Superfluid <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mmultiscripts><mml:mi>He</mml:mi><mml:mprescripts /><mml:none /><mml:mn>3</mml:mn></mml:mmultiscripts><mml:mtext>−</mml:mtext><mml:mtext>B</mml:mtext></mml:mrow></mml:math> surface states in a confined geometry probed by a microelectromechanical oscillator

A microelectromechanical oscillator with a $0.73\phantom{\rule{0.16em}{0ex}}\textmu{}\mathrm{m}$ gap structure is employed to probe the surface Andreev bound states in superfluid $^{3}\mathrm{He}\text{\ensuremath{-}}\mathrm{B}$. The specularity of increased by preplating it 1.6 monolayers $^{4}\mathrm{He}$. In linear regime, temperature dependence damping coefficient measured at various pressures, and normalized energy extracted. increases after lower which attributed decreased minigap states. device also driven into nonlinear where independent critical velocity each pressure measured. observed increase all might be related average gap. behavior warrants microscopic theory beyond single parameter characterization surface.