Signature of quantum Griffiths singularity state in a layered quasi-one-dimensional superconductor

Abstract

Quantum Griffiths singularity was theoretically proposed to interpret the phenomenon of divergent dynamical exponent in quantum phase transitions. It has been discovered experimentally in three-dimensional (3D) magnetic metal systems and two-dimensional (2D) superconductors. But, whether this state exists in lower dimensional systems remains elusive. Here, we report the signature of quantum Griffiths singularity state in quasi-one-dimensional (1D) Ta2PdS5 nanowires. The superconducting critical field shows a strong anisotropic behavior and a violation of the Pauli limit in a parallel magnetic field configuration. Current-voltage measurements exhibit hysteresis loops and a series of multiple voltage steps in transition to the normal state, indicating a quasi-1D nature of the superconductivity. Surprisingly, the nanowire undergoes a superconductor-metal transition when the magnetic field increases. Upon approaching the zero-temperature quantum critical point, the system uncovers the signature of the quantum Griffiths singularity state arising from enhanced quenched disorders, where the dynamical critical exponent becomes diverging rather than being constant.

Quantum Griffiths singularities in TiO superconducting thin films with insulating normal states

“…The quantum vortex creep state evolves to a socalled quantum Griffiths state with the QGS above H MF c2 T ð Þ and below H c (T) 17 . In a region with a sufficiently high magnetic field, the H c of the SIT with a QGS increases slowly at low temperatures and tends to saturate around H Ã c as the temperature approaches 0 K, which is different from the upturn trend of H c (T) observed in SMT systems 1,14,15,17 . This difference between the SIT and SMT systems with a QGS might be related to the different normal state backgrounds for the superconducting rare regions; the normal state background is insulating in the TiO SIT system but metallic in the previous SMT systems.…”

“…This difference between the SIT and SMT systems with a QGS might be related to the different normal state backgrounds for the superconducting rare regions; the normal state background is insulating in the TiO SIT system but metallic in the previous SMT systems. As previously discussed, in SMT systems 1,11,14,16 , the QGS in the low-temperature regime is closely related to the locally ordered superconducting rare regions that are coupled through Josephson couplings. The Josephson interaction strength is critically important for the formation and properties of rare regions, and the interaction strength is different for SMT and SIT systems with metallic and insulating normal states, respectively.…”

“…The superconductor-insulator (metal) transition (SIT/ SMT), a remarkable paradigm of the quantum phase transition (QPT), has been an important issue because this exotic phenomenon not only extends our understanding of the novel physical nature of the QPT but also contributes to the design of quantum devices, such as superconducting qubits 1,2 . The ground state of SIT/SMT can be tuned by a variety of external parameters, such as the magnetic field 3 , thickness 4,5 , disorder 6 , chemical composition 7 , charge density 8 , or gate voltage 9,10 , instead of thermal fluctuations.…”

“…In 2015, a totally different type of SMT called a quantum Griffiths singularity (QGS) was strikingly reported in a molecular-beam-epitaxy (MBE)-grown Ga trilayer 14 that shows diverging dynamic exponents and a continuous line of QCPs. Since this discovery, examples of SMTs with a QGS have been observed in a NbSe 2 monolayer 15 , a LaAlO 3 /SrTiO 3 (110) interface 16 , quasi-one-dimensional Ta 2 PdS 5 nanowires 1 , and ion-gated superconducting surfaces of ZrNCl and MoS 2 single crystals 17 . In the QGS picture, locally ordered superconducting islands (rare regions) that survive in the normal state background exist.…”

Size dependent nature of the magnetic-field driven superconductor-to-insulator quantum-phase transitions

“…Moreover, recent observations in crystalline quasi-two-dimensional (2D) and one-dimensional (1D) superconducting systems revealed an unprecedented quantum-Griffiths singularity [27][28][29][30][31][32][33] , which is experimentally characterized by divergent critical-exponent products of the dynamical critical exponent and the correlation length exponent, $%. This novel phenomenon is attributed to quenched-disorder effects at the transitions, despite the origin of such quenched disorder in clean systems is somewhat obscure [27][28][29][30][31][32]34,35 .…”