Intrinsic Character of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mo stretchy="false">(</mml:mo><mml:mn>3</mml:mn><mml:mo>×</mml:mo><mml:mn>3</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:math>to<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mo stretchy="false">(</mml:mo><mml:msqrt><mml:mn>3</mml:mn></mml:msqrt><mml:mo>×</mml:mo><mml:msqrt><mml:mn>3</mml:mn></mml:msqrt><mml:mo stretchy="false">)</mml:mo></mml:math>Phase Transition in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="normal">P</mml:mi><mml:mi mathvariant="normal">b</mml:mi><mml:mo>/</mml:mo><mml:mi mathvariant="normal">S</mml:mi><mml:mi mathvariant="normal">i</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:mn>111</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:math>
We have investigated the (3 x 3) to (square root 3 x square root 3) reversible phase transition in Pb/Si(111) by means of variable temperature scanning tunneling microscopy and ...