Anomalous metallic phase in tunable destructive superconductors

Abstract

The Little-Parks effect is a flux-dependent modulation of the superconducting transition temperature resulting from fluxoid quantization through holes in a multiply connected superconductor. In hollow superconducting cylinders with diameter smaller than the coherence length, flux-induced supercurrents can give rise to the destructive Little-Parks effect, characterized by repeated reentrant quantum phase transitions between superconducting and metallic phases. Here, we use axial and transverse magnetic fields to control the crossover between conventional and destructive Little-Parks regimes in nanowires with an epitaxial Al shell fully surrounding InAs core. The observed dependences on flux, transverse field, temperature, and current bias are in excellent agreement with theory. Near the crossover between the conventional and destructive regimes, an anomalous metal phase is found. The anomalous metallic phase is characterized by a field-controllable, temperatureindependent resistivity between adjacent superconducting lobes.Quantum phase transitions (QPT) [1, 2] in conventional superconductors serve as prototypes for related effects in more complex, strongly-correlated systems [3], including heavy-fermion materials [4] and high-temperature superconductors [5].While lowtemperature superconductors are well understood in bulk, new phenomena can arise in mesoscopic samples and reduced dimensionality [6,7]. For instance, in two-dimensional films, electrons theoretically condense into either a superconductor or insulator in the lowtemperature limit [8]. Yet, in many instances, an anomalous metallic state with finite temperature-independent resistance is found at low temperatures [9]. In onedimensional wires, incoherent phase slips can destroy superconductivity [10] or give rise to an anomalous metallic state [11], while coherent quantum phase slips can lead to superposition of quantum states enclosing different numbers of flux quanta [12], potentially useful as a qubit [13].Multiply connected superconductors provide an even richer platform for investigating phase transitions. Fluxoid quantization in units of Φ 0 = h/2e [14,15], reveals not only electron pairing but a complex macroscopic order parameter, ∆e iϕ [6,16]. The same physical mechanism underlies the Little-Parks effect, a periodic modulation of the transition temperature, T C , of a superconducting cylinder with magnetic flux period Φ 0 [17]. For hollow superconducting cylinders with diameter, d, smaller than the coherence length, the modulation amplitude can exceed zero-field transition temperature, T C0 , leading to a reentrant destruction of superconductivity near odd half-integer multiples of Φ 0 [18][19][20].Early experimental investigation of the destructive Little-Parks effect reported reentrant superconductivity interrupted by an anomalous-resistance phase around applied flux Φ 0 /2 [21]. Subsequent experiments showed a low-temperature phase with normal-state resistance, R N , around Φ 0 /2, but did not display fully recovered superconductivity at higher ...

Destructive Little-Parks Effect in a Full-Shell Nanowire-Based Transmon

“…At intermediate fields, around ∼50 mT, the qubit frequency falls rapidly, the resonance broadens and disappears. This behavior is associated with the destructive regime around applied flux Φ 0 =2, where ΔðBÞ goes to zero and superconductivity is destroyed [19,20]. At higher fields, B ∼ 60-120 mT the qubit is recovered and shows similar behavior to the low-field regime with a maximum qubit frequency around 90 mT, slightly reduced from its zero-field value.…”

“…At higher fields, B ∼ 60-120 mT the qubit is recovered and shows similar behavior to the low-field regime with a maximum qubit frequency around 90 mT, slightly reduced from its zero-field value. This recovery of qubit frequency reflects the underlying lobe structure of superconductivity in the NW [19]. In the first lobe, one vortex has entered the shell, the superconducting phase twists once around the wire circumference, and topological superconductivity can be realized in the core [20].…”

“…This is more than a detail. In these small-diameter systems, it is known that an axial magnetic field applied to a cylindrical superconducting shell can give rise to an extreme form of the Little-Parks effect [16] characterized by flux-driven reentrant superconductivity [17][18][19], and, in semiconductorsuperconductor hybrids to a possibility to realize topological superconductivity [20].…”

Andreev Modes from Phase Winding in a Full-Shell Nanowire-Based Transmon

“…Tuning the phase difference near δφ ¼ π is usually required to lower ABS transitions to a measurable range [4,5]. However, this may not be the case when operating Josephson devices at finite magnetic fields, where ABS energies can be modulated by orbital effects in the semiconducting segments of NWs [16][17][18][19] and the Little-Parks effect in a NW with a fully enclosed superconducting shell [20][21][22]. Therefore, hybrid transmonlike qubit devices at finite magnetic fields can potentially reveal new information about the underlying Andreev processes, with implications on both junction and qubit parameters.…”

“…Here, we investigate low-energy ABSs in superconducting full-shell NW-based gatemons, which exhibit a destructive Little-Parks effect [20,23,24]. An applied magnetic field parallel to the NW induces a sequence of reentrant superconducting lobes, each associated with a different winding number, n, of the superconducting phase around the shell [21,22,25]. ABSs appear in the low-energy spectrum of the device in the first lobe (n ¼ 1) and are absent in the zeroth lobe (n ¼ 0), consistent with numerical simulations, also presented here.…”