Bosonic Confinement and Coherence in Disordered Nanodiamond Arrays

Abstract

In the presence of disorder, superconductivity exhibits short-range characteristics linked to localized Cooper pairs which are responsible for anomalous phase transitions and the emergence of quantum states such as the bosonic insulating state. Complementary to well-studied homogeneously disordered superconductors, superconductor-normal hybrid arrays provide tunable realizations of the degree of granular disorder for studying anomalous quantum phase transitions. Here, we investigate the superconductor-bosonic dirty metal transition in disordered nanodiamond arrays as a function of the dispersion of intergrain spacing, which ranges from angstroms to micrometers. By monitoring the evolved superconducting gaps and diminished coherence peaks in the single-quasiparticle density of states, we link the destruction of the superconducting state and the emergence of bosonic dirty metallic state to breaking of the global phase coherence and persistence of the localized Cooper pairs. The observed resistive bosonic phase transitions are well modeled using a series-parallel circuit in the framework of bosonic confinement and coherence.

Anomalous Anisotropy in Superconducting Nanodiamond Films Induced by Crystallite Geometry

“…where T 0 characterizes the strength of single quasiparticle correlation [14,28]. The ρ(T) curves, however, deviate from the linear fits below 1.5 K, owing to the remnant superconductivity [14,15]. In contrast to the ρ(T) curve measured in the perpendicular field, the data measured in the parallel field deviate less from the theory at low temperatures.…”

“…A network composed of ordered uniform weak links should give rise to the emergence of the characteristic features of the Josephson effect, e.g., zero-bias supercurrent, modulations of the critical current as a function of magnetic field, and oscillations of the magnetic field dependence of resistivity [33], yet no such characteristic features of the Josephson effect have been reported for granular superconducting diamond. However, Josephson-effect-like traits such as current-induced Josephson noise have been observed in nanodiamond films [34], and strong intergrain and intragrain fluctuations of the superconducting order parameter have been reported for superconducting granular diamond by scanning tunneling microscopy/spectroscopy [10,15,18]. The absence of pronounced Josephson effect in nanodiamond films is highly likely owing to the high degree of disorder.…”

“…By decreasing the mean grain size, a systematic reduction of the coherence length was realized in a set of nanodiamond films [14]. When increasing the mean intergrain spacing or the applied pressure, a bosonic insulating state emerged in nanodiamond films as a result of suppressed intergrain Josephson coupling and localized intragrain superconducting order parameter [15][16][17][18].…”

Long‐Range Ordered Amorphous Atomic Chains as Building Blocks of a Superconducting Quasi‐One‐Dimensional Crystal

“…This phenomenon is highly counterintuitive and intriguing, because in principle, a local lattice distortion, e.g., the pressure-induced short-range disorder in our case, should hinder Cooper pairing and set obstacles for the quantum condensation of Cooper pairs. [32] Superconductor-insulator transitions have been extensively studied for decades in a large variety of materials, where disorder serves as the driving force of the transition. [33] Opposite to the common cases, Figure 3a suggests that the insulator-superconductor transition observed in our quasi-1D system is facilitated by the amorphization of the TaSe 4 chains.…”

“…We note that in contrast to the electrical transport measurements that provide insight into the process of establishment of the percolation path for Cooper pairs, ac susceptibility measurements mainly reflect the formation of the circulating supercurrent. [45] In the case of a disordered superconductor, local Cooper pairing sets in prior to the formation of the circulating supercurrent, [32,45] and thus the onset of superconductivity in electrical transports takes place at lower pressures (≈20 GPa) in contrast to the emergence of diamagnetization in ac susceptibility (≈30 GPa).…”