粒狀結構錫鍺合金的傳輸性質與穿隧電子能態密度

Abstract

無序會影響樣品的超導性質及傳輸性質，其物理機制仍未明確。在這篇論文中利用熱蒸鍍的方式將不同成分的錫鍺合金鍍到玻璃基板上，我們成功的製作了一系列的無序程度不同的顆粒狀樣品，樣品電阻率分佈很很廣(300 microohm-cm~0.5 ohm -cm)。藉這量測樣品在低溫的傳輸性質和穿隧電子能態密度，可以發現無序造成電子電子間的作用力增強，導致金屬絕緣相變的產生。 在臨界溫度以下，顆粒狀樣品超導性質仍然很強，縱使樣品的傳輸性質顯示樣品屬於絕緣態。我們認為顆粒狀的結構限制了無序對超導性質的影響，因此樣品的Tc 和能隙變化很小。但無序程度確實破壞了顆粒間長距離的相位相干，因此在溫度電阻的關係圖上可以觀察到電阻下降的趨勢減緩，同時，在準粒子的穿隧電導的函數形式在能隙附近造成模糊的現象。

It is well-known that disorder influences the superconducting properties and the transport properties of the specimens. Upon evaporating SnGe alloys to micro-slide glass, we fabricated a series of granular SnGe samples with resistivities spanning among a very wide range (300 microohm-cm~0.5 ohm -cm). The transport properties and tunneling density of states at low temperature show that the disorder enhanced electron-electron interaction dominate the metal- insulator transition. And below the critical temperature of Sn, data indicate that the superconductivity of grains which consists the film is robust, even when the film exhibits insulating behavior in transport measurements. The granular structure limits the effect of disorder and therefore, the super- conducting properties of the grain such as Tc and energy gap are barely change. Our result also show that the disorder weaken the Josephson coupling between grains by destroying long phase coherence. Phase slipping between grains results in a long tail in its temperature dependent resistivities and broadens its quasiparticle tunneling density of states below Tc.