Quantum spin liquid ground state in the rare-earth triangular antiferromagnet <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>SmTa</mml:mi><mml:mn>7</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml

The rare-earth-based geometrically frustrated triangular magnets have attracted considerable attention due to the intricate interplay between strong spin-orbit coupling and the crystal electric field (CEF), which often leads to effective spin-1/2 degrees of freedom and therefore promotes strong quantum fluctuations at low temperatures, thus offering an excellent route to stabilize a quantum spin liquid (QSL) ground state. We have investigated the ground state magnetic properties of a polycrystalline sample of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:msub><a:mtext>SmTa</a:mtext><a:mn>7</a:mn></a:msub><a:msub><a:mtext>O</a:mtext><a:mn>19</a:mn></a:msub></a:mrow></a:math> which we propose to have a gapless QSL ground state by employing powder x-ray diffraction (XRD), x-ray absorption spectroscopy (XAS), DC and AC-magnetic susceptibility, <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mi>M</b:mi></b:math> versus <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mi>H</c:mi></c:math> isotherm, specific heat, and muon spin rotation/relaxation measurements (<d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mrow><d:mo>µ</d:mo><d:mi>SR</d:mi></d:mrow></d:math>) down to 30 mK. The combined structural and electronic studies reveal the formation of an edge-sharing equilateral triangular lattice of <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:msup><e:mrow><e:mi>Sm</e:mi></e:mrow><e:mrow><e:mn>3</e:mn><e:mo>+</e:mo></e:mrow></e:msup></e:math> ions in <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"><f:mrow><f:mi>a</f:mi><f:mi>b</f:mi></f:mrow></f:math> plane. The DC and AC magnetic susceptibility, and heat capacity measurements reveal that <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"><g:mrow><g:msub><g:mtext>SmTa</g:mtext><g:mn>7</g:mn></g:msub><g:msub><g:mtext>O</g:mtext><g:mn>19</g:mn></g:msub></g:mrow></g:math> does not exhibit any long-range magnetic ordering transition down to 50 mK. The zero-field (ZF)-<h:math xmlns:h="http://www.w3.org/1998/Math/MathML"><h:mrow><h:mo>µ</h:mo><h:mi>SR</h:mi></h:mrow></h:math> study strongly refutes the long-range magnetically ordered ground state and/or any partial spin-freezing down to at least 30 mK. The ZF-muon-spin relaxation rate is weakly temperature-dependent between 50 and 20 K, rapidly increases below <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"><i:mrow><i:mo>∼</i:mo><i:mn>20</i:mn><i:mspace width="4pt"/><i:mi mathvariant="normal">K</i:mi></i:mrow></i:math> and saturates at low temperatures between 2 K and 30 mK, which has been attributed to a characteristic signature of QSL systems. Further, our longitudinal-field (LF)-<l:math xmlns:l="http://www.w3.org/1998/Math/MathML"><l:mrow><l:mo>µ</l:mo><l:mi>SR</l:mi></l:mrow></l:math> measurements at 0.1 K reveal a dynamic nature of the magnetic ground state. In addition, our high-field specific heat data suggest a gapless nature of spin excitations in this compound.