Semi-classical origin of the extreme magnetoresistance in PtSn4

<p><strong><span>The so-called &ldquo;extreme magnetoresistance&rdquo; (XMR) found in few conductors poses interesting conceptual challenges which address needs in technology. In contrast to the more common XMR in semi-metals, PtSn₄ stands out as a rare example of a high carrier density multi-band metal exhibiting XMR, sparking an active debate about its microscopic origin. Here we report a sharp sensitivity of its XMR upon the field angle, with an almost complete collapse only for one specific current and field direction (B\\b, I\\a). Corroborated by band-structure calculations, we identify a singular open orbit on one of its Fermi surface sheets as the origin of this collapse. This remarkably switchable XMR resolves the puzzle in PtSn₄ as a semi-classical effect of an ultra-pure, compensated carrier metal. It further showcases the importance of Ockham&rsquo;s razor in uncommon magnetotransport phenomena and demonstrates the remarkable physical properties conventional metals can exhibit given they are superbly clean. </span></strong></p>