NMR Study Of Quasi-one-dimensional Ta₄Pd₃Te₁₆

Low-dimensional systems often display rich physical phenomena,such as charge density wave(CDW),spin density wave,and superconductivity.Many superconductors were found at low dimensions where the superconductivity coexists with or adjoins another ordered state and has an unconventional nature.The high transition temperature(Tc)superconductivity has been realized in two-dimensional copper oxides and iron pnictides,where the superconducting phase is located in the vicinity of magnetic and nematic orders.This raises an interest in finding unconventional superconductivity in low-dimensional materials.Finally,I will report 125Te nuclear magnetic resonance and 181Ta nuclear quadrapole resonance studies on single-crystal Ta4Pd3Te16,which has a quasi-one-dimensional crystal structure and superconducts below TC=4.3 K.181Ta with spin I = 7/2 is sensitive to quadrupole interactions,while 125Te with spin I=1/2 can only relax by magnetic interactions.By comparing the spin-lattice relaxation rate(1/T1)of 181Ta and 125Te,we found that electric-field-gradient(EFG)fluctuations develop below 80K.The EFG fluctuations are enhanced with decreasing temperature due to the fluctuations of a charge density wave that sets in at TCDW =20 K.In the superconducting state,a Hebel-Slichter coherence peak appears in the temperature dependence of 1/T1 of 125Te just below Tc,which indicates that Ta4Pd3Te16 is a fully gapped superconductor.Due to coexistence of CDW and superconducting,strong EFG fluctuations eliminate the coherence peak in the temperature dependence of 1/T1 of 181Ta.