- Active devices would include mechanical refrigeration systems and peltier devices - the latter probably being more practical.
- Passive devices would be some sort of liquid convection cooling with the heat source at the bottom and heat sink at the top. The lower density hot fluid would rise to the top.
A quick web search for one-way heat conductor showed up:
... and a thermal rectifier!
Figure 1. Japanese researchers have developed a new diode that only transmits heat currents in one direction, and they think it could represent a new future for thermal computing. Source: PopSci.
The article goes on to say:
Similar work has succeeded with individual electrons in superconductors and in lone nanotubes, according to Technology Review. But this represents the first time anyone has managed the trick in a bulk solid, which in this case consists of two types of perovskite cobalt oxides.
Researchers have long theorized that such diodes, or thermal rectifiers, could become possible with the right material. Such a material would have to have high thermal conductivity at low temperatures and vice versa, so that that heat would flow continuously in one direction -- and then researchers could combine the material with another having the opposite characteristic.
Such a device has clear use in creating heat sinks that keep microchips running cool. Yet Wataru Kobayashi at Waseda University and his colleagues have put forth a more ambitious goal: controlling heat currents to create a new type of information processing with thermal transistors, thermal logic gates, and thermal memory. [Italics mine.]
I originally thought this development was the same thing but @DaveTweed points out -
I think you misunderstood the first [now second] reference about polyethylene molecules -- this creates an anisotropic material (heat flows along one axis, but not along the other two), but cannot produce a "diode" effect.
I'll leave it in out of general interest.
Figure 2. Chains of polyethylene molecules like the one above tend to arrange themselves chaotically, but by figuring out how to make the molecules line up straight, MIT researchers have created a highly conductive new polymer that conducts heat in only one direction. Source: PopSci.