Low-Gap Hf-HfOx-Hf Josephson Junctions for meV-Scale Particle Detection

TL;DR

This paper introduces Hf-HfOx-Hf Josephson junctions as a new low-gap superconductor platform suitable for detecting single THz photons and phonons, advancing ultra-sensitive astrophysical and dark matter detection technologies.

Contribution

It demonstrates the fabrication, structural analysis, and electrical characterization of Hf-based Josephson junctions, establishing their potential for ultra-low threshold detection applications.

Findings

Hf-based junctions exhibit clear Josephson behavior.

Structural analysis shows crystalline films and well-defined oxide barriers.

Electrical measurements reveal key parameters like critical current and superconducting gap.

Abstract

Superconducting qubits have motivated the exploration of Josephson-junction technologies beyond quantum computing, with emerging applications in low-energy photon and phonon detection for astrophysics and dark matter searches. Achieving sensitivity at the THz (meV) scale requires materials with smaller superconducting gaps than those of conventional aluminum or niobium-based devices. Here, we report the fabrication and characterization of hafnium (Hf)-based Josephson junctions (Hf-HfOx-Hf), demonstrating Hf as a promising low-Tc material platform for ultra-low threshold single THz photon and single-phonon detection. Structural and chemical analyses reveal crystalline films and well-defined oxide barriers, while electrical transport measurements at both room and cryogenic temperatures exhibit clear Josephson behavior, enabling extraction of key junction parameters such as critical current, superconducting gap and normal-state resistance. This work presents the first comprehensive study of Hf-based junctions and their potential for next-generation superconducting detectors and qubit architectures leveraging low superconducting gap energies.