Friday, July 31, 2009

Spin-Charge Separation Observed?

It has been predicted that in 1D Tomonaga-Luttinger liquid theory, the strong electronic correlation will cause not only the breakdown of the Fermi Liquid model, but also the phenomenon of spin-charge separation. This is where the spin and charge of the charge carrier no longer form good quantum numbers, and thus, may disperse or undergo transport separately from each other.

Tantalizing indication of this effect has been shown before. For example, the violation of the Wiedemann-Franz law has been observed in the charge and heat currents in 1D organic conductors[1]. Now comes evidence from a different type of measurement - tunneling into a 1D system[2].

Abstract: In a one-dimensional (1D) system of interacting electrons, excitations of spin and charge travel at different speeds, according to the theory of a Tomonaga-Luttinger liquid (TLL) at low energies. However, the clear observation of this spin-charge separation is an ongoing challenge experimentally. We have fabricated an electrostatically gated 1D system in which we observe spin-charge separation and also the predicted power-law suppression of tunneling into the 1D system. The spin-charge separation persists even beyond the low-energy regime where the TLL approximation should hold. TLL effects should therefore also be important in similar, but shorter, electrostatically gated wires, where interaction effects are being studied extensively worldwide.

There are certainly more evidence of this phenomenon each year. And the issue of a "particle" undergoing a "spin-charge" separation is also a fundamental issue. I wouldn't be surprised if this is another example of something that came out of condensed matter that gets "hijacked" into other fields, if it hasn't already.


[1] T. Lorenz et al., Nature v.418, p.614 (2002).
[2] Y. Jompol et al., Science v.325. p.597 (2009).

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