Semi-classical origin of the extreme magnetoresistance in PtSn4

The so-called “extreme magnetoresistance” (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’s razor in uncommon magnetotransport phenomena and demonstrates the remarkable physical properties conventional metals can exhibit given they are superbly clean.所谓在少数导体中发现的极端磁电阻（extreme magnetoresistance, XMR），不仅带来了引人深思的概念性挑战，也契合了技术领域的实际应用需求。与半金属中更为常见的XMR不同，PtSn4作为罕见的高载流子密度多能带金属体系，同样展现出XMR效应，由此引发了关于其微观起源的热烈学术讨论。本研究报道了该体系的XMR对磁场角度具有极强的敏感性：仅在特定的电流与磁场方向（B∥b，I∥a）下，磁电阻几乎完全骤降。经能带结构计算佐证，我们确认其其中一个费米面存在奇异开放轨道，这正是该磁电阻骤降的成因。这种极具特色的可切换XMR效应，解开了PtSn4体系中XMR的未解之谜——其本质为超高纯补偿载流子金属的半经典效应。该研究进一步凸显了奥卡姆剃刀原理在罕见磁输运现象研究中的重要性，同时也证明：只要具备极高的纯净度，常规金属也可展现出极为优异的物理特性。