S. Meng

University of Waterloo, Waterloo, Ontario, Canada

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Publications (10)38.06 Total impact

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    ABSTRACT: The discovery of the spin-ice phase in Dy2Ti2O7 numbers among the most significant findings in magnetic materials in over a decade. Spin ice has since been associated with the manifestation of magnetic monopoles and may even inform our understanding of emergent quantum electrodynamics. The spin-ice model is based on an elegant analogy to Pauling's model of geometrical frustration in water ice, and predicts the same residual entropy, as confirmed by numerous measurements. Here we present results for the specific heat of Dy2Ti2O7, demonstrating why previous measurements were unable to correctly capture its low-temperature behaviour. By carefully tracking the flow of heat into and out of the material, we observe a non-vanishing specific heat that has not previously been detected. This behaviour is confirmed in two samples of Dy2Ti2O7, in which cooling below 0.6K reveals a deviation from Pauling's residual entropy, calling into question the true magnetic ground state of spin ice.
    Nature Physics 06/2013; 9(6):353-356. · 19.35 Impact Factor
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    ABSTRACT: Recent work on low temperature magnetization [1] and ac-susceptibility [2] of the spin ice Dy2Ti2O7 has revealed a number of inconsistencies with earlier magneto-caloric [3] and thermal relaxation [4] measurements. These unsolved puzzles have motivated us to re-investigate the low temperature specific heat of this material. By measuring the thermal relaxation of Dy2Ti2O7, we extract magnetic spin relaxation times and compare them to previous results in the literature.[4pt] [1] K. Matsuhira, et al., J. Phys. Cond. Mat. 13, L737 (2001) [0pt] [2] L. R. Yaraskavitch et al., Phys. Rev. B 85, 020410(R) (2012) [0pt] [3] M. Orendac, et al., Phys. Rev. B 75, 104425 (2007) [0pt] [4] B. Klemke, et al., J. Low Temp. Phys. 163, 345 (2011)
    03/2013;
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    ABSTRACT: We experimentally investigated the switching current Isw of a superconducting single electron transistor (sSET), with competitive Josephson coupling energy EJ and charging energy Ec, in an in situ tunable dissipative environment. At low temperature, averaged Isw shows a clear 1e periodic function of gate induced charge on the island. The relative contrast of this oscillation increases when EJ/Ec is lowered. Increasing dissipation reduce the quantum fluctuations of the phase across the sSET, leading to an increased Isw.
    Journal of Physics Conference Series 12/2012; 400(4):2046-.
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    ABSTRACT: Low-temperature magnetic ac susceptibility measurements of single-crystal dipolar spin ice Dy2Ti2O7 are presented. The relaxation is found to exhibit thermally activated Arrhenius behavior with an activation energy of 9.79 K (∼9Jeff), which is not consistent with a simple scaling of 6Jeff, as previously found for Ho2Ti2O7. There are distinct quantifiable differences between Dy2Ti2O7 and Ho2Ti2O7 absorption spectra. The measured dynamics does not agree with simulations based on current magnetic monopole theory nor thermal relaxation measurements, but instead freezes out at a faster rate.
    Physical review. B, Condensed matter 01/2012; 85(2). · 3.66 Impact Factor
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    ABSTRACT: The pyrochlore material Yb2Ti2O7 displays unexpected quasi-two-dimensional (2D) magnetic correlations within a cubic lattice environment at low temperatures, before entering an exotic disordered ground state below T=265mK. We report neutron scattering measurements of the thermal evolution of the 2D spin correlations in space and time. Short range three dimensional (3D) spin correlations develop below 400 mK, accompanied by a suppression in the quasi-elastic (QE) scattering below ~ 0.2 meV. These show a slowly fluctuating ground state with spins correlated over short distances within a kagome-triangular-kagome (KTK) stack along [111], which evolves to isolated kagome spin-stars at higher temperatures. Furthermore, low-temperature specific heat results indicate a sample dependence to the putative transition temperature that is bounded by 265mK, which we discuss in the context of recent mean field theoretical analysis.
    Physical review. B, Condensed matter 07/2011; 84. · 3.66 Impact Factor
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    ABSTRACT: Specific heat measurements in zero magnetic field are presented on a homologous series of geometrically frustrated, antiferromagnetic, Heisenberg garnet systems. Measurements of Gd3Ga5O12, grown with isotopically pure Gd, agree well with previous results on samples with naturally abundant Gd, showing no ordering features. In contrast, samples of Gd3Te2Li3O12 and Gd3Al5O12 are found to exhibit clear ordering transitions at 243 mK and 175 mK respectively. The effects of low level disorder are studied through dilution of Gd3+ with non-magnetic Y3+ in Gd3Te2Li3O12. A thorough structural characterization, using X-ray diffraction, is performed on all of the samples studied. We discuss possible explanations for such diverse behavior in very similar systems.
    Physical review. B, Condensed matter 06/2010; · 3.66 Impact Factor
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    ABSTRACT: We will present measurements of transport properties of a new type of superconducting device, designed to allow a fully adjustable Hamiltonian with charge term, Josephson coupling term, and dissipation term. This device consists of a superconducting Single Electron Transistor (sSET) and two Superconducting Quantum Interference Devices (SQUIDs). A 2D electron gas embedded 90nm below the substrate surface provides a tunable dissipative environment. A small magnetic field can be applied to drive this hybrid device from the strong Josephson coupling regime to the SET regime. Dissipation and temperature dependence of the switching current out of the zero-voltage state show different characteristics for different settings of competition between Josephson coupling and charging energy.
    03/2009;
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    ABSTRACT: Specific heat measurements on two different geometrically frustrated, Heisenberg, garnet lattices will be presented. The specific heat of an isotopically pure, single crystal sample of Gd3Ga5O12, or GGG, is found to be consistent with previous measurements of the specific heat of GGG ootnotetextSchiffer et al. Phys. Rev. Lett. 74, 2379 (1995). and shows no signs of a standard ordering anomaly despite sharp Bragg peaks that were seen in neutron diffraction experiments. A first measurement of the specific heat of polycrystalline Gd3Li2Te3O12, in contrast, shows a sharp first-order phase transition at 240 mK. We will discuss possible explanations for such diverse behavior in very similar systems.
    03/2009;
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    ABSTRACT: ac susceptibility measurements are presented on the dilute, dipolar coupled, Ising magnet LiHoxY1-xF4 for a concentration x=0.045. The frequency and temperature dependences of the susceptibility show characteristic glassy relaxation. The absorption spectrum is found to broaden with decreasing temperature suggesting that the material is behaving as a spin glass and not as an exotic spin liquid as was previously observed. A dynamical scaling analysis suggests a spin glass transition temperature of 43+/-2 mK with an exponent znu=7.8+/-0.2.
    Physical Review Letters 11/2008; 101(18):187204. · 7.73 Impact Factor
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    ABSTRACT: Recent work has called into question the existence of a spin glass transition in the dilute dipolar Ising magnet LiHoxY1-xF4 [1]. Other work has suggested that there is an exotic spin liquid phase found at a Ho concentration of x = 0.045 [2]. In order to carefully study the dynamics of this system, we have put together a SQUID magnetometer which allows for measurements of ac susceptibility and nonlinear susceptibility over a large frequency range. We present results from measurements on single crystals of LiHoxY1-xF4, particularly on an x = 0.045 sample, in an attempt to either reproduce the exotic ``anti-glass'' physics that was previously observed or to detect a spin glass transition. [1] P. E. Jonnson et al. PRL 98, 256403 (2007) [2] S. Ghosh et al. Science 296, 2195 (2002)
    03/2008;