Prof Radu Coldea

Abstract:

This data archive accompanies the paper "Quantifying and controlling entanglement in the quantum magnet Cs2CoCl4" by Pontus Laurell, Allen Scheie, Chiron J. Mukherjee, Michael M. Koza, Mechtild Enderle, Zbigniew Tylczynski, Satoshi Okamoto, Radu Coldea, D. Alan Tennant, and Gonzalo Alvarez, https://arxiv.org/abs/2010.11164 and Phys. Rev. Lett. (in print 2021).

The archive contains source data and plot files to replicate all figures in the article and its supplemental material, including processed experimental inelastic neutron scattering data and theoretical DMRG results. All figures can be compiled using LaTeX as described in detail in the README.txt file contained in the archive.

The lack of methods to experimentally detect and quantify entanglement in quantum matter impedes our ability to identify materials hosting highly entangled phases, such as quantum spin liquids. We thus investigate the feasibility of using inelastic neutron scattering (INS) to implement a model-independent measurement protocol for entanglement based on three entanglement witnesses: one-tangle, two-tangle, and quantum Fisher information (QFI). We perform high-resolution INS measurements on Cs2CoCl4, a close realization of the S=1/2 transverse-field XXZ spin chain, where we can control entanglement using the magnetic field, and compare with density-matrix renormalization group calculations for validation. The three witnesses allow us to infer entanglement properties and make deductions about the quantum state in the material. We find QFI to be a particularly robust experimental probe of entanglement, whereas the one- and two-tangles require more careful analysis. Our results lay the foundation for a general entanglement detection protocol for quantum spin systems.

Abstract:

Low-temperature thermal conductivity measurements have been conducted on an oxygen-annealed single crystal of Yb2Ti2O7 from 60 mK to 50 K and in magnetic fields up to 8 T applied in the [111] crystallographic direction. The temperature dependence of the conductivity in zero field shows a significant peak in thermal conductivity at T∼13 K and a sharp anomaly at Tc∼0.2 K suggesting that the sample's behavior is representative of the high-purity limit, with low levels of disorder. The magnetic field dependence of the thermal conductivity close to Tc reveals a reentrant magnetic phase for a field in the [111] direction. With this information, analysis of the very low magnetic field behavior of the thermal conductivity suggests the presence of significant fluctuations close to the phase line.