Nature of the high-pressure insulating state in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Sr</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>IrO</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:mrow></mml:m

At ambient pressure, the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:msubsup><a:mi>t</a:mi><a:mrow><a:mn>2</a:mn><a:mi>g</a:mi></a:mrow><a:mn>5</a:mn></a:msubsup></a:math> layered perovskite <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:msub><b:mrow><b:mi>Sr</b:mi></b:mrow><b:mn>2</b:mn></b:msub><b:msub><b:mrow><b:mi>IrO</b:mi></b:mrow><b:mn>4</b:mn></b:msub></b:math> is a correlated small-gap insulator. In the Mott picture, applying uniform pressure should therefore quickly close the gap; experimentally, however, the insulating state persists even under extreme pressures, suggesting that a mechanism other than Mott is at work. Yet, given the complexity of the system, it is unclear to what extent the Mott picture can be really excluded. Here, we thus reexamine the problem. We show that, surprisingly, the pressure-induced enhancement of the screened Coulomb interaction—combined with lattice distortions and spin-orbit driven <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:msub><c:mi>j</c:mi><c:mi>eff</c:mi></c:msub><c:mo>=</c:mo><c:mn>1</c:mn><c:mo>/</c:mo><c:mn>2</c:mn></c:mrow></c:math> orbital ordering—can hold the system close to the metal-insulator transition up to very high pressure.