Hydrostatic Pressure Response of an Oxide Two-Dimensional Electron System

Hydrostatic pressure has the capability of fundamentally changing key properties of quantum matter. Pressure, for example, can alter bond lengths
and angles, and thereby control electronic conduction. The possibility to study the electronic transport of quantum matter films and heterostructures
under large applied pressure has been severely limited due to considerable experimental challenges.

Using diamond-anvil cells and a piston-cylinder instrument, we have developed a method to apply hydrostatic pressure of several gigapascals
(1 GPa=109 Pa) to quantum matter heterostructures, which have been patterned into devices (arXiv 1605.08528 and Phys. Rev. B 93, 235117, 2016).
Applying this technology, we studied the electronic transport of the two-dimensional electron system at the interface between LaAlO3 and SrTiO3.
We find that a pressure of 2 GPa (= 20 kbar) is sufficient to produce a large and reversible effect on the electron system: at low temperature,
the carrier density doubles with increasing pressure. First-principles calculations accompanying the studies pinpoint this behavior to a pressure-induced
decrease of lattice distortions in the LaAlO3 layer.

We are now applying this technology to tune quantum matter devices by applying higher pressure.

This work was done in close collaboration with the groups of T. Kopp (Augsburg University) and R. Valentí (Goethe University Frankfurt).

 

<p> <br /> </p>
<p>Fig. left: Optical microscopy image of a brilliant-cut diamond such as the ones used in a diamond anvil cell.</p>
<p> <br /> Fig. right: Optical micrograph of a sample placed on the bottom diamond of the diamond anvil cell. The diamond is patterned with metallic electrodes that contact the sample at four different places. The four metallic contacts on the sample are visible through the translucent substrate.</p>

 
 

Fig. left: Optical microscopy image of a brilliant-cut diamond such as the ones used in a diamond anvil cell.

 
Fig. right: Optical micrograph of a sample placed on the bottom diamond of the diamond anvil cell. The diamond is patterned with metallic electrodes that contact the sample at four different places. The four metallic contacts on the sample are visible through the translucent substrate.

Fig. left: Measured sheet carrier density <em>n</em><sub>s</sub> as a function of pressure for two different samples. Pressure induces an increase of <em>n</em><sub>s</sub> at low temperatures.<br /><br />Fig. right: Optical microscopy image of a sample in Hall bar configuration used for pressure experiments in the piston cylinder cell.
Fig. left: Measured sheet carrier density ns as a function of pressure for two different samples. Pressure induces an increase of ns at low temperatures.

Fig. right: Optical microscopy image of a sample in Hall bar configuration used for pressure experiments in the piston cylinder cell.
 
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