Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session X1: Magnetic Field Driven Quantum Phase Transitions |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Joe Thompson, Los Alamos National Laboratory Room: Colorado Convention Center Four Seasons 2-3 |
Friday, March 9, 2007 8:00AM - 8:36AM |
X1.00001: Field-tuned quantum critical points Invited Speaker: |
Friday, March 9, 2007 8:36AM - 9:12AM |
X1.00002: Dimensionality and Quantum Criticality: the case of the spin-dimer system BaCuSi$_2$O$_6$ Invited Speaker: Physical properties in the vicinity of a quantum critical point (QCP) are intimately related to system dimensionality. In heavy fermion systems, for instance, the origin of emergent superconductivity and non Fermi liquid behaviour at a pressure- tuned QCP has been suggested to be a consequence of reduced dimensionality. In this talk, I discuss the field-tuned Bose Einstein condensation (BEC) QCP in the spin-dimer system BaCuSi$_2$O$_6$ - also known as Han Purple. Long-range antiferromagnetic order in this system appears above a critical magnetic field $H_{c1}~\sim$~23.5 T due to the closure of the spin gap to triplon excitations. While the divergence of critical fluctuations tends to destabilise any reduction of dimensions at a fermionic QCP, contrary behaviour is demonstrated at the field-tuned bosonic QCP in BaCuSi$_2$O$_6$. The suppression of amplitude fluctuations at the BEC QCP in this system contributes to the effectiveness of geometrical frustration in reducing the effective dimensionality at the QCP. Experimental thermodynamic signatures are presented as evidence for a 2D BEC QCP in BaCuSi$_2$O$_6$. \newline \newline Work performed in collaboration with N. Harrison, C. D. Batista, L. Balicas, M. Jaime, P. A. Sharma, N. Kawashima, E. Palm, T. Murphy, and I. R. Fisher. \newline \newline [1] S. E. Sebastian et al., ``Dimensional reduction at a quantum critical point,'' Nature 441, 617-620 (2006) [Preview Abstract] |
Friday, March 9, 2007 9:12AM - 9:48AM |
X1.00003: Fingerprints of Interacting Hardcore Bosons on a Lattice: Spin Dynamics in Dimer Spin Systems with Field-Tuned Quantum Criticality. Invited Speaker: Spin-dimer based magnetic insulators are model systems for the experimental and theoretical investigation of field-tuned quantum criticality and, in particular, the ground states of strongly interacting hardcore bosons (triplets), for which there are increasing parallels to ultra-cold atoms in optical lattices. We have investigated corresponding quantum phase transitions by inelastic neutron scattering (INS) in spin systems, which cover both the effect of dimensionality and the degree of quasi-particle mobility. These quantities characterize the triplet excitations and definite the magnon-`BEC' phases above the field-induced quantum critical point in these materials. Inorganic compounds like the 3D copper-halide family ACuCl$_{3}$ (A=K, Tl, NH$_{4})$, the strongly frustrated Shastry-Sutherland material SrCu$_{2}$(BO$_{3})_{2}$, and quasi-2D BaCuSi$_{2}$O$_{6}$ all show distinct spin dynamics associated with the boson system, which they represent. The fascinating quasi-1D limit is accessible in novel organic materials, which promote a characteristic quantum phase -- the Luttinger spin-liquid. Recent INS results, which explore this exciting quantum phase, will be compared to those obtained in higher dimensions and elaborate predictions by theory. [Preview Abstract] |
Friday, March 9, 2007 9:48AM - 10:24AM |
X1.00004: Field-induced magnetism and quantum criticality in superconducting CeRhIn$_{5}$ under pressure Invited Speaker: The antiferromagnet CeRhIn5 becomes superconducting under pressure, where superconducting state coexists with the helical magnetic state with Q=(0.5, 0.5, 0.293). Similarly to other heavy fermion superconductors, however, magnetism disappears when the antiferromagnetic transition temperature becomes equal to superconducting temperature, hiding a magnetic quantum critical point. Applying magnetic field reveals a low-temperature specific heat anomaly in the unconventional superconducting state, which defines a quantum phase transition from a solely superconducting state to a phase with coexisting magnetic and superconducting orders [1]. The field-pressure phase boundary at zero temperature is anticipated theoretically [2] and is strikingly similar to that in high-Tc cuprates [3], delineating a correlation between quantum criticality and unconventional superconductivity. \newline \newline [1] T. Park et al., Nature 440, 65 (2006) \newline [2] Q. Si et al., Nature 413, 804 (2001); E. Demler et al., Phys Rev. Lett. 87 067202 (2001) \newline [3] B. Lake et al., Nature 415, 299 (2002); H. J. Kang et al., Nature 423, 522 (2003) [Preview Abstract] |
Friday, March 9, 2007 10:24AM - 11:00AM |
X1.00005: Magnetic-field quantum phase driven transitions in CeBiPt and CeCu$_{6-x}$Au$_{x}$ Invited Speaker: The half-Heussler compounds CeBiPt and LaBiPt are semimetals with very low charge-carrier concentrations as evidenced by Shubnikov-de Haas (SdH) and Hall-effect measurements. Elastic neutron-scattering results reveal a simple antiferromagnetic structure in CeBiPt below $T_{N}$ = 1.15 K. The band structure of CeBiPt sensitively depends on temperature, magnetic field, and stoichiometry. Above a certain, sample-dependent, threshold field ($B \quad >$ 25 T) the SdH signal disappears and the Hall coefficient reduces significantly. These effects are absent in the non-4$f$ compound LaBiPt. Electronic-band-structure calculations can well explain the observed behavior by a 4$f$-polarization-induced Fermi-surface modification. CeCu$_{6-x}$Au$_{x}$ orders for $x \quad >$ 0.1 with an incommensurate antiferromagnetic structure. Here we compare the magnetic fluctuation spectrum obtained from inelastic neutron scattering for a field-driven quantum phase transition at $x$ = 0.2 with that for zero-field transition at the critical concentration $x_{c}$ = 0.1. \newline \newline Work performed in collaboration with J. Wosnitza, G. Goll, A. D. Bianchi, B. Bergk, N. Kozlova, I. Ophale, S. Elgazzar, M. Richter, O. Stockert, T. Yoshino, T. Takabatake and M. Enderle. [Preview Abstract] |
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