Coexistence of Ferroelectricity and Metallicity in Weakly Coupled ( SnSe ) 1.16 ( NbSe 2 ) Crystal

Ferroelectric metals, traditionally considered mutually exclusive, face enduring challenges owing to screening effects of itinerant electrons on ferroelectric order. However, in certain van der Waals (vdW) heterostructures, two-dimensional materials with distinct structural and physical properties can be alternatingly arranged in layers, retaining their individual characteristics and thereby enabling the coexistence of ferroelectricity and metallicity. Here, we report the coexistence of robust in-plane ferroelectricity and exceptional metallicity in a natural vdW superlattice <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mrow> <a:msub> <a:mrow> <a:mo stretchy="false">(</a:mo> <a:mtext>SnSe</a:mtext> <a:mo stretchy="false">)</a:mo> </a:mrow> <a:mrow> <a:mn>1.16</a:mn> </a:mrow> </a:msub> <a:mo stretchy="false">(</a:mo> <a:msub> <a:mrow> <a:mtext>NbSe</a:mtext> </a:mrow> <a:mrow> <a:mn>2</a:mn> </a:mrow> </a:msub> <a:mo stretchy="false">)</a:mo> </a:mrow> </a:math> crystal, exhibiting high-density carriers ( <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:mrow> <g:mo form="prefix">></g:mo> <g:msup> <g:mrow> <g:mn>10</g:mn> </g:mrow> <g:mrow> <g:mn>21</g:mn> </g:mrow> </g:msup> <g:mtext> </g:mtext> <g:mtext> </g:mtext> <g:msup> <g:mrow> <g:mi>cm</g:mi> </g:mrow> <g:mrow> <g:mo>−</g:mo> <g:mn>3</g:mn> </g:mrow> </g:msup> </g:mrow> </g:math> ), superconductivity ( <j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline"> <j:mrow> <j:msub> <j:mrow> <j:mi>T</j:mi> </j:mrow> <j:mrow> <j:mi>c</j:mi> </j:mrow> </j:msub> <j:mtext> </j:mtext> <j:mo>∼</j:mo> <j:mn>3.25</j:mn> <j:mtext> </j:mtext> <j:mtext> </j:mtext> <j:mi mathvariant="normal">K</j:mi> </j:mrow> </j:math> ), and Curie temperature up to 383 K. The weak-coupling electronic and phononic natures stabilize in-plane ferroelectricity against screening by high-density carriers, confirming the decoupled electron mechanism. Moreover, we demonstrate the first ferroelectric memristor, where the metallic channel conductance is manipulated through polarization dynamics. Our Letter establishes a universal platform for designing multi-order parameters quantum-confined materials, and opens new avenues for energy-efficient functional electronics.