Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session X41: New Insights into Quantum Criticality in Metallic SystemsInvited
|
Hide Abstracts |
Sponsoring Units: DCMP DMP Chair: Andrew Christianson Room: LACC 502A |
Friday, March 9, 2018 8:00AM - 8:36AM |
X41.00001: Metallic Quantum Ferromagnets Invited Speaker: Dietrich Belitz This talk will provide an overview of the current understanding of the quantum phase transition in metallic ferromagnets. In clean systems the transition is generically first order or discontinuous, in sharp contrast to the second-order, or continuous, transition in classical ferromagnets. This is due to a coupling between the magnetization and low-temperature soft modes in the conduction-electron system. At sufficiently high temperature the continuous classical transition is observed. Continuity is provided by a tricritical point in the phase diagram, with associated tricritical wings in an external magnetic field. There is good agreement between theory and experiment. Quenched disorder lowers the tricritical temperature and, for sufficiently strong disorder, leads to a second-order transition even at zero temperature. Strong disorder can also lead to additional complications, such as quantum Griffiths effects. Finally, interesting and complicated phase diagrams are observed in systems where antiferromagnetic order competes with the ferromagnetic one, which leads to effects that are only partially understood. |
Friday, March 9, 2018 8:36AM - 9:12AM |
X41.00002: The T-p-H phase diagram of metallic quantum ferromagnets Invited Speaker: Valentin Taufour Studies of the temperature-pressure (T-p) phase diagram of metallic quantum ferromagnets have revealed that ferromagnetic quantum criticality is avoided in two ways [1]: either the transition becomes of the first-order at a tricritical point before being suppressed such as in UGe2 [2,3], or a transition to modulated magnetic phases appear such as in LaCrGe3 [4]. We have shown that the addition of a magnetic field (H) can restore quantum criticality at the end of “wings” in the T-p-H phase diagram in both UGe2 and LaCrGe3 [5]. Our careful study of the “wings” near the tricritical point reveal new rules that apply to the T-p-H phase diagram [6]. We discuss our experimental T-p-H phase diagrams of UGe2, LaCrGe3, and CeTiGe3 and how these compounds illustrate different strength of quantum fluctuations based on recent theoretical results [7]. |
Friday, March 9, 2018 9:12AM - 9:48AM |
X41.00003: Quantum Critical Behavior in the Asymptotic Limit of High Disorder Invited Speaker: Brian Sales The NiCoCrx alloys (with x near 1) are related to the recently discovered high-entropy-alloys, such as NiCoCrFeMn, where configurational entropy stabilizes a random distribution of elements on a face-centered cubic lattice. These alloys have been shown to be chemically homogeneous from the centimeter to the nanometer scale. Here we demonstrate that NiCoCrx single crystal alloys are remarkable model systems for investigating QCP physics in a metallic environment with a high degree of chemical disorder. For NiCoCrx alloys with x = 0.8, the critical exponents associated with a ferromagnetic quantum critical point (FQCP) are experimentally determined from low temperature magnetization and heat capacity measurements. All of the five exponents are in remarkable agreement with predictions of the Belitz-Kirkpatrick-Vojta (BKV) theory in the asymptotic limit of high disorder, and are quite different from Hertz mean field values. Using these critical exponents, excellent scaling of the magnetization data is demonstrated with no adjustable parameters. These results clearly demonstrate that disorder has a fundamental and profound effect on quantum critical behavior near an itinerant ferromagnetic QCP. This work also shows that entropy-stabilized alloys represent a unique platform to study quantum critical behavior in a highly tunable class of materials. Research supported by the DOE Office of Science, Basic Energy Sciences, Materials Science and Engineering Division. |
Friday, March 9, 2018 9:48AM - 10:24AM |
X41.00004: Crystal field anisotropy in a new Ytterbium heavy fermion ferromagnet Invited Speaker: Emilia Morosan The Yb and Ce Kondo compounds display complex magnetic and electronic behavior, from heavy fermion metals to Kondo insulators. Their properties are often the result of competing energy scales, such as crystal field effects, exchange interactions and strong electronic correlations. Here I will discuss a novel regime in the area of strong correlated electron systems, that of fragile magnetism in a low carrier Kondo system Yb3Ir4Ge13. What sets this compound apart from the known low carrier or Kondo isulators is that the underlying electronic properties are set by the non-magnetic analogue Lu3Ir4Ge13, which is itself a low carrier semi-metal. Yb3Ir4Ge13 is therefore the first experimental realisation of multi-site honeycomb model in the dilute Kondo carrier limit. |
Friday, March 9, 2018 10:24AM - 11:00AM |
X41.00005: Multiple fluctuations near an unconventional quantum critical point Invited Speaker: Lekhanath Poudel A quantum critical point (QCP) is a nexus instability where competing and frustrated interactions can drive the formation of new states of matter. Elucidating the underlying critical behavior is key to a fundamental understanding of these phenomena. In the case of metallic systems, the situation is particularly unsettled with mounting violations of the canonical Hertz-Millis-Moriya (HMM) approach based on long wavelength fluctuations of the order parameter. Here, we discuss the critical behavior of the model QCP material CeCu5.8Ag0.2 which appears to fall into the class of materials violating the HMM paradigm. Using state of the art inelastic neutron scattering measurements, we show that the critical dynamics comprises fluctuations at distinct wave vectors indicating intense competition between nearly degenerate ground states. A scaling analysis of the fluctuation spectrum yields energy over temperature (E/T) scaling with an anomalous critical exponent. However, the component of the spectrum corresponding to the magnetically ordered side of the phase diagram is three dimensional and scales as E/T3/2, demonstrating that at least a fraction of the spectrum is consistent with the conventional description of a QCP proposed by HMM. The presence of other low energy fluctuations suggests that a complete description of the QCP requires a coupling between multiple order parameters in order to explain the critical dynamics and associated thermodynamic properties of the class of materials exemplified by CeCu5.8Ag0.2. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700