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Spontaneously broken symmetry in the ground state of Bi-based topological materials can lead to promising Topological superconductors, such as Cu-Bi2Se3, Sr-Bi2Se3 and Nb-Bi2Se3. In recent studies, coexistence of multiple Fermi surface features and superconductivity was found in Nb-Bi2Se3. However, the resultant mutliple Fermi surface--charge density wave has not been experimentally reported yet. In this paper, we report possible evidence of co-occurence of a charge density wave (CDW) ground state and a superconducting (SC) ground state in Nb intercalated Bi2Se3. An intercalation induced Periodic Lattice Distortion appears to help stabilize the CDW state, possibly assisting in the formation of 1D chains and rendering electronic and phonon anisotropy to this intriguing system.

Hexagonally deformed Fermi surfaces and strong nesting, found in topological insulators (TIs) such as $Bi_2Se_3$ and $Bi_2Te_3$, have led to several predictions of the existence of Density Wave order in these systems. Recent evidence for strong Fermi surface nesting in superconducting $Cu-Bi_2Se_3$ and $Nb-Bi_2Se_3$ has further led to speculation about the importance of charge order in the context of unconventional superconductivity. Here, we report the first observation of a novel anomaly in $Bi_2Se_3$ at 140K, which may be associated with a Charge Density Wave (CDW)-like transition. This transition was identified from both structural and electronic measurements, where: a) a periodic lattice distortion at above room temperature was characterized as a diffuse charge order in $Bi_2Se_3$ between \vec{k} and \vec{k}\pm\mathrm{\Delta}\vec{k} from electron diffraction; and b) an opening of energy gap signatured with metal-to-insulator like transition at 140K was identified from resistivity vs temperature measurement. This is further corroborated by nuclear magnetic resonance (NMR) studies of the spin-lattice relaxation ( $\frac{1}{T_1}$) rate of the $^{209}Bi$ nucleus, which also displays a transition at 140K associated with an opening of an energy gap of ~8meV. Additionally, we also observe another anomaly in $\frac{1}{T_1}$ near 200K, which appears to display anisotropy with the direction of the applied magnetic field., Comment: 16 pages, 7 figures