arXiv subjects

Daoxin Yao

Publications and source records attributed to Daoxin Yao.

5 recordsLinked to original sources

arXiv2017

Majorana phi0 Junction in a Disordered Spin-orbit Coupling Nanowire with Tilted Magnetic Field

Majorana Josephson junctions in nanowire systems exhibit a pseudo-$4π$ period current-phase relation in the clean limit. In this work, we study how this current-phase relation responds to a tilted magnetic field in a disordered Majorana Josephson junction within the Bogoliubov-de Gennes approach. We show that the tilted magnetic field induces a $ϕ_0$ phase shift to the current-phase relation. Most importantly, we find that this $ϕ_0$-junction behavior is robust even in the presence of disorders.

cond-mat.mes-hall↗

arXiv2013

Spin-thermodynamics of cold spin-1 atoms decoupled from spatial modes

We study the thermodynamic properties of cold spin-1 atoms with a fixed magnetization M and decoupled from spatial modes. Three temperature domains are found: (0, T1) is a domain of second condensation, namely, both the spatial and spin degrees of freedom are frozen; (T1, T2) is a T - sensitive domain, where the internal energy U \propto T, entropy SE \propto log T, and U/kBT is always less than 3/2; (T2, T3) is the third domain with a maximum entropy. When T is higher than T3, the spatial modes can not be neglected. The appearance of these domains originates from the two gaps: (i) The gap between the ground state and the first excited state, and (ii) the gap between the highest spin-state without spatial excitation and the lowest state with a spatial mode excited. These two gaps are crucial to the low temperature physics and they can be tuned.

cond-mat.stat-mech↗

arXiv2013

A 2-level system of cold sodium atoms with high and tunable susceptibility against the magnetic field

A 2-level spin-system of cold sodium atoms is proposed. Both the cases that the system has arrived at thermo-equilibrium and is in the early stage of evolution have been studied. This system is inert to the magnetic field $B$ in general but very sensitive in a narrow domain around $B=B_0$, where $B_0$ can be predicted and is tunable. A characteristic constant $γ=0.278466$ dedicated to various 2-level systems is found, and leads to a upper limit for the internal energy $U$ of the whole system so that $U\leqγk_B T$. This limit is considerably lower than the energy assigned to the spatial motion of only a single particle. Under thermo-equilibrium, the populations of spin-components measured at distinct $T$ converge to a fixed value when $B=B_0$. The period and amplitude of population oscillation are found to be seriously affected by the special sensitivity against $B$. Rich messages on the dynamic parameters could be obtained via experimental measurements of these systems.

physics.atom-ph↗

arXiv2013

Distinguishing $s^{\pm}$ and $s^{++}$ electron pairing symmetries by neutron spin resonance in superconducting NaFe$_{0.935}$Co$_{0.045}$As

A determination of the superconducting (SC) electron pairing symmetry forms the basis for establishing a microscopic mechansim for superconductivity. For iron pnictide superconductors, the $s^\pm$-pairing symmetry theory predicts the presence of a sharp neutron spin resonance at an energy below the sum of hole and electron SC gap energies ($E\leq 2Δ$) below $T_c$. On the other hand, the $s^{++}$-pairing symmetry expects a broad spin excitation enhancement at an energy above $2Δ$ below $T_c$. Although the resonance has been observed in iron pnictide superconductors at an energy below $2Δ$ consistent with the $s^\pm$-pairing symmetry, the mode has also be interpreted as arising from the $s^{++}$-pairing symmetry with $E\ge 2Δ$ due to its broad energy width and the large uncertainty in determining the SC gaps. Here we use inelastic neutron scattering to reveal a sharp resonance at E=7 meV in SC NaFe$_{0.935}$Co$_{0.045}$As ($T_c = 18$ K). On warming towards $T_c$, the mode energy hardly softens while its energy width increases rapidly. By comparing with calculated spin-excitations spectra within the $s^{\pm}$ and $s^{++}$-pairing symmetries, we conclude that the ground-state resonance in NaFe$_{0.935}$Co$_{0.045}$As is only consistent with the $s^{\pm}$-pairing, and is inconsistent with the $s^{++}$-pairing symmetry.

cond-mat.supr-con↗

arXiv2010

Orbital-weight redistribution triggered by spin order in the pnictides

The one-particle spectral function and its orbital composition are investigated in a three-orbital model for the undoped parent compounds of the iron-based superconductors. In the realistic parameter regime, where results best fit experimental data, it is observed that the magnetization in the xz and yz orbitals are markedly different and the Fermi surface presents mostly xz character, as recently observed in photoemission experiments [T. Shimojima et al., Phys. Rev. Lett. 104, 057002 (2010)]. Since the ferro-orbital order in this regime is at most a few percent, these results are mainly driven by the magnetic order. An analogous analysis for a five-orbital model leads to similar conclusions.

cond-mat.supr-con↗