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We find that the Feynman relation of Bose-Einstein condensates with spin-orbit coupling, which relates the energy of excitations, the static structure factor in condensed phase, and the dispersion of free bosons, is not satisfied in the whole momentum space. The dispersion is highly anisotropic and more divergent in the infrared limit compared to that without spin-orbit coupling because of spontaneous breaking of the O(2) symmetry of the ground state. And the dispersion also exhibits time reversal asymmetry for plane-wave condensates, which is condensed on a momentum with a finite value. We also find that larger spin-orbit coupling makes the excitations out of condensates more coherent.

We investigate the condensation of a two-dimensional homogeneous spin-orbit coupled boson system at zero temperature. We prove that the condensate is stable although the spin-orbit coupling makes the momentum distribution of depletion more divergent in the infrared limit. The stability of the system depends solely on the infrared behavior of the density waves, while the spin waves play a nonessential role. The condensate fraction is a decreasing function of the ratio of spinorbit coupling to the square root of the boson density. The peak of the momentum distribution of depletion stretches anisotropically when the strength of spin-orbit coupling increases.

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It has been known that spin-dependent capacitances usually coexist with geometric capacitances in a magnetic multilayer. However, the charge and energy storage of the capacitance due to spin accumulation has not been fully understood. Here, we resolve this problem starting from the charge storage in the spin degree of freedom: spin accumulation manifests itself as an excess of electrons in one spin channel and an equal deficiency in the other under the quasi-neutrality condition. This enables us to model the two spin channels as the two plates of a capacitor. Taking a ferromagnet/nonmagnet junction as an example and using a method similar to that for treating quantum capacitance, we find that a spin-accumulation (SA) capacitance can be introduced for each layer to measure its ability to store spins. A spatial charge storage is not essential for the SA capacitor and the energy stored in it is the splitting energy of the spin-dependent chemical potentials instead of the electrostatic energy. The SA capacitance is essentially a quantum capacitance due to spin accumulation on the scale of the spin-diffusion length. The SA capacitances can be used to reinterpret the imaginary part of the low-frequency magnetoimpedance

We investigate the drag force on a moving impurity in a spin-orbit coupled Bose-Einstein condensate. We prove rigorously that the superfluid critical velocity is zero when the impurity moves in all but one directions, in contrast to the case of liquid helium and superconductor where it is finite in all directions. We also find that when the impurity moves in all directions except two special ones, the drag force has nonzero transverse component at small velocity. When the velocity becomes large and the states of the upper band are also excited, the transverse force becomes very small due to opposite contributions of the two bands. The characteristics of the superfluid critical velocity and the transverse force are results of the order by disorder mechanism in spin-orbit coupled boson systems.

Using a macroscopic approach, we studied theoretically the heat generation in a typical spin valve with nonmagnetic spacer layer of finite thickness. Our analysis shows that the spin-dependent heat generation cannot be interpreted as the Joule heating of the spin-coupled interface resistance except for some special segments. Moreover, the spin-coupled interface resistance can be negative in certain situation, and thus its "Joule heating" should be understood instead as the work done by the extra field in the ferromagnetic layers and at the spin-selective interfaces. Effective resistances are proposed as alternatives so that the spin-dependent heat generation can still be expressed in a form resembling Joule's law.

In the present paper, we compute the magnetic susceptibility of graphene by using Gaussian correction. The collective excitations away from Fermi points of graphene are gapless, chiral fermions, with linear dispersion. The system is modeled as N massless Dirac fermions in two spatial dimensions interacting with 1/r Coulomb interactions. We find that the magnetic susceptibility is suppressed by the interaction between these collective excitations. And it has ln T correction due to the long-ranged Coulomb interaction, which is different from Landau Fermi liquid theory.