Pseudospin Ferromagnetism in Double-Quantum-Wire Systems

We propose that a pseudospin ferromagnetic (i.e., interwire coherent) state can exist in a system of two parallel wires of finite width in the presence of a perpendicular magnetic field. This novel quantum many-body state appears when the interwire distance decreases below a certain critical value which depends on the magnetic field. We determine the phase boundary of the ferromagnetic phase by analyzing the softening of the spin-mode velocity using the bosonization approach. We also discuss the signatures of this state in tunneling and Coulomb drag experiments.

Figure 1

(a) Schematic double wire system considered in this Letter. (b) and (c) are single particle energy $E_n^0(k)$ of each wire for $B=0$ and $B\ne 0$ cases, respectively.

Figure 2

Calculated critical interlayer distance, $d_c$, as a function of magnetic field ($\propto {\omega }_c$). Electron density in an individual wire, $n_e$, is $0.6,0.7,\dots ,1.0\times {10}^5{\mathrm{cm}}^{-1}$ from top to bottom. Here ${\lambda }_0=500\AA$ and ${\omega }_0=0.05\mathrm{meV}$.

Figure 3

(a) Typical setup for conductance experiment of the double wire system, where the two wires interact in the middle regime ($0<y<L$) and are connected to ideal 1D reservoir in the left- ($y<0$) and right- ($y>L$) hand sides. The upper (active) wire is biased by a voltage $V$, while the lower (passive) wire is biased by $V_R$ and $V_L$ with currents $I_{\uparrow /\downarrow }$ in the two wires, respectively. (b) and (c) are the band energy for electrons in the incoherent reservoirs and in the coherent double wire regime, respectively. The upper and lower bands in (b) are for the antisymmetric and symmetric bands, respectively.

Figure 4

Drag conductance as a function of $\xi ={\Delta }_0/E_F$, following Eq. (9). Results for two electron densities, $\eta$, are shown together. Inset: drag conductance as a function of magnetic field for $d=0.08{\lambda }_0$. $n_{\mathrm{res}}=0.6$ and $0.7\times {10}^5{\mathrm{cm}}^{-1}$ for the lower and upper curves, respectively.