Interference as a Probe of Spin Incoherence in Strongly Interacting Quantum Wires

We show that interference experiments can be used to identify the spin-incoherent regime of strongly interacting one-dimensional conductors. Two qualitative signatures of spin incoherence are found: a strong magnetic field dependence of the interference contrast and an anomalous scaling of the interference contrast with the applied voltage, with a temperature and magnetic field dependent scaling exponent. The experiments distinguish the spin-incoherent from the spin-polarized regime, and so may be useful in deciding between alternative explanations proposed for the anomalous conductance quantization observed in quantum point contacts and quantum wires at low density.

Figure 1

First interference geometry. In spin-polarized conductors amplitudes for an electron to tunnel from the left to the right wire at the points $x_{\mathrm{L}}$ and $x_{\mathrm{R}}$ interfere. Their phase difference $\phi =e\Phi /\hslash c$ depends on the flux $\Phi$ through the interference loop. In the spin-incoherent regime they generically involve different spin configurations that prevent interference.

Figure 2

In our second geometry (inset) the interference contrast $C$ obeys a power law with a temperature and magnetic field dependent exponent $g-g{ln}^2{p}_{\uparrow }/{\pi }^2$. We show $c=C(V)/C(V_0)$, the interference contrast normalized with respect to an arbitrary reference voltage $V_0$. It is compared to its value without magnetic field $c_{B=0}$, for various $p_{\uparrow }$ ($g=1$).