arXiv subjects

J. B. Kycia

Publications and source records attributed to J. B. Kycia.

22 records · Page 2Linked to original sources

arXiv2007

Evidence for gapped spin-wave excitations in the frustrated Gd2Sn2O7 pyrochlore antiferromagnet from low-temperature specific heat measurements

We have measured the low-temperature specific heat of the geometrically frustrated pyrochlore Heisenberg antiferromagnet Gd2Sn2O7 in zero magnetic field. The specific heat is found to drop exponentially below approximately 350 mK. This provides evidence for a gapped spin-wave spectrum due to an anisotropy resulting from single ion effects and long-range dipolar interactions. The data are well fitted by linear spin-wave theory, ruling out unconventional low energy magnetic excitations in this system, and allowing a determination of the pertinent exchange interactions in this material.

cond-mat.stat-mech↗

arXiv2006

Specific Heat of the Dilute Ising Magnet LiHo$_x$Y$_{1-x}$F$_4$

We present specific heat data on three samples of the dilute Ising magnet $\HoYLF$ with $x = 0.018$, 0.045 and 0.080. Previous measurements of the ac susceptibility of an $x = 0.045$ sample showed the Ho$^{3+}$ moments to remain dynamic down to very low temperatures and the specific heat was found to have unusually sharp features. In contrast, our measurements do not exhibit these sharp features in the specific heat and instead show a broad feature, for all three samples studied, which is qualitatively consistent with a spin glass state. Integrating $C/T$, however, reveals an increase in residual entropy with lower Ho concentration, consistent with recent Monte Carlo simulations showing a lack of spin glass transition for low x.

cond-mat.dis-nn↗

arXiv2005

Measurements of 1/ f noise in Josephson junctions at zero voltage: Implications for decoherence in superconducting quantum bits

Critical current fluctuations with a 1/ f spectral density (f is frequency) are potentially a limiting source of intrinsic decoherence in superconducting quantum bits (qubits) based on Josephson tunnel junctions. Prior measurements of this noise were made at nonzero voltages whereas qubits are operated in the zero voltage state. We report measurements of 1/ f noise in a dc superconducting quantum interference device first, coupled to a resonant tank circuit and operated in a dispersive mode at zero voltage, and, second, operated conventionally with a current bias in the voltage regime. Both measurements yield essentially the same magnitude of critical current 1/ f noise.

cond-mat.supr-con↗

arXiv1998

Suppression of Superconductivity in UPt_3 Single Crystals

High quality single crystals of UPt_3 have been prepared by vertical float-zone refining in ultra-high vacuum. We find that the superconducting transition temperature can be varied systematically by annealing, revealing that the transition temperature intrinsic to UPt_3 is 563 +/- 5 mK. The suppression of the superconducting transition from defects is consistent with a modified Abrikosov-Gor'kov formula that includes anisotropic pairing, Fermi surface anisotropy, and anisotropic scattering by defects.

cond-mat.supr-con↗