S. Nakatsuji, et al., Nature Phys. \textbf{4}, 603 (2008).}$^,$\footnote{ M. Okawa, et al., Phys. Rev. Lett. \textbf{104}, 247201 (2010).} Ultrapure single crystals of this material exhibit intrinsically singular thermodynamic and transport behaviors, which are extremely sensitive to a magnetic field.\footnote{Y. Matsumoto, et al., Science \textbf{331}, 316 (2011).}$^,$\footnote{Y. Machida, et al., Phys. Rev. Lett. \textbf{109}, 156405 (2012).}$^,$\footnote{M. Sutherland et al., arXiv:1408.0033}. In particular, $T/B$ scaling of the magnetization has been observed over four decades of $T/B$, projected to extend down to fields as small as 0.1 mT. In this talk, we will discuss our results on the zero field criticality by the $T/B$ scaling in a broad regime of $T$ and $B$,\footnote{Y. Matsumoto et al., arXiv:1407.6142.} and through an extensive series of pressure measurements.\footnote{T. Tomita et al., preprint} We will show that the intrinsic quantum criticality of YbAlB$_4$ occupies an extended region of pressure, indicating a formation of a phase. Furthermore, we will present that the strange metal region is clearly surrounded and separated from a high-pressure magnetic instability by a finite pressure range of Fermi liquid behavior.\\[4pt] This work is based on the collaboration with Yosuke Matsumoto, Takahiro Tomita, Kentaro Kuga, Yoshiya Uwatoko, Yasuyuki Shimura, Piers Coleman, Andriy H. Nevidomskyy, E. O'Farrell, T. Sakakibara, Y. Karaki, S. Suzuki, H. Cao, D. MacLaughin, M. Okawa, S. Shin [Preview Abstract] |
Monday, March 2, 2015 1:39PM - 2:15PM |
B52.00005: Kondo effect and quantum criticality in Ce-based pnictides Invited Speaker: Yongkang Luo The pnictides have not only triggered enthusiasm in searches for high-$T_{c}$ superconductors, but also paved a new way for investigating the Kondo effect and quantum criticality. In this talk, I will start with the phase diagram of CeFeAs$_{\mathrm{1-x}}$P$_{x}$O which hosts two possible quantum critical points (QCPs) [1]. Due to the entanglement of 3$d$ and 4f magnetism, CeFeAsO is not a good candidate for investigating quantum criticality, therefore we turned to CeNiAsO. The Ce-sublattice shows two successive AFM transitions at $T_{N1}=$9.3 K and $T_{N2}=$7.3 K, while the Ni-sublattice is nonmagnetic [2]. Under pressure, both AFM transitions are suppressed, and a QCP is obtained at $p_{c}=$6.5 kbar. Similar phenomenon was also observed by P/As-substitution, which leads to a critical doping at $x_{c}=$0.4. The quantum fluctuations near these QCPs are discussed, and the possibility of a Kondo-destruction type QCP is addressed [3]. Finally, I will briefly talk about the pressure effect on the 122 cousin, CeNi$_{2}$As$_{2}$ [4], which seems to provide a rare paradigm of quantum criticality in the low carrier density limit. \\[4pt] In collaboration with: Z. Xu, J. Dai, G. Cao, L. Pourovskii, Q. Si, N. P. Ong, and J. D. Thompson \textit{et al.} \\[4pt] [1] Y. Luo \textit{et al.}, Phys. Rev. B \textbf{81,} 134422 (2010).\\[0pt] [2] Y. Luo \textit{et al.}, J. Phys.: Condens. Matter \textbf{23}, 175701 (2011).\\[0pt] [3] Y. Luo \textit{et al.}, Nature Materials \textbf{13}, 777 (2014).\\[0pt] [4] Y. Luo \textit{et al.}, Phys. Rev. B \textbf{86}, 245130 (2012). [Preview Abstract] |
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