Entanglement study of the 1D Ising model with Added Dzyaloshinsky-Moriya interaction

We have studied occurrence of quantum phase transition in the one-dimensional spin-1/2 Ising model with added Dzyaloshinsky-Moriya (DM) interaction from bi- partite and multi-partite entanglement point of view. Using exact numerical solutions, we are able to study such systems up to 24 qubits. The minimum of the entanglement ratio R $\equiv$ \tau 2/\tau 1 < 1, as a novel estimator of QPT, has been used to detect QPT and our calculations have shown that its minimum took place at the critical point. We have also shown both the global-entanglement (GE) and multipartite entanglement (ME) are maximal at the critical point for the Ising chain with added DM interaction. Using matrix product state approach, we have calculated the tangle and concurrence of the model and it is able to capture and confirm our numerical experiment result. Lack of inversion symmetry in the presence of DM interaction stimulated us to study entanglement of three qubits in symmetric and antisymmetric way which brings some surprising results.Comment: 18 pages, 9 figures, submitte

Microwave response of superconducting pnictides: extended s±s_{\pm} scenario

We consider a two-band superconductor with relative phase $\pi$ between the two order parameters as a model for the superconducting state in ferropnictides. Within this model we calculate the microwave response and the NMR relaxation rate. The influence of intra- and interband impurity scattering beyond the Born and unitary limits is taken into account. We show that, depending on the scattering rate, various types of power law temperature dependencies of the magnetic field penetration depth and the NMR relaxation rate at low temperatures may take place.Comment: 11 pages, 5 figure

Infrared spectra of the low-dimensional quantum magnet SrCu2(BO3)(2): Measurements and ab initio calculations

The reflectance of the insulating quasi-two-dimensional quantum magnet SrCu2(BO3)2 has been examined over a wide temperature and frequency range for light polarized parallel (a axis) and perpendicular (c axis) to the copper- and boron-oxygen sheets. The spectra have been measured for temperatures below the structural phase transition Ts=395 K for both polarizations; above Ts a limited study of the in-plane properties was undertaken in the far-infrared region only. Several new modes appear in the reflectance just below Ts along the a and c axes, while others are visible only for T⪡Ts. Below Ts, the intensity of some of the new modes displays little or no temperature dependence, while the intensity of some vibrations increases dramatically with decreasing temperature. Ab initio calculations have been performed for the room-temperature phase using density-functional theory, and the frequencies and atomic characters of the infrared-active phonons at the zone center were obtained using the direct method. The agreement between the calculated and experimentally observed frequencies is quite good, and assignments of the modes are discussed. The vibrational features that are observed only at low temperature appear to be magnetic in origin

Infrared spectra of the low-dimensional quantum magnet SrCu2(BO3)(2): Measurements and ab initio calculations

The reflectance of the insulating quasi-two-dimensional quantum magnet SrCu2(BO3)2 has been examined over a wide temperature and frequency range for light polarized parallel (a axis) and perpendicular (c axis) to the copper- and boron-oxygen sheets. The spectra have been measured for temperatures below the structural phase transition Ts=395 K for both polarizations; above Ts a limited study of the in-plane properties was undertaken in the far-infrared region only. Several new modes appear in the reflectance just below Ts along the a and c axes, while others are visible only for T⪡Ts. Below Ts, the intensity of some of the new modes displays little or no temperature dependence, while the intensity of some vibrations increases dramatically with decreasing temperature. Ab initio calculations have been performed for the room-temperature phase using density-functional theory, and the frequencies and atomic characters of the infrared-active phonons at the zone center were obtained using the direct method. The agreement between the calculated and experimentally observed frequencies is quite good, and assignments of the modes are discussed. The vibrational features that are observed only at low temperature appear to be magnetic in origin